Consciousness As A Memory System Part 2

Our Theory Is Consistent With the System 1 (Unconscious) and System 2 (Conscious) Distinction

Our memory theory of consciousness is fully consistent with the distinction that Kahneman and Tversky (Kahneman, 2011; see also Carruthers, 2015) made between the slow, effortful, logical, calculating, conscious System 2 and the fast, automatic, stereotypic, unconscious System 1. Our theory would simply add that conscious System 2 was made possible by the original purpose of consciousness—to be the contents of episodic memory.

Conscious memory and memory are two interrelated concepts. Conscious memory is when we consciously store certain information in our minds, while memory is when we can recall that information at a later time. Conscious memory is crucial to our study, life, and work, and the quality of memory directly affects our success and happiness.

Everyone's memory has its inherent limitations. However, we can improve memory through conscious memory. For example, we can consciously deepen the impression of information through techniques such as concentration and association methods, and try to recall it later. We can improve our memory level indirectly through continuous practice to improve our memory level.

At the same time, we can also improve our memory through some living habits. Getting enough sleep, eating a healthy diet, and exercising regularly can all help improve your memory. In addition, learning new things and constantly challenging ourselves can also promote the development of brain function, so that we can better maintain a good memory.

Improving conscious memory and memory requires patience and persistence. Only through continuous practice and exploration can we become better memory experts. Let us face challenges with a positive attitude and confidence, and believe that we will be able to achieve excellent results in this field! It can be seen that we need to improve our memory. Cistanche can significantly improve our memory, because Cistanche can also regulate the balance of neurotransmitters, such as increasing the level of acetylcholine and growth factors, which are very important for memory and learning. Importantly, in addition, meat can also improve blood flow and promote oxygen delivery, which can ensure that the brain receives sufficient nutrition and energy, thereby improving the vitality and endurance of the brain.

Click know ways to improve brain function

From the Contents of Memory to Problem-solving and Abstract Reasoning

How did consciousness move from being solely the contents of episodic memory to being involved with problem-solving, abstract reasoning, and the other abilities made possible by System 2? We speculate that consciousness evolved and became involved in these other abilities due to consciousness being a key element of the episodic memory system’s function of flexibly and creatively combining episodic memories to imagine the future.

We envision an early stage of this type of combination that would simply allow us to predict the future. For example, episodic memories of finding a delicious berry near a specific cave each autumn might combine with another episodic memory of being chased by a bear near that cave. The outcome is that we can predict that if we go to pick the berries, we might end up being chased by a bear.

In addition to merely envisioning how the future might unfold, at some later point, this conscious memory creative recombination process envisioned two or more possible future outcomes. In one future, when we go to pick the berries, we are chased by the bear, whereas in another future, we are not chased.

Once consciousness can compare two possible futures, problem-solving comes in when we think about what we can do to help bring about the future that we want and to avoid the future that we do not. For example, memories of ways to determine whether an animal is in its lair or not may come to mind. Other memories may remind us that a bear can only chase one person at a time. Comparing these types of memory retrievals—that perhaps we may now refer to as thoughts —can allow a plan to develop. Problem-solving in consciousness/working memory via episodic memory retrieval is now taking place.

Once problem-solving is occurring, it is a small step to conscious abstract reasoning. As multiple events stored in episodic memory generalize into semantic memory, abstractions automatically occur. Episodic memories of individual dogs, bears, and rabbits allow for the general semantic memory categories of dog, bear, and rabbit to be formed. A more abstract semantic memory category of animals can then emerge and be contrasted with the abstract semantic memory category of plants, and so on.

Language

Much has been written about the development of language that will not be repeated here (eg, Pinker, 1994). Succinctly, we believe that language developed from a conjunction of consciousness and semantic memory.

One of the things that makes language an interesting case, however, is that although we can certainly speak with full conscious awareness and deliberation, it is our observation that we can also speak unconsciously, without thinking about it. We will return to this important concept in a later section. For now, we simply want to introduce the idea that just because a function developed with consciousness does not mean that it must be present only with consciousness.

Conscious Perception as a Memory

At this point in our paper, one might be willing to accept our theory that consciousness evolved as part of the episodic memory system but say, “So what? How does this explanation help us understand consciousness (or, for that matter, episodic memory)?”

If we believe that consciousness evolved as part of the episodic memory system, as a critical part of that system that allows us to store prior experiences in memory and retrieve them so that the memories of these experiences can be flexibly and creatively combined to allow future planning and intentional action, then there is no reason that consciousness needs to operate in real-time. If consciousness is a system for memory encoding and retrieval—and not direct action—there is no reason that it cannot function properly with a small delay. We would argue that we do not consciously perceive events directly in real-time. We perceive the world as a memory. In other words, technically, we are not consciously perceiving anything directly; we are experiencing a memory of perception.

We suggest that we experience the world by remembering sensory memories. Moreover, most of the time, we are not experiencing these bottom–up sensory memory processes by themselves. We experience sensory memory processes influenced by top–down episodic and/or semantic memory processes, such that the percept that is consciously perceived is a mashup between the bottom–up sensory memory processes and the top–down episodic and semantic memory processes.

Postdictive Effects Explained

Our memory theory of consciousness can now explain postdictive effects. For example, Sergent et al (2013) showed that not only does using a stimulus before its presentation improves the conscious perception of the stimulus but coming after the stimulus presentation can as well. Sergent and colleagues concluded that (p. 154):

the initial sensory processing associated with a stimulus can occur preconsciously because its conscious or nonconscious fate can change drastically beyond this phase. Conscious perception would thus relate to the secondary amplification of preconscious information held in sensory areas. … this secondary amplification does not have to be a direct consequence of the initial processing of the stimulus itself but can be triggered by a subsequent and independent event.

Our memory theory of consciousness is consistent with this explanation and can allow us to understand it better. Attention is drawn to the unconscious perception by the poststimulus cue, and we then experience the conscious perception in the same way that we experience all conscious perceptions—by remembering it.

The Conscious Memory of Unconscious Decisions and Actions

If we are willing to consider that we—at least as conscious selves—do not perceive the world directly but rather remember it, then we are ready to explain conscious decisions and actions. Our theory is simply that the brain processes that decide and act are unconscious. Our conscious decisions and conscious actions are memories of those unconscious decisions and actions. We believe that this explanation—that decisions and actions are fundamentally occurring through unconscious brain processes—is consistent with an evolutionary perspective that would argue that there is no single conscious decision-making system in the brain. Instead, various processes are unconsciously engaged to make specific decisions, such as when to eat, sleep, avoid, approach, grasp, release, and so on (Cisek, 2019).

We do think, however, that unconscious brain processes will sometimes engage the conscious memory system to facilitate optimal decision-making and performance in certain situations. To explain these notions further, we will provide an example using Kahneman and Tversky’s System 1 and System 2 processing (Kahneman, 2011; see also Carruthers, 2015).

System 1 Decisions and Actions

Let’s first consider System 1 decisions. These are the fast, automatic, unconscious decisions that require little or no thought or effort. Let’s say that we are working, perhaps engrossed in thought writing a paper on our computer. We suddenly decide, “I’d like a glass of water.” Before we finish typing the paragraph we are working on, and still thinking about the sentence that comes next, we rise, walk into the kitchen, open the cabinet door, reach inside, grasp a glass, pull it out, close the cabinet door, hold the glass under the faucet, turn the cold water on, watch the glass fill, turn the water off, raise the glass to our lips, tilt the end upward, take a sip, and, while holding the glass steady so as not to spill, walk back to our computer, set the glass down, sit down, and get back to work.

We would argue that our decision to get a glass of water could well have been unconsciously initiated and acted out, as could every part of the sequence. We believe that almost all of the time when we walk or grasp an object, completely unconscious brain processes carry out these actions (consistent with Aglioti et al, 1995; Chen et al, 2015; and Cisek, 2019). Insofar as we are consciously aware of what we are doing, we suggest that this conscious awareness is a memory of this decision and action. On this account, consciousness is epiphenomenal concerning decisions and actions, but not epiphenomenal in general because it plays an important role via the episodic memory system.

We would argue that our decision to get a glass of water could well have been unconsciously initiated and acted out, as could every part of the sequence. We believe that almost all of the time when we walk or grasp an object, completely unconscious brain processes carry out these actions (consistent with Aglioti et al, 1995; Chen et al, 2015; and Cisek, 2019). Insofar as we are consciously aware of what we are doing, we suggest that this conscious awareness is a memory of this decision and action. On this account, consciousness is epiphenomenal concerning decisions and actions, but not epiphenomenal in general because it plays an important role via the episodic memory system.

System 2 Decisions and Actions

Now let’s consider some analogous System 2 decisions and actions. Perhaps, instead of working on our computers, we are participating in a dangerous Hunger Games-like activity. We are thirsty, and we can see the cool spring up ahead. But to reach it, we need to either make our way across a bubbling lava field with floating rocks that we have to step on or run across a grassy meadow filled with poisonous snakes and spiders. We carefully consider our options. In the end, we decide that we will have a better chance of jumping from floating rock to floating rock across the lava. We carefully step on one rock, get our balance, and wait for another to float nearby. We time our jump perfectly and land in a crouch, distributing our weight. We continue this way until we reach the spring. We can see the glass we need, but to get it, we need to carefully reach our hand through razor-sharp barbed wire. We contort and angle our hands and fingers to reach the glass and delicately pull it back through. We fill our glass from the stream and drink down the precious liquid.

Here, we have a series of decisions and actions that need to be thoughtfully and carefully carried out. Instead of acting automatically (perhaps while thinking about something else), we have to consciously consider and fully attend to each of these decisions and actions. However, we believe that the actual decisions and actions themselves are made and carried out by our unconscious self and that we experience the conscious decision being made or action taking place only after the fact.

Unconscious Perceivers, Decision Makers, and Actors

Another way of saying this is that it is the System 1 unconscious part of our brain that perceive, make decisions, and act (consistent with Cisek, 2019), and the System 2 conscious parts that provide an additional layer of information that our unconscious brain can use (or not) to make decisions and act accordingly. System 2 uses consciousness, and thus all of the explicit memory systems, to review what we know about lava flows, snakes, and spiders (from semantic memory); how well we did the last time we had to jump from rock to rock (from episodic memory); and how, by counting in our head and watching the floating rock (using working memory), we might be able to time a jump perfectly.

The Conscious Memory System

Thus far, we have sometimes been using the term episodic memory in its standard definition (ie, memory for prior events) and sometimes as shorthand for all of the explicit memory systems: working memory, episodic memory, and semantic memory. Because we believe that all of these explicit memory systems are truly part of one system—the explicit or conscious memory system—going forward, we will use the terms episodic memory and episodic memory system just in their narrow senses and the terms conscious memory and conscious memory system in this broader sense, referring to all explicit memory systems.

Challenges for Our Theory

If we are correct that consciousness and explicit forms of memory are all part of the same system, then there should not be unconscious examples of explicit memory. We could immediately argue that there cannot be examples of unconscious explicit memory, as that would be the same as saying that there are examples of unconscious conscious memory. Nonetheless, it has been shown through carefully conducted experiments that unconscious processes similar to episodic memory, using similar anatomical networks, have enabled participants to perform inferences that would usually require conscious awareness to perform (eg, Schneider et al, 2021). In addition, other carefully conducted experiments have shown unconscious (ie, guessing) above-chance performance on delayed-response working memory tasks that would usually require keeping information consciously in mind (eg, Trübutschek et al, 2017). Do these experimental results mean that our memory theory of consciousness must be false? Although we readily admit that such experimental results are problematic for our theory and need to be explained, we would argue that they do not negate it, for the reasons presented in the next two sections.

Unconscious Episodic Memory?

In the Schneider et al (2021) study, participants were exposed to either weak masking of stimuli that allowed for conscious processing or strong masking of stimuli that necessitated unconscious, subliminal processing. Conscious processing led to an improvement in reported accuracy as well as a reduction in reaction time. Unconscious processing led to a reduction in reaction time but did not improve accuracy, which was a chance. Further, this reduction in reaction time for unconscious processing was only observed in “intuitive” decision makers who habitually responded according to their instincts (using System 1), and not in “deliberative” decision makers who preferred relying on consciously accessible knowledge (using System 2). The fMRI experiments that showed the neuroanatomical correlates of this unconscious processing were conducted exclusively with intuitive decision-makers.

Our first comment is that it is possible that even the strongly masked stimuli were minimally or partially conscious because it is difficult to exclude this possibility in experiments of this type (eg, Holender, 1986; Timmermans and Cleeremans, 2015). Thus, one explanation of these results is that the strongly masked stimuli engaged the episodic memory system because the stimuli are minimally or partially conscious for some individuals.

Our second comment is that if we agree that the strongly masked stimuli are processed unconsciously, it is possible that they still do engage the episodic memory system, but only partially, and not strongly enough for a full, true, conscious episodic memory to be formed. Support for this view comes from the fact that these strongly masked stimuli produced a change in reaction time, but not a change in accuracy. Thus, we would argue that although the strongly masked stimuli unconsciously activated the episodic memory network and produced a change in reaction time, there was no change in accuracy, no true episodic memory was formed, and therefore, there was no requirement for consciousness.

Unconscious Working Memory?

In the Trübutschek et al (2017) study, participants identified the location of visual stimuli after a delay. Stimuli were rated by the participants on a 1 (unseen) to 4 (clearly seen) scale. The participants were instructed to guess the location even if they were unable to see the stimulus. Behaviorally, the participants performed greater than chance on both the seen and the unseen trials. Magnetoencephalographic data were also obtained to determine if the same or different neural mechanisms were used by the participants when identifying the seen (correct) trials versus the unseen (correct) trials, with the hypothesis that if different neural mechanisms were engaged, accuracy on the unseen (correct) trials was not simply due to the participants misclassifying trials as unseen that were, in actuality, glimpsed. The magnetoencephalographic data clearly showed two different neural mechanisms.

Trübutschek and colleagues (2017) discovered that conscious and nonconscious working memory used different brain mechanisms and that nonconscious working memory used an “activity-silent mechanism” based on slowly decaying calcium-mediated synaptic weights. The authors then postulated that perhaps this activity-silent mechanism underlies both conscious and nonconscious working memory, which they supported with modeling (but not empirical data).

Our comment on this study is simply that many examples of unconscious processing lead to a future change in behavior or performance; priming and procedural memory being two. Thus, although we do not dispute the findings that there may be an activity-silent mechanism that supports unconscious processing of a spatial delayed response task, we would suggest that calling this processing nonconscious working memory may not be using the best nomenclature.

ANSWERS AND SOLUTIONS

Let’s now review the many previously inexplicable findings discussed earlier and consider how our memory theory of consciousness can provide explanations for each, along with some additional inferences.

Order Problems: Consciousness After the Perception, Decision, Action

If the contents of our consciousness (ie, what we are consciously aware of) are a memory of the perception, decision, and action, then there is no difficulty with consciousness occurring after the perception, decision, and action.

Tolling Bells and Cocktail Parties

Thus, there is no difficulty with our being able to count off the strokes of the clock even though we did not pay attention to them until the last chime; our conscious awareness is always a memory of the chimes. Similarly, it is not surprising that when we hear our name at a cocktail party, we can hear the earlier part of the sentence; we are remembering it, just as we do with all of our other experiences. This feature of our awareness just becomes more apparent to us when we reflect on certain types of situations.

Motor Cortex First, Conscious Decision to Move Second

The experiment conducted by W. Grey Walter now makes sense as well. In normal individuals (without electrodes implanted in their brains) who are controlling a slide show with a carousel and a push-button controller, their experience is that they make a conscious decision to advance the slide, consciously use their thumb to push the button, and then, the slide advances. However, what occurs is that the individuals make an unconscious decision to advance the slide—then consciously remember that unconscious decision, unconsciously uses their thumb to push the button—then consciously remember that unconscious action, and then the slide advances. The conscious memory for the decision and action are “timestamped” by the brain to occur not only in the proper order but also at the proper time such that it appears that this conscious decision and conscious action coincided with the unconscious decision and unconscious action even though the conscious memory of these events was experienced after the events themselves. This is not strange or mysterious: It is the nature of memory that remembered events are referred to a previous time.

In the case of the patients with electrodes implanted in their motor cortex, the patients unconsciously decide to advance the slide—then consciously remember that decision. They unconsciously decide to use their thumb to push the button, which creates the motor cortex readiness potential that triggers the slide to advance, the slide begins to advance, they consciously remember the slide beginning to advance, then consciously remember pushing the button, generating this feeling of the slide projector anticipating their decisions.

In an experiment related to motor movement, Libet (1985) compared the time in which participants consciously decided to move their wrist (determined by participants noting the time they made their decision on a special clock) with the measured readiness potential of this voluntary action at the scalp. The readiness potential has been interpreted as representing the final stages of planning preparation for movement. What was startling was that Libet (1985) found that the readiness potential preceded the voluntary decision by ∼350 ms. The author concluded that the initiation of a spontaneous voluntary act “begins unconsciously.”

We did not introduce this important experiment before now because it is quite controversial for at least two reasons. The first is that not everyone who has tried to replicate the experiment has been able to do so, although some have (eg, Vinding et al, 2014), which should set that issue to rest. The second is that Schurger et al (2012) conducted a terrific set of related experiments and analyses that they suggest explain the readiness potential not as representing the final stages of motor preparation, but rather as representing spontaneous subthreshold fluctuations in neuronal activity.

We do not disagree with the work done by Schurger and colleagues (2012), as their explanation may be the correct one for this phenomenon. We would simply like to point out that our memory theory of consciousness makes Libet’s (1985) initial interpretation comprehensible: Decisions and actions are initiated unconsciously and then we experience the conscious memory of those decisions and actions. If we believe Libet’s (1985) interpretation, and these motor results are generalizable, our conscious memory for our decisions and actions may occur ∼350 ms after the decisions and actions are unconsciously initiated.

The Incredible Slowness of Consciousness

We can now understand why it does not matter that consciousness is too slow for the real-time decisions and actions of athletes, musicians, and others who need to react quickly. All decisions and actions are occurring unconsciously. Our conscious memory of these decisions and actions occurs later.

Conscious Sensations Referred Backward in Time Stimulation of the Hand Versus the Somatosensory Cortex

Our memory theory of consciousness also helps us to understand some of Libet and colleagues' (1979) other experimental results and how these results are informative regarding the timing of consciousness. Recall that the authors found that it took ∼500 ms of cortical stimulation before a conscious experience of a tingle occurred. If the stimulation was <500 ms, the participants did not report feeling anything. Libet and colleagues (1979, p. 222) referred to this extended time as “the neuronal adequacy for consciousness.” They explained that we are not aware of this delay because events are referred backward in time after neuronal adequacy has been achieved. The idea is that when we feel a touch on our arm, the impulses travel through our peripheral nerves, spinal cord, and brain until they reach the somatosensory cortex. If the stimulus activates our cortex for at least 500 ms, we consciously feel the touch, and it is referred backward in time such that we do not notice any delay in the conscious perception (Blackmore, 2017; Dennett, 1991; Libet et al, 1979).

The first point to make here is that our new understanding of consciousness—that we do not perceive events directly but only remember them—makes it easy to understand this finding of Libet and colleagues (1979): Once the 500-ms threshold for conscious sensation is crossed, we can simply remember the sensory memory of the touch. It is not even surprising that it is referred backward in time— again, it is fundamental to memory that it allows us to experience events that occurred earlier.

The second point that Libet and colleagues' (1979) experimental results could suggest is that 500 ms is the amount of time that our conscious perceptions are delayed. In other words, if this result from these authors is generalizable to other conscious sensory experiences, then our conscious perception of the world may be delayed by half a second—although referred backward in time so that we do not notice the delay.

Chronostasis

The problem with the stopped clock illusion is that the final fixation of the clock is projected backward in time to fill in the period when we were making the saccade. This is no longer a problem because our visual perceptions are not directly experienced; they are consciously remembered. In other words, we are consciously perceiving a memory that is delayed ∼500 ms. Thus, a top–down process in our visual system projects the final fixation backward in time to fill in what would have been the missing perceptual experience while the saccade was taking place. Problem solved.

Postdictive Effects

Because conscious perception is a memory, likely delayed by ∼500 ms and referred backward in time, we now have an easy and comprehensible explanation of postdictive effects.

Rabbits

In the case of the cutaneous rabbit, there are five taps at the wrist, three near the elbow, and two at the shoulder, yet we consciously experience intervening taps as well. Again, because sensations are consciously remembered (500 ms later) rather than consciously experienced, it is not a problem for some top–down process to interpose, backward in time, intervening taps between our wrist and elbow and between our elbow and shoulder such that we consciously perceive a little rabbit running up our arm. An analogous explanation can explain the illusory and invisible audiovisual rabbits.

Color Fusion Effects

Color fusion effects can be explained similarly. When a red disk is presented for 40 ms by itself, there is the obligatory delay, and then we consciously perceive the red disk by remembering it. When the red disk is followed by the green disk in the same location, the colors are fused in our sensory memory (because they are occurring in the same time window) and, after the 500-ms delay, we perceive the fused yellow image by remembering it.

TMS Pulses

It should no longer be surprising that a TMS pulse between 20 and 370 ms can induce postdictive effects. Because conscious perception is delayed, if there is a disruption to the visual stream during the delay period, it can alter the conscious perception of the prior stimulus just like a physical stimulus can.

Color Phi Illusion

Similarly, we can now explain why it is that when we watch the color phi illusion and see a blue dot at the top of a frame followed by a blank screen, and then a red dot at the bottom of the frame, we consciously experience the blue dot traveling down and changing color before we see the red dot. Again, a top–down process has interposed, backward in time, the intervening dots and the color change into our conscious perception—easy to do because that conscious perception is a memory.

What about the suggestion by Keuninckx and Cleeremans (2021, p. 1) that the color phi illusion may simply be related to “inherent dynamical and nonlinear sensory processing in the brain” and not related to consciousness, per se? We would argue that our work helps to elucidate one part of this phenomenon (how events are referred backward in time), while theirs helps to elucidate another (why there is a sense of motion and color switch before the second stimulus is seen).

Creating Uniformity: Remembering the Gist

Our memory theory of consciousness may also help to explain why we do not notice that our peripheral vision is grayscale or that our vision is filled with the blobs and stripes related to our fixations and saccades with black areas in between. Although here we admit that we may be pushing the explanatory power of our theory past its limits, one possible explanation relates to the type of information that our conscious memory system remembers. In general, we tend to remember the general concept, idea, or gist of the information (Reyna and Brainerd, 1995). Because we now understand that we do not directly consciously perceive visual information—we remember it— we may be remembering the gist of the visual scene in the same way that we might remember the gist of a conversation, movie, or list of items. If consciousness does not have the function of capturing our occurrent sensory input, then these features of our visual experiences are not problematic.

Our view of conscious perception is thus consistent with that espoused by Cohen et al (2016). Using an understanding of perception that arises from the field of visual ensembles and summary statistics, they described how observers can extract the gist of the scene with just a few fixations.

Does Conscious Perception Overflow Working Memory?

Block (2011) and others have suggested that phenomenally conscious perception has rich content with a greater capacity that “overflows” the more limited access consciousness of perception. Evidence supporting this overflow idea comes from the Sperling (1960) paradigm, in which an array of letters (eg, in a 3 × 4 grid) is briefly shown. Participants generally report seeing all (or almost all) of the letters, yet they can report only three to four letters. Powerfully, however, when they are cued to report the letters from any row, they can recall three to four letters in that row, suggesting that all 12 of the letters were potentially accessible. Our memory theory of consciousness would explain that the full array of items is present briefly in unconscious perceptual processes, although we only experience the conscious perception of the items that our attention is drawn to by the poststimulus cue, as only after our attention is drawn to one row of letters are those items transferred into sensory memory and then into working memory.

This explanation is analogous to the one we previously discussed with Sergent and colleagues (2013). Kentridge (2013, p. R71) noted that Sergent and colleagues’ result “does not necessarily invalidate the distinction between access and phenomenal consciousness, but it does lend weight to the alternative, and perhaps simpler, position that consciousness is just consciousness.” We agree with Kentridge (2013) and Cohen et al (2016) that although distinguishing between phenomenal and access consciousness appears to be a useful distinction, it leads to strange situations in which we can have a phenomenally conscious experience that our conscious mind does not have access to. This could be rephrased to say that there can be phenomenally conscious experiences that are unconscious—an idea that does not make much sense to us. We believe that such distinctions have been postulated to solve some of the problems of consciousness—problems that we believe our memory theory of consciousness can explain without the need to invoke phenomenal and access consciousness.

Mindfulness

We can now understand why it is difficult to control our thoughts when we practice mindfulness. Our theory is that consciousness did not develop for us to perform high-level abstract reasoning using language, logic, visuospatial abilities, or other cognitive capacities to allow us to carry out intentional actions. Instead, consciousness developed for us to remember events and information, as well as to creatively and flexibly recombine those events and information. We speculate that much of this remembering—and even the recombination of the remembered events and information —can occur without volitional control over consciousness. In other words, we may consciously perceive events and, at a later time, consciously imagine the recombination of elements of those events, even if the recombination is being directed by unconscious processes. As anyone knows who has practiced mindfulness, it can take great effort to sustain conscious attention to a single object—because, we argue, that is not what consciousness developed to do.

If we consider mindfulness from our new perspective, we might imagine the following processes occurring. A thought is generated unconsciously, perhaps of a meeting we are anticipating later today. Our attention is captured by this thought. Depending on the goals of our mindfulness session, we may be content to simply be metacognitively aware of this thought, observing with some detachment the different emotions the thought produces (eg, the excitement that the meeting might go well as well as anxiety that it might go poorly). Or, we may attempt to nudge our awareness from the meeting to our breath as we try to consciously attend to air going in and out of our nostrils.

The Subjective Experience of Consciousness

One of the most exciting consequences of our memory theory of consciousness is how it might explain certain aspects of the subjective experience of consciousness.

Stream of Consciousness

We all feel that James’s (1890) metaphor of a stream of consciousness is intuitively correct, with the momentary now where we are standing in the river, past events flowing progressively downstream, and future upstream events that are going to occur rushing toward us. Part of the power of this metaphor is that it is fairly linear. Yet, we know that the brain is processing a massive amount of information in parallel. Why do we experience events serially instead of in the parallel manner that the brain processes them? We would argue that it is because it is a property of our conscious memory system to remember—and thus to consciously experience—events serially in time. Once we decouple real-time sensory input from consciousness, we no longer need the two to be processed by the brain in the same way.

We also believe that our memory theory of consciousness explains, at least on one level, why events are bundled together over time such that they seem continuous. Again, we would argue that it is part of the neural architecture of our conscious memory system to store and retrieve events that are bundled together and time-stamped in a certain order.

In the Cartesian Theater

We sometimes have the intuitive experience that we, as conscious selves, are sitting inside our head—in the proverbial Cartesian theater—peering out at the world through our eyes, as if we are watching a movie. We believe that this feeling is present because we are not experiencing our perceptions directly; we are experiencing a memory of our perceptions. Who is this homunculus sitting in the Cartesian theater? It is our conscious self remembering our perceptions, decisions, and actions. Why did it develop this way? We believe that it developed this way to allow the flexible recombination of prior events and information through imagination, like a movie director moving scenes around on a storyboard.

Do we now have to deal with an infinite regress of homunculi sitting in Cartesian theaters? We would argue not. We have one conscious self. Our conscious self is sitting in the theater, mostly passively, watching memories of experiences. The various parts of our unconscious self are processing information in parallel, sometimes paying attention to what is going on with the conscious self but mostly ignoring it. There is only one conscious homunculus. It stops right there.

Consistent With Higher-order Theories

Higher-order theories of consciousness claim that a mere first-order representation (eg, being presented with a red stimulus) would only lead to consciousness if we are in some way aware of having that experience (ie, being aware that we are seeing red). These theories also claim that conscious experiences involve some type of minimal inner awareness of one’s ongoing mental functioning due to the first-order representation being monitored or represented by a relevant higher-order representation (Brown et al, 2019).

Although our memory theory of consciousness differs from higher-order theories of consciousness in many ways, we believe that our theory is consistent with the idea that we are not conscious of the first-order brain mechanisms that process the presentation of a red stimulus in front of our eyes and that we only become conscious of this stimulus when (sitting in the Cartesian theater) we experience the memory of its perception. Thus, we believe that our memory theory can explain this intuitive sense that we do not experience first-order representations directly, but only indirectly. Higher-order theories would say that consciousness is experiencing higher-order representations of the first-order representations, whereas our memory theory would say that consciousness is remembering the first-order representations.

Resonant Metaphors

Our memory theory of consciousness helps explain why some metaphors resonate with us intuitively. Now that we understand why the Cartesian theater feels natural, we can understand why Plato’s allegory of the cave resonates with us. We do not perceive the real world directly; we only perceive shadows or reflections of the real world through memory. Similarly, now that we understand how both the feeling of the theater and the serial appearance of reality are created by our conscious memory system, we can understand why the two metaphors of the movie The Matrix are so powerful: the thought that we are not truly experiencing the world directly and that the world is made up of massively parallel processing streams of data.

Horse and Rider

We would like to introduce one additional metaphor here that captures some of how we think about the conscious and unconscious self. Imagine our brain as a horse and rider together. Our unconscious, System 1 self is the horse, which is in control of the moment-to-moment journey we are taking. Just as we do not need to provide detailed instructions to a horse on how to cross a rocky field or jump over a short wall, neither do we need to provide detailed instructions to our unconscious as to how to carry a cup full of hot coffee across the room and down a flight of stairs—we just need to look at the cup and our unconscious self does the rest. Our conscious, System 2 self is the human rider, who is mostly just going for a ride. The rider can, of course, provide either moment-to-moment or more general, overall instructions to the horse, and the horse is usually happy to oblige.

How does this interaction between the conscious rider and the unconscious horse happen? Metaphorically, the rider says a few words, tugs gently on the reins, or squeezes their legs to let the horse know which way the rider wants to go. Approximately 500 ms later, the rider can then sense whether the horse has, indeed, made the desired decision and moved in the desired direction. Of course, there are sometimes conflicts—such as when the horse wants to go down the easy path but the rider wants to travel up the mountain.

How is it that our System 2 rider can inform careful, considered decisions? Well, it is sunny out there in the Plains, and so the rider always wears a special pair of sunglasses. These sunglasses have a high-tech video screen built into them. These sunglasses have no lenses, only the built-in screen—a screen that has a delay of ∼500 ms. In other words, the rider is always perceiving the world by looking at the screen, which shows the visual world a little bit after the fact. But these special sunglasses allow a variety of amazing options: the rider can either (a) look out at the world (via sensory memory) 500 ms after it has passed by; (b) access prior autobiographical episodic memories using an active, creative, memory-building process; (c) access prior semantic information; (d) keep information on the screen so that it can be manipulated in working memory; or (e) use a combination of these features to flexibly, creatively imagine possible future outcomes.

When faced with a difficult problem, the rider can use all of these tools to come up with one or more possible solutions, which the rider then communicates to the horse, and the horse makes the actual decision—which may or may not be the same as what the rider suggested. Note that because the rider is always perceiving the world 500 ms after the fact, the rider depends on the horse to make decisions without the rider’s input whenever quick, System 1 decisions are needed.

Oh, and there is just one other issue about these special sunglasses that need to be mentioned: The images come from the horse. The horse is in control of the videos that the sunglasses are showing the rider. We can think of this part of the metaphor as explaining the 500-ms delay that the rider experiences when perceiving the world. But the horse is also in charge of whether the rider views the world, prior autobiographical episodic memories, semantic information, working memory, or imagination. As always, the rider can communicate to the horse which images they wish to see, but the horse does not always comply, either because it cannot or because it wishes to show the rider another image. This is why mindfulness is so hard; the horse has a mind of its own.

To summarize this metaphor, we consider the rider (with their sunglasses) to be the conscious memory system—remembering rather than directly perceiving, deciding, and acting. We believe that this conscious memory system was always involved in providing information that could be used by the unconscious brain to make decisions that are informed by past events and information. Through continued evolution, we believe that the conscious memory system developed additional capacities in humans as described above. By contrast, the horse represents all of the unconscious brain processes.

Limitation of These Explanations of the Subjective Experience of Consciousness

We wish to clearly state that we are well aware that our so-called explanations of the subjective experience of consciousness do not even begin to get at the hard problem of consciousness—how a collection of neurons and supporting brain tissue produces subjective experience. We are, however, hopeful that our slightly increased understanding of the phenomenology of the subjective experience of consciousness can help other researchers look in the right locations and do the right experiments to tackle the hard problem. Our suggestion to them is to focus on the conscious memory system.

Lesion Patients

Our memory theory of consciousness makes it easy to understand how individuals with visual apperceptive agnosia and individuals with blindsight can frequently respond correctly to visual tasks despite lacking conscious awareness of visual objects and other stimuli. Although the visual aspects of their conscious memory system are not functioning properly, such that their sensory and working memory are impaired—meaning that perceptions do not enter consciousness—their unconscious self can still perceive stimuli and respond accordingly.

The Causal Role of Consciousness and How Consciousness Contributes to Evolutionary Success

We have made our case that consciousness did not develop to play a direct causal role in decisions and actions and instead developed as part of the conscious memory system. However, as implied by our horse and rider metaphor, we believe that, in modern human beings —and probably many other animals as well— consciousness is essential to make good decisions and take proper actions. Consciousness enables System 2 (the rider) to use working memory as well as all prior autobiographical and semantic information to inform important decisions. Consciousness is thus tremendously important for evolutionary success: Without consciousness, System 2 decisions could not be made. If we had no consciousness, we could still make decisions, but they would always be fast, System 1 (horse-only) decisions. Consciousness allows us to make slow, carefully considered System 2 decisions. We will discuss these issues in more detail later on when we discuss the implications of our memory theory of consciousness.

Consciousness Is not Epiphenomenal

Although we have argued that conscious memory is important for evolution, we have not yet discussed whether the actual subjective experience of consciousness is epiphenomenal. We believe that subjective experience is an inherent property of the conscious memory system and that to say that we can have one without the other would be analogous to saying that we can have molecular motion without heat. Just as ½MV2 = 3 2/ KT, we believe that the use of the conscious memory system produces subjective experience. As mentioned earlier, we do not have the answer to this hard problem of consciousness, but we are hopeful that our theory will move the field toward finding that answer.

NEUROANATOMICAL CORRELATES AND DISORDERS OF CONSCIOUSNESS

As might be expected from our experience in philosophy, experimental psychology, cognitive neuroscience, and neurology, our hypothesis of the neuroanatomical correlates of consciousness relates to brain regions and structures and not to underlying cells, cellular assemblies, or neural oscillations (eg, Lou et al, 2017). We understand that cellular and molecular microstructures may be crucial to gaining a full understanding of the neurophysiologic basis of consciousness, including the hard problem. Again, we hope that this discussion of what we consider to be key brain regions and structures will help others to dive deeper and achieve a more complete understanding of the hard problem. Because much of our discussion of the possible neuroanatomical correlates of consciousness is related to individuals with various brain disorders, we will consider these two topics together.

Other Theories of the Neuroanatomical Correlates of Consciousness

There are currently four major theories that make predictions regarding the neural correlates of consciousness: recurrent processing theory (Lamme, 2015, 2018), global neuronal workspace theory (Mashour et al, 2020), integrated information theory (Tononi et al, 2016), and higher-order thought theory (Brown et al, 2019). Some of these theories specifically address the hard problem, whereas others, like ours, only try to point the way toward possible solutions. As pointed out by Yaron et al (2022), each of these four theories emphasizes largely different cortical regions as being critical for consciousness.

Recurrent Processing Theory

Recurrent processing theory suggests that conscious processing depends on horizontal connections and recurrent loops between lower- and higher-brain regions that are extended in time and space and involve changes mediated by NMDA-dependent feedback activations (Lamme, 2015). Posterior cortical regions associated with the visual processing of information are emphasized, with the prefrontal cortex contributing to, but not essential for, conscious processing (Lamme, 2018).

Global Neuronal Workspace Theory

Arising out of the global workspace theory (Baars, 2005; described earlier), global neuronal workspace theory proposes that conscious processes occur when information in specialized processors enters a large-scale reverberant brain-scale network of high-level cortical areas linked by long-distance re-entrant loops and becomes ignited, allowing global access by other specialized processors (Mashour et al, 2020). The parietal and prefrontal cortical areas are critical for routing information between other cortical processors. At the neuronal level, large pyramidal cells in cortical layers II/III and V play key roles in the neuroanatomical correlates of consciousness.

Integrated Information Theory

Integrated information theory attempts to directly address the hard problem by starting from the essential phenomenal properties of experience and infers postulates about the characteristics that are required of its physical substrate (Tononi et al, 2016). It also provides a mathematical quantity of integrated information that yields a measure of the degree of consciousness of any system. The occipital and parietal lobes are considered to be critical and sufficient for conscious experience.

Higher-order Theories

As introduced earlier, higher-order theories postulate that a first-order representation, such as awareness of a rose, would not be sufficient for conscious experience to arise. An organism must be in some way aware of itself as being in a first-order state to be conscious of it. Proponents of higher-order theories consider the prefrontal cortex to be important for conscious perception (Brown et al, 2019).

Neuroanatomical Correlates of the Conscious Memory System

Having reviewed some of the leading theories that suggest which brain regions are important for consciousness, we will now state our hypothesis, which we will then work to support. Because we contend that the conscious memory system supports both consciousness and all forms of explicit memory, we hypothesize that the neuroanatomical correlates of consciousness are the neuroanatomical structures that are involved in all forms of explicit memory.

Which structures are involved in explicit memory? The hippocampus should certainly be included along with related structures, such as the neighboring entorhinal and perirhinal cortex, as well as Papez’s circuit, including the fornix, mamillary bodies, and anterior nucleus of the thalamus. We would also argue that the cerebral cortex is necessary for explicit memory. We might immediately think of the inferolateral temporal cortex for semantic memory, and then perhaps the frontal and parietal cortex for working memory, including regions that are involved with the default mode network, such as the medial prefrontal cortex, posterior cingulate cortex, precuneus, and angular gyrus (eg, Zheng et al, 2021). But, we take the view espoused by Murray et al (2020, p. 2) in their book, The Evolutionary Road to Human Memory. They argue that the entire cerebral cortex is important for memory, writing:

In our opinion, every cortical area contributes to memory, each in a specialized way. As our ancestors traveled along their evolutionary trajectories, cortical areas accumulated over time; and, in each instance, this happened for the same fundamental reason: to transcend problems and exploit opportunities that these animals faced in their time and place.

The Evolutionary Road to Human Memory (Murray et al, 2020) provides a wonderful summary of the animal, and human brain lesion, and neuroimaging studies that support the view that all cortical structures are not only involved with, but are critical for, a specific type of memory that is needed for a specific type of task, whether it be navigating the wilderness, distinguishing the sounds of prey and predators, or recognizing faces.

We contend not only that every cortical region contributes to memory, but that they each also contribute to a specific domain of conscious awareness. For example, we believe that the following speculations are likely correct:

Visual areas in the occipital cortex are necessary for visual consciousness, including visual imagery.

The auditory cortex in the superior temporal cortex is necessary for auditory consciousness.

The parietal cortex (particularly of the nondominant hemisphere) is necessary for conscious awareness of space (particularly on the contralateral side).

The primary somatosensory cortex in the postcentral gyrus of the parietal lobe is necessary for certain subdomains of sensory consciousness such as graphesthesia (identification of numbers or letters written on the skin) and stereognosis (identification of objects by touch).

The primary motor cortex in the precentral gyrus of the frontal lobe is necessary for conscious awareness of the fine motor movements that are used to play musical instruments, thread needles, and perform other delicate tasks.

The frontal eye fields are necessary for conscious awareness of eye movements.

Broca’s area is necessary for conscious awareness of our speech, whether vocalized or just “in our head.”

The insular cortex is necessary for conscious awareness of our body.

The prefrontal cortex areas that facilitate complex thought, working memory, problem-solving, and judgment are necessary for the conscious awareness that comes with these higher-level abilities.

The work of Gazzaniga (2015) and others with split-brain patients has demonstrated that when the corpus callosum is severed, the individual may be left with two separate consciousnesses in one brain that, seemingly, work together just fine without any apparent functional difficulty or conflict (or, at least, no more internal conflict than any of us have with our unsplit brain from time-to-time). We believe that something analogous occurs not only with the left and right hemispheres but also with each region of the cortex.

We further suggest that each region of the cortex is autonomously conscious, and its island of consciousness is not dependent on any central executive or other region. That is, the minimally sufficient cortical region needed for conscious awareness may be any cortical region, whether it be a sensory region enabling conscious perception, a motor region enabling conscious movement, or an association region enabling some type of multimodal thought. We believe that this must be the case because, as far as we are aware, there is no single cortical region (unilateral or bilateral) that, when removed, renders the individual unconscious. Thus, we contend that the visual conscious awareness in the occipital cortex is independent of the auditory consciousness in the superior temporal cortex, and both are independent of the conscious awareness and guidance of motor movements occurring in the frontal cortex.

What is the evidence for this hypothesis that any cortical region may be autonomously conscious? In large part, it comes from the experience of working with several thousand patients who have had strokes or neurodegenerative diseases affecting every part of their cortex and is supported by the human patient literature. It is well known that damage to subcortical structures that are part of the reticular activating system (such as portions of the midbrain and thalamus) can lead to unconsciousness (eg, Kinney et al, 1994), but, again, we know of no cortical regions that lead to unconsciousness when they are damaged. Indeed, it might be that some of these subcortical reticular activating system structures (such as the thalami) act as a hub, switching between different conscious cortical regions.

The literature supporting our view that (a) disruption of no cortical region (even widespread frontal or occipital/parietal regions) leads to unconsciousness but (b) virtually all cortical regions contribute to consciousness has been well reviewed by the opposing front versus back cortical theories of consciousness (Boly et al, 2017; Michel and Morales, 2020; Odegaard et al, 2017). We believe that our theory can reconcile those views espoused by the opposing front versus back camps.

For example, if posterior brain regions are critical for consciousness, as suggested by recurrent processing theory and integrated information theory, how is it that patients with posterior cortical atrophy or bilateral occipital and parietal strokes are not unconscious? These patients most certainly have deficits of conscious awareness, but we would never say that they are unconscious. Similarly, if the prefrontal cortex is critical for consciousness, as suggested by global neuronal workspace theory and higher-order theories, what about patients with behavioral variant frontotemporal dementia or bilateral frontal strokes? There is no doubt that the consciousness in these patients is impaired, but we would not say that they are the physical manifestation of unconscious philosophical zombies appearing to have a conscious inner world when they have none. We believe that they could consciously experience the beauty of a sunset as well as anyone else. Which group of patients is not conscious (in addition to those with reticular activating system damage)? We believe that it is individuals with either widespread or diffuse cortical dysfunction. These awake but not-conscious individuals are described as having encephalopathy or delirium.

Exactly how large would a cortical region need to be to support some form of independent consciousness? We do not know the answer, but we will suggest some methods to address that question in Future Directions.

Note, however, that we are not saying that the only function of the cortex is to provide conscious awareness of specific modalities. The cortex certainly performs much additional work that is solely involved in the unconscious processing of information.

We will also point out that saying that the entire cortex is involved in consciousness is not the same as saying that the entire brain is involved in consciousness. For those readers who think of the cortex as being more or less synonymous with the brain, please note that although the cerebral cortex comprises 82% of the mass of the human brain, it contains only 16 billion (19%) of the 86 billion neurons that are in the brain (Herculano-Houzel, 2009).

We now turn to a brief review of some of the major brain regions and structures that are involved in the conscious memory system, along with some of the relevant neurologic disorders that impair consciousness in one way or another.

Hippocampus, Related Structures, and Individuals With Amnesia

When considering the hippocampus, we typically also consider both neighboring medial temporal lobe structures such as the entorhinal and perirhinal cortex, as well as anatomically connected structures such as the fornix, mamillary bodies, and anterior nucleus of the thalamus. Whether because of neurodegenerative disease, infection, inflammation, stroke, seizure, or surgery, the cognitive effects of damage to the hippocampus and related structures are well known. Disruption of episodic memory invariably occurs, leading to anterograde and some retrograde amnesia. Consciousness, at least in the ordinary sense of the term, does not appear to be disrupted by damage to the hippocampus and related structures. Individuals with such damage can certainly consciously experience many perceptions, decisions, and actions.

However, individuals with damage to the hippocampus and related structures do show impairment in several aspects of cognition that we would argue are related to consciousness. First, individuals with hippocampal damage typically lose the ability to consciously perceive subtle differences in visual scenes, and individuals with neighboring perirhinal cortex damage typically lose the ability to consciously perceive subtle differences in faces (Mundy et al, 2013). Second, these individuals show a reduced ability to imagine the future (Addis et al, 2009) and therefore to plan for it. Third, by losing the ability to form new episodic memories, these individuals are impaired in their ability to update their sense of self. We consider the ability to imagine the future and to update one’s sense of self to be important aspects of consciousness.

Lastly, we speculate that consciousness would almost certainly be impaired if the hippocampus and related structures were completely absent from birth. Although studies have shown that individuals with perinatal damage to some regions of the hippocampus develop normal semantic memory and do not show any obvious impairments in consciousness (Elward and Vargha-Khadem, 2018), we believe that consciousness would not be normal in individuals with complete absence or complete dysfunction of the hippocampus and related structures since birth.

Occipital Cortex, Visual System, Anton Syndrome, Blindsight

We described previously how individuals with damage to the occipital cortex leading to visual apperceptive agnosia or hemifield blindness can sometimes perform tasks unconsciously that depend on vision even though they cannot perform the task with conscious awareness. We believe that these cases support the idea that it is the visual cortex in the occipital lobes that provide conscious awareness of vision.
Individuals with damage to their entire occipital cortex bilaterally, leading to complete cortical blindness, may deny that they are blind (Anton or Anton-Babinski syndrome), which is a form of anosognosia or unawareness of their deficit (Das and Naqvi, 2022). We believe that this syndrome is one example of a general phenomenon whereby the brain region that generates a specific aspect of consciousness—in this case, visual perception and visual imagery—is the same part that is responsible for the awareness of whether that aspect of consciousness is present, absent, or distorted. We would predict that Anton syndrome would not be present if the damage to the visual system affected pathways before the occipital lobes (such as the eyes, optic nerves, tracts, radiations, or lateral geniculate nuclei). Thus, we believe that the phenomenon of Anton syndrome supports the idea of visual consciousness being present in the occipital cortex.

Parietal Cortex, Spatial Neglect, and the “Aha” Moment of Recollection

The parietal lobe plays an important role in attention to, or awareness of, one side of the world. Although both parietal lobes contribute to awareness of both the left and the right side, damage to the parietal lobe of the language-dominant hemisphere (usually left) typically produces a mild and temporary loss of awareness (or neglect) of the contralateral right side, whereas damage to the nondominant (usually right) parietal lobe typically produces prominent and sometimes permanent neglect of the contralateral left side (Mesulam, 1999).

Neglect most commonly occurs for sensory stimuli that are localized in space, such as visual and tactile stimuli. Individuals with neglect may not notice food on the left half of their dinner plate, may find it difficult to pay attention to someone who is speaking to them on their left, and may not notice a touch to the left side of their body.

What is particularly striking about individuals with right parietal lobe damage and left neglect is the fact that they are typically completely unaware that the left side of the world is missing. As in Anton syndrome, individuals with neglect have anosognosia and are unaware of their deficit. We believe that parietal damage-induced neglect supports the idea of spatial awareness (consciousness) of one side of the world being present in the parietal cortex, particularly in the nondominant hemisphere.

Other parietal lobe functions may also be relevant for consciousness. Except for the retrosplenial cortex, damage to the parietal lobes is not known to impair episodic memory. Yet virtually every recognition memory task evaluated with fMRI or event-related potentials (ERPs) produces activation of the parietal cortex (Simons et al, 2008). How are we to reconcile this discrepancy? We answer that the so-called parietal old–new effect (in which previously seen or old items show greater parietal activation compared with novel or new items) is part of the neural correlate of the conscious awareness that an item has been seen before. It is that aha moment when we consciously think, “Yes, I remember that” (Ally et al, 2008).

Frontal Cortex, Motor System, and Corticobasal Syndrome

Regarding consciousness and the frontal cortex, we begin by noting that neglect also occurs for movements and activities after damage to the supplementary motor cortex (Laplane and Degos, 1983). Individuals with this type of damage might abandon washing, shaving, or brushing their hair on one side. Similarly, individuals with damage to the frontal eye fields typically show a form of neglect in that they experience difficulty moving their eyes voluntarily to the opposite side. We believe that these motor forms of neglect support the idea that the frontal lobes are important for the conscious control of movements and activities.

Some individuals with brain lesions experience a bizarre delusion in which they do not recognize or believe that their paralyzed limb cannot move (ie, anosognosia) or even that it is part of their body (ie, somatoparaphrenia). Brain regions implicated in somatoparaphrenia include portions of the insula and the middle and inferior frontal gyri (Gandola et al, 2012). Thus, conscious awareness of movement, and even awareness that a body part is one’s own, may be related to proper cortical functioning.

Some individuals with corticobasal syndrome experience alien limb phenomena, in which an affected limb appears to move on its own—without conscious control. We have seen patients in which the usually useless limb may rise and make simple movements. When the patient is performing tasks that would typically require two hands, such as tying shoelaces, the useless limb can sometimes be cajoled into helping, which it then may do easily and automatically (A.E.B. observation). Although individuals with corticobasal syndrome show involvement in the basal ganglia in addition to the cortex, atrophy and/or hypometabolism of the frontal and parietal cortex is prominent and generally detectable in brain imaging studies. This phenomenon supports the idea of the importance of the cortex in conscious motor control.

Individuals with behavioral variant frontotemporal dementia show atrophy and/or hypometabolism of various regions of the frontal cortex, leading to behavioral problems. Many of these individuals demonstrate utilization behavior, which occurs when individuals see a tool and automatically start to use it. An individual may pick up a pair of scissors and begin cutting or a pen and begin writing. We view utilization behavior as an example of damage to the frontal cortex, leading to impaired conscious control of behavior but preserved unconscious actions. There are many other examples of damage to the frontal lobes leading to a loss of conscious control of behavior (eg, Phineas Gage [Damasio et al, 1994]), which we will not review here.

Apathy is a very common symptom in individuals with a variety of damage to the prefrontal cortex. Here, we would argue that some of the so-called higher frontal lobe functions, such as planning and abstract reasoning, are impaired because conscious awareness and control of such functions have been impaired. Not consciously realizing that one should be planning and acting leads to apathy.

Temporal Lobes, Auditory Cortex, Inferolateral Temporal Cortex, Names, Words, and Meaning

Important aspects of the temporal lobe cortex include parts of the insula, the auditory cortex, and the vast store of information that comprises semantic memory. Individuals with damage to the bilateral auditory cortex lose conscious awareness of sounds but still may react to them, which is a phenomenon that is considered analogous to blindsight (Cavinato et al, 2012). Animal studies have shown experimentally that damage to the bilateral auditory cortex does not necessarily change behaviors in response to sounds (Floody et al, 2010). Thus, we have evidence that the auditory cortex is involved in the conscious awareness of sounds in a manner that is consistent with our hypothesis.

Evidence from both imaging and individuals with brain lesions suggests that the inferolateral temporal cortex is critical for conscious awareness of the names of people, animals, and tools (Damasio et al, 1996). Moreover, although unilateral left-sided damage may impair access to just the names of such items, bilateral damage may lead to a complete loss of knowledge of animals, plants, and man-made objects. Individuals with neurodegenerative diseases, including semantic dementia and Alzheimer's disease (AD), frequently experience this loss of knowledge in the later stages—not knowing what a rabbit, pumpkin, or remote control is—which, we would argue, is the loss of a form of awareness of, or consciousness of, the items. In addition, even very early on in the course of their disease, once the concept of an item is completely lost from semantic memory, individuals with these semantic memory deficits are not consciously aware that anything is wrong—they just believe that they may never have encountered the missing items and therefore have no knowledge of them.

Properties of the Cortex That Support Consciousness

We hope that we have made our case that each cortical area contributes to specific conscious awareness related to the function of that cortical area and that the destruction of any cortical area will disrupt or abolish the domain of consciousness that was supported by that area without disrupting other domains of consciousness. Our hypothesis that all cortical regions contribute to consciousness is consistent with a recent neuroimaging study that compared conscious versus unconscious object recognition and found widespread areas of cortical involvement during conscious object recognition (Levinson et al, 2021).

Our anatomical hypothesis also provides one way to reconcile the different predictions made by the four major theories of consciousness regarding which cortical regions are most important (see Yaron et al, 2022, for review), arguing that they all are, but none is critical. We are not implying that subcortical structures are not necessary for consciousness—they most certainly are—but they are not sufficient for consciousness. Furthermore, subcortical structures do not contain the necessary neuronal architecture that allows for phenomenology or qualia of consciousness to occur.

Although we consider cerebral cortex architecture as the unit of neuronal assemblies that allows consciousness to occur, exactly how consciousness arises from the cortex is unclear. We will leave it to others to determine whether consciousness is related to the spindle neurons (also known as von Economo neurons) found in layer V, thick tufted pyramidal neurons in layer VB, largely pyramidal cells in cortical layer II/III, other neuronal types, or none of these. It may be that assemblies of neurons are the unit of consciousness and that looking at single cells to understand consciousness is similar to studying the nature of quarks inside the neutrons of iron atoms to understand why iron filings are attracted to magnets. Thus, it may be that concepts such as the perturbation complexity index (PCI) that evaluate the integrity of brain networks will be key to understanding consciousness (Koch et al, 2016).

Supposing that assemblies of neurons in the cortex are the unit of consciousness, how many layers of the cortex are required? Is only a 6-layered cortex conscious, or is a 5-, 4-, or 3-layered cortex sufficient? Can a 3-layered allocortex produce some “low-level” perceptual or emotional consciousness, whereas a 6-layered neocortex is required for higher-level self-consciousness and abstract reasoning? Because our memory theory of consciousness is that consciousness is developed as part of the conscious memory system, which includes hippocampally-based episodic memory, we speculate that some conscious awareness is present in even the allocortex.

Whatever the correct answer, we would argue that our lack of understanding of exactly how the cortex produces consciousness does not prevent us from using this hypothesis of the involvement of the cortex in consciousness to discuss some implications, which we will do now.

IMPLICATIONS

Our memory theory of consciousness, with regions of the cerebral cortex as the fundamental units that allow for conscious awareness, leads to several implications regarding which animals are conscious, which neurologic and psychiatric disorders may impair consciousness, and how the conscious mind and unconscious brain work together day by day, minute by minute, and second by second. These implications, in turn, raise ethical implications, which we will also briefly discuss.

Animal Minds

In the prior section, we speculated that conscious awareness of basic perceptions and emotions may be present with a 3- or 4-layered allocortex, whereas conscious abilities such as problem-solving may require a 6-layered neocortex.

Consciousness in Mammals

Because all mammals have a neocortex (Kaas, 2019), we argue that all mammals are conscious. Paralleling their differences in cortical structure, we believe that the consciousness of mice differs in its complexity from that of a dog, which differs from that of a chimpanzee, which differs from that of a human. For example, Pine et al (2021, p. 701) reviewed some of the changes in the neuroanatomy between nonhuman and human primates, such as the expansion of homotypical association areas and the hippocampus and how these expansions are related to “(i) a subjective sense of participating in and re-experiencing remembered events; and (ii) a limitless capacity to imagine details of future events.” Although we certainly agree that humans developed these capacities to a greater extent than all other species, we also believe that all mammals have some conscious awareness of (ie, memory for) perceptions, decisions, and actions. See Carruthers (2015) for a similar argument that is also based on neuroanatomical homology.

Does this mean that all mammals have human-like conscious memory abilities to mentally time-travel? Suddendorf and Corballis (2007, p. 307) argued that there is little evidence to suggest that nonhuman mammals have developed this mental time-traveling ability, at least in the way that humans do, stating, “We maintain that the data so far continue to suggest that mental time travel is unique to humans.” Although we do not contest their statement, we would still argue that nonhuman mammals possess some form of conscious memory that allows them to have some conscious awareness that provides them with evolutionary advantages, such as being able to determine temporal order (Eichenbaum et al, 2005).

What about the mirror self-recognition test? In this test, animals have a spot of color applied to their head when they are anesthetized or otherwise unaware of its application, in a location that they can only see in a mirror, such as their forehead. If the animal looks in the mirror and reaches for the spot or tries to rub the spot off, then we know that the animal recognizes itself in the mirror. If not, we presume that the animal does not realize that it is itself in the mirror.

Although several mammals have been shown to pass this test, including the four great apes, bottlenose dolphins, and Asian elephants (de Waal, 2019), most other mammals have not, including our feline and canine companions (although dogs can pass an odor version of the test [Horowitz, 2017]). We believe that this test tells us something about visual perception and the recognition of self-consciousness, but we would argue that just because an animal fails the mirror test does not mean that it has no conscious awareness of any type.

Consciousness in Nonmammalian Species

What about consciousness in other vertebrates such as birds, lizards, amphibians, and fish? Magpies have been shown to pass the mirror self-recognition test (Prior et al, 2008), as has a species of fish (Kohda et al, 2019). Does this mean that certain bird and fish species are self-conscious? de Waal (2019) argued that passing the mirror test indicates at least some rudimentary self-awareness; however, one researcher suggested that we should consider all the data that shed light on the cognitive capacities of a species before concluding its self-awareness (or lack thereof) (Vonk, 2020).

Our theory would be aligned with de Waal’s (2019), that consciousness and self-awareness among species are on a continuum. Based on both experimental work and the brain anatomy of vertebrates, we believe that there is evidence that most vertebrates have at least some rudimentary conscious memory system because they have some form of a hippocampus (or a brain structure analogous to it) and some cortex (or analogous structure). It follows logically that those vertebrates that have the requisite anatomy for the conscious memory system would experience at least some conscious awareness, although it might be little more than perceptions and/or emotions. Some researchers have argued that at least one nonmammalian vertebrate species, the California scrub jay, can use its memory to spontaneously plan for the future without reference to its current motivation— something that had previously been thought to be a uniquely human ability (Raby et al, 2007; see also Carruthers, 2015).

Our theory is also consistent with many of the ideas put forth by Ginsburg and Jablonka (2021), who go even further than we do. They suggested that “unlimited associative learning” can be considered a marker of minimal consciousness. They noted that such learning is present not only in almost all vertebrates, but also in octopods, squid, cuttlefish, honeybees, and cockroaches.

Ethical Implications of Conscious Vertebrates

We are not vegetarians and do not want to imply that the inevitable ethical conclusions that stem from our theory mean that we should all become vegetarians (or at least, nonvertebrate consumers) to avoid harming conscious animals. However, we would argue that we as societies and individuals should consider the ethical implications of consuming cows, pigs, chickens, and other vertebrates that we argue have forms of conscious awareness.

Disorders of Consciousness

Now that we have a better understanding of both the phenomenology of consciousness and the neuroanatomical structures needed for it, we can speculate that several psychiatric, neurologic, and developmental brain disorders may be disorders of consciousness.

Strokes

We reviewed earlier how strokes that damage certain areas of the cerebral cortex result in specific impairments in consciousness that are related to the functions of those particular areas. Here, we will simply add that strokes in the subcortical white matter of the corona radiata may also cause impairments in consciousness by disconnecting cortical regions from one another, leading to, for example, Wernicke aphasia (Mesulam et al, 2015) or alexia without agraphia (Geschwind, 1965). In brief, strokes that affect cortical and/or subcortical white matter frequently impair one or more domains of consciousness, the conscious memory system, and the ability to use previously learned information to problem-solve and plan for the future.

For more information:1950477648nn@gmail.com