A Longitudinal Study Of Episodic And Semantic Autobiographical Memory in AMCI And Alzheimer’s Disease Patients Part 2

2.3.2. Assessment of Autobiographical Memory

The Autobiographical Memory Interview (AMI) [31] is a semi-structured interview used to assess memory retrieval in two domains: personal semantic and autobiographical incidents that are considered episodic. 

Autobiographical events refer to things that are of great significance or deep impression on a person's life. They may be good memories or setbacks and difficulties, but in any case, they have a profound impact on our growth and development.

At the same time, memory is also one of the important functions of the human brain. It is the basis of our learning, cognition, and expression. The impact of autobiographical events on memory is also quite important.

First, autobiographical events can help us strengthen our memory, especially for those events that are of great significance and emotional resonance. Studies have shown that we pay more attention and attention to some events with emotional value, leaving a deeper impression in the brain, and this impression can last for a long time.

Second, autobiographical events can also help us improve our memory. By recalling and recording autobiographical events, we can stimulate neuronal activity in the brain, strengthen the connection and communication between neurons, and thus promote the development of the brain and the improvement of memory.

Finally, autobiographical events can also help us maintain an optimistic attitude, which is also very important for the improvement of memory. Positive emotions can promote nerve conduction in the brain and enhance the vitality of neurons, which helps to improve memory.

In short, there is a close connection between autobiographical events and memory. By recalling and recording autobiographical events, we can not only enhance our memory but also improve our emotional state and make ourselves more positive. Therefore, we should attach importance to the collection and recording of autobiographical events, pass these precious experiences to the next generation, and also continuously improve and strengthen our memory. It can be seen that we need to improve memory, and Cistanche can significantly improve memory because Cistanche has antioxidant, anti-inflammatory, and anti-aging effects, which can help reduce oxidative and inflammatory reactions in the brain, thereby protecting the health of the nervous system. In addition, Cistanche can also promote the growth and repair of nerve cells, thereby enhancing the connectivity and function of neural networks. These effects can help improve memory, learning ability, and thinking speed, and can also prevent the occurrence of cognitive dysfunction and neurodegenerative diseases.

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Questions about personal semantic content (involving retrieval of personal facts from one's past life) and autobiographical incidents (involving retrieval of episodes or incidents from one's past) are chosen to evoke memories from three periods (childhood, early adult life, and recent life). 

In the Personal Semantics section, the subject is asked to recall information and the scores vary from 0 to 2 depending on the quality of the memory (better memory, better score). 

Subjects can obtain a maximum of 21 points in each of the three major periods, and 63 points in the whole test; in this section, the AMI offers alternative questions to facilitate responses in people with different circumstances and contexts. In the Autobiographical Incident section, which evaluates episodic memory, subjects should evoke three incidents per period. 

The score depends on the descriptive richness of the incident and its specificity in time and place. 

If the memory specifies the temporal moment and place, it obtains 3 points; if it is not very specific and does not include the time or place, it obtains 2 points; if it is a vague memory, it is awarded 1 point; and finally, if there is no answer or the answer is based on semantic memory, 0 points are awarded; a maximum of 27 points may be attained in the test. 

Two independent judges individually assessed the responses to calculate inter-judge reliability; ratings were correlated using Pearson's correlations and obtained r > 0.83, which guarantees reliable correction.

2.3.3. Follow-Up Assessment

Fifty-nine participants underwent a follow-up assessment in which they were readministered the AMI as well as the neuropsychological tests. The average time between baseline and follow-up was 18.1 months (range 16 to 19; SD = 0.78) and did not differ significantly between the groups.

2.4. Data Analysis

Two mixed ANOVAs with 3 groups (healthy older control, aMCI, and AD; between subjects) × 2 times (T1 and T2; within-subjects) were applied to two types of memory (episodic or semantic). Simple effects tests were applied to analyze the significant interactions. All analyses were carried out using the SPSS 21 (IBM Corp, Armonk, NY, USA) statistical package.

3. Results

A mixed ANOVA was performed with three groups (HOC, aMCI, and AD, between subjects) × 2 times (T1 and T2; within-subjects) on the episodic autobiographical memory scores. 

Results showed significant main effects for both the time (F (1, 56) = 29.32; p < 0.001; η 2 = 0.344) and group (F (2, 56) = 66.01; p < 0.001; η 2 = 0.213), as well as the interaction (F (2, 56) = 13.38; p < 0.001; η 2 = 0.323; see Figure 1). 

Given the significant interaction, two simple-effects tests were applied. Regarding the differences between groups at each time, the differences were significant at baseline (F (2, 56) = 30.88; p < 0.001; η 2 = 0.525), with greater recall in healthy older adults than in aMCI (p = 0.010) and AD (p < 0.001), and greater recall in aMCI than in AD (p < 0.001). 

At the follow-up assessment, the between-groups comparison also showed significant differences (F (2, 56) = 95.25; p < 0.001; η 2 = 0.773), with greater recall in healthy older adults than in aMCI (p < 0.001) and AD (p < 0.001), and greater recall in aMCI than in AD (p < 0.001). 

Regarding the differences between times for each group, the simple-effects test showed a non-significant effect in the healthy older adult group (F (1, 56) = 0.72; p = 0.399; η 2 = 0.013), but a significant decrease in both the aMCI group (F (1, 56) = 25.41; p < 0.001; η 2 = 0.312) and the AD group (F (1, 56) = 18.31; p < 0.001; η 2 = 0.246).

About the semantic autobiographical memory scores, the mixed ANOVA showed significant main effects for both the time (F (1, 56) = 15.38; p < 0.001; η 2 = 0.216) and group (F (2, 56) = 54.59; p < 0.001; η 2 = 0.213), and a significant time x group interaction (F (2, 56) = 10.19; p < 0.001; η 2 = 0.661; see Figure 1). 

Given the significant interaction, two simple-effects tests were applied. Regarding the differences between groups each time, the differences were significant at baseline (F (2, 56) = 33.82; p < 0.001; η 2 = 0.547), with no difference between healthy older adults and aMCI, but greater recall in healthy older adults than in AD (p < 0.001), and greater recall in aMCI (p < 0.001) than in AD (Figure 1). 

At the follow-up assessment, the between-groups comparison also showed significant differences (F (2, 56) = 59.78; p < 0.001; η 2 = 0.547), with greater recall in healthy older adults than in aMCI (p < 0.001) and AD (p < 0.001), and greater recall in aMCI than in AD (p < 0.001). 

Regarding the differences between times for each group, the simple-effects test showed a non-significant effect in the healthy older adult group (F (1, 56) = 1.19; p = 0.280; η 2 = 0.021), but a significant decrease in both the aMCI group (F (1, 56) = 5.75; p = 0.022; η 2 = 0.091) and the AD group (F (1, 56) = 21.23; p < 0.001; η 2 = 0.275).

4. Discussion

The results obtained complement previous findings, confirming that episodic AM was worse when the pathology was more serious; this pattern observed at baseline was maintained at the follow-up. Regarding the longitudinal findings, no significant change was observed in the scores of the healthy controls, but the aMCI and AD subjects showed a significant decrease in their scores on episodic and semantic autobiographical memory. 

As the results show, there is a pattern of episodic AM deterioration in the groups of patients as compared to the healthy controls that are maintained in the two-time points evaluated, suggesting that when the pathology became more severe, this deterioration was also greater. Some studies have found that episodic memory is impaired with normal aging, finding differences in episodic memory between young and older adults [32,33]. 

Furthermore, this deterioration in episodic memory is also observed in those studies that compare middle-aged adults with older adults, finding a gradual and progressive deterioration of episodic memory as the person gets older [4,18]. In our study, no deterioration in episodic memory was observed between times in the group of healthy older adults, since the period was only 18 months. 

Perhaps, if we could compare their current scores with those obtained years ago, we would have observed this pattern. Regarding the aMCI group, a decrease in episodic recall was observed, although this decrease was not as pronounced as that observed in the AD group. The reduction in episodic autobiographical memory in aMCI could be related to the dysfunction of neocortical structures [12]. 

In AD, one of the earliest symptoms is a deficit in anterograde episodic memory [34], followed by a retrograde impairment [35]. Moreover, in patients with aMCI and AD, the MTL, particularly the hippocampus and entorhinal cortex, has been found to undergo early volume loss [35], which is associated with a decline in both anterograde and retrograde memory performance. 

Therefore, the differences observed in episodic AM between the groups of patients could be because, in aMCI, MTL volume lies between that of healthy elderly people and patients with AD [36]. 

In semantic AM, two results stand out when comparing the groups. While healthy controls and aMCI at baseline showed differences from the AD group, in the follow-up, differences were obtained between healthy controls and aMCI, and between both groups and AD. 

The results obtained in aMCI could explain the contradictions found in some studies. Some studies did not detect any impairment in autobiographical semantic memory in healthy older adults [37] and aMCI patients [12]. 

A possible explanation for the maintenance of semantic memory in the aMCI group could be that the details provided by the participants were not linked to a spatial or temporal context, and therefore did not depend on the hippocampus. Furthermore, this result suggests that neural systems that support these memories, such as the lateral temporal cortex, may remain relatively intact in aMCI [12]. 

In contrast, other studies demonstrated that personal semantic memory is compromised in aMCI in comparison with healthy elderly controls [16] and pointed to a decline in semantic autobiographical memory for recent memories [15]. 

As the authors have indicated, these differences in the previous findings may be due to differences in the patient populations studied. When studying the same group at two different time points, it has been observed that both results can make sense, and the deterioration in this type of memory in these patients would be confirmed. 

This result demonstrates the semantic AM deterioration in the aMCI group eighteen months after the first evaluation and suggests that a decline in autobiographical memory starts as soon as the consolidation of autobiographical information is disturbed by hippocampal damage [15]. 

Hippocampal volume change gradually intensifies on a continuum, ranging from healthy elderly individuals exhibiting a fairly intact hippocampal structure to aMCI individuals experiencing smaller hippocampal subfields, and finally, to AD patients presenting severe atrophy in all the hippocampal subfields [38]. A possible explanation for our findings is that the initial consolidation of personal semantic facts depends on the hippocampus; therefore, it is also susceptible to early hippocampal damage [15]. 

In addition, these results are corroborated by the longitudinal analysis of the groups, where a significant deterioration was found in both groups of patients. Some limitations must be indicated. 

First, the sizes of the sample groups were unequal, with a difference in the number of participants in the healthy and patient groups. Second, we did not correlate the autobiographical memory function with the subjects' radiological findings, volumetric assessment of the hippocampus, or functional imaging study. 

Finally, it should be noted that the instruments for evaluating AM components differ across studies, making it difficult in some cases to compare the results. In this regard, it would be interesting to standardize the evaluation instruments to facilitate comparisons. 

In addition, it should be noted that when using the Personal Semantics and Autobiographical Incident scores as a combination of the three-time points evaluated, it is difficult to compare recent memories and old memories; in future studies, it would be interesting to compare both types of memories to know if there is a differential influence on their consolidation. 

In summary, the present study showed that autobiographical memory was impaired in patients with AD and aMCI. This deterioration was found mainly in episodic memory in both groups. However, while the deterioration in semantic memory was confirmed in AD, a pattern was observed in the aMCI group that evolved toward deterioration over eighteen months.

Author Contributions: Conceptualization, J.C.M.; data curation, E.S., I.D., M.A., and E.R.; funding acquisition, J.C.M.; investigation, E.R., and I.D.; methodology, A.P.; resources, E.S. and I.D.; software, A.P.; writing-original draft, E.S., I.D., M.A., and E.R.; writing-review and editing, J.C.M. and A.P. All authors have read and agreed to the published version of the manuscript.

Funding: This work was supported by the Spanish Ministerio de Ciencia, Innovación y Universidades (Spain) [Grant PID2019-103956RB-I00].

Institutional Review Board Statement: The study was conducted according to the guidelines of the Declaration of Helsinki.

Informed Consent Statement: Informed consent was obtained from all subjects involved in the study

Data Availability Statement: The data presented in this study are available on request to the authors. The data are not publicly available due to privacy reasons.

Conflicts of Interest: The authors declare no conflict of interest.

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