The temporal unraveling of autobiographical memory narratives in patients with temporal lobe epilepsy or excisions

Retrieval of temporal structure at recall can occur automatically

Temporal-structure, namely, the order in which events unfold over time, is one of the fundamental principles of episodic memory organization. A seminal empirical demonstration of the prominence of temporal structure in memory organization is the Temporal Contiguity Effect (TCE), whereby the proximity between two items at encoding predicts the likelihood of those two items being retrieved consecutively during recall. Recent studies have found that TCE occurs under a wide variety of conditions in which strategic control processes at encoding are reduced or even eliminated. This suggests that the encoding of temporal structure occurs automatically. Extending these findings, in the current study we asked whether the retrieval of temporal structure, as reflected by indices of the TCE, is influenced by strategic control processes at retrieval. To manipulate participants' ability to rely on strategic control processes, we compared standard recall performance (Full Attention condition) to a condition in which attention was divided between recall and a concurrent task (Divided Attention condition), which has been shown to disrupt such control processes. Across two experiments-one with standard encoding conditions and one with continual distraction during encoding-we found no differences in any index of the TCE between the two conditions. These results are all the more striking considering that in both experiments, dividing attention negatively affected overall recall performance compared to the Full Attention condition. Thus, while recall performance is reduced when disrupting strategic processes, the ability to use temporal structure to drive recall is not affected.

Forgetting Rates of Prose Memory in Mild Cognitive Impairment

BACKGROUND

Some authors report steeper slopes of forgetting in early Alzheimer's disease (AD), while others do not. Contrasting findings are thought to be due to methodological inconsistencies or variety of testing methods, yet they also emerge when people are assessed on the same testing procedure.

OBJECTIVE

We aimed to assess if forgetting slopes of people with mild cognitive impairment due to AD (MCI-AD) are different from age-matched healthy controls (HC) by using a prose paradigm.

METHODS

Twenty-nine people with MCI-AD and twenty-six HC listened to a short prose passage and were asked to freely recall it after delays of 1 h and 24 h.

RESULTS

Generalized linear mixed modelling revealed that, compared to HC, people with MCI-AD showed poorer encoding at immediate recall and steeper forgetting up to 1 h in prose memory as assessed by free recall and with repeated testing of the same material. Forgetting rates between groups did not differ from 1 h to 24 h.

CONCLUSION

The differences observed in MCI-AD could be due to a post-encoding deficit. These findings could be accounted either by a differential benefit from retrieval practice, whereby people with MCI-AD benefit less than HC, or by a working memory deficit in people with MCI-AD, which fails to support their memory performance from immediate recall to 1 h.

Forgetting rates of gist and peripheral episodic details in prose recall

In a seminal study, Slamecka and McElree showed that the degree of initial learning of verbal material affected the intercepts but not the slopes of forgetting curves. However, more recent work has reported that memories for central events (gist) and memory for secondary details (peripheral) were forgotten at different rates over periods of days, with gist memory retained more consistently over time than details. The present experiments aimed to investigate whether qualitatively different types of memory scoring (gist vs. peripheral) are forgotten at different rates in prose recall. In three experiments, 232 participants listened to two prose narratives and were subsequently asked to freely recall the stories. In the first two experiments participants were tested repeatedly after days and a month, while in the third experiment they were tested only after a month to control for repeated retrieval. Memory for gist was higher than for peripheral details, which were forgotten at a faster rate over a month, with or without the presence of intermediate recall. Moreover, repeated retrieval had a significant benefit on both memory for gist and peripheral details. We conclude that the different nature of gist and peripheral details leads to a differential forgetting in prose free recall, while repeated retrieval does not have a differential effect on the retention of these different episodic details.

Vague retellings of personal narratives in temporal lobe epilepsy

PURPOSE

Aside from deficits identified in single-word level retrieval, individuals with temporal lobe epilepsy (TLE) exhibit clinical oddities, such as circumstantiality in their language production. Circumstantiality refers to the use of language which is pedantic, repetitive, and overly detailed. This becomes particularly evident when elicitation tasks impose minimal structure, or when impersonal narratives are retold over consecutive occasions. Personal reminiscence is highly specific and localised in time, placing unique demands on cognitive-linguistic systems. It is hypothesised that the nature of this elicitation paradigm will produce a unique psycholinguistic phenotype in those with TLE. Among controls there is a compression of output for impersonal narratives, meaning that they use fewer words over less time and are more fluent. The opposite effect is observed when personal narratives are retold.

METHODS

To investigate the micro- and macrolinguistic processes underpinning personal discourse production in TLE, we examined the elicited language output of 15 surgically naïve individuals with TLE and 14 healthy controls. Participants were asked to recall and re-tell an autobiographical memory on four immediately consecutive occasions, representing an alternative unstructured elicitation. Following transcription and coding of output, a detailed multi-level discourse analysis of output volume, fluency, cohesion, and coherence was conducted.

RESULTS

As anticipated, a distinctly different pattern emerged in TLE when compared with controls who did not compress their output volume across repetitions but instead produced greater novelty, and a more coherent and refined account over time. Individuals with TLE consistently told a less distinct story across repetitions, with disturbances in fluency, cohesion, and coherence.

CONCLUSION

This reflects a reduced capacity to produce a coherent mental representation, in all likelihood related to the neurolinguistic demands of recalling and retelling specific personal events.

Episodic representation: A mental models account

This paper offers a modeling account of episodic representation. I argue that the episodic system constructs mental models: representations that preserve the spatiotemporal structure of represented domains. In prototypical cases, these domains are events: occurrences taken by subjects to have characteristic structures, dynamics and relatively determinate beginnings and ends. Due to their simplicity and manipulability, mental event models can be used in a variety of cognitive contexts: in remembering the personal past, but also in future-oriented and counterfactual imagination. As structural representations, they allow surrogative reasoning, supporting inferences about their constituents which can be used in reasoning about the represented events.

Emotional Autobiographical Memory Associated with Insular Resection in Epileptic Patients: A Comparison with Temporal Lobe Resection

The insula is involved in a wide variety of functions, including social and emotional processing. Despite the numerous connections it shares with brain structures known to play a role in autobiographical memory (AM), little is known on the contribution of the insula to AM processing. The aim of the study was to examine emotional AM retrieval in patients with insular resection for drug-resistant epilepsy. Ten patients who underwent partial or complete insular resection (IR) were matched on age, sex, and education, to fifteen patients who underwent temporal lobectomy (TL), and to fifteen healthy controls. Participants were asked to recall four positive, four negative, and four neutral memories from their past using the autobiographical interview procedure. The results suggest that AM for emotional and neutral events after IR was comparable to that of healthy controls, whereas deficits were observed after TL. However, an independent examiner judged IR patients' memories as poorer than those of healthy controls on the episodic richness scale, suggesting a lack of some aspects of rich and vivid remembering. Furthermore, analysis on subjective self-rated scales revealed that, contrary to healthy controls, patients with IR judged their neutral memories as more emotional. This study suggests that AM is generally preserved after IR. However, given the small sample size and varied lesion location, one cannot totally exclude a potential role of specific insular sub-regions on some aspects of autobiographical memory. In addition, IR patients showed poor emotional judgment for neutral memories, which is congruent with previous findings of altered emotional processing in this population.

Autobiographical memory in epileptic patients after temporal lobe resection or bitemporal hippocampal sclerosis

The human hippocampus is believed to be a crucial node in the neural network supporting autobiographical memory retrieval. Structural mesial temporal damage associated with temporal lobe epilepsy (TLE) provides an opportunity to systematically investigate and better understand the local and distal functional consequences of mesial temporal damage in the engagement of the autobiographical memory network. We examined 19 TLE patients (49.21 ± 11.55 years; 12 females) with unilateral mesial TLE (MTLE; 12 with anterior temporal lobe resection: 6 right MTLE, 6 left MTLE) or bilateral mesial TLE (7 BMTLE) and 18 matched healthy subjects. We used functional MRI (fMRI) with an adapted autobiographical memory paradigm and a specific neuropsychological test (Autobiographical Memory Interview, AMI). While engaged in the fMRI autobiographical memory paradigm, all groups activated a large fronto-temporo-parietal network. However, while this network was left lateralized for healthy participants and right MTLE patients, left MTLE and patients with BMTLE also showed strong activation in right temporal and frontal regions. Moreover, BMTLE and left MTLE patients also showed significant mild deficits in episodic autobiographical memory performance measured with the AMI test. The right temporal and extra-temporal fMRI activation, along with the impairment in autobiographical memory retrieval found in left MTLE and BMTLE patients suggest that alternate brain areas-other than the hippocampus-may also support this process, possibly due to neuroplastic effects.

Narrativity and Referential Activity Predict Episodic Memory Strength in Autobiographical Memories

Narrativity has been proposed as an indicator of episodic memory strength when people discuss their past (Nelson and Horowitz in Discourse Processes 31:307-324, 2001. https://doi.org/10.1207/S15326950dp31-3_5 ). Referential Activity, the extent to which words convey a speaker's experience of being present in the event being described, has been independently hypothesized to indicate episodic memory strength (Maskit in J Psycholinguist Res, 2021. https://doi.org/10.1007/s10936-021-09761-8 ). These hypotheses are tested using a linguistic measure of narrativity and a computerized measure of referential activity to predict previous independent ratings of episodic memory strength that used the Levine et al. (Psychol Aging 17(4):677-689, 2002. https://doi.org/10.1037//0882-7974.17.4.677 ) measure of internal details in retold personal memories provided by Schacter (Addis et al. in Psychol Sci 19(1):33-41, 2008. https://doi.org/10.1111/j.1467-9280.2008.02043.x ). Raters scored narrativity on four brief near and far past memories elicited from 32 subjects, using Nelson's narrative temporal sequence method based on Labov's (J Narrat Life Hist 7(1-4):395-415, 1997. https://doi.org/10.1075/jnlh.7.49som ) analysis of spoken narratives of personal experience; computerized weighted scores of referential activity (WRAD) were obtained on these same 128 memories. Data analysis showed that narrative temporal sequences predict internal details and WRAD predict internal details. Adding WRAD to narrative temporal sequences improved the prediction of internal details.

Linking Detail to Temporal Structure in Naturalistic-Event Recall

Decades of memory research demonstrate the importance of temporal organization in recall dynamics, using laboratory stimuli (i.e., word lists) at seconds- to minutes-long delays. Little is known, however, about such organization in recall of richer and more remote real-world experiences, in which the focus is usually on memory content without reference to event order. Here, 119 younger and older adults freely recalled extended real-world experiences, for which the encoding sequence was controlled, after 2 days or 1 week. We paired analytical tools from the list-learning and autobiographical memory literatures to measure spontaneous contextual dynamics and details in these recall narratives. Recall dynamics were organized by temporal context (contiguity and forward asymmetry), and organization was reduced in older age, despite similar serial position effects and recall initiation across age groups. Across participants, organization was positively associated with richness of episodic detail, providing evidence for a link between reexperiencing past events and reinstating their spatiotemporal context.

vmPFC Drives Hippocampal Processing during Autobiographical Memory Recall Regardless of Remoteness

Our ability to recall past experiences, autobiographical memories (AMs), is crucial to cognition, endowing us with a sense of self and underwriting our capacity for autonomy. Traditional views assume that the hippocampus orchestrates event recall, whereas recent accounts propose that the ventromedial prefrontal cortex (vmPFC) instigates and coordinates hippocampal-dependent processes. Here we sought to characterize the dynamic interplay between the hippocampus and vmPFC during AM recall to adjudicate between these perspectives. Leveraging the high temporal resolution of magnetoencephalography, we found that the left hippocampus and the vmPFC showed the greatest power changes during AM retrieval. Moreover, responses in the vmPFC preceded activity in the hippocampus during initiation of AM recall, except during retrieval of the most recent AMs. The vmPFC drove hippocampal activity during recall initiation and also as AMs unfolded over subsequent seconds, and this effect was evident regardless of AM age. These results recast the positions of the hippocampus and the vmPFC in the AM retrieval hierarchy, with implications for theoretical accounts of memory processing and systems-level consolidation.

The status of semantic memory in medial temporal lobe amnesia varies with demands on scene construction

Semantic memory is typically preserved in medial temporal lobe (MTL) amnesia. However, there are instances of impairment, such as in the recall of semantic narratives. As some forms of semantic knowledge play out in a spatial context, one possible explanation is that semantic memory impairments, when observed, relate to demands on scene construction - the ability to bind and maintain spatial information in a coherent representation. To investigate whether semantic memory impairments in MTL amnesia can be understood with reference to a deficit in scene construction, the current study examined knowledge of scripts that vary in the extent to which they play out in a scene context in nine patients with MTL amnesia and eighteen healthy control subjects. Scripts are routine activities characterized by an ordered set of actions, including some that are essential for completing the activity. Comparing performance on scene-based scripts (e.g., buying groceries at the grocery store) and object-based scripts (e.g., addressing a letter), we found that patients generated the same number of total action steps as controls for both types of script, but patients were selectively impaired at generating essential actions steps for scene-based scripts. Furthermore, patients made more sequencing and idiosyncratic errors than controls in the scene-based, but not in the object-based, scripts. These findings demonstrate that the hippocampus plays a critical role in the retrieval of semantic knowledge about everyday activities when such retrieval entails scene construction.

Benefit of wakeful resting on gist and peripheral memory retrieval in healthy younger and older adults

Retrieval is greater if new learning is followed by a period of wakeful rest, minimising the likelihood of retroactive interference. It is not known if this benefit extends to recollection of both gist and peripheral details, nor whether age affects the benefit of wakeful resting in either of these types of recollection. Forty-five younger and forty older adults were presented with prose passages for later recall followed by a period of either interference or wakeful resting. Younger participants outperformed older participants in remembering peripheral details, but not on gist memory. Wakeful resting led to higher overall recollection in both age groups, both for gist and for peripheral details. Also, wakeful resting was more beneficial for gist than peripheral memory in older but not younger adults. We discuss these novel findings and their theoretical implications for a memory consolidation account of the benefits of wakeful resting.

Network-wide abnormalities explain memory variability in hippocampal amnesia

Patients with hippocampal amnesia play a central role in memory neuroscience but the neural underpinnings of amnesia are hotly debated. We hypothesized that focal hippocampal damage is associated with changes across the extended hippocampal system and that these, rather than hippocampal atrophy per se, would explain variability in memory between patients. We assessed this hypothesis in a uniquely large cohort of patients (n = 38) after autoimmune limbic encephalitis, a syndrome associated with focal structural hippocampal pathology. These patients showed impaired recall, recognition and maintenance of new information, and remote autobiographical amnesia. Besides hippocampal atrophy, we observed correlatively reduced thalamic and entorhinal cortical volume, resting-state inter-hippocampal connectivity and activity in posteromedial cortex. Associations of hippocampal volume with recall, recognition, and remote memory were fully mediated by wider network abnormalities, and were only direct in forgetting. Network abnormalities may explain the variability across studies of amnesia and speak to debates in memory neuroscience.

First-person view of one's body in immersive virtual reality: Influence on episodic memory

Episodic memories (EMs) are recollections of contextually rich and personally relevant past events. EM has been linked to the sense of self, allowing one to mentally travel back in subjective time and re-experience past events. However, the sense of self has recently been linked to online multisensory processing and bodily self-consciousness (BSC). It is currently unknown whether EM depends on BSC mechanisms. Here, we used a new immersive virtual reality (VR) system that maintained the perceptual richness of life episodes and fully controlled the experimental stimuli during encoding and retrieval, including the participant’s body. Our data reveal a classical EM finding, which shows that memory for complex real-life like scenes decays over time. However, here we also report a novel finding that delayed retrieval performance can be enhanced when participants view their body as part of the virtual scene during encoding. This body effect was not observed when no virtual body or a moving control object was shown, thereby linking the sense of self, and BSC in particular, to EMs. The present VR methodology and the present behavioral findings will enable to study key aspects of EM in healthy participants and may be especially beneficial for the restoration of self-relevant memories in future experiments.

Comparing and Contrasting the Cognitive Effects of Hippocampal and Ventromedial Prefrontal Cortex Damage: A Review of Human Lesion Studies

The hippocampus and ventromedial prefrontal cortex (vmPFC) are closely connected brain regions whose functions are still debated. In order to offer a fresh perspective on understanding the contributions of these two brain regions to cognition, in this review we considered cognitive tasks that usually elicit deficits in hippocampal-damaged patients (e.g., autobiographical memory retrieval), and examined the performance of vmPFC-lesioned patients on these tasks. We then took cognitive tasks where performance is typically compromised following vmPFC damage (e.g., decision making), and looked at how these are affected by hippocampal lesions. Three salient motifs emerged. First, there are surprising gaps in our knowledge about how hippocampal and vmPFC patients perform on tasks typically associated with the other group. Second, while hippocampal or vmPFC damage seems to adversely affect performance on so-called hippocampal tasks, the performance of hippocampal and vmPFC patients clearly diverges on classic vmPFC tasks. Third, although performance appears analogous on hippocampal tasks, on closer inspection, there are significant disparities between hippocampal and vmPFC patients. Based on these findings, we suggest a tentative hierarchical model to explain the functions of the hippocampus and vmPFC. We propose that the vmPFC initiates the construction of mental scenes by coordinating the curation of relevant elements from neocortical areas, which are then funneled into the hippocampus to build a scene. The vmPFC then engages in iterative re-initiation via feedback loops with neocortex and hippocampus to facilitate the flow and integration of the multiple scenes that comprise the coherent unfolding of an extended mental event.

Different neural routes to autobiographical memory recall in healthy people and individuals with left medial temporal lobe epilepsy

Individuals with medial temporal lobe epilepsy (mTLE) are poor at recalling vivid details from autobiographical memories (AM), instead retrieving gist-like schematic memories. Recent research has suggested that this impoverished recall in comparison to controls may reflect (1) differential engagement of anterior vs posterior regions of the hippocampus (HC) and/or (2) differences between the engagement of the HC vs the ventromedial prefrontal cortex (vmPFC). Here we examined these hypotheses by comparing connectivity amongst hippocampal regions and between vmPFC and other brain regions during construction (retrieval of a particular event) vs elaboration (retrieval of perceptual detail) phases of AM recall in 12 individuals with left mTLE and 12 matched controls. Whereas functional connectivity amongst hippocampal regions changed from AM construction to elaboration in controls, the pattern of intra-hippocampal connectivity was unvarying in patients. Furthermore, patterns of connectivity from the vmPFC differed between phases in distinct ways in the two groups of participants. In patients, vmPFC activation was correlated with other prefrontal and lateral temporal cortices during construction and with visual-perceptual cortices during elaboration. While controls did not show a difference in whole-brain connectivity, they did uniquely show a dynamic shift from vmPFC connectivity to anterior HC during construction and to posterior HC during elaboration. Together, these findings suggest that impoverished AM recall in mTLE is a consequence of reduced activation and flexibility of bilateral hippocampal networks and greater reliance on neocortical contributions to memory retrieval.

Characterizing cerebellar activity during autobiographical memory retrieval: ALE and functional connectivity investigations

Previous neuroimaging research has shown that the cerebellum is often activated during autobiographical memory (AM) retrieval. However, the reliability of that activation, its localization within the cerebellum, and its relationship to other areas of the AM network remains unknown. The current study used Activation Likelihood Estimation meta-analysis (ALE) as well as resting-state and task-related functional connectivity analyses to better characterize cerebellar activation in relation to AM. The ALE meta-analysis was run on 32 neuroimaging studies of AM retrieval. The results revealed a cluster of reliable AM-related activity within the Crus I lobule of the right posterior cerebellum. Using the peak ALE coordinate within Crus I as a seed region, both task-related and resting state functional connectivity analyses were run on fMRI data from 38 healthy participants. To determine the specificity of connectivity patterns to Crus I, we also included a cerebellar seed region in right Lobule VI previously identified in an ALE meta-analysis as associated with working memory. Resting-state functional connectivity analyses indicated that Crus I was intrinsically connected with other areas of the AM network as well as surrounding and contralateral cerebellar regions. In contrast, the Lobule VI seed was functionally connected with cerebral and cerebellar regions typically associated with working memory. The task-related connectivity analyses revealed a similar pattern, where the Crus I seed exhibited significant connectivity with key nodes of the AM network while the Lobule IV seed did not. During a semantic control task, both Crus I and Lobule VI showed significant correlations with a network of regions that was largely distinct from the AM network. Together these results indicate that right Crus I lobule is reliably engaged during AM retrieval and is functionally connected to the AM network both during rest, and more importantly, during AM retrieval.

The Functional and Structural Neuroanatomy of Systems Consolidation for Autobiographical and Semantic Memory

It is well established that patients with memory impairment have more difficulty retrieving memories from the recent past relative to the remote past and that damage to the medial temporal lobe (MTL) plays a key role in this pattern of impairment. The precise role of the MTL and how it may interact with other brain regions remains an area of active research. We investigated the role of structures in a memory network that supports remembering. Our chapter focuses on two types of memory: episodic memory and semantic memory. Findings from studies of patients with brain damage and neuroimaging studies in patients and healthy individuals were considered together to identify the functional and structural neuroanatomy of past remembrance.

Age-related changes to oscillatory dynamics in hippocampal and neocortical networks

Recent models of hippocampal function have emphasized its role in relational binding - the ability to form lasting representations regarding the relations among distinct elements or items which can support memory performance, even over brief delays (e.g., several seconds). The present study examined the extent to which aging is associated with changes in the recruitment of oscillatory activity within hippocampal and neocortical regions to support relational binding performance on a short delay visuospatial memory task. Structural magnetic resonance imaging and MEG were used to characterize potential age-related changes in hippocampal volume, oscillatory activity, and subsequent memory performance, and the relationships among them. Participants were required to bind the relative visuospatial positions of objects that were presented singly across time. Subsequently, the objects were re-presented simultaneously, and participants were required to indicate whether the relative spatial positions among the objects had been maintained. Older and younger adults demonstrated similar task accuracy, and older adults had preserved hippocampal volumes relative to younger adults. Age-group differences were found in pre-stimulus theta (∼5Hz) and beta (∼20Hz) oscillations, and this pre-stimulus activity was related to hippocampal volumes in younger adults. Age-group differences were also found in the recruitment of oscillatory activity from the pre-stimulus period to the task. Only younger adults showed a task-related change in theta power that was predictive of memory performance. In contrast, older adults demonstrated task-related alpha (∼10Hz) oscillatory power changes that were not observed in younger adults. These findings provide novel evidence for the role of the hippocampus and functionally connected regions in relational binding that is disrupted in aging. The present findings are discussed in the context of current models regarding the cognitive neuroscience of aging.

Medial temporal and neocortical contributions to remote memory for semantic narratives: evidence from amnesia

Studies of remote memory for semantic facts and concepts suggest that hippocampal lesions lead to a temporally graded impairment that extends no more than ten years prior to the onset of amnesia. Such findings have led to the notion that once consolidated, semantic memories are represented neocortically and are no longer dependent on the hippocampus. Here, we examined the fate of well-established semantic narratives following medial temporal lobe (MTL) lesions. Seven amnesic patients, five with lesions restricted to the MTL and two with lesions extending into lateral temporal cortex (MTL+), were asked to recount fairy tales and bible stories that they rated as familiar. Narratives were scored for number and type of details, number of main thematic elements, and order in which the main thematic elements were recounted. In comparison to controls, patients with MTL lesions produced fewer details, but the number and order of main thematic elements generated was intact. By contrast, patients with MTL+ lesions showed a pervasive impairment, affecting not only the generation of details, but also the generation and ordering of main steps. These findings challenge the notion that, once consolidated, semantic memories are no longer dependent on the hippocampus for retrieval. Possible hippocampal contributions to the retrieval of detailed semantic narratives are discussed.

Linking DMN connectivity to episodic memory capacity: what can we learn from patients with medial temporal lobe damage?

Computational models predict that focal damage to the Default Mode Network (DMN) causes widespread decreases and increases of functional DMN connectivity. How such alterations impact functioning in a specific cognitive domain such as episodic memory remains relatively unexplored. Here, we show in patients with unilateral medial temporal lobe epilepsy (mTLE) that focal structural damage leads indeed to specific patterns of DMN functional connectivity alterations, specifically decreased connectivity between both medial temporal lobes (MTLs) and the posterior part of the DMN and increased intrahemispheric anterior–posterior connectivity. Importantly, these patterns were associated with better and worse episodic memory capacity, respectively. These distinct patterns, shown here for the first time, suggest that a close dialogue between both MTLs and the posterior components of the DMN is required to fully express the extensive repertoire of episodic memory abilities.

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Focal structural damage correlates with widespread functional change in DMN in mTLE.

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Greater DMN connectivity alterations reflect worse clinical memory measures.

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Structural integrity moderates influence of functional connectivity on memory.

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Interhemispheric integration of MTL into posterior DMN may be key to better memory.

FMRI contributions to addressing autobiographical memory impairment in temporal lobe pathology

Episodic autobiographical memory (AM) allows one, through the recollection of sensory-perceptual details, thoughts and feelings, to become aware of an event as belonging to one’s own past as well as being able to project into one’s future. Because AM provides a sense of self-continuity, contributes to the integrity of the self, and helps predicting future experiences, any deficit of AM may have debilitating consequences for everyday life functioning. Understanding AM failure and the underlying neural mechanisms has the potential to shed light on brain reorganization mechanisms and engagement of compensatory processes. Functional magnetic resonance imaging (fMRI) provides the most promising imaging method to tackle these issues. We reviewed evidence from the few studies that used fMRI to investigate the functionality of the residual tissue, the neural reorganization and compensatory mechanisms in patients with neurological conditions due to impaired medial temporal lobe. Overall, these studies highlight the importance of the left hippocampus, which when atrophied and not functional leads to AM deficits but its residual functionality may support relatively normal AM recollection. When damaged hippocampal tissue is not functional, other brain regions (e.g., the medial prefrontal cortex) may be involved to compensate impairment, but they appear generally ineffective to support detailed episodic recollection.

Functional and effective hippocampal-neocortical connectivity during construction and elaboration of autobiographical memory retrieval

Autobiographical memory (AM) provides the opportunity to study interactions among brain areas that support the search for a specific episodic memory (construction), and the later experience of mentally reliving it (elaboration). While the hippocampus supports both construction and elaboration, it is unclear how hippocampal-neocortical connectivity differs between these stages, and how this connectivity involves the anterior and posterior segments of the hippocampus, as these have been considered to support the retrieval of general concepts and recollection processes, respectively. We acquired fMRI data in 18 healthy participants during an AM retrieval task in which participants were asked to access a specific AM (construction) and then to recollect it by recovering as many episodic details as possible (elaboration). Using multivariate analytic techniques, we examined changes in functional and effective connectivity of hippocampal-neocortical interactions during these phases of AM retrieval. We found that the left anterior hippocampus interacted with frontal areas during construction and bilateral posterior hippocampi with visual perceptual areas during elaboration, indicating key roles for both hippocampi in coordinating transient neocortical networks at both AM stages. Our findings demonstrate the importance of direct interrogation of hippocampal-neocortical interactions to better illuminate the neural dynamics underlying complex cognitive tasks such as AM retrieval.

Are autobiographical memories inherently social? Evidence from an fMRI study

The story of our lifetime – our narrative self – is constructed from our autobiographical memories. A central claim of social psychology is that this narrative self is inherently social: When we construct our lives, we do so in a real or imagined interaction. This predicts that self-referential processes which are involved in recall of autobiographical memories overlap with processes involved in social interactions. Indeed, previous functional MRI studies indicate that regions in the medial prefrontal cortex (mPFC) are activated during autobiographical memory recall and virtual communication. However, no fMRI study has investigated recall of autobiographical memories in a real-life interaction. We developed a novel paradigm in which participants overtly reported self-related and other-related memories to an experimenter, whose non-verbal reactions were being filmed and online displayed to the participants in the scanner. We found that recall of autobiographical vs. non-autobiographical memories was associated with activation of the mPFC, as was recall in the social as compared to a non-social control condition; however, both contrasts involved different non-overlapping regions within the mPFC. These results indicate that self-referential processes involved in autobiographical memory recall are different from processes supporting social interactions, and argue against the hypothesis that autobiographical memories are inherently social.