Phase-Amplitude Coupling and Phase Synchronization Between Medial Temporal, Frontal and Posterior Brain Regions Support Episodic Autobiographical Memory Recall.

Episodic autobiographical memory (EAM) is a complex cognitive function that emerges from the coordination of specific and distant brain regions. Specific brain rhythms, namely theta and gamma oscillations and their synchronization, are thought of as putative mechanisms enabling EAM. Yet, the mechanisms of inter-regional interaction in the EAM network remain unclear in humans at the whole brain level. To investigate this, we analyzed EEG recordings of participants instructed to retrieve autobiographical episodes. EEG recordings were projected in the source space, and time-courses of atlas-based brain regions-of-interest (ROIs) were derived. Directed phase synchrony in high theta (7-10 Hz) and gamma (30-80 Hz) bands and high theta-gamma phase-amplitude coupling were computed between each pair of ROIs. Using network-based statistics, a graph-theory method, we found statistically significant networks for each investigated mechanism. In the gamma band, two sub-networks were found, one between the posterior cingulate cortex (PCC) and the medial temporal lobe (MTL) and another within the medial frontal areas. In the high theta band, we found a PCC to ventromedial prefrontal cortex (vmPFC) network. In phase-amplitude coupling, we found the high theta phase of the left MTL biasing the gamma amplitude of posterior regions and the vmPFC. Other regions of the temporal lobe and the insula were also phase biasing the vmPFC. These findings suggest that EAM, rather than emerging from a single mechanism at a single frequency, involves precise spatio-temporal signatures mapping on distinct memory processes. We propose that the MTL orchestrates activity in vmPFC and PCC via precise phase-amplitude coupling, with vmPFC and PCC interaction via high theta phase synchrony and gamma synchronization contributing to bind information within the PCC-MTL sub-network or valuate the candidate memory within the medial frontal sub-network.

Gender identity better than sex explains individual differences in episodic and semantic components of autobiographical memory: An fMRI study.

Advances in the literature of sex-related differences in autobiographical memory increasingly tend to highlight the importance of psychosocial factors such as gender identity, which may explain these differences better than sex as a biological factor. To date, however, none of these behavioral studies have investigated this hypothesis using neuroimaging. The purpose of this fMRI study is to examine for the first time sex and gender identity-related differences in episodic and semantic autobiographical memory in healthy participants (M=19, W=18). No sex-related differences were found; however, sex-related effects of masculine and feminine gender identity were identified in men and women independently. These results confirm the hypothesis that differences in episodic and semantic autobiographical memory are best explained by gender but are an interaction between biological sex and gender identity and extend these findings to the field of neuroimaging. We discuss the importance of hormonal factors to be taken into consideration in the future.

Gender identity better than sex explains individual differences in episodic and semantic components of autobiographical memory and future thinking.

A recently tested hypothesis suggests that inter-individual differences in episodic autobiographical memory (EAM) are better explained by individual identification of typical features of a gender identity than by sex. This study aimed to test this hypothesis by investigating sex and gender related differences not only in EAM but also during retrieval of more abstract self-knowledge (i.e., semantic autobiographical memory, SAM, and conceptual self, CS), and considering past and future perspectives. No sex-related differences were identified, but regardless of the sex, feminine gender identity was associated with clear differences in emotional aspects that were expressed in both episodic and more abstract forms of AM, and in the past and future perspectives, while masculine gender identity was associated with limited effects. In conclusion, our results support the hypothesis that inter-individual differences in AM are better explained by gender identity than by sex, extending this assumption to both episodic and semantic forms of AM and future thinking.

The formation of episodic autobiographical memory is predicted by mental imagery, self-reference, and anticipated details.

Introduction: Despite the ecological nature of episodic memory (EM) and the importance of consolidation in its functioning, studies tackling both subjects are still scarce. Therefore, the present study aims at establishing predictions of the future of newly encoded information in EM in an ecological paradigm. Methods: Participants recorded two personal events per day with a SenseCam portable camera, for 10 days, and characterized the events with different subjective scales (emotional valence and intensity, self-concept and self-relevance, perspective and anticipated details at a month, mental images…). They then performed a surprise free recall at 5 days and 1 month after encoding. Machine learning algorithms were used to predict the future of events (episodic or forgotten) in memory at 1 month. Results: The best algorithm showed an accuracy of 78%, suggesting that such a prediction is reliably possible. Variables that best differentiated between episodic and forgotten memories at 1 month were mental imagery, self-reference, and prospection (anticipated details) at encoding and the first free recall. Discussion: These results may establish the basis for the development of episodic autobiographical memory during daily experiences.

Common and distinct correlates of construction and elaboration of episodic-autobiographical memory: An ALE meta-analysis.

The recollection of episodic-autobiographical memories (EAMs) entails a complex temporal dynamic, from initial "construction" to subsequent "elaboration" of memories. While there is consensus that EAM retrieval involves a distributed network of brain regions, it is still largely debated which regions specifically contribute to EAM construction and/or elaboration. To clarify this issue, we conducted an Activation Likelihood Estimation (ALE) meta-analysis based on the Preferred Reporting Items for Systematic-Reviews and Meta-Analyses (PRISMA) method. We found common recruitment of the left hippocampus and posterior cingulate cortex (PCC) during both phases. Additionally, EAM construction led to activations in the ventromedial prefrontal cortex, left angular gyrus (AG), right hippocampus, and precuneus, while the right inferior frontal gyrus was activated by EAM elaboration. Although most of these regions are distributed over the default mode network, the current findings highlight a differential contribution according to early (midline regions, left/right hippocampus, and left AG) versus later (left hippocampus, and PCC) recollection. Overall, these findings contribute to clarify the neural correlates that support the temporal dynamics of EAM recollection.

Lifelong impairment in episodic re-experiencing: Neuropsychological and neuroimaging examination of a new case of Severely Deficient Autobiographical Memory.

Autobiographical memory (AM) represents a complex and multimodal cognitive function, that allows an individual to collect and retrieve personal events and facts, enabling to develop and maintain the continuity of the self over time. Here we describe the case of DR (acronym of the fictional name Doriana Rossi), a 53-year-old woman, who complains of a specific and lifelong deficit in recalling autobiographical episodes. Along with an extensive neuropsychological assessment, DR underwent a structural and functional MRI examination to further define this impairment. The neuropsychological assessment revealed a deficit in episodic re-experiencing of her own personal life events. DR showed reduced cortical thickness in the Retrosplenial Complex in the left hemisphere, and in the Lateral Occipital Cortex, in the Prostriate Cortex and the Angular Gyrus in the right hemisphere. An altered pattern of activity in the calcarine cortex was detected during ordering of autobiographical events according to her own personal timeline. The present study provides further evidence about the existence of a severely deficient autobiographical memory condition in neurologically healthy people, with otherwise preserved cognitive functioning. Furthermore, the present data provide new important insights into neurocognitive mechanisms underpinning such a developmental condition.

Spoken discourse in episodic autobiographical and verbal short-term memory in Chinese people with dementia: the roles of global coherence and informativeness.

Introduction: Memory and discourse production are closely related in healthy populations. A few studies in people with amnestic mild cognitive impairment and people with dementia (PWD) suggested similar links, although empirical evidence is insufficient to inform emerging intervention design and natural language processing research. Fine-grained discourse assessment is needed to understand their complex relationship in PWD. Methods: Spoken samples from 104 PWD were elicited using personal narrative and sequential picture description and assessed using Main Concept Analysis and other content-based analytic methods. Discourse and memory performance data were analyzed in bivariate correlation and linear multiple regression models to determine the relationship between discourse production and episodic autobiographical memory and verbal short-term memory (vSTM). Results: Global coherence was a significant predictor of episodic autobiographical memory, explaining over half of the variance. Both episodic autobiographical memory and vSTM were positively correlated with global coherence and informativeness, and negatively with empty speech indices. Discussion: Coherence in personal narrative may be supported by episodic autobiographical memory and vice versa, suggesting potential mechanism of interventions targeting personhood through conversation. Indices of global coherence, informativeness, and empty speech can be used as markers of memory functions in PWD.

Autobiographical Memory in Healthy Aging: a Decade-long Longitudinal Study.

Autobiographic memory (AM) - which is generally considered to be the most advanced human memory system - is subject to a myriad of psychological and neurobiological factors. We, therefore, examined AM longitudinally during the transition from midlife to young-old age and from young-old to old age in two birth cohorts (born 1930-1932 and 1950-1952) hence starting at age 55.14 ± 0.94 vs. 73.85 ± 0.96, respectively. Participants (n = 239) of the Interdisciplinary Longitudinal Study on Adult Development and Aging were recruited of whom 166 could be reexamined after 9 ± 0.9 years. AM was investigated for three periods of life using an established semi-structured interview; potential cognitive decline was assessed on a broad test battery. All subjects stayed cognitively healthy. Analysis of variance with repeated measures revealed age-related semantization effects with a significantly lower number of specific and thereby a higher number of general AMs exclusively from young-old to old age. This effect did not coincide with cognitive decline. In the follow-up period, a significant decrease of event-related details was significantly more pronounced in the young-old than in the old cohort and details were better recalled by the young than the old cohort. At baseline, this difference was significant for the recent past only but involved all periods at follow-up. According to our findings, AM changes in healthy aging accelerate during the transition from young-old to old age and may herald other cognitive deficits. Additionally, these AM changes in cognitively healthy subjects point at an economic process of adaptation.

Episodic Autobiographical Memory Impairment and Differences in Pronoun Use: Study of Self-Awareness in Functional Amnesia and Transient Global Amnesia.

The subjective experience associated to memory processing is the core of the definition of episodic autobiographical memory (EAM). However, while it is widely known that amnesia affects the content of memories, few studies focused on the consequences of an impairment of EAM on the subjective self, also called the I-self. In the present study, we explored the I-self in two puzzling disorders that affect EAM: functional amnesia, which has an impact on autobiographical memory, and transient global amnesia (TGA), which only affects episodic memory. I-self was assessed through an original measure of self-integration in autobiographical narratives, namely the use of general or personal pronouns. Results showed that patients with functional amnesia tended to use general pronouns, whereas patients with TGA preferentially used the first person. The link between I-self and depersonalization-derealisation tendencies was also explored, showing dissociative tendencies in patients with functional amnesia but not in patients with TGA. We discuss these results from a combined neuropsychological and psychopathological perspective, with a view to proposing an explanatory model of the links between self-awareness and the episodic component of autobiographical memory.

Place identity, autobiographical memory and life path trajectories: The development of a place-time-identity model.

The ability to remember, recognize and reconstruct places is a key component of episodic autobiographical memory. In this respect, place forms an essential basis for the unfolding of experiences in memory and imagination. The autobiographical memory is seen to contribute to a sense of self and place identity. The aim of this study was to concertedly analyze paintings, autobiographical narrations and places of birth and life of clients under treatment at a psychiatric clinic in Switzerland who were manifesting psychiatric disorders, e.g. depression, anxiety disorders, bipolar disorder, personality disorder, substance dependence, and dementia. Each client exhibited distinctive attitudes and approaches towards life characterized by unique personal mental constructs for living in given places of time episodes that worked towards shaping the development of their identities as well as the development of their health. For these clients, place and time function together to leave a mark, a trajectory, that can hinder or help the resolution of a psychiatric condition. Based on six representative cases, we illustrate how each painting, each biographical narration and each interview reveals deeper structures of individual perception, emotions, feelings, coping strategies, and capacities to reflect and identify with place-time trajectories. Based on this analysis, a place-time-identity model has been developed, which emphasizes the importance of narration, the structure of personality, and emotional experiences in the development of the 'relay station' of episodic autobiographical memory, self and autonoetic consciousness: these three elements are not only connected through their embeddedness in time, but also through their embeddedness in place. In this context, place provides an external fundus of memory, capable of supporting humans in healthy recollection and remembering. The process of placing appears to contribute to the creation of self-esteem and identity. This psycho-geographical place-life-time approach is contrasted to phenomenological place-space-time theories of Husserl, Heidegger, Bachelard, and Sloterdijk.

The precuneus and hippocampus contribute to individual differences in the unfolding of spatial representations during episodic autobiographical memory.

Spatial information is a central aspect of episodic autobiographical memory (EAM). Space-based theories of memory, including cognitive map and scene construction models, posit that spatial reinstatement is a required process during early event recall. Spatial information can be represented from both allocentric (third-person) and egocentric (first-person) perspectives during EAM, with egocentric perspectives being important for mental imagery and supported by the precuneus. Individuals differ in their tendency to rely on allocentric or egocentric information, and in general, the subjective experience of remembering in EAM differs greatly across individuals. Here we examined individual differences in spatial aspects of EAM, how such differences influence the vividness and temporal order of recollection, and their anatomical correlates. We cued healthy young participants (n =63) with personally familiar locations and non-locations. We examined how cue type affects (i) retrieval dynamics and (ii) phenomenological aspects of remembering, and related behavioural performance to regional brain volumes (n =42). Participants tended to spontaneously recall spatial information early during recollection, even in the absence of spatial cues, and individuals with a stronger tendency to recall space first also displayed faster reaction times. Across participants, place-cued memories were re-experienced more vividly and were richer in detail than those cued by objects, but not more than those cued by familiar persons. Volumetric differences were associated with behavioural performance such that egocentric remembering was positively associated with precuneus volume. Hippocampal CA2/CA3 volumes were associated with the tendency to recall place-cued memories less effortfully. Consistent with scene construction theories, this study suggests that spatial information is reinstated early and contributes to the efficiency and phenomenology of EAM. However, early recall of spatial information is not universal and other routes to recall exist, challenging some aspects of these models. Variability among participants highlights the importance of an individual differences approach to studying EAM.

Common Recruitment of Angular Gyrus in Episodic Autobiographical Memory and Bodily Self-Consciousness.

Parietal cortex and adjacent parts of the temporal cortex have recently been associated with bodily self-consciousness (BSC). Similarly, growing evidence suggests that the lateral parietal cortex is crucial for the subjective aspects of episodic autobiographical memory (EAM), which is based on the conscious experience of reliving past events. However, the neuroanatomical relationship between both fundamental aspects remains currently unexplored. Moreover, despite the wealth of neuroimaging data on EAM, only few neuroimaging studies have examined BSC and even fewer examined those aspects of BSC that are most closely related to EAM. Here, we investigated whether regions in the inferior parietal lobule (IPL) that have been involved in spatial aspects of BSC (self-location and first-person perspective), as described by Ionta et al. (2011) are also active in studies investigating autobiographical memory. To examine this relation, we thus compared the regions indicated in the study by Ionta et al. (2011) based on data in healthy participants and neurological patients, with the results from a meta-analytical study we performed based on functional neuroimaging studies on EAM and semantic autobiographical memory (SAM). We report an anatomical overlap bilaterally in the angular gyrus (AG), but not in other parietal or temporal lobe structures between BSC and EAM. Moreover, there was no overlap between BSC and SAM. These preliminary data suggest that the bilateral AG may be a key structure for the conscious re-experiencing of past life episodes (EAM) and the conscious on-line experience of being located and experiencing the world in first-person (BSC).

Damage to the default mode network disrupts autobiographical memory retrieval.

Functional neuroimaging studies have implicated the default mode network (DMN) in autobiographical memory (AM). Convergent evidence from a lesion approach would help clarify the role of the DMN in AM. In this study, we used a voxelwise lesion-deficit approach to test the hypothesis that regions of the DMN are necessary for AM. We also explored whether the neural correlates of semantic AM (SAM) and episodic AM (EAM) were overlapping or distinct. Using the Iowa Autobiographical Memory Questionnaire, we tested AM retrieval in 92 patients with focal, stable brain lesions. In support of our hypothesis, damage to regions within the DMN (medial prefrontal cortex, mPFC; posterior cingulate cortex, PCC; inferior parietal lobule, IPL; medial temporal lobe, MTL) was associated with AM impairments. Within areas of effective lesion coverage, the neural correlates of SAM and EAM were largely distinct, with limited areas of overlap in right IPL. Whereas SAM deficits were associated with left mPFC and MTL damage, EAM deficits were associated with right mPFC and MTL damage. These results provide novel neuropsychological evidence for the necessary role of parts of the DMN in AM. More broadly, the findings shed new light on how the DMN participates in self-referential processing.

Social cognition in a case of amnesia with neurodevelopmental mechanisms.

Episodic-autobiographical memory (EAM) is considered to emerge gradually in concert with the development of other cognitive abilities (such as executive functions, personal semantic knowledge, emotional knowledge, theory of mind (ToM) functions, language, and working memory). On the brain level its emergence is accompanied by structural and functional reorganization of different components of the so-called EAM network. This network includes the hippocampal formation, which is viewed as being vital for the acquisition of memories of personal events for long-term storage. Developmental studies have emphasized socio-cultural-linguistic mechanisms that may be unique to the development of EAM. Furthermore it was hypothesized that one of the main functions of EAM is the social one. In the research field, the link between EAM and social cognition remains however debated. Herein we aim to bring new insights into the relation between EAM and social information processing (including social cognition) by describing a young adult patient with amnesia with neurodevelopmental mechanisms due to perinatal complications accompanied by hypoxia. The patient was investigated medically, psychiatrically, and with neuropsychological and neuroimaging methods. Structural high resolution magnetic resonance imaging revealed significant bilateral hippocampal atrophy as well as indices for degeneration in the amygdalae, basal ganglia, and thalamus, when a less conservative threshold was applied. In addition to extensive memory investigations and testing other (non-social) cognitive functions, we employed a broad range of tests that assessed social information processing (social perception, social cognition, social regulation). Our results point to both preserved (empathy, core ToM functions, visual affect selection, and discrimination, affective prosody discrimination) and impaired domains of social information processing (incongruent affective prosody processing, complex social judgments). They support proposals for a role of the hippocampal formation in processing more complex social information that likely requires multimodal relational handling.