Pascale Piolino

Episodic and semantic remote autobiographical memory in ageing

Many laboratory studies have demonstrated an age effect on episodic memory which is in contrast with the preservation of semantic memory. The aim of this study was the assessment of age effects on autobiographical memory according to the length of the retention interval, taking into account the episodic and semantic components. A total of 52 subjects, aged between 40 and 79, were divided into four age groups. They were tested with a sophisticated autobiographical questionnaire consisting of two tasks, one involving the recall of semantic information and another the recall of episodic events. Results revealed that episodic recall deteriorated more with age and retention interval than semantic recall. These data, gathered using an ecological test, confirm age differences demonstrated by laboratory tests on the episodic-semantic distinction. Furthermore, the profile of results obtained for the recall of specific detailed events, and analysed according to age of encoding, confirms the distribution of episodic memories across the lifespan, as modelled by Rubin, Wetzler, and Nebes (1986) with the cue-word technique.

Episodic Autobiographical Memories over the Course of Time: Cognitive, Neuropsychological and Neuroimaging Findings.

The critical attributes of episodic memory are self, autonoetic consciousness and subjectively sensed time. The aim of this paper is to present a theoretical overview of our already published researches into the nature of episodic memory over the course of time. We have developed a new method of assessing autobiographical memory (TEMPau task), which is specially designed to measure these specific aspects, based on the sense of re-experiencing events from across the entire lifespan. Based on our findings of cognitive, neuropsychological and neuroimaging studies, new insights into episodic autobiographical memories are presented, focusing on the effects of age of the subjects interacting with time interval in healthy subjects and lesioned patients. The multifaceted and complex nature of episodic memory is emphasized and it is suggested that mental time travel through subjective time, which allows individuals to re-experience specific past events through a feeling of self-awareness, is the last feature of autobiographical memory to become fully operational in development and the first feature to go in aging and most amnesias. Our findings highlight the critical role of frontotemporal areas in constructive autobiographical memory processes, and especially hippocampus, in re-experiencing episodic details from the recent or more distant past.

Re-experiencing old memories via hippocampus: a PET study of autobiographical memory

The time-scale of medial temporal lobe (MTL) involvement in storage and retrieval of episodic memory is keenly debated. To test competitive theories of long-term memory consolidation, the present work aimed at characterizing which cerebral regions are involved during retrieval of recent and remote strictly episodic autobiographical memory. Using positron emission tomography (PET), we examined mental retrieval of recent (0-1 year) and remote (5-10 years) autobiographical memories, controlling for the nature of the autobiographical memories (i.e., specificity, state of consciousness, vividness of mental visual imagery, emotion) retrieved during scanning by behavioral measures assessed at debriefing for each event recalled. Cognitive results showed that specificity and emotion did not change with time interval although both autonoetic consciousness and mental image quality were significantly higher for recent memories, suggesting an underlying shift in the phenomenal experience of remembering with the passage of time. The SPM analysis revealed common activations during the recollection of recent and remote memories that involved a widespread but mainly left-sided cerebral network, consistent with previous studies. Subtraction analysis demonstrated that the retrieval of recent (relative to remote) autobiographical memories principally activated the left dorsolateral prefrontal cortex whereas the retrieval of remote (relative to recent) autobiographical memories activated the inferior parietal cortex bilaterally. ROIs analysis revealed more hippocampal activity for remote memories than for recent ones and a preferentially right-sided involvement of the hippocampal responses whatever the remoteness of autobiographical memories. New insights based on higher hippocampal response to the remoteness of episodic autobiographical memories challenge the standard model and are less discrepant with the multiple trace theory.

Neural Substrates of the Self-Memory System: New Insights from a Meta-Analysis

The self has been the topic of philosophical inquiry for centuries. Neuropsychological data suggest that the declarative self can be fractionated into three functionally independent systems processing personal information at several levels of abstraction, including episodic memories of ones own life (episodic autobiographical memory, EAM), semantic knowledge of facts about ones own life (semantic autobiographical memory, SAM), and semantic summary representations of ones personal identity (conceptual self, CS). Our proposal here was to present a comprehensive description of the neural networks underpinning self‐representations. To this aim, we performed three meta‐analyses, one each for EAM, SAM, and CS, using the activation likelihood estimation (ALE) method. We expected a shift from posterior to anterior structures associated with the incrementally increasing level of abstraction of self‐representations. The key finding was that EAM predominantly activates posterior and limbic regions including hippocampus. SAM is associated with anterior activations and also posterior and limbic activations in a lesser degree than EAM. CS mainly recruits medial prefrontal structures. Interestingly, medial prefrontal cortex is activated irrespective of the level of abstraction, but a more caudal part is recruited during CS, while SAM and EAM activate more rostral portions. To conclude, in line with the previous proposals, our results corroborate the idea that the declarative self is not monolithic but a multidimensional construct comprising distinct representations at different levels of abstraction. Hum Brain Mapp, 2013.

Mental time travel into the past and the future in healthy aged adults: An fMRI study

Remembering the past and envisioning the future rely on episodic memory which enables mental time travel. Studies in young adults indicate that past and future thinking share common cognitive and neural underpinnings. No imaging data is yet available in healthy aged subjects. Using fMRI, we scanned older subjects while they remembered personal events (PP: last 12 months) or envisioned future plans (FP: next 12 months). Behaviorally, both time-periods were comparable in terms of visual search strategy, emotion, frequency of rehearsal and recency of the last evocation. However, PP were more episodic, engaged a higher state of autonoetic consciousness and mental visual images were clearer and more numerous than FP. Neuroimaging results revealed a common network of activation (posterior cingulate cortex, precuneus, prefrontal cortex, hippocampus) reflecting the use of similar cognitive processes. Furthermore, the episodic nature of PP depended on hippocampal and visuo-spatial activations (occipital and angular gyri), while, for FP, it depended on the inferior frontal and lateral temporal gyri, involved in semantic memory retrieval. The common neural network and behavior suggests that healthy aged subjects thought about their future prospects in the past. The contribution of retrospective thinking into the future that engages the same network as the one recruited when remembering the past is discussed. Within this network, differential recruitment of specific areas highlights the episodic distinction between past and future mental time travel.

Reduced specificity of autobiographical memory and aging: Do the executive and feature binding functions of working memory have a role?

Autobiographical memory (AM) is built up from various kinds of knowledge, from general to specific, via generative processes. Aging seems to particularly affect the episodic autobiographical information while preserving information that is more semantic. However, the mechanism of this deficit has not yet been thoroughly tested in relation to working memory. This study is designed to investigate, in a group of 100 subjects, the relationships between age, accessibility to different levels of AM specificity, and two main components of working memory: the central executive and the episodic buffer. We used a new task composed of four embedded verbal autobiographical fluencies (VAF) - from low to highest specificity levels - exploring lifetime periods, general events, specific events, and details, plus tasks exploring free recall of episodic AM and updating, shifting, inhibition, and feature binding in working memory. The results demonstrate that age-related difficulties increase with level of specificity of autobiographical knowledge, i.e., from semantic to episodic aspects. Moreover, regression analyses mainly show that increase in age-related deficit with level of specificity of AM is largely mediated by performance on executive functions (updating and inhibition) and to a lesser extent feature binding in working memory. The results confirm in episodic AM the executive/working memory aging hypothesis, and for the first time highlight the role of episodic buffer in associating the various different details of specific events that elicit the conscious recollection.

What happens to personal identity when semantic knowledge degrades? A study of the self and autobiographical memory in semantic dementia

While the self has been extensively explored in amnesic patients with severe episodic but not semantic memory disturbance, little is known about the self in semantic dementia (SD), which generally features the reverse pattern of impairment. In the present study, we investigated the structural (self-representations) and functional (consciousness) dimensions of the self in a group of eight SD patients in the early to moderate stages of the disease. We used two original tasks designed to probe both structural characteristics, namely the strength and the certainty of self-concept and the episodic/semantic nature of self-representations, and functional characteristics, namely autonoetic/noetic level of consciousness, self-evaluation and self-projection into the past, present and future. Results for the structural self showed impairment on the semantic aspects of the self-representations, except for those related to the present. Moreover, SD patients were affected regardless of the episodic or semantic nature of self-representations into the future. As regards the functional self, self-projection and level of consciousness were only impaired for the future. This study confirms the persistence of a feeling of identity in SD over time for the past and present selves. However, it also highlights the loss of the future self in SD patients. These results are discussed in relation to models of long-term memory and future thinking focusing on the interplay of episodic and semantic memory and mental time travel.

Age effect on components of episodic memory and feature binding: A virtual reality study.

OBJECTIVE The aims were (1) to explore the effects of normal aging on the main aspects of episodic memory--what, where, and when,--and on feature binding in a virtual environment; (2) to explore the influence of the mode of learning, intentional versus incidental; and (3) to benchmark virtual environment findings collected with older adults against data recorded in classical neuropsychological tests. METHOD We tested a population of 82 young adults and 78 older adults without dementia (they participated in a short battery of neuropsychological tests). All the participants drove a car in an urban virtual environment composing of 9 turns and specific areas. Half of the participants were told to drive through the virtual town; the other half were asked to drive and to memorize the environment (itinerary, elements, etc.). All aspects of episodic memory were then assessed (what, where, when, and binding). RESULTS The older participants had less recollection of the spatiotemporal context of events than the younger with intentional encoding (p < .001), but similar recollection with incidental encoding (except for verbal spatial aspect). The younger participants showed better binding than older ones regardless of the type of encoding (p < .001). For the older participants the virtual test was sensitive to mnesic complaints as well as general cognitive changes (p < .05 to p < .01). CONCLUSION We view these results as an indication that virtual environments could provide helpful standard tools for assessing age effects on the main aspects of episodic memory.

Autonoetic consciousness in Alzheimer's disease: Neuropsychological and PET findings using an episodic learning and recognition task

OBJECTIVE This study aims to map in patients with mild Alzheimers disease (AD) the correlations between resting-state brain glucose utilization measured by FDG-PET and scores reflecting autonoetic consciousness in an episodic learning and recognition task. METHODS Autonoetic consciousness, that gives a subject the conscious feeling to mentally travelling back in time to relive an event, was assessed using the Remember/Know (R/K) paradigm. RESULTS AD patients provided less R responses (reflecting autonoetic consciousness) and more K ones (indicating the involvement of noetic consciousness) than healthy controls. Correct recognitions associated with a R response correlated with the metabolism of frontal areas bilaterally whereas those associated with a K response mainly correlated with the metabolism of left parahippocampal gyrus and lateral temporal cortex. CONCLUSIONS These data show that recollection is impaired in AD and recognition is more based on a feeling of familiarity than in controls. In addition, the findings of our correlative approach indicate that the impairment of episodic memory is mainly subserved by the dysfunction of frontal areas and of the hippocampal region.

Autobiographical memory and autonoetic consciousness in a case of semantic dementia

Investigations of retrograde amnesia have contributed to a better understanding of the cerebral structures involved in remote memory. Such studies have suggested that neocortical regions such as the anterior temporal lobe play a major role in both the storage and retrieval of remote episodic and semantic information. Semantic dementia (SD), characterised as a focal anterior temporal lobe atrophy, offers an opportunity to study episodic remote memory, especially in the absence of day-to-day memory dysfunctioning, which takes place in permanent amnesic syndromes. Few studies have investigated autobiographical retrograde amnesia in SD. We present the findings from a patient (AT) at the early stage of SD. First, we have compared episodic and semantic components of autobiographical memory using two specially designed fluency tasks. The results demonstrated good recall of autobiographical events from all time periods and poor retrieval of names of acquaintances, albeit to a lesser degree, with respect to recent life. Second, we have investigated strictly episodic autobiographical memory and autonoetic consciousness by means of a sophisticated autobiographical test and the Remember/Know procedure which used a more stringent criterion of episodicity. The results demonstrated a relatively good recall of autobiographical memories (whatever their nature) but poor retrieval of remote specific detailed memories compared to recent ones. Moreover, patient AT provided Remember judgements to the same extent as control subjects regardless of the time interval covered although his responses were not justified in terms of the actual contextual information retrieved beyond the last 5 years. These findings provide further evidence that strictly episodic recollection is restricted to the recent past in SD. These data are discussed according to their relevance to the episodic and semantic distinction and to models of long-term memory consolidation.