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We investigated for the first time the episodic/semantic distinction in remembering the past and imagining the future in traumatic brain injury (TBI), and explored cognitive mechanisms that may underlie their deficits. Fifteen severe TBI patients and 15 control participants performed a battery of neuropsychological tests and a set of verbal fluency tasks designed to assess semantic (personality traits knowledge and general events), and episodic (specific events and details) facets of self-representations according to three time periods (remote/retrograde past, recent/anterograde past, future). Compared to controls, TBI patients showed deficits in both semantic and episodic self-representations, regardless of the time period, and controlling for basic cognitive functions. By contrast, a subjective evaluation of self-concept measuring the degree of certitude and the valence of self did not differ between patients and controls. The deficits were mainly predicted by altered executive function (i.e., updating) for past periods, as well as by general semantic and feature binding in working memory for the future period, independently of the injury characteristics. For controls, only episodic self-representation for each time period was mediated by executive or working memory functions, while semantic self-representation was mediated by the certitude of the self. This study highlights the dual role of semantic and episodic representations in temporally extended self, and shows the global disruption of self-representations across extended time in severe TBI. This encourages the extension of past and future thinking research to TBI populations to provide important insights into the nature and origin of these deficits and their role in recovery and to suggest future lines of research on rehabilitation procedures.

We investigated the episodic/semantic distinction in remembering the past and imagining the future and explored cognitive mechanisms predicting events' specificity throughout the lifespan. Eighty-three 6- to 81-year-old participants, divided into 5 age groups, underwent past, present and future episodic (events' evocation) and semantic (self-descriptions) autobiographical tasks and a complementary cognitive test battery (executive functions, working and episodic memory). The main results showed age effects on episodic events' evocation indicating an inverted U function (i.e., developmental progression from 6 to 21years and aging decline). By contrast, age effects were slighter on self-descriptions while self-defining events' evocation increased with age. Furthermore, age effects on episodic events' evocation were mainly mediated by age effects on cognitive functions and personal semantics. These new findings indicate a developmental and aging episodic/semantic distinction for both remembering the past and imagining the future, and suggest that above similarities, these abilities could have a fundamentally different basis.

According to Tulving, episodic memory allows humans to travel mentally through subjective time into either the past or the future, this ability being at the origin of adaptation, organization and planning of future behavior. The main aim of this review is to present a state of art of episodic mental time travel and a lifespan perspective from children to elderly people. We examine the numerous similarities between remembering the past and envisioning the future which have been highlighted in cognitive, neuroimaging, and neuropsychological studies. We also present studies that have given evidence that remembering the past and imagining the future differ somewhat. We focus on demonstrating that hippocampal dysfunction is associated with disturbances in the recall of episodic autobiographical details in past memories, but also in the imagining of episodic detailed future events. More specifically, we discuss that the future seems to involve higher semantic processes mediated by the inferior frontal and lateral temporal gyri. We propose that the study of mental travel in personal time could be undertaken in line with the distinction between the memory of (episodic) experiences and (semantic) personal knowledge of one's life, which constitutes a major part of the self and constraints what we have been, what we are now, and what we might yet become.