Lost in time : a neurophilosophical quest to understand the perception of time in MCI patients

Tese de doutoramento, Ciências Biomédicas (Neurociências), Universidade de Lisboa, Faculdade de Medicina, 2017Introduction: Mild cognitive impairment (MCI) patients often complaint about difficulties in dealing with time questions, an issue that compromises their daily planning and orientation. The conscious experience of duration has been the most studied time experience and is generally assessed through duration judgments and passage of time judgments. This temporal experience may also impact other aspects of human life, namely intertemporal decision making. In the same vein, the connexion between time and memory has long been debated among neuroscientists, psychologists and philosophers. Among these scholars, Bergson, a 20th century French philosopher, was the leading proponent of a strong bond between time and memory, through the concept of duration. Time, for Bergson, is also interwoven with other dimensions of human consciousness, such as will. Thus, mild cognitive impairment can offer us a human disease model to see if and how memory impairments affect human time perception and to explore their broader effects upon subjects’ lives. Bergson seems to favour the idea of an affective and qualitative time experience interlinked with memory issues, akin of the situation of judging time passage. These ideas contrast with an Aristotelian idea of counting time intervals, similar to interval length judgments and currently conveyed by internal clock models, which neglects the role that feelings may play in time experience. In the case that the results obtained support Bergson’s intuitions, further avenues of work will be open to explore the relation between memory deficits and affective time experience. Objectives: This study aims to investigate the perception of time in patients with Mild Cognitive Impairment. The experience of time duration, with respect to both interval length judgments and passage of time judgments, and the consequences for decision making, using an intertemporal choice, are assessed. We intend to see how the results obtained fit into a philosophical framework that interlink memory and time and make suggestions regarding future work. Methods: Fifty-five MCI patients and fifty-seven healthy controls undergo an experimental protocol for time perception on interval length, a questionnaire for the subjective passage of time, an intertemporal choices questionnaire and a neuropsychological evaluation. In the experimental protocol for interval Length judgements, participants have to estimate and produce the duration of short time intervals of 7 s, 32 s, 58 s, following a prospective paradigm (they are told in advance that they will have to estimate and produce time intervals). They also have to estimate a duration of the time to draw a clock and the duration of the neuropsychological interview, following a retrospective paradigm (they are not told that they will have to estimate time intervals). In the passage of time judgments protocol, participants are inquired about their subjective impressions about the speed of time course and have to rate their impressions into a scale ranging from the very fast to the very slow. To check decision-making, participants are submitted to an intertemporal choice questionnaire where they have to choose between small and immediate reward or a larger but delayed reward. Finally, participants undergo a neuropsychological evaluation, where they are submitted to tests of cognitive functions, particularly memory and executive functions, as well as scales to evaluate their emotional state, namely depressive and anxiety symptoms. Results: Patients with MCI present no changes in the perception of interval length. However, they report the time passing slower than controls. This experience is significantly correlated with memory deficits, but not with performance in executive tests, depressive or anxiety symptoms. Patients with MCI have no alterations in temporal preferences in comparison with the healthy controls. These results from a study in neuroscience, put into a philosophical framework, suggest that Bergson and Aristotle, at the end, consider different aspects of time perception, in the first case referring to feelings of time passage and in the second case to the estimation of time intervals. However, both philosophers highlight the connexions of different aspects of time perception with different types of memory. Thus, passage of time judgements is linked to long-term memory and interval length judgements is associated with working memory. Conclusions: Memory deficits do not affect either the perception of interval length or temporal preferences, but are associated with alterations in the subjective experience of time. Following Bergson’s footsteps, we may say that memory is associated with an affective and qualitative experience of time. Future works investigating time perception in patients with memory deficits should careful consider this dimension when designing the experimental protocols