Maladie d’Alzheimer et appropriation de la durée d’action

Abstract

In the course of Alzheimer disease (AD), different authors have reported disturbances of the perception of time. Incapacity to be on top of the time dimension in daily life is a major handicap as witnessed by caregivers of these patients. Very basic stimuli of very short duration and out of context have been used in research on temporality so far. The objective of the research presented here is to determine, whether in the course of AD, the capacity of time representation and time perception for daily activities is affected or not. In AD, we have noticed that the semantic memory for temporal knowledge is significantly altered while the estimation of duration based upon a script is preserved. To approach the representation of perception of time duration for daily activities in AD patients, we applied a combined methodology. A temporal semantic knowledge scale, a time duration estimation test about 12 defined daily activities as well as patient's interviews about temporality in daily life, registered and transcribed verbatim are used. We studied 6 patients with mild to moderately severe AD with comparable sociocultural characteristics and stage of the disease. We analysed the interviews and studied for each activity, verbal outputs relating to themes of temporality such as chronological reference points and time duration estimations as compared to information relating to the activity itself, the location in which the activity took place. The answers are classified according to their pertinence and whether they have been spontaneous or sollicited. We confirm that temporality is significantly altered in the course of mild to moderate AD. Analysis of the patients’ responses to questions exploring above-mentioned aspects of temporality revealed that time duration estimation was more altered than memory of chronological reference points. The approach presented here widens the comprehension of the different alterations as well as the understanding of some underlying processes involved in the perception of time. A reduction of attentional resources allocated to time can explain the observed alterations as proposed by the model of internal clock and attentional gate. We hypothesize that units of time representation have episodic, semantic and procedural components; moreover, our results support the notion that a link exists between retrospective time duration estimation and autonoetic travel as described by Tulving. The results of this research are in favor of the hypothesis that two ways may exist to manage temporality, as proposed by Chambon, one, controlled, conscious and intentional and a second, automated one which would rely on non-intentional and unconscious processes. Analysing the cognitive processes involved in our approach of temporality in AD allows to hypothesize an intersection between episodic, semantic memory and scripts knowledge included in procedural memory. Our results suggest the possibility of an interaction between episodic and semantic memory; this could explain our observation that memory of chronological reference points is relatively less affected in AD. Analysis of the cognitive processes involved in the representation of elapsing time as perceived by Alzheimer patients may potentially explain some of the difficulties these patients face in their daily life. Based upon these findings, a simple scheme of exploration could be introduced in medical practice, reducing the need for more sophisticated and time consuming diagnostic exploration. This deepened understanding may lead to improvements of care with potentially significant impact on daily life of patients and their caregivers.