Maladie d’Alzheimer et évaluation de la temporalité de la vie quotidienne : l’estimation de durée est-elle mieux préservée en mémoire située ou déclarative ?

Abstract

In the course of Alzheimer's disease (AD) disturbances of the perception of time has been reported by different authors, who used essentially very basic stimuli of very short duration and out of context. Incapacity to be on top of the time dimension in daily life is a major handicap as witnessed by caregivers of these patients. Analysis of the cognitive processes involved in the representation of elapsing time as perceived by Alzheimer patients may potentially elucidate some of the difficulties these patients face in their daily life. The objective of the research presented here is to determine, whether in the course of AD the capacity to estimate the duration of current daily activities is affected or not. Currently no validated tools are available to neuropsychologists and clinicians to assess temporality in Alzheimer disease (AD) patients under daily life conditions. In order to explore this question, we created a time duration estimation test for twelve current daily activities. A preliminary exploration of this method was carried out by using a control group of 440 healthy subjects of different ages and educational levels and with a group of 22 AD patients with mild and moderate stages of the disease. Simultaneously, a neuropsychological assessment has been carried out to evaluate different cognitive abilities of patients. In the control group, gender has no influence on the duration estimation. Age and cultural level do not influence the estimation of time duration of 2/12 activities. The estimation of time duration of these two activities can be used as a short version of the test. Then we compared the group of AD patients to a control group, which has been matched for age, sex and educational level. No significant difference in this time duration estimation task between the control group and the patients was noticed. We conclude that the cognitive processes relevant for this test seems to persist longer in AD as compared with other processes. The time duration estimation does not correlate with any neuropsychological scale and is in particular not related with the clock drawing test result. Surprisingly, depression did not have any influence on the time duration estimation scale in our AD group. It appears that two dimensions of temporality can be distinguished: the first dimension is one that the subject experiences while actually carrying out an activity and this dimension seems to be influenced by depressive mood. The second dimension would apply if an activity is not actually carried out but, if the subject uses only his representation of the activity; on the latter depression does not appear to have an influence. Our scale does not solicit episodic processes relating to a precise spatio-temporal context, but seem to rely on an acquired global experience of temporality, which is the result of cumulative experience of a person either having actually executed these activities or having merely observed them. We hypothesize that in order to estimate the duration of the daily activities patients would rather use procedural memory processes connected to the scripts of the actions knowledge, which seems to be longer preserved in AD patients. 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 semantic memory and scripts knowledge included in procedural memory and to suggest that a rehabilitation proposal can be done: procedural mechanisms could be helpful to support semantic processes.