Aller au contenuAller au menuAller à la recherche

Nadine Betbeder

La Trace mnésique visuo-spatiale chez l’Homme confronté au Temps: Naviguer ou trouver une stratégie de déplacement ; Consolider et se rappeler après un long délai

Le 15 novembre 2009

Visuo-spatial memory in humans confronted to the passage of time: Navigate though space and find an optimal strategy Consolidate and retrieve after a long delay Directeur de thèse Bruno Bontempi

Summary

While the detrimental effects of human aging on cognitive functions are well documented, how normal aging affects spatial memory processing and the organization of recent and long-term memories remains unclear. What are the cognitive strategies used when one is confronted to spatial navigation in large environments? How are the selection and use of these strategies affected by aging? How are recent and long-term remote memories organized as a function of aging during systems-level consolidation? These are the questions we sought to address during the course of this Ph.D. thesis by developing a series of virtual environments aimed at assessing spatial navigation and memory performance in young adults and aged participants.
In a first series of experiments, participants were tested for object location memory in a virtual environment (a medieval castle) that enabled shifts in spatial viewpoints between study and test. We found that aged participants exhibited poor performance relative to young adults only in the shifted view conditions, thus providing strong evidence for a deficit in allocentric, but not egocentric, spatial recognition memory. This age-related deficit was independent of memory load but was a function of the angle of rotation. In contrast to young adults, aged participants exhibited difficulties in processing efficiently distal cues of the environment and were more prone to adopt alternative strategies that rely less heavily on complex associations between allocentric and egocentric representations. Manipulations of the task demand and the spatial layout of the environment led us to the conclusion that aging seems to preferentially interfere with the capacity to form or use mental representations built upon all pieces of the environmental features which typically, are never in full view in real world large-scale environments. In a second set of experiments, participants were tested in an ecologically-relevant virtual version of the Morris water maze which mimics that classically used in rodents. Aged participants performed more poorly compared to middle-aged and young adults and formed a more schematic spatial memory. They favoured a directional single cue-based strategy to locate the hidden platform contrasting with young adults who formed complex geometrical relationships between distal cues of the environment. A neuropsychological test battery confirmed that binding of unrelated items and abilities to mentally manipulate information were two processes involved in solving the water maze task. Thus, upon acquisition, aged participants had difficulties in forming experientially detailed cognitive maps and in binding unrelated features of the environment into a cohesive spatial memory, possibly indicative of altered hippocampal-frontal circuitry. We next proceeded to examine the organization of spatial memory in aged participants as a function of time. Long-term memory assessed 4 weeks after acquisition revealed a more rapid decline in young adults compared to elderly participants, suggesting that the passage of time differentially affects the content of spatial memory (i.e. contextually detailed versus schematic), richly detailed spatial memories being more vulnerable to decay than schematic ones. This concept of memory transformation (i.e. memories are not stored in the cortex in their original form during the course of memory consolidation) was supported by findings of a last experiment in which we provide evidence that aged participants failed in detecting changes in the spatial layout of the water maze as memories matured over time.
All these findings are discussed in the context of the current debate about the concept of memory consolidation which opposes the standard model of memory consolidation to the multiple trace theory, two views which make different predictions about the contribution of the hippocampus to remote memory storage and retrieval. In light of our own findings, we attempt to propose an integrative view of the functioning of the hippocampal-cortical interface during recent and remote memory retrieval as a function of normal aging.

Cnrs 5228

Discipline
Sciences de la Vie et de la Santé

Spécialité
Neurosciences et Pharmacologie

Adresse du laboratoire
Centre de Neurosciences Intégratives et Cognitives, CNRS UMR 5228, Université Bordeaux 1, Directeur : Georges DiScala

Mots clés
Mémoire spatial, stratégies allocentriques et égocentriques, dialogue hippocampo-cortical, consolidation mnésique, rappel

Key words
Aging - Spatial memory - Allocentric and egocentric strategies - Hippocampal-cortical dialogue - Memory consolidation - Memory retrieval

Focus


Nadine Betbeder a préparé sa thèse sous la direction de Bruno Bontempi au Centre de Neurosciences Intégratives et Cognitives de l’Université Bordeaux 1 (CNRS UMR 5228, directeur: Georges DiScala).