La dépression synaptique à long terme : un mécanisme pour la mémoire et l’apprentissage au niveau du cervelet

Abstract

Le cervelet, partie du cerveau qui coordonne lafonction motrice, a un rôle clé dans l’apprentissagemoteur, voire dans certains processus cognitifs. Il est aujourd’hui couramment admis que lamodification à long terme de l’efficacité de latransmission synaptique est la base cellulaire dela mémoire et de l’apprentissage. La cellule dePurkinje, élément central de l’organisation cytoarchitectoniquedu cervelet et de la fonction cérébelleuse,est le siège d’une plasticité neuronaleparticulière appelée « dépression à long terme ». En quoi consiste cette « dépression » ? Quels ensont les mécanismes cellulaires et moléculaires ? Quels éléments permettent de considérer quecette plasticité est le mécanisme de base de l’apprentissagemoteur ? Telles sont les questionsabordées dans cet article.

It is commonly thought that a persistent change in the efficacy of the synaptic transmission is the basic mechanism underlying learning and memory. The cerebellum, key structure of the motor function, exhibits a synaptic plasticity named cerebellar long-term depression or LTD. This phenomenon appears in the Purkinje cell when the two main excitatory inputs (one consists of the parallel fibers which relay information on the task to accomplish and the other one includes the climbing fiber which conveys error signals) are activated in combination, resulting in a persistent decrease of the efficacy of the parallel fiber- Purkinje cell synapse. Studies made in the last 20 years show that activation of ionotropic and metabotropic glutamate receptors triggers complex signal transduction processes, leading to the phosphorylation and the internalization of AMPA receptors, a subtype of glutamatergic receptors. The aim of this paper is firstly to present mechanisms involved in LTD induction and maintenance. The second part introduces briefly experimental data that show that LTD is indeed strongly associated with motor learning. Recent studies on the involvement of the cerebellum in cognitive tasks also suggest that LTD may play some role other than that in the sole motor learning.