Functional adaptation of reactive saccades in humans: a PET study

M. Desmurget (1) , Denis Pelisson (2) , J. Grethe , G. Alexander , C. Urquizar (3) , C. Prablanc , S. Grafton

1 ISC-MJ - Institut des sciences cognitives Marc Jeannerod - Centre de neuroscience cognitive - UMR5229
2 Lyon Neuroscience Research center
3 Espace et Action

It is known that the saccadic system shows adaptive changes when the command sent to the extraoc-ular muscles is inappropriate. Despite an abundance of supportive psychophysical investigations, the neurophys-iological substrate of this process is still debated. The present study addresses this issue using H 2 15 O positron emission tomography (PET). We contrasted three conditions in which healthy human subjects were required to perform saccadic eye movements toward peripheral visual targets. Two conditions involved a modification of the target location during the course of the initial saccade, when there is suppression of visual perception. In the RAND condition, intra-saccadic target displacement was random from trial-to-trial, precluding any systematic modification of the primary saccade amplitude. In the ADAPT condition, intra-saccadic target displacement was uniform, causing adaptive modification of the primary saccade amplitude. In the third condition (station-ary, STAT), the target remained at the same location during the entire trial. Difference images reflecting regional cerebral-blood-flow changes attributable to the process of saccadic adaptation (ADAPT minus RAND; ADAPT minus STAT) showed a selective activation in the oculo-motor cerebellar vermis (OCV; lobules VI and VII). This finding is consistent with neurophysiological studies in monkeys. Additional analyses indicated that the cerebel-lar activation was not related to kinematic factors, and that the absence of significant activation within the frontal eye fields (FEF) or the superior colliculus (SC) did not represent a false negative inference. Besides the contribution of the OCV to saccadic adaptation, we also observed , in the RAND condition, that the saccade amplitude was significantly larger when the previous trial involved a forward jump than when the previous trial involved a backward jump. This observation indicates that saccade accuracy is constantly monitored on a trial-to-trial basis. Behavioral measurements and PET observations (RAND minus STAT) suggest that this single-trial control of saccade amplitude may be functionally distinct from the process of saccadic adaptation.

Domaines: Neurosciences

M. Desmurget, Denis Pelisson, J. Grethe, G. Alexander, C. Urquizar, et al.. Functional adaptation of reactive saccades in humans: a PET study. Experimental Brain Research, 2000, 132 (2), pp.243-259. ⟨10.1007/s002210000342⟩. ⟨hal-02199457⟩