Measure of Fatigue in Functional MRI (FATIGUE)

The purpose of this study is to determine more objective, central and peripheral indices of fatigue state by exploring the neural and behavioral correlates of the alert process while keeping the idea to corroborate these results with those obtained during the performance of physical exercises and neuropsychological tests "classics" of attention, motivation, and functions evaluation. The interest of this study is to manipulate and compare the phasic and tonic alert mechanism through the activation of an extrinsic motivational system during fatigue. The investigators have chosen the alert since it is a basic cognitive process defined as the ability to increase attentional resources with the expectation of a target stimulus resulting in reduced response time. It can be phasic (extrinsic), favored by the presence of a warning signal preceding the target (preparation time) or tonic (intrinsic) occurring without warning signal (wakefulness). The evaluation of the alert is classically realized by a simple reaction time task with the presence or not of warning signal soliciting wether the tonic alert or the phasic alert.

The investigators suppose to revisit the healthy population with brain model alert issued in 2010 which highlighted the predominant role of the regions of the dorsolateral prefrontal cortex, parietal, cingulate and thalamus (non-motor) in maintaining attention and temporal preparation alert task.

The investigators identify also functional, motor and cognitive components of basal ganglia of thalamus. Cognitive-motor paradigm and neurological dysfunctions observed in multiple sclerosis population will help to identify and separate the cognitive role and motor brain regions, particularly the thalamus and basal ganglia. New neurological hypotheses are proposed