Résumé
Movements and behaviors during REM sleep in RBD are very diverse. Their detailed investigation on video during polysomnography has allowed the improvement of their characterization and the development of hypotheses about the mechanisms of their generation and execution.
The diversity and complexity of the behaviors observed, associated with the prominent role of language during the episodes, have suggested a strong implication of the cortex in the generation of the behavior. Singing and giving English lessons or political discourse can’t be generated without the implication of the cortex. On the other hand, the more frequent elementary movements and the associated periodic limb movements during sleep also suggest a role of the brainstem.
In patients with Parkinson’s disease, the discrepancy between the quality of movement while awake (slow, weak, reduced in amplitude) compared to the quality of movement during REM sleep in RBD (fast, strong, large amplitude) has suggested that the execution of movement during RBD is different from that of the awake state. One hypothesis is that REM sleep is associated with a restoration of the dopaminergic transmission. Another one is that the basal ganglia are bypassed during RBD. This bypass hypothesis is supported by the jerky aspect of the movement observed during RBD, indicating that the movements are not “smoothed” by the basal ganglia. Finally, the observation of the same improvement of movement during RBD in multiple system atrophy, a dopa-resistant parkinsonian syndrome, thus excludes the hypothesis of the restoration of dopaminergic transmission in REM sleep as a mechanism.
Interestingly, these hypotheses were further confirmed by neuroimaging and neurophysiology studies showing, respectively, that the supplementary motor area was associated with the cortical generation of the movement during RBD and that the basal ganglia were probably bypassed during the execution of movement during RBD in Parkinson’s disease.