Origine pyramidale des variations phasiques bulbaires observées lors de l'endormement

Abstract

(1) In a previous paper 40 we found numerous bulbar areas with neuronal activity enhanced with the onset of sleep of the ‘encéphale isolé’ preparation. Some of these activations occur in bursts, integrated recordings showing phasic deflections occuring in synchrony with cortical spindles. Earlier data (histological as well as neurophysiological) suggested that the pyramidal tract would be implicated in the triggering of these phasic bulbar activations. (2) Vago-aortic sleep induction triggers phasic pyramidal activations similar to those previously recorded in bulbar areas; moreover, these baroreceptive fiber stimulations trigger a ‘pyramidal synchronization’ with spindles occurring after the beginning of the stimulation, when cortical spindles appear. The same results are obtained during spontaneous phases of sleep. Simultaneous recordings of phasic bulbar and pyramidal activities were closely related. These phasic bulbar activations are suppressed by decortication or by contralateral pyramidal tract lesion. Contralateral stimulation of the motor cortex can evoke potentials in the bulbar areas which are phasically activated during sleep. These potentials are no longer evoked after contralateral pyramidal tract lesion at the pontine level. (3) We discuss the relationships between pyramidal neuronal discharges and cortical spindles, the origin of pyramidal spindles, and finally the paradoxical occurence of pyramidal phasic discharges occurring during the slow wave phases of sleep. (4) This experiment suggests the intervention of a bulbo-cortico-bulbar circuit during the onset of slow wave sleep; we hypothesized that this circuit may interfere with somesthetic control during the onset of cortical synchronization and sleep.