Facilitation Et Inhibition Des Potentiels Évoqués Corticaux Dans L'éveil Cérébral

Abstract

Sensory arousal and arousal produced by stimulation of the mesencephalic legmentum in the encéphale isolé cat are regularly accompanied by an increase of the evoked potential recorded in the various neocortical receiving areas, when the testing stimulus is applied on the adequate thalamic relay nucleus or on the optic nerve (for the visual area). The processes of this cerebral dynamogenie effect, which can be very marked, include: a) the facilitation of the afferent transmission through the thalamus; b) the facilitation of intracortical synaptic transmissions in the receiving areas together with those which underly the so-called secondary responses in the associative areas. Factor b is the most important and constant one. A similar diffuse cortical facilitation follows the stimulation of the thalamic reticular system. A single conditioning shock applied in the mesencephalic reticular formation or on the n. centro-median may be as effective as the fast repetitive stimulation of the same structures.

When the testing stimulus is applied on peripheral receptors (visual, auditory, cutaneous) the effect of arousal on the evoked responses of the corresponding receiving areas is no more facilitatory but becomes generally inhibitory. This paradoxical inhibition is ascribed predominantly to a process of occlusion (« masking »). An explanation is proposed for these constrasting results of reticular arousal and their physiological significance is discussed.