The relation between electro-cortical waves and responsiveness of the cortico-spinal system

Abstract

1. 1. Studies of the responsiveness to electrical stimulation of the system of cortical neurones giving rise to evoked volleys in the medullary pyramid have been carried out in cats. 2. 2. Phasic variations in responsiveness and relayed activity have been correlated with phasic changes of cortical surface potential during the elicitation of augmenting waves and during spontaneous spindle waves. Relayed pyramidal volleys appear during the initial surface positivity of each of these cortical wave forms. During the positive and early negative phases of the surface potential waves, the responsiveness of the efferent neurone system is augmented. During the late phase of cortical negativity, and for 50–150 msec. thereafter, responsiveness of the efferent neurone system is depresses. These changes affect the indirect portion of the evoked pyramidal volley to a significantly greater extent than the direct portion of the volley. 3. 3. Responsiveness of this corticifugal neurone system has also been tested during the elicitation of that particular form of recruitment wave which develops upon stimulation of the midline nuclei of the diffuse thalamic projection system. During this type of recruitment response there is no relayed pyramidal volley. Neither is there any detectable alteration in responsiveness of the efferent neurone system. 4. 4. The marked differences in the effects associated with these electrically similar potential changes indicate the existence of at least two fundamentally different mechanisms subserving thalamo-cortical relationships.