Relation between changes in the preparatory brain potential and excitability of the H-reflex, and localization of a focal ischaemic brain lesion.

In the sample of 15 hemiparetics, ischaemic focus was localized cortically 8 times, deep subcortically 7 times. Use was made of a method that permits simultaneously to record both the cortical potential changes associated with preparation for voluntary movement, and excitability changes of the H-reflex. A slightly depressed amplitude of the preparatory brain potential and a relatively satisfactory facilitation of the H-reflex was observed in the light cortical focal brain ischaemia. A striking deformation up to disorganization of the preparatory brain potential and the absence of facilitation of the H-reflex in subjects with deeper subcortical ischaemic foci may be related to an impairment of the generator of the slow preparatory potential (thalamus, mesencephalon) and to a discruption of cooperation in the complex cerebral cortex - middle thalamus.