Wakefulness-sleep modulation of cortical and subcortical somatic evoked potentials in man

Abstract

Amplitude changes of early and late components of cortical and subcortical somatic evoked potentials (SEP) were determined during wakefulness-sleep steady state shifts in patients with implanted electrodes used as an electrophysiological procedure for the surgical treatment of unilateral tremor and rigidity. SEP were produced by threshold motor stimulation of the median nerve and simultaneously recorded from contralateral scalp, thalamic and subthalamic regions, while patients spontaneously shifted from initial wakefulness (W1), to slow wave sleep (SWS I, II, IV), paradoxical sleep (PS) and final wakefulness (W2). 1. (1) During W1, cortical responses were formed by early (P50) and late (P100, 200, 300) components. Subcortical type A responses were formed only by early (N or P20) components recorded within a circumscribed region including VPL thalamic nucleus and medial lemniscus. Subcortical type B and C responses were formed by only late components (P100 and P100, 300 respectively) and were recorded intermixed within a widespread region including VL and Ce thalamic nuclei, zona incerta, nucleus subthalamicus, prelemniscal radiations and reticular formation. 2. (2) Early cortical and subcortical components significantly increased when patients shifted from PS to W2 but showed no systematic changes during other wakefulness-sleep state shifts. 3. (3) Late cortical and subcortical components significantly decreased when patients shifted from W1 to SWS I and increased from PS to W2. In addition, late cortical components significantly decreased from SWS I to II and remained unchanged from SWS II to IV while late subcortical components remained unchanged from SWS I to II and significantly decreased from SWS II to IV. These components were maximally depressed during SWS IV and PS; however new cortical (P150, N250, P450) and subcortical (P250 or N300) components appeared during SWS IV but not during PS.