Inversion de polarite de la variation contingente negative au cours d'etats d'endormissement*

Summary In 25 subjects repeated examination of contingent negative variation (S 1 − S 2 = 1 sec) under relatively unconstrained experimental conditions (simple, monotonous task, long recording sessions with eyes closed) favorized drowsiness and falling asleep. These periods of low vigilance level, observed in 7 subjects, are characterized by: (1) a global reduction in spontaneous EEG, measured by a diminution in the alpha/theta + delta index (FFT on bipolar leads P 3 − P 4 ); (2) an inversion in alpha reactivity in the S 1 − S 2 interval, which, instead of diminishing, tends to augment ‘paradoxically’; and (3) an inversion in the polarity of the CNV, which can reach a positive value as high as +15 to +20 μV. These electrophysiological phenomena are not accompanied by significant modifications in reaction time. The results are interpreted as the translation of an active ‘internal inhibition’ process, induced by repetition of monotonic stimuli. They are compared with animal data obtained by Marczynski and Sherry (1972) and Skinner and Yingling (1977).