[Effect of the intensity of stimulation on the variability and interactions of various late components of the somatosensory evoked potentials in humans].

Human evoked potentials (EP) to paired somatosensory pain stimuli were recorded from the vertex. Amplitude of the N150 and P250 components of the second EP decreased within 600-1000 ms interstimulus interval. The depression occurred was more intensive with an increase of the first (conditioning) stimulus strength. As a rule, depression of N150 component was more pronounced. Selective averaging of EPs indicated that, when the stimulus intensity was stable, variations in the amplitudes of identical components in response to the first and second stimuli were not usually negatively correlated; positive correlation was frequently found. This can be regarded as a proof that there is no direct relation between the inhibitory after-processes in the cellular generators of the studied EP components and the degree of their previous activation. Such variations can reflect the sequence of periods of an increase and a decrease in the generator activity under conditions of stable stimulus intensity.