Periodic microstimulation of single mechanoreceptive afferents produces frequency-following responses in human EEG

Dense multichannel recordings of scalp electroencephalogram were obtained in the vicinity of primary somatosensory cortex, time-locked to repetitive train microstimulation of single, physiologically characterized skin mechanoreceptive afferents in the median nerve of a single human subject. Frequency-domain analysis of cross-trial averages for fast-adapting type one and slowly adapting type one afferents revealed prominent, topographically organized "driving" responses in the electroencephalogram at the frequency of stimulation, which vanished under various statistical and experimental control conditions. The responses also exhibited systematic declines in amplitude both across and within trials, and orderly changes in scalp topography as a function of the location of afferents' receptive fields on the hand. The observed response properties are tentatively explained in terms of characteristics of the pattern of afferent drive impressed on the cortex by microstimulation.