SI neurons undergo substantial and rapid response modifications (either increases or decreases) during repetitive tactile stimulation. Recovery occurs in a few minutes following cessation of stimulation. The modifications are reproducible (1) if stimulus parameters are not changed and (2) if time for recovery is provided between exposures to repetitive stimuli. Stimuli identical to those which modify SI neuron response rarely lead to changes in the response of mechanoreceptive afferents. The effects of repetitive brushing stimuli on distribution of sensitivity within the RFs of SI neurons are complex and differ from one neuron to the next, but there is a common ingredient: the response generated by stimulus contact with one (or more rarely, several) RF sector(s) becomes enhanced. The changes in the distribution of sensitivity within the RF exhibited by different SI neurons sampled in the same radial penetration are consistent, whereas in tangential penetrations different neurons exhibit diverse, apparently unrelated changes. Simultaneous multichannel recordings reveal that a repetitive stimulus exerts similar effects on the response and RFs of local (separated by no more than 100 micrometers) neuron groupings.