Attenuation of somatosensory responses to self-produced tactile stimulation.

Sensory stimulation resulting from one's own behavior or the outside world is easily differentiated by healthy persons who are able to predict the sensory consequences of their own actions. This ability has been related to cortical attenuation of activation elicited by self-produced stimulation. To date, however, the neural processes underlying this modulation remain to be elucidated. We therefore recorded whole-scalp magnetoencephalographic (MEG) signals from 10 young adults either when they were touched by another person with a brush or when they touched themselves with the same device. The main MEG responses peaked at the primary somatosensory cortex at 54+/-2 ms. Signals and source strengths were about a fifth weaker to self-produced than external touch. Importantly, attenuation was present in each subject. Control recordings indicated that the suppression was neither caused by hand movements as such nor by visual cues. The very early start of the attenuation already about 30 ms after stimulation onset is in line with the hypothesis of forward mechanisms, based on motor commands, as the basis of differentiation between self-produced and externally produced tactile sensations.