TIME-COURSE AND MAGNITUDE OF MOVEMENT-RELATED GATING OF TACTILE DETECTION IN HUMANS - I - IMPORTANCE OF STIMULUS LOCATION

The time course and spatial extent of movement-related suppression of the detection of weak electrical stimuli (intensity, 90% detected at r est) was determined in 118 experiments carried out in 47 human subject s. Subjects were trained to perform a rapid abduction of the right ind ex finger (D2) in response to a visual cue. Stimulus timing was calcul ated relative to the onset of movement and the onset of electromyograp hic (EMG) activity. Electrical stimulation was delivered to 10 differe nt sites on the body, including sites on the limb performing the movem ent (D2, D5, hand, forearm and arm) as well as several distant sites ( contralateral arm, ipsilateral leg). Detection of stimuli applied to t he moving digit diminished significantly and in a time-dependent manne r, with the first significant decrease occurring 120 ms before movemen t onset and 70 ms before the onset of EMG activity. Movement-related a nd time-dependent effects were obtained at all stimulation sites on th e homolateral arm as well as the adjacent trunk. A pronounced spatiote mporal gradient was observed: the magnitude of the movement-related de crease in detectability was greatest and earliest at sites closest to the moving finger and progressively weaker and later at more proximal sites. When stimuli were applied to the distant sites, only a small (s imilar to 10%), non-time-dependent decrease was observed during moveme nt trials. A simple model of perceptual performance adequately describ ed the results, providing insight into the distribution of movement-re lated inhibitory controls within the CNS.