REPRESENTATION OF TACTILE SIGNALS IN PRIMATE SUPPLEMENTARY MOTOR AREA

1. We have studied the neuronal activity in the supplementary motor ar ea (SMA) of two monkeys who categorized the speed of moving tactile st imuli delivered to the glabrous skin of the hand ipsilateral to the si te of cortical recording and contralateral to the responding arm. 2. A large number of SMA neurons responded to the stimuli of all speeds ( 176 of 522) but only when those stimuli controlled behavior. 3. A seco nd class of SMA neurons responded differentially in the categorization task (35 during the stimuli and 51 during the reaction time period) a nd predicted its outcome. 4. To dissociate the interrupt target switch es presses from the tactile categorization responses, sixteen neurons, which responded to the stimuli in all speeds, and 11 neurons, which d ischarged differentially, were tested in a visual control task. None o f these two classes of neurons responded in this situation. 5. It is c oncluded that the SMA ipsilateral to sensory input and contralateral t o the responding arm is involved in the sensory decision process in th is somesthetic categorization task.