Comparison of the neuronal activity in the SMA and the ventral cingulate cortex during prehension in the monkey. Cadoret, Genevi[grave]eve and Allan M. Smith. Centre de Recherche en Sciences Neurologiques, D[acute]epartement de Physiologie, Universit[acute]e de Montr[acute]eal.
APStracts 3:0222N, 1996.
Two monkeys were trained to use the thumb and forefinger to lift and hold an instrumented apparatus within a narrow position window for 1 second. The device was equipped to measure the position and the grip and lifting forces exerted by the animal. On blocks of trials the weight and surface texture could be varied or a force-pulse perturbation could be systematically delivered 750 ms after the object entered the window. If unopposed the perturbation would displace the hand from the position window, and in preparation for this perturbation the monkeys either increased their grip force before the perturbation or they raised the object higher within the position window. Two clearly separated clusters of cells in the medial wall of the frontal lobe were found to be active in relation to the task. One group of cells (n=115) was located in the caudal and medial part of area 6, in the supplementary motor area (SMA) and the other (n=92) in the ventral bank of the cingulate sulcus (CMAv), in area 23c. In each area, neurons were characterized by their sensorimotor features clearly related to the hand in addition to their modulated activity in the task. In the SMA, 71% (42/59) of the neurons tested for receptive fields responded to peripheral and mainly proprioceptive stimulation and 71% of them (30/42) received inputs from the hand. In the CMAv, 77% (48/62) of the neurons responded to peripheral proprioceptive stimulation, and 77% (37/48) exhibited receptive fields originating from the hand. Intracortical microstimulation (ICMS) applied to 43 sites in the SMA evoked discrete hand movements at 12 loci whereas in the CMAv hand movements were observed at 8/27 sites tested with an average threshold of greater than 15 [mu] A. A strong similarity was observed between the SMA and CMAv neurons in their sensorimotor features as well as the modulation of their activity in relation to the prehension task. In both areas, the activity was poorly related to grip force and significant correlations with peak grip force was observed for only 9% and 7% of the CMAv and SMA neurons respectively. In the SMA, only 5 cells exhibited increased activity prior to the perturbation and in the CMAv no changes in activity were found despite the presence of clear preparatory increases in grip force in anticipation of the perturbation. The perturbation evoked reflex-like excitation of 38% (25/65) of the neurons in the CMAv and 28% (20/71) of the cells in the SMA which were similar in magnitude and latency (around 50 ms) in both areas. In both the SMA and CMAv, most of the neurons increased their firing rate less than 200 ms before the grip force onset and the overlap in the distribution of neuronal response times suggests a parallel activation of the SMA and CMAv neurons during the prehension task.

Received 19 June 1996; accepted in final form 19 September0 1996.
APS Manuscript Number J488-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996