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
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