Abstract
The functional properties of neurons located in the rostral part of
inferior area 6 were studied in awake, partially restrained macaque
monkeys. The most interesting property of these neurons was that
their firing correlated with specific goal-related motor acts rather
than with single movements made by the animal. Using the motor acts
as the classification criterion we subdivided the neurons into six
classes, four related to distal motor acts and two related to proximal
motor acts. The distal classes are: ldquoGrasping-with-the-hand-and-the-mouth
neuronsrdquo, ldquoGrasping-with-the-hand neuronsrdquo, ldquoHolding
neuronsrdquo and ldquoTearing neuronsrdquo. The proximal classes
are: ldquoReaching neuronsrdquo and ldquoBringing-to-the-mouth-or-to-the-body
neuronsrdquo. The vast majority of the cells belonged to the distal
classes. A particularly interesting aspect of distal class neurons
was that the discharge of many of them depended on the way in which
the hand was shaped during the motor act. Three main groups of neurons
were distinguished: ldquoPrecision grip neuronsrdquo, ldquoFinger
prehension neuronsrdquo, ldquoWhole hand prehension neuronsrdquo.
Almost the totality of neurons fired during motor acts performed
with either hand. About 50% of the recorded neurons responded to
somatosensory stimuli and about 20% to visual stimuli. Visual neurons
were more difficult to trigger than the corresponding neurons located
in the caudal part of inferior area 6 (area F4). They required motivationally
meaningful stimuli and for some of them the size of the stimulus
was also critical. In the case of distal neurons there was a relationship
between the type of prehension coded by the cells and the size of
the stimulus effective in triggering the neurons. It is proposed
that the different classes of neurons form a vocabulary of motor
acts and that this vocabulary can be accessed by somatosensory and
visual stimuli.
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