Neuronal activity in cerebellar cortex related to control of prehensile force.

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Abstract
Monkeys [Macaca fascicularis] were trained to produce a range of maintained prespecified forces by carefully controlling the pressure exerted between the thumb and forefringer in a lateral precision grip. An investigation of the electromyographic activity of both the intrinsic and extrinsic muscles of the hand indicated that antagonist muscles were all actively contracting during the maintained precision grip. In the intermediate zone of the cerebellar cortex, the majority of Purkinje cells, which were identified by the climbing fiber discharge and which modulated firing frequency (15/21 or about 71%), responded with a decrease in tonic activity during maintained grasping. The majority of unidentified neurons with modulated firing frequency and that never produced a climbing fiber discharge (61/70 or about 85%) responded with increased firing frequency during the maintained precision grip. There were significant positive linear regression coefficients between spike frequency and both force and rate of force change among units in the unidentified category. There were significant negative linear regression coefficients were found between spike frequency and both force and rate of force change for a few (n = 3) Purkinje cells. The majority of both Purkinje and unidentified neurons in the intermediate zone of the cerebellar cortex responded to light pressure, hair displacement, muscle tapping and imposed displacement of the wrist and fingers. The discharge of Purkinje cells in this region of the cerebellar cortex is apparently best related to the reciprocal inhibition of antagonist muscles during movement, but in situations requiring coactivation of antagonists, the Purkinje cells are inhibited.

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