Cerebellar control of constrained and unconstrained movements. II. EMG and nuclear activity

The aim of this study was to see in monkeys if neurons in dentate and lateral interposed deep cerebellar nuclei are preferentially active in relation to certain movements relative to others. Simple and compound digit movements were trained with digits, hand, and elbow constrained in a cast. The constrained simple movement was flexion of Thumb or Index; the constrained compound movement, flexion of Thumb+Index. An unconstrained compound movement consisted of a reach to, pinch of, and retrieval of a small food reward (Reach+Pinch). Electromyographic (EMG) recording showed that many muscles in the upper extremity, shoulder girdle, and trunk were active in all movements. EMG/muscle stimulation during the constrained digit movements showed that the digit prime movers were active during, sufficient for, and necessary for performance of these digit tasks. By contrast, EMG/muscle stimulation showed that the proximal muscles (though co-active during the tasks) were neither sufficient nor necessary for performance of the digit tasks. A fraction of those neurons that were active during both the constrained and the unconstrained movements fired at a higher frequency during the unconstrained task. Some neurons were active during Reach+Pinch only; a few others were active during one or more of Thumb, Index, Thumb+Index only. There was no distinct preferential discharge relationship to the compound Thumb+Index as compared with the simple Thumb or Index. These correlational data are consistent with an interpretation that the cerebellar discharge influenced all of these movements-simple and compound, constrained, and unconstrained-no one type seemingly more than any other.