Simple and complex spike activity of cerebellar Purkinje cells during active and passive movements in the awake monkey.

Two Rhesus monkeys (Macaca mulatta) were trained to pursue a target light signal by moving the hand at the wrist joint. Additionally, a d.c. motor could be attached to the lever in order to perform similar passive movements. During performance of the task, single Purkinje cells were recorded from the intermediate part of the cerebellar anterior lobe. Electromyographic activity of the flexor and extensor muscles of the forearm was recorded simultaneously. Passive hand movements evoked changes in the complex spike and simple spike discharge of Purkinje cell. The complex spike responded most sensitively to the beginning of the movement; the activity pattern had phasic character and could be related specifically to the movement direction. The simple spike response was usually weak and hence revealed-less specific relations. During active movements the simple spike frequency change was generally stronger than during passive movements and reached a maximum (or minimum) at the beginning of hand deflexion. The complex spike activity during active movements was characterized by a contrast between the time phases before and after the movement onset. In most of the cases, where a phase of increased activity stopped at the movement onset, the sensory feed-back signal seen during passive movements was cancelled. The possible consequences of the convergence of the complex and simple spike signal for the motor control function of the cerebellum are discussed.