Responses of subthalamic and pallidal neurons to striatal stimulation: an extracellular study on awake monkeys.

The unitary activity of subthalamic neurons (corpus Luysii) and of GP neurons was recorded extracellularly on awake monkeys (Macaca cynomolgus). Striatal stimulation induces in subthalamic (Sth) neurons a short latency spike discharge (10-15 msec) followed by a long lasting depression of the spontaneous activity. As, according to anatomical studies, the subthalamic nucleus is principally connected to the globus pallidus (GP), electrophysiological relations between striatal and GP neurons and between GP and Sth neurons were studied. Striatal stimulation induced an inhibitory-excitatory sequence in GP neurons and pallidal stimulation induced only a depression of the activity of Sth neurons. Since no GP neurons are excited at short latency by striatal stimulation, possible events along a striato-subthalamic pathway are discussed.