Saccadic eye movements in response to drug action in the midbrain

A technique that combines local injection of GABAergic drugs, neuronal recording, and electrical stimulation in awake, behaving monkeys has been used to study the mid-brain eye-movement system. Cells in the substantia nigra pars reticulata (SNr) that project to the superior colliculus tonically suppress saccadic eye movements and do so via a GABAergic mechanism. Removal of this suppression leads to facilitation and elicitation of saccadic eye movements. Furthermore, the integrity of the nigrotectal pathway is especially important for eye movements guided by memory. Since the SNr is thought to be part of the basal ganglia output system, this work may point to two general principles of basal ganglia function: a mechanism involving ‘disinhibition’ and a relative specialization for memory-guided movements.