High-dimensional encoding of movement by single neurons in basal ganglia output.

The substantia nigra pars reticulata (SNpr), an output structure of the basal ganglia, is hypothesized to gate movement execution. Previous studies in the eye movement system focusing mostly on saccades have reported that SNpr neurons are tonically active and either pause or increase their firing during movements, consistent with the gating role. We recorded activity in the SNpr of two monkeys during smooth pursuit and saccadic eye movements. SNpr neurons exhibited highly diverse reaction patterns during pursuit, including frequent increases and decreases in firing rate, uncorrelated responses in different movement directions and in reward conditions that resulted in the high dimensional activity of single neurons. These diverse temporal patterns surpassed those in other oculomotor areas in the medial-temporal cortex, frontal cortex, basal ganglia, and cerebellum. These findings suggest that temporal properties of the responses enrich the coding capacity of the basal ganglia output beyond gating or permitting movement.