Organization of reward and movement signals in the basal ganglia and cerebellum

The basal ganglia and the cerebellum are major subcortical structures in
the motor system. The basal ganglia have been cast as the reward center of
the motor system, whereas the cerebellum is thought to be involved in
adjusting sensorimotor parameters. Recent findings of reward signals in
the cerebellum have challenged this dichotomous view. To compare the basal
ganglia and the cerebellum directly, we recorded from oculomotor regions
in both structures from the same monkeys. We partitioned the
trial-by-trial variability of the neurons into reward and eye-movement
signals to compare the coding across structures. Reward expectation and
movement signals were the most pronounced in the output structure of the
basal ganglia, intermediate in the cerebellum, and the smallest in the
input structure of the basal ganglia. These findings suggest that reward
and movement information is sharpened through the basal ganglia, resulting
in a higher signal-to-noise ratio than in the cerebellum.