The Journal of Neuroscience, October 1, 2001, 21(19):7804-7814
Role of Tonically Active Neurons in Primate Caudate in
Reward-Oriented Saccadic Eye Movement
Yasushi
Shimo and
Okihide
Hikosaka
Department of Physiology, Juntendo University, School of Medicine,
Tokyo 113-8421, Japan
Recent studies have suggested that the basal ganglia are essential
for reward-oriented behavior. A popular proposal is that the
interaction between sensorimotor and reward-related signals occurs in
the striatal projection neurons. However, the role of interneurons
remains unclear. Using the one-direction-rewarded version of the
memory-guided saccade task (1DR), we examined the activity of tonically
active neurons (TANs), presumed cholinergic interneurons, in the
caudate. Many TANs (73/155, 47.1%) responded, usually with a pause, to
a visual cue that indicated both the saccade goal and the presence or
absence of reward. For most TANs (44/73, 60.3%), the response was
spatially selective (contralateral dominant), but was not modulated by
the reward significance. TANs are thus distinct from caudate projection
neurons, which have responses to the cue that are both spatially
selective and reward contingent, and from midbrain dopamine neurons,
which have cue responses that are spatially nonselective and reward
contingent. TANs were nonetheless sensitive to the reward schedule: in
the all-directions-rewarded version (ADR) compared with 1DR, the cue responses of TANs were smaller, less frequent, and less spatially selective. In 1DR, it would first be detected that reward is not given
regularly, and this process would then promote discrimination of
individual stimuli in relation to reward. We propose that TANs would
contribute to the detection of the context that requires discrimination, whereas dopamine neurons would contribute to the stimulus discrimination. These features of TANs might be explained by
their cytoarchitecture, namely, as large aspiny neurons.
Key words:
tonically active neurons; caudate nucleus; motivation; monkey; saccade; basal ganglia
Copyright © 2001 Society for Neuroscience 0270-6474/01/21197804-11$05.00/0
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