title: Reward-dependent spatial selectivity of anticipatory activity in monkey caudate neurons.
abstract: Many neurons show anticipatory activity in learned tasks. This phenomenon appears to reflect the brain's ability to predict future events. However, what actually is predicted is unknown. Using a memory-guided saccade task, in which only one out of four directions was rewarded in each block of trials, we found that a group of neurons in the monkey caudate nucleus (CD) showed activity before presentation of an instruction cue stimulus. Among 329 CD neurons that were related to memory-guided saccade tasks, 156 showed the precue activity and 91 of them were examined fully. Remarkably, the magnitude of the precue activity varied across the four blocks of the one-direction-rewarded (1DR) condition, depending on which direction was rewarded. A majority of neurons with precue activity (83/91, 91%) showed significant directional preference. The best and worst directions were usually in the contralateral and ipsilateral directions, respectively. Within a block, the precue activity increased rapidly for the best direction in 1DR and decreased gradually for the worst direction in 1DR and all-directions-rewarded (ADR) condition. The precue activity was weak in ADR. The precue activity did not reflect the likelihood of a particular cue stimulus, because the probability of the cue appearing in each direction was the same regardless of the rewarded direction. These results suggest that each CD neuron indicates a particular position-reward association prospectively, usually with contralateral preference. Assuming that the CD neurons have access to saccadic motor outputs, the precue activity would create a motivational bias toward the contralateral space, even before an instruction is given by the cue stimulus.
authors.affiliation: Department of Physiology, Juntendo University School of Medicine, Tokyo 113-8421, Japan.
authors.forename: Yoriko
authors.initials: Y
authors.lastname: Takikawa
authors.forename: Reiko
authors.initials: R
authors.lastname: Kawagoe
authors.forename: Okihide
authors.initials: O
authors.lastname: Hikosaka
mesh_terms: D000161:Acoustic Stimulation; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D002421:Caudate Nucleus / Q000166:cytology / Q000502:physiology*; D003463:Cues; D005403:Fixation, Ocular / Q000502:physiology; D008251:Macaca; D008297:Male; D008568:Memory / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D012201:Reward; D012438:Saccades / Q000502:physiology