Monkey brain activity modulated by reward preferences: a positron emission tomography study.

Motivation, depending on the relative preference and magnitudes of rewards, can influence our goal-directed action. Reward preferences can modulate neurons in the striatum (ventral and dorsal portions), lateral prefrontal and orbitofrontal cortex, but it remains unclear where in the brain and how any motivational change affects subsequent rewarding action. The present study sought to test whether the lateral prefrontal and other regions in monkeys during a visuo-motor task may change the activities in response to the reward preferences. After defining the rating of reward preference in a choice test, we measured regional cerebral blood flow of two Japanese monkeys during the task where the cognitive requirement was always the same, but the motivational significance varied by different rewards (raisin, banana flavored pellet, plain pellet, and banana), using positron emission tomography with H2(15)O. We showed that lateral prefrontal, orbitofrontal, parietal, striatal (ventral and dorsal), and cerebellar activities may be modulated depending on the reward preferences. The present results may include the brain regions subserving motivational changes by subjective reward significances.