Abstract
It has been said that the insular cortex (IC) plays a role in gustation, pain, visceral sensation and so on. Recent brain activation studies show that IC reacts to reward-related behavior. To investigate the neural correlates, we recorded single neuronal responses of IC while monkeys were performing a reward schedule task. This task consists of 1, 2, 3 and 4 visual discriminations to earn reward. In certain reward condition the visual cue was stepwise brightened in relation to reward proximity whereas in uncertain reward condition the cue brightness was randomly picked up. In middle to anterior part of IC, 85/120 neurons responded only to rewarded trials in certain reward condition, and 45 of them responded to all trials in uncertain condition, suggesting that substantial number of neurons in anterior IC react to possible reward as occurs in gambling. Reward expectancy underlies these responding manners. We are currently recording the neurons in posterior IC to study whether the similar response can be observed. At present no neurons seem to signal reward expectancy but rather relate to each task event. Though the further research is needed, the IC could be functionally segregated between anterior and posterior part. [J Physiol Sci. 2007;57 Suppl:S57]
