Neural Mechanisms on Motivational Process and Reward Expectancy in the Brain

Abstract

In our daily life, we make plans and act based on the motivation to reach a goal. During the course of the activity, we continually compare our current status against our expectation for reaching a goal, with expectation increasing over the course of the activity. This implies that there are neural signals underlying the increasing expectation. We developed a task, a cued multitrial reward schedule task, to control level of motivation and investigate the degree of reward expectancy. In this task, monkeys can obtain rewards only after a series of trials had been correctly completed. When there was a cue to indicate how many correct performances were required for a reward, the monkeys made progressively fewer errors as the rewarded trial approached, indicating that the monkeys expectancy of an impending reward grew. We recorded the activity of single neurons in the anterior cingulate of Rhesus monkey, which is one of the loop structure that is involved in initiating movements in response to motivationally or emotionally significant stimuli. The single neurons in the anterior cingulate showed responses that were progressively increasing through the schedules as the reward expectancy increased.