If performance-based extrinsic monetary reward is added to a task intrinsically motivated to perform, the intrinsic motivation drops(undermining effect). While a subject was performing a task based on intrinsicmotivation, the lateral prefrontal cortex and the striatum responded to the task-start cue and positive feedback, respectively, without extrinsic monetary reward. However, the intrinsic motivation is once decreased by the underminig effect, neither the lateral prefrontal responses to the task-start cue nor the striatal responses to the positive feedback appeared without extrinsic monetary reward. Subjects prefer choosing a tool for a task by herself/himself(self-determined choice condition)to being chosen by someone else(forced-choice condition), and the performance also reflects the preference. Whereas the ventromedial prefrontal response to the failure feedback was suppressed under forced-choice condition, the response to failure feedback was hold at the similar level to the positive feedback under self-determined choice condition. These findings suggest that the lateral and ventromedial prefrontal cortices as well as the striatum are involved in intrinsic motivation and its variation.