Contrasting effects of reward expectation on sensory and motor memories in primate prefrontal neurons

The value of reward obtained with successful behavior is important for guiding purposeful behavior. The lateral prefrontal cortex (LPFC) has been implicated in working memory that guides goal-directed behavior. However, mechanism that integrates the reward value into the working memory for goal-directed behavior is not understood. To help clarify this issue, we examined the effect of reward expectation on the neuronal process in the LPFC associated with memory-based sensorimotor processing. By temporally dissociating visuospatial sensory and saccade-directional motor memories in the LPFC, we here show that reward expectation significantly enhanced the directional selectivity of sensory working memory but did not affect the directional selectivity of motor memory. The enhancement of sensory working memory in the neuronal population was sustained during the delay but extinguished soon after the motor memory appeared. These results suggest that the expectation of high reward value primarily affects the sensory working memory that may be used for behavioral guidance rather than preparation for forthcoming saccades. It thus appears that the LPFC is a neuronal substrate for working memory used to guide a reward-oriented behavior, rather than reflecting an efficient control of motor action in motivated states.