Prediction of relative and absolute time of reward in monkey prefrontal neurons.

We studied single-neuron activity in the monkey dorsolateral prefrontal cortex during a saccade task, in which correct responses were rewarded after a delay of 0.5 or 1.5 s in one trial-block, and after 1.5 or 3-s delay in the other trial-block. Activity of some neurons depended on the relative length of the delays (longer or shorter) within each block, and activity for the 1.5-s trials was significantly different between the blocks. Activity of another group of neurons reflected the absolute length of delay: hence, the activity in the 1.5-s trials did not differ between the blocks. These results indicate that both relative and absolute time of future reward is represented in subsets of neurons in the dorsolateral prefrontal cortex.