Previous studies have shown that the dorsolateral prefrontal cortex (DLPFC) plays a key role in short-term memory. The posterior parietal cortex (PPC) is thought to integrate sensory information and form the multimodal spatial information necessary for action planning and execution. The premotor cortex (PMC) is connected with both the DLPFC and PPC and is thought to be involved in planning and preparing a specific motor action on the basis of the information provided from these areas. Although accumulating evidence supports the notions above, few studies have evaluated the functions of these cortical areas under the same conditions, such as with the same behavioral task. Here we show how the DLPFC, PPC, and PMC participate in the execution of a delayed response task by disturbing the neural activity of these areas by using repetitive transcranial magnetic stimulation (rTMS).
Two monkeys performed a spatial delayed response task, in which one of eight buttons arranged in a circle was illuminated (cue), and they were required to remember the position and press the corresponding button following a variable delay. 10-Hz 1-s rTMS was delivered 0.5 s after the beginning of the delay period. rTMS to DLPFC significantly impaired the task performance in a delay-dependent manner when the target button was in the hemifield contralateral to the stimulated hemisphere regardless of which hand was used, whereas rTMS to PMC significantly impaired the performance when the contralateral hand of the stimulated hemisphere was used regardless of the target position. In the case of rTMS to PPC, the task performance was impaired when the target button in a contralateral hemifield of the stimulated hemisphere was reached by using the hand contralateral to the target hemifield. Thus, the impairment caused by DLPFC stimulation was visual field dependent, and that caused by PMC was effector dependent, whereas that caused by PPC was a combination of the two. Together, these results showed that the DLPFC, PPC, and PMC differentially contributed to the performance of the delayed response task.