Effects of repetitive transcranial magnetic stimulation over dorsolateral prefrontal and posterior parietal cortex on memory-guided saccades

We investigated the role of the dorsolateral prefrontal cortex (DLPFC) and the posterior parietal cortex (PPC) in a visuospatial delayed-response task in humans. Repetitive transcranial magnetic stimulation (20 Hz, 0.5 s) was used to interfere temporarily with cortical activity in the DLPFC and PPC during the delay period. Omnidirectional memory-guided saccades with a 3-s delay were used as a quantifiable motor response to a visuospatial cue. The question addressed was whether repetitive transcranial magnetic stimulation (rTMS) over the DLPFC or PPC during the sensory of memory phase affects accuracy of memory-guided saccades. Stimulation over the primary motor cortex served as control. Stimulation over the DLPFC significantly impaired accuracy of memory-guided saccades in amplitude and direction. Stimulation over the PPC impaired accuracy of memory-guided saccades only when applied within the sensory phase (50 ms after cue offset), but not during the memory phase (500 ms after cue offset). These results provide further evidence for a parieto-frontal network controlling performance of visuospatial delayed-response tasks in humans. It can be concluded that within this network the DLPFC is mainly concerned with the mnemonic respresentation and the PPC with the sensory representation of spatially defined perceptual information.