P 64. Cartography of causal contributions of human frontal cortex to visual attention

Abstract

It is widely known that the human frontal cortex is involved in the allocation of visual attention, however, the exact causal functional contributions of individual subregions are not well understood. In the present study, we used a simple visual localization task and applied rTMS pulses to map frontal cortical subregions likely to generate significant visuo-spatial biases during the spatial deployment of attention prior to perception. A group of nine adult healthy subjects executed a task based on the localization of small rectangular black dots. Targets were displayed unilaterally (left or right) or bilaterally (left and right) for a brief period (40 ms). In a systematic mapping approach, a stimulation grid of 9 (3 × 3) sites was anchored 2 cm rostral to the motor hand area. Three pulses of real or sham 10 Hz rTMS were delivered in a counterbalanced manner, at each of the grid locations 50 ms post target onset to interfere with the ongoing neural processing. As a main finding, significant deterioration of detection performance, as measured by effective reaction time, for stimuli in the contralateral hemifield and increased performance for ipsilateral targets were observed for two grid regions anatomically associated with the right FEF and right middle frontal gyrus. We conclude that the disruptive effects of TMS on a simple spatial localization task for which a well-balanced deployment of attention is required are exquisitely spatially selective, and are found in specific frontal cortical subregions.