Single-pulse TMS on the FEF area induces a "narrow" focus of attention
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The role of spatial attention has often been represented as a fixed "spotlight", which highlights a specific region in the visual space disregarding other locations. However, the focus of attention can also be adjusted in size, like a "zoom-lens", according to the task demand. Although neuroimaging data supported this hypothesis, showing that the increasing size of the attended region causes an increased retinotopic extent of activation in striate and extra-striate visual areas, the causal role of fronto-parietal network in this focus size-dependent modulation in visual cortex has not been clarified. In the present study participants were asked to detect as fast as possible a visual target, which could appear at three possible eccentricities from the fixation. A non-informative cue was used to modulate the size of the attended region. In a half of the trials, a small circle cue, which included only the first eccentricity, was used to narrow the attentional focus (zoom-in). In the other half, a large circle cue, which included all the three possible eccentricities, had the role to induce participants to broaden the attended region (zoom-out). Single-pulse transcranial magnetic stimulation (TMS) on the right and left FEF areas or Vertex was used to interfere with the focus size-dependent modulation. Results show that only TMS over the right FEF area was able to interfere with the modulation of the attentional focus size. Precisely, when TMS was delivered after the onset of a large cue, participants failed to zoom-out the focus of attention. The process of zoom-in, instead, was not inhibited by TMS on the right FEF. Our results provide causal link between the role of the right FEF area and the modulation of the attentional resources allocated in the visual field.