The pulvinar nucleus is richly interconnected with most of visual cortex, leading many to propose a visual role for this enigmatic part of the brain. However, little is known about its role in visual processing. On the basis of lesion, imaging, and recording studies, it has been proposed that pulvinar plays a role in directing visual attention to particular regions of space. In the proposed experiments, we plan to directly examine this hypothesis using electrical microstimulation and reversible inactivation. We will measure both visual detection performance and neuronal responses in extrastriate cortex, with and without perturbation. The detection task will be of a change in motion direction, and we already know that cortical area MT is involved in this kind of perceptual capability. The design allows two distinct comparisons to be made, each critical to this hypothesis. First, we know that directed attention produces behavioral benefits and local changes in the gain of response of extrastriate neurons; activation of pulvinar should mimic this change and reversible inactivation should eliminate it. Also, we will be able to conclude whether the effects measured perceptually could be mediated through known cortical circuits supporting visual discrimination. ? ?
