Abstract
Visuo-parietal (V-P) cortex is critically important for redirecting attention. It is also the dominant source of cortical feedback signals to primary visual cortex (1°VC) in the cat. The signals are transmitted either directly or via the massive V-P to LPl to 1°VC pathway. Unilateral cooling deactivation of V-P cortex completely blocks the ability to redirect attention from a cynosure to a novel stimulus moved into the contralateral half of the visual field, yet additional cooling deactivation of contralateral V-P cortex has the positive, paradoxical effect of restoring proficient orienting into the previously defective field. We reasoned that if feedback projections and 1°VC contribute in significant ways to the ability of cats to reorient attention we should detect decreased neural activity in 1°VC during unilateral V-P deactivation and an amelioration of the depression during bilateral V-P deactivation. The latter would suggest that normal signal amplification in 1°VC is a pre-requisite for the ability to redirect attention to a new location.
We used optical imaging of intrinsic 1°VC signals and single neuron physiology to assay the neural impact of deactivating V-P feedback pathways. In accord with the anatomy, cooling deactivation of V-P cortex reduced activity and broadened tuning in the grating-orientation preference map in ipsilateral 1°VC. Yet, contrary to expectation, additional deactivation of contralateral V-P cortex had an additive effect, and reduced neural activity and broadened orientation tuning even further. The opposite direction of the impacts of the bilateral cooling on the neural and behavioral measures promotes the view that neither 1°VC nor feedback activity are critical for the reorienting of attention to a novel stimulus moved into the visual field. These data suggest that the process of redirecting attention, at least in this instance, is primarily an executive feed-forward function of V-P cortex.
Supported by NINDS, NSF, DAAD, MPG.