Visual neurons typically receive information from a limited portion of the retina, and such receptive fields are a key organizing principle for much of visual cortex. At the same time, there is strong evidence that receptive fields transiently shift around the time of saccades. The nature of the shift is controversial: Previous studies have found shifts consistent with a role for perceptual constancy; other studies suggest a role in the allocation of spatial attention. Here we present evidence that both the previously documented functions exist in individual neurons in primate cortical area V4. Remapping associated with perceptual constancy occurs for saccades in all directions, while attentional shifts mainly occur for neurons with receptive fields in the same hemifield as the saccade end point. The latter are relatively sluggish and can be observed even during saccade planning. Overall these results suggest a complex interplay of visual and extraretinal influences during the execution of saccades.

The whisker-to-barrel cortex is widely used to study neurovascular coupling, but the cellular basis that underlies the perfusion changes is still largely unknown. Here, we identified neurons recruited by whisker stimulation in the rat somatosensory cortex using double immunohistochemistry for c-Fos and markers of glutamatergic and GABAergic neurons, and investigated in vivo their contribution along with that of astrocytes in the evoked perfusion response. Whisker stimulation elicited cerebral blood flow (CBF) increases concomitantly with c-Fos upregulation in pyramidal cells that coexpressed cyclooxygenase-2 (COX-2) and GABA interneurons that coexpressed vasoactive intestinal polypeptide and/or choline acetyltransferase, but not somatostatin or parvalbumin. The evoked CBF response was decreased by blockade of NMDA (MK-801, Ϫ37%), group I metabotropic glutamate (MPEPϩLY367385, Ϫ40%), and GABA-A (picrotoxin, Ϫ31%) receptors, but not by GABA-B, VIP, or muscarinic receptor antagonism. Picrotoxin decreased stimulus-induced somatosensory evoked potentials and CBF responses. Combined blockade of GABA-A and NMDA receptors yielded an additive decreasing effect (Ϫ61%) of the evoked CBF compared with each antagonist alone, demonstrating cooperation of both excitatory and inhibitory systems in the hyperemic response. Blockade of prostanoid synthesis by inhibiting COX-2 (indomethacin, NS-398), expressed by ϳ40% of pyramidal cells but not by astrocytes, impaired the CBF response (Ϫ50%). The hyperemic response was also reduced (Ϫ40%) after inhibition of astroglial oxidative metabolism or epoxyeicosatrienoic acids synthesis. These results demonstrate that changes in pyramidal cell activity, sculpted by specific types of inhibitory GABA interneurons, drive the CBF response to whisker stimulation and, further, that metabolically active astrocytes are also required.

A fundamental concept in neuroscience is the receptive field, the area of space over which a neuron gathers information. Until about 25 years ago, visual receptive fields were thought to be determined entirely by the pattern of retinal inputs, so it was quite surprising to find neurons in primate cortex with receptive fields that changed position every time a saccade was executed [1]. Although this discovery has figured prominently into theories of visual perception, there is still much debate about the nature of the phenomenon: Some studies report forward remapping[1-3], in which receptive fields shift to their postsaccadic locations, and others report convergent remapping, in which receptive fields shift toward the saccade target [4]. These two possibilities can be difficult to distinguish, particularly when the two types of remapping lead to receptive field shifts in similar directions [5], as was the case in virtually all previous experiments. Here we report new data from neurons in primate cortical area V4, where both types of remapping have previously been reported [3,6]. Using an experimental configuration in which forward and convergent remapping would lead to receptive field shifts in opposite directions, we show that forward remapping is the dominant type of receptive field shift in V4.