Our finding that enhanced coupling occurs with attention only between FEF visual neurons and V4 suggests that V4 neurons have preferential

connections with FEF visual neurons rather than any other FEF cell type. The pattern of anatomical connections between FEF and V4 supports this conclusion. The majority of FEF projections to V4 arise from the supragranular layers (Barone et al., 2000 and Pouget et al., 2009), and neurons in the supragranular layers of the FEF subserve visual selection (Thompson et al., 1996). With attention, an increase in gamma synchrony between FEF supragranular-layer visual cells and V4 with Y-27632 nmr the appropriate phase relationships may increase effective communication between the two areas to enhance processing of signals related to the attended location (Fries, 2005, Gregoriou et al., 2009a and Gregoriou et al., 2009b). Moreover, the absence of any effect of attention on synchrony

between MEK inhibitor drugs FEF movement cells and V4 further indicates that attentional mechanisms at the network level are largely independent and distinct from movement processing. If visual FEF cells subserve visual selection and provide top-down inputs to extrastriate cortex, whereas movement FEF neurons mediate saccade execution via projections to oculomotor centers what is the role of visuomovement neurons? Previous studies have indicated that the responses of visuomovement neurons do not mediate saccade preparation and have suggested that they may provide a corollary discharge to update the visual representations every time the Thalidomide eyes move (Ray et al., 2009). Similar presaccadic enhancements have also been recorded in areas that are anatomically distant from the brainstem saccade generator such as area V4 and area 46 (Boch and Goldberg, 1989, Fischer and Boch, 1981 and Moore et al., 1998). It is thus possible that such a corollary discharge signal is provided by FEF visuomovement neurons once a saccade is bound to occur. Our task was not designed

to test this possibility. Given that no saccades were executed during our attention task the absence of coupling between FEF visuomovement neurons and V4 is not surprising. A very recent study showed that FEF cells mediating saccade selection are affected by activation of both D1 and D2 dopamine receptors, whereas those contributing to visual modulation of V4 are sensitive only to D1 receptor agonists (Noudoost and Moore, 2011). This is in line with the finding that in infragranular layers, source of saccade-related signals in the FEF, both D1 and D2 receptors are found, whereas in supragranular layers, source of FEF signals responsible for the enhancement of activity in V4, D2 receptors are less frequent (Lidow et al., 1991 and Santana et al., 2009).