, 2001, Sato

and Schall, 2003 and Thompson et al., 1996) and these selection signals do not depend on the generation of a saccade (Thompson et al., 1997). Moreover, when the saccade is directed to a stimulus outside the RF, FEF neurons are activated by distracters similar to the target (Bichot and Schall, 1999) confirming that visual Wnt drug selection signals are independent of saccade production signals in the FEF. Finally, electrical microstimulation of the FEF in an antisaccade task demonstrated that covert attention is independent of the actual saccade preparation (Juan et al., 2004). Although the evidence listed above argues against a causal role of saccadic activity in attentional processes, a direct test should include a comparison of the responses of all classes of FEF neurons (Bruce and Goldberg, 1985) in both covert attention and saccade tasks, as well as a comparison of their roles in top-down attentional feedback to visual cortex. Our study now does that. We employed an endogenous attention task and a manual response, to preclude any preparation for a saccade. An earlier study also examined the source of attentional signals among FEF neurons (Thompson et al., 2005). Using a pop-out visual search task that required no saccadic response, the authors showed that only cells with visual responses in the FEF (visual

and visuomovement) modulated their activity with the locus of attention. Saccade-related movement neurons were suppressed in the attention task and this suppression was not spatially selective. Our data on firing rates 3-Methyladenine are in large agreement with Thompson et al. and extend their results in two ways. First, during sustained attention, we found that only purely visual neurons increased their activity with attention to the RF and at this time the activity of movement neurons decreased when attention was directed toward their movement

field. The suppression of saccade-related movement neurons with attention may be the result of local processing within the not FEF so that saccades are inhibited downstream based on behavioral context. Indeed, SC, which lies closer to the brainstem saccade generator, receives projections mainly from the infragranular layers of the FEF where most movement neurons lie (Fries, 1984, Pouget et al., 2009 and Segraves and Goldberg, 1987). Second, while Thompson et al. used a task characterized by exogenous shifts of attention (pop-out), we used a task that required endogenous shifts of attention. It has been previously suggested that endogenous, rather than exogenous, shifts of attention are mediated by oculomotor processes related to the preparation for a saccade (Awh et al., 2006, Klein, 1980 and Rizzolatti et al., 1994). The two studies together, therefore, demonstrate that neither in exogenous nor in endogenous attention do FEF saccade-related movement neurons contribute to shifts of attention.