Previous single-unit studies on the FEFs have identified visual and saccade-related neurons as well ITF2357 manufacturer as neurons with both visual and saccade-related responses (= visuomotor neurons), in every case having their response field in the contralateral VF (Bruce & Goldberg, 1985; Bruce et al., 1985). It has been known for a long time that focussed spatial attention increases the visual responses of visual and visuomotor neurons

to targets in their receptive field independent of a subsequent execution of an eye movement to the target (Schall & Hanes, 1993; Thompson et al., 2005). However, only recently it became clear that the FEF is indeed involved in visual search. As shown by Schall and co-workers (Schall & Hanes, 1993; Thompson et al., 2005), FEF neurons indicate the difference between Akt inhibitor a target and the distractor placed in their response field by changing their discharge a certain time after stimulation onset (= target selection

time) in case the item is the target. The fact that target selection time of neurons correlates with target detection time suggests a causal role of these neurons. This notion finds support by reversible inactivation experiments, which led to increased reaction times for targets in the contralateral VF (Wardak et al., 2006). So far the FOR in which target selection takes place during visual search and other forms of covert attention shifting has not been addressed in single-unit studies of the FEF. However, based on one study of the influence of eye position on the visual and saccade-related responses of FEF neurons (Goldberg & Bruce, 1990), it is usually assumed that the FEF represents at least overt shifts of attention in eye-centred coordinates. Neurons in the lateral Dimethyl sulfoxide intraparietal area (LIP) exhibit many features reminiscent of the FEF, such as visual, visuomotor

and pure saccade-related responses, receptive fields largely confined to the contralateral VF as well as an increase of visual responses by spatial attention. Moreover, it has also been shown that LIP neurons increase their discharge if a search item placed inside the receptive field is a target rather than a distractor (Oristaglio et al., 2006; Balan et al., 2008; Mirpour et al., 2009). Similar to reversible inactivation of the FEF, also inactivation of the LIP slowed down visual search (Wardak et al., 2004). However, in contrast to neurons in the FEF, responses of LIP neurons to overt shifts of attention exhibit a clear dependency on eye position (Andersen et al., 1990, 1993). Actually, eye position modulates the gain of visual as well as saccade-related responses in a linear manner (Andersen et al., 1990). In view of the well-established commonalities between overt and covert shifts of attention, one might expect that also the latter show gain fields.