1B and C). We were particularly

interested in the role of bottom-up information in the guidance of attention, so the saliency of the target stimulus was achieved by virtue of color difference from surrounding (distractor) stimuli. The monkeys had no prior knowledge of the stimulus color or location in each trial, making the detection of the stimulus entirely defined by bottom-up factors. Additionally, as planning of eye movements is intricately connected with visual attention circuits (Kustov & Robinson, 1996; Moore & Fallah, 2001), we required monkeys to maintain fixation throughout the trial and, instead, signal the location or presence of the salient stimulus with the release of a lever. Neural selleck screening library activity recorded during the task allowed us to test the correlation between neuronal activity in the two areas and salient stimulus detection, rather than execution of eye movements. The first set of experiments Epigenetics inhibitor relied on a spatial version of a delayed match-to-sample task, which required localization

of the salient stimulus. The second set of experiments used a reaction-time variant of the task, requiring an immediate behavioral response after detection of the stimulus. The tasks allowed us to probe different aspects of the guidance of attention. The first question we wished to address with respect to the influence of dlPFC and PPC on behavior was whether neuronal activity correlated with behavioral choices equally strongly in the two areas. We therefore analysed data from a behavioral task which required monkeys to identify the location of a salient color stimulus in an array of stimuli and decide whether a subsequent single stimulus

matched it in spatial location or not, by releasing much a lever (delayed match-to-sample task, Fig. 1B). The task involved trials of four levels of increasing difficulty by adjusting the similarity of the distractor colors relative to the cue (Fig. 1D, solid box): One level of difficulty involved trials with a red distractor stimulus when the cue was green or vice versa, two levels of difficulty involved trials with intermediate levels of chromatic difference between cue and distractors and the fourth level of difficulty involved trials with distractor stimuli identical to the target (catch trials), which were rewarded randomly. In order to have sufficient numbers of error trials, we only used trials of the third level of difficulty for this analysis. During the course of the experiments, we repeatedly alternated recording in dlPFC and LIP, and also obtained simultaneous recordings from the two areas (25 and 33% of sessions used in each area involved simultaneous recordings). As a consequence, an equivalent level of behavioral performance was obtained in the recording sessions from the two areas.