Neural coding and timing of visual target selection in the frontal eye field

How does the brain select visual targets for eye movements? We recorded neural activity while macaques performed visual search in which they were trained to move their eyes to a target stimulus among an array of distractor stimuli for a reward. Three signals were used to measure the relationship between the decision to move the eyes to a target and neural activity: spike rates from neurons in the frontal eye field (FEF), local field potentials from FEF, and event-related potentials recorded from the skull. We found that (1) FEF neurons cooperated and competed to select visual targets, measured using correlations between spike times of simultaneously recorded neurons, (2) FEF neurons interacted more when the visual search task was easier (i.e., the target and distractors were easily discriminable), measured using a multivariate analysis and decreased firing variability before eye movements, (3) FEF neurons decreased firing variability around the time of target selection by the mean firing rate, (4) FEF neurons were distinguished both functionally and biophysically, on the basis of action potential width, (5) FEF selected search targets from distractors before the macaque homologue of a human cognitive event-related potential (the N2pc) that marks the allocation of attention, and (6) the time between visual search array presentation and the time that FEF neurons discriminated between target and distractors was later when there were more stimuli the animal needed to choose from.