Saccade target selection in frontal eye field of macaque. I. Visual and premovement activation

We investigated how the brain selects the targets for eye movements, a process in which the outcome of visual processing is converted into guided action. Macaque monkeys were trained to make a saccade to fixate a salient target presented either alone or with multiple distractors during visual search. Neural activity was recorded in the frontal eye field, a cortical area at the interface of visual processing and eye movement production. Neurons discharging after stimulus presentation and before saccade initiation were analyzed. The initial visual response of frontal eye field neurons was modulated by the presence of multiple stimuli and by whether a saccade was going to be produced, but the initial visual response did not discriminate the target of the search array from the distractors. In the latent period before saccade initiation, the activity of most visually responsive cells evolved to signal the location of the target. Target selection occurred through suppression of distractor evoked activity contingent on the location of the target relative to the receptive field. The evolution of a signal specifying the location of the salient target could be dissociated from saccade initiation in some cells and could occur even when fixation was maintained. Neural activity in the frontal eye fields may participate in or be the product of the decision process guiding eye movements.