The influence of behavioral context on the representation of a perceptual decision in developing oculomotor commands.

To make decisions about sensory stimuli, the brain must weigh the evidence that supports or opposes the alternative interpretations. In the present study, we evaluated the hypothesis that a quantity reflecting the weight of sensory evidence is represented in brain circuits responsible for the behavioral response used to indicate the decision. We trained monkeys to decide the direction of random-dot motion and to indicate their decision with an eye movement to one of two choice targets. We interrupted decision formation with electrical microstimulation of the frontal eye field, causing an evoked eye movement that is influenced by ongoing oculomotor activity. For the "pro-saccade" version of the task, in which the correct target was at a known location in the direction of motion, the microstimulus-evoked eye movement reflected both the impending pro-saccadic response and the temporal accumulation of motion information used to select that response. In contrast, for the "colored-target" task, in which the correct target was of a particular color but at an unpredictable location, little ongoing oculomotor activity was evident. The results suggest that formation of the decision and formation of the behavioral response share a common level of neural organization, but only when the decision is associated with a specific, predictable movement.