Understanding how the brain changes its mind: Microstimulation in the macaque frontal eye field reveals how saccade plans are changed

Abstract

Accumulator models that integrate incoming sensory information into motor plans provide a robust frame work to understand decision making. However, their applicability to situations that demand a change of plan raises an interesting problem for the brain. This is because interruption of the current motor plan must occur by a competing motor plan, which is necessarily weaker in strength. To understand how changes of mind get expressed in behavior, we used a version of the double-step task called the redirect task, in which monkeys were trained to modify a saccade plan.Wemicrostimulated the frontal eye fields during redirect behavior and systematically measured the deviation of the evoked saccade from the response field to causally track the changing saccade plan. Further, to identify the underlying mechanisms, eight different computational models of redirect behavior were assessed. It was observed that the model that included an independent, spatially specific inhibitory process, in addition to thetwoaccumulators representing the preparatory processes of initialandfinalmotorplans, best predicted the performanceandthe pattern of saccade deviation profile in the task.Suchaninhibitory process suppressed the preparation of the initialmotorplan, allowing the final motorplantoproceedunhindered.Thus,changesofmindareconsistentwiththenotionofaspatiallyspecific,inhibitoryprocessthatinhibitsthe current inappropriate plan, allowing expression of the new plan. © 2012 the authors.