Significance of Research:

To date, it has been difficult to dissociate the relative contributions of frontal and parietal cortex in visuomotor control. Previous research has shown that these regions are co-activated in paradigms in which subjects make eye movements or shift attention. The series of functional magnetic imaging (fMRI) experiments presented in this paper provide evidence that the two regions can be functionally dissociated and suggest a specific role for the frontal cortex in early motor planning. The observation that certain early motor planning signals are localized to frontal cortex illuminates one of the most intense debates in cognitive neuroscience over the past half decade -- whether the parietal lobe is concerned with attention or with early motor planning. The importance of our paper in this debate was captured by the New and Views commentary that appeared in Nature Neuroscience describing our article. To investigate early motor planning, we instructed normal subjects to either look toward (pro-saccade) or away from (anti-saccade) a visual target that appeared in the periphery after a variable delay and measured activation in parietal and frontal cortex with fMRI. This paper provides the first neuroimaging evidence that the frontal cortex but not the parietal lobe is selectively activated when an individual intends to make one movement and not the other - before the target for that movement has appeared. These observations therefore not only tease apart the relative functions of the two regions, but provide evidence that the frontal cortex may be relatively more important in movement selection - before a target is specified. The parietal cortex, in contrast, is more concerned with transforming spatial information about the target into the appropriate motor output. Not only does our paper speak to the parietal versus frontal debate, but it also provides critical information for using these techniques to now investigate patients with specific disorders of the frontal lobes. Specifically, we have identified control signals in the frontal lobes that should be altered in schizophrenia, attention deficit hyperactivity disorder, and other frontal disorders. We can now determine if these signals are indeed altered and whether treatment therapies can effectively restore function in a task assaying frontal lobe function, like the anti-saccade task.