When the hero of a movie walks off into the sunset, our eyes have to perform two tasks to keep him in focus: they have to rotate, or converge slightly, in a coordinated fashion, and they have to accommodate for his increasing distance. Simple as this sounds, scientists have not known much about how the cerebral cortex--the outer layer of the brain--influences these types of eye movements, referred to as vergence and accommodation. But now Paul D. Gamlin and Kyunghee Yoon of the University of Alabama have defined a region in the frontal cortex involved in this task: in yesterdays issue of Nature, they report that an area close to the frontal eye field region--which controls another type of quick eye movement--seems to be responsible for these visual actions in rhesus monkeys.
To identify this brain area, the scientists presented two monkeys with targets that moved toward or away from them either in steps or continuously. Both animals had been trained to focus on objects, and as they followed the targets in this study, the scientists recorded the activity of individual neurons in the frontal cortex of their brains. They found that neurons from a certain area were active only when the monkey's eyes were moving to focus. The researchers conclude that a region in the frontal cortex controls all classes of voluntary eye movements. Therefore, they suggest, the current boundaries of the frontal eye field region in the brain, which does not include the newly discovered area, should be expanded.