Unusual Data On Rapid Eye Movements Shed New Light On Brain And Inhibiting Behavior

A study of eye movements of 41 individuals, ages 4 to 29 and divided into four age groups, led to the discovery that younger people simply don't have the ability to ignore secondary targets, even when told in advance, said Paul van Donkelaar in a presentation today at the Brain & Mind Research Symposium of the Association of Pacific Rim Universities in Sydney, Australia.

Van Donkelaar, a professor of human physiology and researcher in the University of Oregon's Institute of Neuroscience, said his team probably was seeing a lack of communication between the frontal cortex and brain stem. "We think the inability to inhibit behavior has to do with the development of the frontal cortex and its ability to tell the rest of the brain to do or not to do something," he said.

The frontal cortex is known to play a role in such things as impulse control, motor function, problem-solving and socialized behavior. The brain stem controls basic activity, such as keeping the heart beating and the lungs breathing.

The research, as yet unpublished, is part of a larger project funded through a grant from the National Institutes of Health to van Donkelaar and colleague Marjorie Woollacott. They are studying the interaction of postural control and proficiency in daily living skills, particularly among youngsters with cerebral palsy. In this case, the researchers began looking at how healthy children orient toward an object of interest through eye movements alone.

The study took an unexpected twist when doctoral student Sandy Saavedra reported a high level of multiple saccades, which are rapidly occurring glances toward a secondary object, van Donkelaar said. "My initial reaction was to just throw them out," he said. "In adult studies there are so few multiple saccades that they are statistically insignificant, maybe just 5 percent of the time and attributed to mistakes by the participants. But in these results, we were seeing multiple saccades in 25 percent of the trials. It was a complete surprise. So we started asking what was happening and what it means."

Looking at and comparing the four age groups let the researchers recognize a trend. The 4- to 6-year-old children had difficulty stopping themselves from looking at a secondary object placed into their peripheral vision. They also initiated multiple saccades at a rapid pace and in much higher levels than adults, and did so 150 milliseconds sooner than adults, "which in brain time is an eternity," van Donkelaar said.

"In the 4-to-6-year-old and the 7-to-9-year-old groups, there was a similar relationship. The younger kids had a lot of trouble keeping their eyes fixated on the original target, but that problem was much more muted in the 7- to 9-year olds," he said.

The data appear to be tapping into the relationship between the frontal cortex, where decision-making skills develop, and how a decision influences the brain stem that controls eye movements, van Donkelaar said. "What we think is happening is that these multiple saccade trials are initiated so quickly that the frontal cortex isn't playing much of a role in the signaling of the brain stems in younger children," he said.

So how do the new findings fit into the group's overall research? It is believed that for cerebral palsy patients the development of the cortex will be delayed well beyond childhood. Thus eye movements and focusing along with other components involved in motor control may explain why it's more difficult for a cerebral palsy patient than a healthy adult to successfully pick up an object and manipulate it. Simply put, the cortex isn't fully participating in the game.