"These results explain why certain behaviors such as defensive and aggressive movements, smiling and grasping food are so similar around the world. It is because the instructions for these movements are built-in and not learned," he adds.

Over the last 20 years, neuroscientists have identified an area called the primary motor cortex, which, when stimulated, triggers simple muscle movements. The fact that they were able to produce only motions by single muscles and other simple movements reinforced the idea that only simple movements were hard-wired into primate brain circuitry.

Then, last year Michael Graziano at Princeton University pointed out that previous stimulation experiments in the motor cortex the area that controls bodily motions had been done using very short electrical pulses that last less than a half-second. He further suggested that longer pulses might stimulate more complicated motions. Working with alert macaques, he and his colleagues found that applying such long-duration signals did in fact elicit several of these complex behaviors, much as they had predicted.

Kaas and his colleagues, research assistant professor Iwona Stepniewska and doctoral student Pei-Chun Fang, decided to follow the Princeton researchers' lead and try long-duration stimuli in the simpler brain of the Galago. When they did, they also found that this type of stimuli triggered complex behaviors. In fact, they were able to stimulate a larger number of complex movements than the Princeton group had reported, including aggressive facial patterns, defensive forelimb movements, and hand-to-mouth and reaching-and-grasping movements.

The Princeton researchers stimulated areas in the motor cortex. The Vanderbilt researchers found that they could also elicit these behaviors by stimulating a nearby area of the brain called the posterior parietal cortex. This area is heavily in
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Contact: David F. Salisbury
david.salisbury@vanderbilt.edu
615-343-6803
Vanderbilt University
15-Mar-2005