NEW YORK (Reuters Health) - New research in monkeys is shedding light on how the brain controls the body's movement--suggesting that single spots in the brain govern actions far more complex than previously thought.

It is known that a brain's motor cortex contains a "map" of the body that is used to control movement, but the exact role of this area in performing movement is unclear. Whether the motor cortex is primarily involved in muscle control or "higher-order" control of movement--such as direction and trajectory--is a central question.

In the new study, researchers at Princeton University in New Jersey found that electrical stimulation of particular sites in monkeys' motor cortex caused the animals to take on complex "postures"--such as coordinating the arm, hand and mouth into an "eating" stance--as opposed to initiating simple muscle contraction.

This is in contrast to the "traditional" view that each location within the motor cortex controls only a muscle, according to the study's lead author, Michael S.A. Graziano. In this view, if you stimulate a given spot in the cortex, then the single muscle it governs contracts, he told Reuters Health. This would also mean that another part of the brain must be in charge of tapping the right spots in the motor cortex to execute movement.

But, Graziano said, "our results show that the motor cortex is not a look-up table of muscles. Instead, each spot in the motor cortex corresponds to a complex, coordinated motor act."

In his team's research with monkeys, such complex acts included bringing a gripped hand to the mouth as if eating food, and bringing the hand near the face while turning the head away, as if for protection.

"The fact that a single spot in the (motor) cortex can represent such a complex part of the animal's repertoire is new and totally unexpected," Graziano said.

The findings are published in the May 30th issue of the journal Neuron.

Dr. Richard J. Krauzlis, who wrote a commentary accompanying the report, agreed that the study suggests that stimulating the motor cortex "elicits postures that are far more complex than would be expected based upon current thinking."

Krauzlis, a researcher at the Salk Institute for Biological Studies in La Jolla, California, told Reuters Health that understanding how complex movements are generated is important for human health.

He pointed out that various nervous system disorders--including stroke and Parkinson's disease--involve problems with motor control.

"Understanding the basic mechanisms underlying motor control is therefore a crucial step toward developing therapies, if not outright cures, for these nervous system disorders," Krauzlis said.

SOURCE: Neuron 2002;34:673-674, 841-851.

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