Motor cortex helps drive serial memory.

In the brain, storing knowledge about the order of previously viewed information may make for a moving experience. A part of the brain's outer layer thought by many researchers only to control muscle movements also helps to discern sequence information in the absence of any bodily activity, a new study finds.

Memory of serial order facilitates many tasks, from dialing telephone numbers to inferring the meaning of what someone says in a conversation.

Thought and action mingle intimately in a network of brain areas that collectively store and remember sequential information, proposes a team of neuroscientists. In the March 12 SCIENCE, they report that the motor cortex plays an influential role in that network.

"The motor cortex is potentially involved in a number of different functions, each subserved by a different brain circuit," contends Apostolos P. Georgopoulos of the University of Minnesota in Minneapolis. He conducted the study with Minnesota coworkers Adam F. Carpenter and Giuseppe Pellizzer.

The researchers implanted microscopic electrodes in the brains of two monkeys. These devices recorded the electrical activity of 925 neurons in each animal's motor cortex.

While using a joystick to hold a cursor in the center of a computer screen, the monkeys saw from three to five yellow shapes presented one after the other until all the shapes were visible. One shape then changed its color to blue. To get a reward, the animals then had to move the cursor to the shape that in the initial sequence had immediately followed the blue one.

A majority of the 925 motor neurons changed their patterns of activity as each succeeding yellow shape appeared. The cells were just as active when the monkeys simply watched the shapes appear as when the animals moved the cursor with the joystick, the researchers say.

Moreover, groups of from 2 to 16 motor neurons often generated signature activity patterns as successive shapes were presented in a trial.

The abrupt shift of electrical activity in small populations of motor neurons as an animal goes from one item to the next in a list may assist in the process of forming a memory of serial order, Georgopoulos theorizes.

"These are exciting new findings," remarks neuroscientist James C. Houk of Northwestern University Medical School in Chicago. "I think of the motor cortex as involved in task execution, but it may well participate in memory for serial order."

Houk has helped to develop a model of the brain network that regulates memories for the order of sequenced information. That model features a part of the brain, the prefrontal cortex, that influences the ability to act on the

basis of serial recall.

Although its precise functions remain unknown, the motor cortex may work with the prefrontal cortex to help forge serial-order memories, Houk suggests,