New Insights into the Brain’s Motor Cortex

National Institutes of Health

The brain’s primary motor cortex is a thin band of nerve cells and circuits that extends from the top of the head and downward on both sides. It’s long been thought to have a straightforward role as the brain’s command center for voluntary muscle movements, sending out signals that trigger movements in specific body parts. Complex movements were believed to be coordinated by other areas of the brain.

A century ago, a systematic study involved electrically stimulating different human brain areas during surgery to see the resulting body movements. The study revealed a well-organized “body map.” This research led to a familiar drawing of the cortical band that’s taught in biology classrooms to this day. The drawing shows the motor cortex as an orderly continuum from head to toe. One end primarily controls face-related movements, followed by regions that control the hands and then the feet.

In recent decades, studies have questioned this linear body map in the motor cortex. For instance, studies in nonhuman primates suggested that the map may be divided into concentric zones instead of a continuous row. So digits like fingers might be in the middle, surrounded by areas for the wrists, elbows, then shoulders. Other studies found that large portions of the primary motor cortex seemed to prompt no muscle movements at all, but revealed connections to brain areas controlling other functions.

To learn more, a team led by Drs. Evan Gordon and Nico Dosenbach at Washington University in St. Louis used an advanced imaging method called precision fMRI to reexamine the function and organization of the human motor cortex. The technique involved repeatedly scanning each person’s brain over many hours to create high-resolution brain maps for each individual. Results appeared in Nature on April 19, 2023…

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