Columbia Study Uncovers Hidden Body Map in Mouse Secondary Motor Cortex

Complex motions involving multiple body parts rely on a newly discovered blueprint of the mouse body hidden within the secondary motor cortex, researchers reported in a study published in Nature Communications.

Animals coordinate many body parts simultaneously with apparent ease, yet robotic systems still struggle with these multi-limb tasks, according to News-Medical. This newly mapped neural architecture could help scientists understand dextrous movements that are often lost following brain injuries like strokes.

“Coordinating many body parts at once seems effortless for animals, but it’s so complex that robots still struggle with it,” said Weihao Xu, PhD, lead author of the study and former postdoctoral research scientist at Columbia’s Zuckerman Mind Brain Behavior Institute.

Studying the motor cortex in rodents presents unique challenges because mice cannot move individual body parts in complete isolation. While direct stimulation of the primary motor cortex, or M1, reveals clear sub-regions controlling specific body parts such as a single finger twitch, the secondary motor cortex, known as M2, has long yielded ambiguous mapping results.

Using high-speed wide-field optical brain imaging developed in the lab of Dr. Elizabeth Hillman, researchers analyzed brain activity patterns while mice moved and rested. Spontaneous neural activity during rest periods unexpectedly revealed small spots in M2 whose patterns synchronized directly with the sensory cortex.

“We put these small spots together, and found that they formed a body map hidden in the intrinsic chatter of M2, a part of the brain that wasn’t supposed to have a body map,” Xu said.

Neural wiring connects M2 with the sensory cortex

To verify the surprising discovery, the research team employed two-color wide-field optical mapping to isolate the activity of corticospinal neurons projecting down the spinal cord. This analysis confirmed the map resided specifically within M2 rather than M1.

Anatomical checks of the neural wiring further demonstrated that the synchronized sub-regions in M2 and the sensory cortex were directly connected. Subsequent behavioral observations verified that specific movements, such as a mouse raising both forepaws to its mouth and licking them, activated the corresponding points predicted by the new M2 map.

“All of these features of M2 explain why understanding the activity patterns of M2 has been so challenging,” said Elizabeth Hillman, corresponding author of the study and now chair of the Department of Imaging Sciences at St. Jude Children’s Research Hospital. “Confusingly, M2 chatters when the body is still, and cares more about complicated movements than simple ones.”

Future directions for movement disorders and robotics

Hillman said that these insights will improve how researchers interpret moment-to-moment movement planning and coordination in the brain. The findings offer potential applications for understanding human movement disorders and developing more advanced robotics.

“All in all, I hope that other researchers will leverage this discovery to further understand how activity in the brain becomes movement in the body, and how the brain’s resting activity can reveal its hidden wiring,” Xu said.

Frequently asked questions about the M2 body map study

Why was the body map in M2 so difficult to find?

Unlike the primary motor cortex, M2 exhibits high levels of spontaneous activity when the body is resting and responds preferentially to complex, multi-part movements rather than isolated single-limb actions. Traditional direct stimulation methods failed to clarify these patterns until researchers analyzed resting neural chatter using optical imaging.

What specific imaging techniques did the research team use?

Researchers utilized high-speed wide-field optical brain imaging techniques developed in the Hillman lab, alongside two-color wide-field optical mapping to distinguish the activity of specific neurons sending signals down the spinal cord.

Where was the study conducted and published?

The research was carried out at Columbia University’s Zuckerman Mind Brain Behavior Institute and published in the journal Nature Communications today.