Researchers at Columbia University and St. Jude Children’s Research Hospital found a previously unknown body map in the mouse brain’s secondary motor cortex, according to a study in Nature Communications.
The discovery identifies specific neural activity patterns in the M2 brain region that correspond to different body parts. This finding challenges previous assumptions that this area lacked a structured body map.
This biological blueprint could help scientists understand how the brain coordinates the complex, multi-part movements required for tasks like bringing food to the mouth.
“Coordinating many body parts at once seems effortless for animals, but it’s so complex that robots still struggle with it,” said Dr. Weihao Xu, the study’s lead author, who conducted the research as a doctoral student and postdoctoral research scientist in the laboratory of Dr. Elizabeth Hillman at Columbia’s Zuckerman Mind Brain Behavior Institute.
Scientists find a hidden body map
The primary motor cortex (M1) has long been known to possess an orderly “body map.” In this area, specific zones control individual muscles or limbs.
The secondary motor cortex (M2) was previously thought to lack such organization. Neuroscience News reported that earlier research relied on direct electrical stimulation. Those studies yielded ambiguous results in M2. This led scientists to believe the region functioned primarily as an abstract motor planning center.
Studying motor control in mice is difficult. Even a well-trained rodent is unable to move a single body part in isolation.
The breakthrough occurred while observing mice at rest rather than during active movement.
The team was initially searching for the primary brain regions that drive movement. But they observed that sensory areas exhibited strong fluctuations in activity during periods of rest. Each sensory area’s resting activity was synchronized with a small area of the secondary motor cortex (M2).
“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.” Dr. Xu said
Investigators identified localized patches in M2 by analyzing these spontaneous neural fluctuations. These patches fired in synchrony with established body-part representations in the sensory cortex.
News-Medical said that anatomical tracing confirmed these findings. The tracing showed the M2 sub-regions were structurally wired to the sensory cortex through projections from S1 regions.
M2 activity tracks movement complexity
M2 activity is specifically tied to the complexity of a movement. During simple movements, involvement in M2 is short-lived.
Activity is sustained longer during more complex actions. This pattern shows how the brain plans and updates movement from moment to moment.
Dr. Elizabeth Hillman, the study’s corresponding author and now chair of the Department of Imaging Sciences at St. Jude Children’s Research Hospital explained that the difficulty in previous studies stemmed from how M2 shifts between states.
“All of these features explain why it has been so difficult to interpret motor cortex activity patterns during movements,” Dr. Hillman said. “Secondary motor cortex activity shifts between different states: from synchronized fluctuations during rest, to engaging transiently for simple movements, and sustaining during more complex movements involving multiple body parts.”
The Zuckerman Institute reported the map could help researchers understand the dexterous movements lost following brain injuries such as strokes. This map could also assist in developments for targeted neurorehabilitation and the construction of better robots.
Dr. Xu is now a data scientist in industry. He said his training in machine learning and computer science at Columbia was essential to analyzing these complex data patterns.
“Columbia encouraged me to take challenging courses and bring what I learned back to the project,” Dr. Xu said. “I use these skills every day now. All in all, I hope that other researchers will use 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,” he said.