Brainstem Pathway for Hand Control Found, Offering Stroke Therapy Hope

The intricate choreography of human hand movement relies on a surprisingly complex network extending beyond the brain’s cortex, according to research published this month in the Proceedings of the National Academy of Sciences. A team led by researchers at the University of California, Riverside, has mapped a pathway involving the brainstem and spinal cord that plays a crucial role in grasping, holding, and manipulating objects – and this discovery offers potential new avenues for therapies aimed at restoring hand function after stroke or other neurological injuries.

Rethinking the Command Center

For decades, the cerebral cortex – the brain’s outer layer responsible for higher-level functions like conscious thought and voluntary movement – has been considered the primary command center for hand control. However, this new research suggests that evolutionarily older structures within the brainstem similarly contribute significantly to this process. “For a long time, we thought fine hand movements in humans were controlled almost entirely by the cortex,” explains Shahab Vahdat, an assistant professor of bioengineering at UCR and lead author of the study. “What we are observing is that evolutionarily older brainstem structures also play an important role.”

The brainstem, a vital stalk connecting the brain to the spinal cord, regulates fundamental functions like breathing, posture, and balance. The study focused on the medulla, the lowest portion of the brainstem, which acts as a major relay station for signals traveling between the brain and the body. Researchers identified two specific regions within the medulla that consistently showed activity during controlled hand movements in both mice, and humans.

Mapping the Pathway with fMRI

To investigate this interplay, the researchers employed functional magnetic resonance imaging (fMRI) to observe brain activity during controlled hand movements. fMRI allows scientists to visualize brain activity by detecting changes in blood flow. In mice, the animals were trained to press a lever with their forepaw while brain and brainstem activity were recorded. Human volunteers performed a similar task, squeezing a device with varying levels of force using their fingers while undergoing fMRI scans.

The team deliberately sought to determine if the network controlling forelimb movement in rodents mirrored that of humans. “We wanted to see whether the same underlying network that controls forelimb movement in rodents might also exist in humans. It wasn’t a given, since humans have more advanced motor control,” Vahdat said. Despite the differences in brain complexity, the researchers found striking similarities in how these regions communicate.

A Conserved Circuit and Spinal Relay

The fMRI scans revealed that the two identified regions of the medulla were consistently active during the tasks and strongly connected to sensorimotor areas of the brain. Importantly, these same regions appeared in both mice and humans, suggesting a conserved circuitry across mammals. This conservation implies that this pathway has been refined through evolution due to its functional importance.

The study also revealed a previously underappreciated role for segments C3 and C4 of the cervical spinal cord. Researchers found that these segments act as a relay station, transmitting signals from the brainstem to the lower spinal cord, which directly activates the muscles in the hand. This is the first time brain activity in humans has demonstrated this specific function for C3 and C4 in hand control.

Implications for Stroke Rehabilitation

The findings suggest that voluntary hand movement isn’t a simple, direct pathway from the cortex to the muscles, but rather a multi-stage process where cortical signals are integrated with brainstem and spinal networks. This understanding has significant implications for stroke rehabilitation. Damage to cortical motor regions is a common consequence of stroke, often resulting in lasting difficulty using the hands. Identifying alternative pathways, like the one described in this study, could provide new targets for therapies designed to stimulate surviving circuits and restore function.

“These pathways give us additional targets to explore,” Vahdat said. “If we can engage them after a stroke, they may help compensate and restore function in the hands and arms.” Current stroke rehabilitation strategies often focus on retraining cortical pathways, but this research suggests that targeting the brainstem and spinal cord could offer a complementary approach.

What Comes Next: Expanding the Understanding of Motor Control

The researchers emphasize that this study is a starting point. Future research will focus on further delineating the specific functions of the identified brainstem regions and exploring how they interact with other brain areas involved in motor control. Further investigation is also needed to determine how this pathway is affected in different neurological conditions beyond stroke. The team also plans to explore the potential for non-invasive neuromodulation techniques – such as transcranial magnetic stimulation – to stimulate these pathways and improve hand function in patients with neurological injuries. The full study, published in Proceedings of the National Academy of Sciences, details the methodology and findings, offering a valuable resource for other researchers in the field.

Publication details: Vishwas Jindal et al, Medullary and C3–C4 propriospinal pathways underlying mammalian forelimb movement control, Proceedings of the National Academy of Sciences (2026). DOI: 10.1073/pnas.2518217123

Journal information: Proceedings of the National Academy of Sciences