The study led by UC Riverside, published in the Proceedings of the National Academy of Sciences, identifies a conserved network that links cortex, brainstem and spinal cord to control voluntary hand and arm movement. Until now, fine hand control in humans was thought to be driven almost entirely by the cortex, but these results show that evolutionarily older brainstem structures make an important contribution.
The researchers combined functional magnetic resonance imaging with comparable tasks in mice and humans. Mice were trained to press a small lever with their forepaw while investigators recorded activity in the brain and brainstem. Human volunteers performed a similar task in the scanner, squeezing a device with varying levels of force using their fingers. The scans highlighted two medulla regions that were consistently active and strongly connected with sensorimotor cortical areas, and the same regions appeared in both species.
The study also shows that two cervical spinal segments, C3 and C4, act as a relay between the brainstem and the lower spinal cord that directly activates hand muscles. Taken together, the findings describe a multi-stage pathway in which cortical signals are integrated with brainstem and spinal networks before reaching muscles. Identifying these additional pathways may provide new targets for neuromodulation therapies and could help restore hand and arm function after stroke.
- Key points: medulla involvement, conserved circuitry, C3–C4 relay
Difficult words
- cortex — outer layer of the brain involved in thinking
- brainstem — lower brain area connecting brain and spinal cord
- medulla — part of the brainstem that controls basic functions
- spinal cord — bundle of nerves running down the backbone
- relay — structure that passes signals from one area
- neuromodulation — medical approach to change nerve activity
- conserved — kept similar across different species over time
- sensorimotor — relating to both sensing and movement control
- cervical — related to the neck region of the spine
- pathway — sequence of connected neural structures carrying signals
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Discussion questions
- How could the discovery of brainstem and C3–C4 pathways change rehabilitation after a stroke? Give reasons and examples.
- Why is it important that the same medulla regions appeared in both mice and humans for this research?
- What practical or ethical issues might arise when developing neuromodulation therapies targeting these pathways?
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