CUHK study uncovers how the brain coordinates muscles for voluntary movement, setting new benchmark for precision neurosurgery Discovery of the brain’s movement “building[...]

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CUHK study uncovers how the brain coordinates muscles for voluntary movement, setting new benchmark for precision neurosurgery
Discovery of the brain's movement "building blocks" opens breakthrough avenues for brain-machine technology and paralysis rehabilitation

A new study by the Faculty of Medicine at The Chinese University of Hong Kong (CU Medicine) has revealed how the human brain controls muscles for voluntary movement. By studying patients undergoing awake brain surgery, researchers discovered that the brain organises individual muscles into functional "building blocks" (muscle synergies) to coordinate multiple muscle groups simultaneously.

The findings resolve a long-standing debate in neuroscience while offering transformative insights for the future design of brain-machine interfaces (BMI), setting a new benchmark for precision neurosurgery. The study has been published in the prestigious international scientific journal Proceedings of the National Academy of Sciences (PNAS).

Brain bundles muscles into building blocks to control movement

Even simple daily actions, such as walking or picking up a cup, require the brain to control and coordinate multiple muscle groups concurrently. For decades, neuroscientists have debated how the central nervous system directs highly complex muscle operations: whether it controls each muscle individually or commands them through combined units known as "muscle synergies".

To decode this mechanism, the CUHK research team, comprising neuroscientists and neurosurgeons, studied the muscle signals of 13 patients undergoing awake craniotomy surgery for glioma tumour removal. During awake brain surgery, patients remained conscious while neurosurgeons applied mild direct electrical stimulation to the primary motor cortex (M1), the brain region that controls voluntary movements. Researchers collected and analysed real-time electromyographic (EMG) data on muscle responses while patients performed voluntary upper-limb tasks before and during surgery.

Results showed that 69% of the muscle synergies observed during preoperative voluntary movements could be matched to muscle synergies evoked by direct electrical stimulation during surgery. Furthermore, neuroimaging analysis revealed that the human motor cortex contains two subdivisions, each with a distinct pattern of muscle group organisation.

Dr Jodie Xie Jingping, the study's first author and Postdoctoral Fellow in the School of Biomedical Sciences at CU Medicine, said: "This study confirmed M1 controls the activities of multiple muscles by activating fundamental building blocks of movement known as 'muscle synergies'."

Implications for brain-machine interfaces and motor rehabilitative interventions

Professor Vincent Cheung Chi-kwan, Associate Professor in the School of Biomedical Sciences at CU Medicine, explained: "Brain-machine interfaces (BMIs) is an emerging medical technology where electrodes are implanted into the motor cortex of paralysed patients. By recording the neural signals generated when patients consciously attempt to move their limbs, the system decodes and translates these signals to drive assistive devices that help them communicate or regain mobility. Since M1 is a primary implantation site of BMIs for movement control, our findings will help inform the design of more precise and effective BMI systems, providing an important scientific basis for electrode placement strategies. The findings also offer valuable insights for designing and improving future motor rehabilitative interventions."

Real-time muscle mapping for safer brain surgery

The team exploited direct electrical stimulation of the human brain to monitor and record activities of multiple muscles in real-time. Before removing a brain tumour during an awake surgery, a neurosurgeon stimulates the patient's brain to map critical movement areas. If stimulating a specific spot triggers a muscle reaction, the surgeon knows that area must be preserved to prevent post-operative paralysis.

Dr Peter Woo Yat-ming, Honorary Clinical Associate Professor in the Department of Surgery at CU Medicine, said: "This procedure enables neurosurgeons to map the brain even more precisely, minimising any undesired functional impairment after surgery. By understanding the true functional substrates of the motor cortex, we can build stronger bridges between fundamental neuroscience and patient care."

Professor Cheung concluded, "With this study, we hope to demonstrate how neurosurgeons and neuroscientists can work together to solve fundamental open questions about the human brain whose solutions should ultimately benefit patients."

This study was supported by the General Research Fund (GRF) under the Research Grants Council of the University Grants Committee.