How Brain Cells Coordinate Movement Planning

Researchers at the University of Freiburg’s BrainLinks-BrainTools research centre have identified how neurons in the premotor and primary motor cortices coordinate movement planning and execution, according to a study published in Cell Reports. The findings reveal that premotor neurons communicate with both inhibitory and excitatory populations in the primary motor cortex during planning, a mechanism the team calls the switching population hypothesis.

Neural Coordination in Movement Planning and Execution

Understanding how the brain transitions from planning a movement to actually executing it has long challenged neuroscientists. According to Dr. Julian Ammer, senior researcher in the Optophysiology Research Group at the University of Freiburg, researchers previously lacked clarity on how movement planning coordinates between the premotor and primary motor cortex. Both regions show activity before a movement occurs, yet premature movement is somehow prevented.

To investigate this, researchers trained rats to move a lever with their hand upon feeling a vibration and release it to earn a drop of sugar water. During this task, the research team recorded neural activities. The rodent brain shares structural similarities with the human brain in this regard, housing both the premotor and primary motor cortices that govern movement.

The Switching Population Hypothesis Explained

The study demonstrates that during the planning phase, neurons in the premotor cortex transmit signals to both inhibitory and excitatory neurons within the primary motor cortex. According to the research findings, the command to initiate movement only occurs when neural activity in the premotor cortex shifts specifically toward neurons that communicate primarily with excitatory neurons in the primary motor cortex. Once this shift happens, an external trigger—such as the lever vibration in the experiment—allows the movement to execute.

The research team proposes that this shifting pattern, termed the switching population hypothesis, should replace the two previously dominant hypotheses regarding motor cortex interaction.

Interdisciplinary Methods and Prosthetic Applications

The breakthrough relied heavily on combining specialized research techniques across different academic fields at the University of Freiburg. Prof. Dr. Ilka Diester, spokesperson of BrainLinks-BrainTools and professor of optophysiology, designed the study alongside Prof. Dr. Joschka Bödecker, professor of computer science at the Faculty of Engineering. Diester’s group used light signals to influence individual neuron activity, while Bödecker’s team developed an artificial intelligence model to interpret complex activity patterns and predict behavioral outcomes.

Adding an anatomical perspective, Prof. Dr. Andreas Vlachos, Head of the Department of Neuroanatomy at the Institute of Anatomy and Cell Biology, utilized electron microscope images. Vlachos demonstrated the physical connections between the premotor cortex and the inhibitory and excitatory neurons in the primary motor cortex at the cellular level, reinforcing the validity of the switching population hypothesis.

These basic research discoveries carry long-term clinical potential. According to Prof. Dr. Ilka Diester, the insights could eventually aid in the development of treatments or assistive devices for individuals with mobility impairments. Sensors could potentially detect movement signals directly in the human brain and transmit those commands to a smart prosthesis, improving the precision of mind-controlled medical devices.

Frequently Asked Questions

What is the switching population hypothesis?

It is a proposed model stating that precise movement execution is enabled when neural activity in the premotor cortex shifts to target specific excitatory neurons in the primary motor cortex.

How does this research help mind-controlled prostheses?

By clarifying how the brain coordinates movement planning and execution, engineers and scientists can design better brain sensors to detect and translate neural signals into precise actions for smart prosthetic limbs.

Which institutions conducted the study?

The study was conducted by researchers from neuroscience and artificial intelligence fields at the BrainLinks-BrainTools research centre at the University of Freiburg.