M2 and Cortico-Basal Ganglia Control of Fine Motor Function

    Bodily movement is one of the most important and easily observed brain functions. Movement can be seen through the gestures of an individual’s body, but also on the circuit and molecular/cellular levels. The motor cortex is responsible for the planning and initiation of movements, and there are several mechanisms for the fine-tuning of motor control.There are several regions and circuits of the brain that perform fine motor control functions, including the cortico-basal ganglia circuit, which A.J. Miller-Hansen studies in the paper Cortico-Basal Ganglia Plasticity in Motor Learning.

Miller-Hansen investigates the motor learning of mice on a rotarod over the course of eight days. As the mice continue to attempt not to fall off of the rotarod, they exhibit motor learning as their balance improves and their latency, or time taken to fall, increases. This motor learning is the result of plasticity, as long term potentiation and long term depression underlie this process. Miller-Hansen explains that spatial changes in connections and activity patterns occur in the cortico-basal circuit during motor learning. This also occurs in the motor cortex, showing that learning involves both the initiation of movement as well as the fine-tuning that occurs further downstream. Therefore, motor learning is a highly complex process in which spatial adaptations can be observed in many structures, indicating change in planning, initiation, and refining of motor function based on required actions. Furthermore, the process can be seen as an interaction between cortex and the basal ganglia.

Processes of motor control can have a significant contribution to the treatment of Parkinson’s Disease, as this is caused by the degeneration of dopaminergic cells involved in the regulation of movement. In the paper entitled Optogenetic Stimulation of the M2 Cortex Revert Motor Dysfunction in a Mouse Model of Parkinson’s Disease, Magno et al. tests the effectiveness of optogenetic stimulation on the secondary motor cortex. This manipulation leads to an improvement in the regulation of motor function in mice with Parkinson’s Disease. Once activated, the secondary motor cortex projects to the dorsal medial striatum, the location of the previously mentioned neuronal plasticity, to enable greater control of locomotor activity. 

The work of Miller-Hansen and Magno et al. displays a promising method of treating Parkinson’s Disease. While current treatment involves deep-brain stimulation, the secondary motor cortex and dorsomedial striatum can be targeted to aid individuals affected by Parkinson’s Disease by initiating upstream changes in electrical activity and synaptic plasticity. Therefore, the connection between the secondary motor cortex, dorsomedial striatum, and basal ganglia plays a critical role in the regulation of locomotor activity, providing a target for electrical stimulation to help regain locomotor control.

References

Roth, R. H., & Ding, J. B. (2024). Cortico-basal ganglia plasticity in motor learning. Neuron, 112(15), 2486–2502. https://doi.org/10.1016/j.neuron.2024.06.014

Magno et al. (2019). Optogenetic Stimulation of the M2 Cortex Reverts Motor Dysfunction in a Mouse Model of Parkinson’s Disease. Journal of Neuroscience, 37(17), 3234-3248. https://www.jneurosci.org/content/39/17/3234