The effects of chronic stress on the motor cortex have been understudied, despite findings suggesting impaired neuroplasticity in that region. The motor cortex is a brain region that governs the planning and execution of voluntary movements, and in addition it is the site where the acquisition of new motor skills takes place.
A healthy Motor Cortex for Healthy Movements
Neuroplasticity, which refers to the growth of new brain cells or new connections among brain cells, is essential in that region for learning new movements and improving motor skills. Indeed, it implicates the ability to grow new neuronal connections (i.e., connections between brain cells)thereby indicating that learning has taken place.
For example, when learning to ride a bike, new connections are created to allow the brain to memorize a set of movements and solidify it into your cellular memory. In doing so, you are able to build skills you learned from your previous practices and with time improve until you master the movement (that’s neuroplasticity)
By contrast, impaired neuroplasticity is reflected in part by damages to the structural integrity of glial cells (i.e., a type of cells in the brain that provide metabolic and physical support to neurons; without them, neurons simply waste away) in the limbic brain regions (i.e., brain area associated with emotion processing), prefrontal cortex (i.e., brain area involved in thinking, planning, judgment, reasoning, etc…) and in the motor cortex.
Similar damages have been associated with neuropsychiatric conditions like depression and other neurodegenerative disorders such as Alzheimer’s disease, but not enough work had been done to identify the mechanisms at play in the motor cortex during stress.
Stress Damages Cells in the Motor Cortex
The current study seeks to focus on the structural and functional effects of stress in the motor cortex by comparing stress-resilient and stress-susceptible mice (i.e., the mice were bred to be either resilient to stress or susceptible to it.)
After subjecting these mice to social stress for 10 days (i.e., introducing a mouse to the home cage of another aggressive, bigger mouse), they found that stress-susceptible mice displayed some form of motor retardation and were unable to learn new motor skills even after being removed from the stressful situation. These behavioral effects were attributed to the loss of neuronal connections in the primary motor cortex (i.e., a crucial player in the production of skilled movements like drawing, writing, etc…).
Gross motor skills (e.g., sitting, running, throwing a ball, etc…) were also impaired to the extent that mice vulnerable to stress could not learn new gross motor skills and new fine motor skills (i.e., skilled movements). Resilient mice on the other hand could learn new gross motor skills, but they were unable to learn new fine motor skills. It is further important to add that because these changes were structural, they were also permanent.
Although, this study involves mice, the results can be extrapolated to humans to show the effects of continuous social stress on the brain. More importantly, it highlights the fact that stress has the potential to affect other aspects of our life aside from our emotions and our cognition (i.e., thoughts).
Gellner AK, Sitter A, Rackiewicz M, Sylvester M, Philipsen A, Zimmer A, Stein V. Stress vulnerability shapes disruption of motor cortical neuroplasticity. Transl Psychiatry. 2022 Mar 4;12(1):91. doi: 10.1038/s41398-022-01855-8. PMID: 35246507.