Hui-quan Li and Nicholas Spitzer were interested in how motor learning occurs, the process by which we become better and better at specific motor tasks via trial and error (e.g., using chopsticks, speaking fluently, and quick reflexes…). This obviously involves a form of neural plasticity, as our brains need to change in some way to strengthen the circuits that improve a behavior, while refining those that detract from it. Motor learning has been intensely studied in the realm of neuroplasticity, involving circuits in the cortex, basal ganglia, brainstem, cerebellum, and spinal cord. However, whether neurotransmitter switching contributes to this form of learning was unknown. Neurotransmitter switching is an under-appreciated form of plasticity, as in most high school and college textbooks, neurons are assigned a neurotransmitter (e.g., dopamine neuron) which sticks with them for life, making the concept of a plastic ‘switchable’ neurotransmitter repertoire foreign to most students. Today I’m going to try and make the case for neurotransmitter switching, using this beautiful study as a template!

The authors started by examining how the brain changes in response to a week of aerobic exercise (a running task, shown below). They trained mice to run on a wheel throughout the week, and then tested their motor coordination on a rotating rod (rotarod) and a balance beam. They demonstrated that after a week of training, mice that ran increased their speed on the running wheel, fell off the rotarod at higher speeds of rotation, and kept better balance on the balance beam than mice that didn’t run. This learning effect lasted for up to 2 weeks following training, suggesting that mice learned the motor behavior, but this ‘motor memory’ can be lost if it is not reinforced with more exercise.