The role of motor cortex in the acquisition and production of learned motor sequences
Contributors: Olveczky, Bence P.; Graybiel, Ann M.; Murthy, Venkatesh N.; Sanes, Joshua R.; Hogle, James M.
Published: 2014
Language: eng
Description: Motor skill learning underlies much of what we do, be it hitting a tennis serve, playing the piano, or simply brushing our teeth. Yet despite its importance, little is known about the neural circuits that implement the learning process or how the motor program is represented in the brain. Here I explore the role of motor cortex through lesion studies in rats trained on a motor skill. First, I interrogate whether motor cortex is necessary for the production of a complex motor sequence by training animals to produce temporally precise self-initiated movement sequences on a lever-pressing task. The movement sequences that emerged over months of training were remarkably complex, yet very precise. This motor skill, once mastered, survives large bilateral motor cortex lesions, suggesting that motor cortex is not required for generating movement sequences after consolidation. Next, I explored the role of motor cortex in motor skills that require dexterous manipulations. 

Animals trained to make constrained spatially precise movements using a joystick were impaired after motor cortex lesions. The role of motor cortex thus depends on the nature of the movements involved but not on the sequencing of movements. Third, I explored the function of motor cortex in sensorimotor transformations by training animals on the same lever-pressing task but with external cues instead of self-initiated movement. Surprisingly, these animals were also not impaired after lesions, suggesting that the method of learning the motor sequence has no consequence once the motor sequences are consolidated. Lastly, I explored the role of motor cortex in learning motor skills. Animals that were lesioned after being exposed to the lever-pressing task could learn to adjust the timing of their movements, indicating that motor cortex is not required for adapting a previously-acquired motor sequence. Lesions of motor cortex prior to any training, however, severely disrupted learning. 

Even with extended training, animals were unable to fully master the task, demonstrating that motor cortex is necessary for the acquisition of new motor skills even when it is not required for their execution.
Notes: Keywords: lesions, motor, motor cortex, rat.

Thesis Ph.D. Harvard University 2014