Humans move about their environment quite easily, performing seemingly simple motor tasks without much thought. Walking is the perfect example, but this ‘simple’ motor task is actually quite complex. Think of the many muscles throughout the body that must work together in a well-coordinated manner to produce this smooth movement. The central nervous system (brain and spinal cord) are quite good at telling muscles when to be active or inactive and by how much. In essence, the brain must activate motor circuitry within the brainstem and spinal cord which then activates nerve cells (i.e. motoneurones) that project to and activate skeletal muscle to help produce movement. Motor impairments such as those caused by stroke or spinal cord injury often result in a disruption of this pathway, thus reducing one’s ability to move voluntarily. Due to reduced mobility, persons with motor impairments are at an increased risk of exhibiting the host of disuse-related diseases that are also becoming epidemic in the general population in North America, including obesity, type II diabetes and osteoporosis. An increase in mobility and thus caloric expenditure would help mitigate the effects of such diseases. To do so however, a gain in motor function is necessary.
Arm cycling is a common means used in neurorehabilitation settings and is actually quite similar to locomotion. It is rhythmic and alternating and like locomotion, has special spinal circuitry that contributes to its production. Arm cycling provides users with a means to exercise and be physically active while also placing stress on the central nervous system which may increase ones motor function. Relatively little is known, however, about 1) the brains role in producing this this complex movement or 2) how the excitability of spinal motoneurones (those cells that eventually activate the muscle) influences one’s ability to cycle. The research conducted in our lab examines these issues and is aimed at providing a better understanding of how the brain and spinal cord work together to produce complex motor outputs, such as arm cycling. The hope is that our findings can be used to improve current best-practice neurorehabilitation procedures for those with motor impairments.
Strong evidence exists that spinal circuitry, known as central pattern generators, (CPGs) are capable of inducing stepping-like movements and activation patterns in the absence of supraspinal influences. Ultimately however, the CPG must activate MNs to produce movement, for it is the MNs that project to and activate muscles for movement. Thus, a fundamental understanding of the factors regulating MN excitability is required before practical applications can be made in a clinical setting.
The majority of research focusing on spinal MN excitability during complex movements such as locomotion has been conducted in experimental animals. While providing useful information, the goal of animal research is ultimately to assist in our understanding of human motor physiology. My research program will determine whether similar basic mechanisms controlling MN excitability in animal preparations are relevant to human movement.