PhD defence B.G. (Brandon) Rasman

Brief summary on the aim of the doctoral thesis:

Our ability to maintain upright stance across different environments requires the brain to accurately estimate the state of the body within the surrounding world and generate the appropriate motor actions needed to balance upright. When balancing in new environments, the brain must (1) identify the source of unexpected self-motion, and (2) associate ongoing motor commands with novel sensory feedback to adapt motor control. This thesis examines how humans adapt and perceive their movements to maintain standing balance. In a series of studies, participants balanced in conditions with modified sensorimotor, mechanical and/or environmental factors. There were three key findings from this research. One, the human balance system demonstrates remarkable adaptability, recalibrating motor control to maintain standing balance under a variety of conditions that are initially destabilizing to upright posture. A key example of this adaptation occurred when participants learned to stand with long sensorimotor delays (~500-560 ms) in balance control. Two, the brain can generalize these learned control policies across differing balance contexts. Three, the balance system can operate according to its own sensorimotor principles that are not always accessible to our conscious awareness. Collectively, to adapt motor behavior and maintain stable perception for standing balance, the nervous system infers the spatio-temporal relationships between sensory and motor signals to form and update probabilistic estimates of self-motion. These studies have implications for understanding the neuromechanical principles governing human balance, and for developing new methodologies to rehabilitate individuals with balance impairments.