BME PhD Defense: Abbey McGrew
Postural Control of the Head During Whole Body Translations
Supervised by Professor Greg Gdowski
In primates, the head neck system can be thought of as a large mass that is located distally from the trunk atop the flexible cervical spinal column. This most basic mechanical relationship of the head and the body affords us with the ability to change the headâs position with respect to the body with many degrees of freedom. This ability, however, has its drawbacks. When the whole body is moved, the head/neck system can function like that of an inverted pendulum. Consequently, if uncontrolled the mass of the head could result in undesirable and involuntary movement relative to the trunk. Such, head movements could unintentionally change its orientation in space compromising our ability to utilize sensory signals for spatial localization (vision and hearing). They also have the potential to be injurious to the spinal column. The central nervous system is thought to employ several reflexes that contribute to the overall stability of the head/neck system.
Both the anatomy and fundamental physiology of these pathways are well known, yet remarkably little is known about how they function when the body is translated in space. The goal of this dissertation was investigate the role that vestibular sensory information plays in controlling the head when the body is translated in space. Specifically, we asked: How does the brain use vestibular information to control the forces on the head that occur during whole body translation? This dissertation takes an approach to answer this question; beginning at the level of overall behavior, moving up to muscle activation with underlies that behavior, and finally the central nervous system mechanisms that could activate musculature in more natural circumstances. Our results show that the central nervous system does indeed actively control of the head during whole body translation and serves to reduce forces on the head which could in turn reduce the size of head movements and protect the neck from injury. These results are profoundly different from the behavior of the CNS during whole body rotation and represent a significant difference in postural control of the head during translation.