The Role of the Central Nervous System in the Integration of Proprioceptive Information

The proprioceptive system provides feedback on human performance that makes it possible to learn and perform novel tasks. Proprioception predominately arises in the peripheral nervous system at the muscle spindle organ. Mechanical stimulus such as vibration has been implicated in altering muscle spindle afferent signals used as feedback. Researchers have utilized this understanding to document gross performance changes resulting from a muscle spindle disruption paradigm. Findings of this work have demonstrated that the altered proprioceptive feedback alters performance both during and after vibration exposure. This has also led many to postulate that altered proprioceptive feedback due to environmental working conditions may be responsible for many incidences of musculoskeletal injury, including low back pain. In order to more fully understand how proprioceptive feedback is integrated into a motor response it was required to investigate activity within the central nervous system, itself the target of the spindle afferent, both before and after receiving a modulate afferent. We developed a protocol based on measures of average velocity to test for this activity. Our investigation began we examining whether or not average velocity, in the form of seated sway velocity, would be sensitive to applied vibration. We found that while vibration was applied; mean sway speed increased significantly above pre vibration levels, regardless of feedback and task difficulty. A computer based pursuit task was then implemented in order to investigate performance relative to timing of vibration exposure. Our results revealed a significant decrease in pursuit velocity during vibration from pre-vibration velocity. Additionally, subjects demonstrated an equal magnitude but opposite increase in pursuit speed after vibration was removed. This protocol was then replicated in a functional-MRI to compare the gross motor pursuit task performance with the corresponding BOLD imaging data. We observed a similar decrease/increase pattern of joystick pursuit velocity. The corresponding cortical activity revealed patterns of inhibition consistent with cognitive inhibition. The current findings support proprioception as a central inhibitory control mechanism that shifts cortical networks dependent on available sensory stimulus