A study of the effects of sensory state on rhesus monkey postural control

Abstract

Although many take the seemingly simple ability to balance in order to maintain posture for granted, approximately 8 million American adults have chronic balance impairment issues derived from vestibular dysfunction. For patients suffering from severe vestibular dysfunction, maintaining balance in daily activities, such as walking on an uneven surface at night, turning one's head, or attempting to stand on a moving surface, can prove extremely challenging. Unfortunately, many vestibular-loss sufferers are left with limited treatment options and can become permanently debilitated. In order to aid the vestibular-impaired population in partially restoring postural stability, it is important to develop rehabilitative solutions. For subjects suffering from severe bilateral vestibular loss, but with intact eighth nerve function, the invasive vestibular prosthesis is a potential rehabilitative solution. This must be developed and fully characterized in non-human primates in parallel with human implementation. In this research, we characterized the postural response of a severely vestibular-lesioned non-human primate instrumented with a prototype invasive vestibular prosthesis. We showed that the severely vestibular-impaired animal aided by the prosthesis was able to utilize the partially restored vestibular cues to increase its stability compared to the severely-impaired state. We also explored the impact on balance of (1) supplying an additional cue (light-touch) and (2) compensative strategies that the subject develops when suffering from mild or severe vestibular-impairment. We determined that the severely-impaired animal decreased its trunk sway when provided the light-touch cue, however a mildly-impaired animal did not. We also determined that an animal with mild vestibular impairment spontaneously compensated for its vestibular loss to stabilize itself both for stationary support surface conditions and for support surface perturbations. This thesis is the first time that animal posture measures for different levels of vestibular impairment have been used in conjunction with a feedback controller model to investigate the postural control mechanisms used. The results reported within this thesis begin to establish the baseline database of primate postural responses to a wide variety of test situations for different levels of vestibular impairment that will be needed for further investigation and evaluation of rehabilitative solutions, such as prototype vestibular implant systems.