Traditional and Non-Traditional Inputs to the Vestibular System

One of the primary functions of the vestibular system is to provide stabilizing reflexes to the eye, head, and body. These reflexes are often coordinated with inputs from the visual and proprioceptive systems. More recently, research has shown that other, non-traditional, stimuli also affect the vestibular system, though the scope of this research has been limited. This thesis explores the effect of both traditional and non-traditional inputs on the vestibular system by characterizing their influence compensatory movements. We begin by looking at the influence of the vestibular periphery and efference copy on compensatory eye movements (Chapter 2). While each of these has been described individually (as the vestibular-ocular reflex (VOR) and pre-programmed eye movements (PPEM) respectively), there is currently controversy in the field regarding 1) to what extent PPEM influence gaze stabilization in healthy animals, and 2) how these two inputs interact with each other. We propose a model of gaze stability in which VOR and PPEM work cooperatively, and compare model predictions to our data as well as data others have reported. We found that our model accurately predicted eye movements for all behavioral contexts tested. In Chapter 3, we describe the effect of single high-intensity noise exposure on the vestibular system. Currently, controversy surrounds whether, and to what extent, noise damages the semi-circular canals. We characterized changes to both ocular and head stability to better answer this question and found that after noise exposure there was loss of both ocular and head stability. However, the exact nature of this deficit was not as expected and the influence of cervical pathways after vestibular lesion is discussed. Finally, in Chapter 4, we examine the effect of galvanic vestibular stimulation (GVS) and optokinetic stimulation on standing posture. We propose a model of postural stability inspired by the velocity storage model of ocular stability. While others have proposed more complex models that make similar predictions, those predictions have not been explicitly tested and, further, it’s not clear if the added complexity is necessary. We found that, while simple, our model could correctly predict subjects’ responses to both stimuli, suggesting that the body interprets and uses sensory information for postural stability in a manner similar to that for ocular stability. Taken together these findings demonstrate that the influence of non-traditional inputs and pathways to vestibular system is substantial and should be considered both in laboratory and clinical settings. Specifically, we showed in Chapter 2 that PPEM are not merely an enhanced or adapted VOR, but part of a unique gaze stabilization system that merits independent consideration. In Chapter 3, we showed that a single noise exposure can cause significant functional damage to the vestibular system, suggesting that patients with noise-induced hearing loss should be tested for vestibular loss as well. Finally, in Chapter 4, we showed that GVS can be integrated like natural vestibular stimulation but only if it is properly conditioned first. This is of particular importance for vestibular prosthetic design, which uses GVS to substitute for lost vestibular input.PHDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/143914/1/hastepha_1.pd