The goal of this proposal is to investigate vestibular precision by quantifying the variability in behavioral responses that result from the neural noise inherent to the peripheral and central vestibular systems. Because neural noise contaminates the signals that are transduced by the ear and processed by the brain, vestibular- mediated behavioral responses vary even when identical stimuli are provided. In this proposal, we focus on vestibular precision in human subjects and investigate its sources, its effects on behavior, and its degradation when the periphery is damaged and its potential plasticity. Specifically, we will investigate: SA 1: Vestibular precision in normal subjects ? physiology: A) We will measure the angular and linear vestibulo-ocular reflex (VOR) using novel motion combinations that reinforce or cancel eye movement responses, which will allow us to determine the distribution and magnitude of noise produced in the sensory (canal, otolith) pathways and in the oculomotor pathway. We hypothesize that normal subjects will demonstrate a bimodal distribution of noise with either sensory or motor predominance, and that subjects with more sensory noise will demonstrate other behavioral characteristics that reflect this characteristic (e.g., higher perceptual thresholds); and B) We will assay vestibular noise from trial-trial variations in the VOR and will compare VOR dynamics with those predicted by a Bayesian model using the assayed noise. We predict variations in VOR dynamics across subjects, age and stimulus amplitudes will be consistent with Bayesian processing of noise. Potential confounding factors will be carefully controlled, including attention, fatigue, and non-vestibular cues. SA 2: Vestibular precision after peripheral damage ? pathophysiology: A) We will examine the changes in vestibular precision that occur when one vestibular nerve is damaged (by a vestibular schwannoma, VS) and after the damaged nerve is surgically sectioned, and will investigate if precision measurements can provide evidence of pathologic noise produced by the damaged nerve and therefore help predict clinical outcome when the nerve is sectioned. We hypothesize that changes in signal reliability due to the VS will be traceable to both the reduced redundancy caused by loss of afferent fibers and to aberrant noise generated by the damaged vestibular nerve and that changes in precision after neurectomy will correlate the outcome measures that characterize patient disability; and B) We will examine the plasticity of vestibular precision in the oculomotor and perceptual realms with the goal of determining if precision can be improved. Using novel training approaches that provide challenging signal extraction tasks, we hypothesize that subjects will improve their vestibular precision on the trained task. As secondary outcome measures, we will determine if training one behavior generalizes to the non-trained behavior and if patient?s symptoms are affected by improved precision.
This project will investigate the role of noise in the vestibular system, and in particular its effects on the variability (precision) of vestibular-mediated behaviors. We will study vestibular precision in normal subjects and patients with peripheral vestibular damage, and will investigate its potential plasticity. The goals are to develop a better understanding of the role played by noise in the vestibular system in normal and pathologic populations, and to determine if the brain can learn to improve signal recognition within its inherently noisy neural environment, which would result in improved behavioral precision.
