In years 4 and 5 this project has focussed on three tasks: 1. Developed a practical methodology to determine optimal stimulation levels that will enable maximizing balance and locomotor task performances during task performance or training. This will enable ease of application of SR stimulation in practice. In order to improve the efficacy of implementation of this countermeasure a practical methodology to determine customized subject specific optimal amplitude if noise was needed to be implemented. Towards this goal we have developed and tested a practical methodology of finding the optimal amplitude of stimulation using perceptual thresholds indicated by seated subjects using the joystick on a game pad in response to applied electrical vestibular stimulation with sinusoidal signals of varying amplitudes. We mapped the optimal stimulation levels to the threshold curve obtained in previous experiments in which subjects performed both the balance and locomotor tasks and determined that the optimal levels of stimulation were in the range of 20-40% of threshold. 2. We examined how vestibular SR stimulation (VSR) affects measures of brain structure, functional network integrity, and vestibular function using Diffusion Tensor Imaging (DTI), Functional Connectivity MRI (magnetic resonance imaging), and Functional MRI. We have developed a methodology for using a MRI compatible tapper device which elicits vestibular evoked myogenic potentials (VEMPs). This device enables the mapping of the functional vestibular cortex. We are conducting a further validation study comparing functional MRI data in response to both the tapper device and to auditory tone bursts to map the functional vestibular cortex. We have collected data on 8 participants thus far, and the preliminary analyses reveal good correspondence in the activation patterns for the two methods. We will complete data collection on 15 participants and analyze the data for publication. We will then move on to image vestibular responses to the low level VSR stimulation. 3. We investigated the safety of use and possible effects of VSR alone and combined with L-DOPA in patients with Parkinsons Disease (PD). SVS (stochastic vestibular stimulation) or sham stimulation was administered to 10 PD patients in a double-blind placebo controlled cross-over pilot study. Motor symptoms and balance were evaluated in a defined off-medication state and after a 200 mg test dose of L-DOPA, using UPDRS-III, Posturo- Locomotor- Manual (PLM) movement times (MT), static posturography, and force plate measurements of the correcting response to a balance perturbation. Results suggest that short term use of SVS is safe, improves corrective postural responses, and has a small positive effect on motor symptoms in PD patients off treatment.