Assessing the Impact of mTBI on Multisensory Integration while Maneuvering on Foot

Background: A Service Member's success in combat operations is largely dependent on the ability to shoot, move, and communicate on the battlefield. The critical task requires the execution of numerous complex subtasks that involve processing simultaneous inputs from the auditory, visual, vestibular, tactile, and proprioceptive senses. However, to this point, very little effort has been devoted to directly evaluating complex multisensory integration ability in Service Members with traumatic brain injuries (TBIs). In this study, we propose to study performance in normal Service Members and Service Members with mild TBI (mTBI) in a novel multisensory task that requires them to use auditory cues to localize and identify visual targets while walking on a moving treadmill.Objective/Hypothesis: Our hypotheses are: (1) The ability to conduct aurally aided visual search tasks while walking on a moving platform will be influenced both by unimodal sensory acuity and multimodal sensory integration. (2) Service Members with blast injury or mTBI have multimodal integration deficits that will cause them to perform worse than would be predicted for normal Service Members with similar levels of unimodal sensory acuity. (3) These multimodal integration deficits can be correlated with clinical measures of vestibular function even in cases where those measures fall within a clinically normal range.Specific Aims: (1) Characterize aurally aided visual search performance in normal subjects who are stationary or in motion. (2) Compare aurally aided visual search performance in the normal population to performance with patients who are blast exposed or have experienced mTBI. (3) Attempt to correlate performance in an aurally aided visual search task to clinical measures of vestibular and neurological function.Study Design: The study will be conducted in the CAREN system at the National Intrepid Center of Excellence. The CAREN is an immersive virtual reality system that combines a wide-angle visual display with a motorized treadmill mounted on a moveable hydraulic platform. For the purposes of this study, the CAREN will be modified to include a 64-speaker audio array, which will allow spatialized audio-visual targets to be presented to the study participants. In this study, visual targets will be presented in the context of a large number of visual distracters. In some cases, an auditory cue will also be presented at the location of the target. The subject's task will be to detect and identify the target as quickly as possible. Total visual search times will be measured with and without audio cues and with and without motion for 25 subjects in each of three groups: normal controls; military personnel who have borderline-normal vestibular function due to blast exposure; and military personnel who have clinically abnormal vestibular function due to mTBI. In order to isolate the effects of multisensory integration, search times measured with the blast-exposed and mTBI patients will be compared to those measured on normal patients who have been degraded to the same level of visual and auditory acuity through the addition of visual and auditory noise. Performance will also be correlated to clinical measures of vestibular and neurological function to determine if performance in complex multimodal tasks can be predicted from existing clinical tests.Innovation: Although CAREN systems have been used for rehabilitation in mTBI patients for some time, this experiment will be one of the first to provide a sensitive objective measure of integrated audio, visual, vestibular, and somatosensory function in a task that has direct operational relevance to the tasks faced by dismounted Soldiers on patrol.Impact: The study will provide information about the integration of multisensory information in mTBI patients, help inform return-to-duty standards for military personnel, and provide insights into the development of new rehabilitative strategies for blast-injured Service Members.