Functional Near-Infrared Spectroscopy (fNIRS) Assessing Neural Activity During Virtual Reality Walking Intervention

Each year, an estimated 2.9 million Americans sustain traumatic brain injuries (TBI) that result in emergency department visits, hospitalizations, and death. Although there are many treatment strategies in the early weeks and months after TBI, millions of individuals live with residual disability. This residual, chronic disability often includes significant impairments in functional abilities, like mobility, along with unresolved neurophysiological deficits. Because better mobility is directly linked to improved quality of life and enhanced societal participation, interventions designed to improve mobility in chronic TBI are essential.

One candidate intervention that could improve mobility in chronic TBI is virtual reality (VR). VR systems are computer-based applications that allow an individual to view and dynamically interact with a simulated environment in real-time. Evidence suggests that VR may enhance motor learning and ultimately neuroplasticity (the ability to reorganize synaptic connections in response to learning), as VR provides users with increased sensory stimulation, a more immersive environment, and real-time feedback. VR has been used to improve balance and mobility deficits associated with multiple neurologic conditions, including TBI. Neuroimaging studies have found that VR engagement can activate various cortical networks, including the visual cortex, parietal cortex, and premotor cortex, among others, which may impact motor outcomes. Craig has been evaluating the impact of VR use in TBI since 2012 when they conducted a site-specific study evaluating VR balance training in the home in comparison to a written home exercise program. Importantly, it was found that both interventions elicited significant improvements in clinical measures of balance in individuals with chronic TBI, but did not find between group differences.

In the current Traumatic Brain Injury Model Systems (TBIMS) grant, the investigator hypothesized that combining treadmill training (TT) and VR would increase cortical excitability which would concurrently enhance activation of the neuromuscular system. Subsequently, this intervention would improve walking, balance, and cognitive outcomes - as evaluated with gold standard clinical measures. However, more research is needed to test this hypothesis and address knowledge gaps, as efficacy for TT + VR has not been established, specific "responders" to TT + VR interventions have not been identified, and the plausible mechanisms associated with response have not been established. Specifically, studies have not yet evaluated the relationship between clinical outcomes and cortical activation.

To address these gaps, the investigators are proposing a translational research approach. Translational research integrates basic and clinical science to better understand disorders like chronic TBI and to create enhanced diagnostics and treatments to expedite recovery processes. Here, the investigators propose to pair a neuroscience method with clinical interventions in adults with chronic TBI. Specifically, they plan to use portable a neuroimaging device, functional near-infrared spectroscopy (fNIRS), to measure neural activity during a TT + VR intervention to support future research and clinical initiatives in VR.

fNIRS is a neuroimaging technique that uses near-infrared light to evaluate changes in brain activity via proxy measures of oxygenated (HbO) and deoxygenated hemoglobin (HbR). Specifically, following neural activity, oxygen is pulled from hemoglobin resulting in an immediate increase of HbR. Next, the oxygen reduction elicits an increase in localized cerebral blood flow (CBF) - a mechanism called neurovascular coupling. As CBF increases, a greater concentration of HbO can be detected. Both HbR and HbO have optical properties, meaning that their concentrations can be measured with near-infrared light. Thus, fNIRS can detect localized neural activity by evaluating HbR and HbO, and increases in HbO concentrations reflect site-specific increases in neural activity.

In summary, this proposed pilot study is designed to assess the feasibility of using portable fNIRS to measure neural activity during a TT + VR intervention in adults with TBI. Establishing feasibility will allow us to use fNIRS in future studies comparing different intervention types. These outcomes will advance VR research and enhance the scientific understanding of clinical and physiological outcomes following VR interventions, ultimately informing clinical care.