Novel Methodology for Evaluating the Neural Underpinnings of Balance in Adults with Acquired Brain Injury

Research Objectives: To evaluate the neural underpinning of balance in adults with chronic acquired brain injury (ABI) by investigating relationships between balance task performance and task-dependent cortical brain activity as measured by portable functional near-infrared spectroscopy (fNIRS)

Design: Pilot randomized control trial; evaluation of pre-intervention (baseline) data

Setting: University laboratories

Participants: 23 participants with chronic ABI (9 Male; Mean Age 52.57; Mean Time Since Injury: 13.86 years)

Interventions: Yoga (active) and low-impact exercise (control); this analysis is evaluating pre-intervention data only.

Main Outcome Measures: Four balance tasks (eyes open or closed on a firm or soft surface) were completed on a BTrackS force plate (balancetrackingsystems.com) with simultaneous portable fNIRS using the NIRSport2 (nirx.net). Balance metrics: amount of sway in multiple axes. FNIRS metrics included average change in oxygenated hemoglobin (∆ HbO) in the following bilateral regions of interest (ROIs): primary motor cortices (M1), premotor cortices (PMC) and primary somatosensory cortex (S1). All fNIRS data were processed and reduced using standard steps with Satori (nirx.net) software. Pearson correlations tested for relationships between balance task performance (sway) and brain activity (∆ HbO) in ROIs for each balance task.

Results: Correlational analyses revealed negative relationships between the amount of sway during easier balance tasks (eyes open-firm surface and eyes open-soft surface) and fNIRS channels positioned over bilateral M1 (Right M1: p=0.022, r=-0.535; Left M1: p=0.041, r=-0.5). Specifically, better balance (i.e., less sway) was associated with more M1 activity. Conversely, positive relationships were found between the amount of sway during the hardest balance task (eyes closed-soft surface) and three channels positioned over bilateral PMC (1st channel over Left PMC: p=0.026, r=0.473; 2nd channel over Left PMC: p=0.043, r=0.445; Right PMC: p=0.049, r=0.446). Here, more activity in bilateral PMCs was associated with poorer balance (i.e., more sway).

Conclusions: Using novel methodology, moderate strength positive correlations were observed between balance and activity in bilateral premotor cortices and moderate negative correlations were observed between balance and activity in bilateral primary motor cortices. These results may indicate that excessive activity in motor planning regions (i.e., PMC) disrupts balance performance, whereas activity in neural substrates that support motor execution (i.e., M1) support better balance. These findings may reflect the neural underpinnings of balance performance in adults with ABI, but much more research is needed. Still, functional balance deficits in patients with chronic ABI might be mediated by activity in motor and premotor regions; these insights could inform treatment planning and future intervention studies for adults with ABI.

Author(s) Disclosures: None