Hemodynamic responses of the prefrontal cortex following cold water immersion during an eyes-closed balance assessment

Purpose This study aimed to examine the impact of cold water immersion (CWI) on balance and the corresponding hemodynamic responses that occur within the prefrontal cortex (PFC). Measuring PFC activation during balance will identify cognitive mechanisms underlying postural control, which can be used to identify balance impairments or fall risk. Methods Twenty-three participants completed two separate testing visits consisting of a 10-min CWI at 15 °C and thermoneutral water immersion (TWI) at 35 °C. A 30-s eyes-closed balance assessment was performed pre- and post-exposure to identify changes in Path Length, Sway Range, and Sway Velocity. Oxygenated (O 2 Hb) and deoxygenated hemoglobin (HHb) were measured over the PFC using functional near-infrared spectroscopy during all balance assessments. Results There were no detectable differences for Sex in any variable, nor significant differences in Path Length ( p = 0.94), Sway Range ( p = 0.92), and Sway Velocity ( p = 0.81) between the CWI and TWI exposures. For the TWI, there were no differences in O 2 Hb ( p = 0.15) or HHb ( p = 0.28) between the pre- and post-exposure balance assessments. The CWI exposure resulted in a significant decrease in O 2 Hb ( p ≤ 0.01) and an increase in HHb ( p ≤ 0.01). Conclusion The demands of thermoregulation and balance maintenance following CWI resulted in distinct cerebral hemodynamic patterns which potentially reflected increased neural demand during the tasks. Increase in HHb and decrease in O 2 Hb suggest a unique response during the refractory period between the CWI and balance assessment that may reflect competing thermoregulatory processes associated with rewarming.