Balance Perturbations in Simulated Low-Gravity Modulate Human Premotor and Frontoparietal Electrocortical Theta, Alpha, and Beta Band Spectral Power

We aimed to identify the influence of bodyweight unloading on healthy human electrical brain and muscle dynamics during standing balance. Using an underwater environment to simulate reduced gravity, we recorded high-density electroencephalography and lower limb electromyography from 10 individuals (5 female). During five standing balance conditions, we adjusted the water depth (1: on-land, 2: chest-level, 3: waist-level) and applied external fluid forces to the front of the body in the posterior direction (4: low and 5: high external fluid forces). Reduced bodyweight decreased ankle plantar flexor muscle activity and increased alpha band (8-13 Hz) spectral power from right premotor cortex. Underwater balance perturbations increased muscle activations surrounding the ankle and knee joints and increased theta band (4-8 Hz) spectral power from right premotor cortex. Concurrently, alpha and beta band (13-30 Hz) spectral power decreased from left prefrontal and right premotor cortices, along with reduced alpha band spectral power from left parietal cortex.