Abstract
Low levels of bipolar binaural white noise based imperceptible stochastic electrical stimulation to the vestibular system (stochastic vestibular stimulation, SVS) have been shown to improve stability during balance tasks in normal, healthy subjects by facilitating enhanced information transfer using stochastic resonance (SR) principles. We hypothesize that detection of time-critical sub-threshold sensory signals using low levels of bipolar binaural SVS based on SR principles will help improve stability of walking during support surface perturbations. In the current study 13 healthy subjects were exposed to short continuous support surface perturbations for 60 s while walking on a treadmill and simultaneously viewing perceptually matched linear optic flow. Low levels of bipolar binaural white noise based SVS were applied to the vestibular organs. Multiple trials of the treadmill locomotion test were performed with stimulation current levels varying in the range of 0–1500 μA, randomized across trials. The results show that subjects significantly improved their walking stability during support surface perturbations at stimulation levels with peak amplitude predominantly in the range of 100–500 μA consistent with the SR phenomenon. Additionally, objective perceptual motion thresholds were measured separately as estimates of internal noise while subjects sat on a chair with their eyes closed and received 1 Hz bipolar binaural sinusoidal electrical stimuli. The optimal improvement in walking stability was achieved on average with peak stimulation amplitudes of approximately 35% of perceptual motion threshold. This study shows the effectiveness of using low imperceptible levels of SVS to improve dynamic stability during walking on a laterally oscillating treadmill via the SR phenomenon.
Highlights
In general terms, stochastic resonance (SR) can be thought of as “noise benefit” by increasing information transfer in the presence of non-zero level of noise
These data show that this subject is responsive to stochastic vestibular stimulation (SVS) showing peak improvement at a non-zero peak SVS current level that gradually reduces at higher current levels consistent with SR phenomenon
The optimal response for this subject to improve stability during walking on the perturbed surface was at the stimulation level with peak current amplitude of 500 μA, which was approximately at this subjects’ perceptual motion threshold
Summary
Stochastic resonance (SR) can be thought of as “noise benefit” by increasing information transfer in the presence of non-zero level of noise (for reviews, see Collins et al, 2003; Moss et al, 2004; McDonnell and Abbott, 2009; Aihara et al, 2010). The application of mechanical noise to the feet has been shown to improve balance control through the reduction of sway in young and elderly subjects (Priplata et al, 2002, 2003), in patients with diabetes and stroke (Priplata et al, 2006) and patients with functional ankle joint instabilities (Ross and Guskiewicz, 2006; Ross et al, 2013). There have been a few studies that showed the effectiveness of applying sub-sensory vibratory noise to the soles of the feet during over-ground walking comparing elderly population with young control subjects (Galica et al, 2009). In a follow-up study, this group showed the effectiveness of applying sub-sensory vibratory noise to the soles of the feet during treadmill walking in a set of control subjects (Stephen et al, 2012)
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