title: Vestibular control of standing balance is enhanced with increased cognitive load.
abstract: When cognitive load is elevated during a motor task, cortical inhibition and reaction time are increased; yet, standing balance control is often unchanged. This disconnect is likely explained by compensatory mechanisms within the balance system such as increased sensitivity of the vestibulomotor pathway. This study aimed to determine the effects of increased cognitive load on the vestibular control of standing balance. Participants stood blindfolded on a force plate with their head facing left and arms relaxed at their sides for two trials while exposed to continuous electrical vestibular stimulation (EVS). Participants either stood quietly or executed a cognitive task (double-digit arithmetic). Surface electromyography (EMG) and anterior-posterior ground-body forces (APF) were measured in order to evaluate vestibular-evoked balance responses in the frequency (coherence and gain) and time (cumulant density) domains. Total distance traveled for anterior-posterior center of pressure (COP) was assessed as a metric of balance variability. Despite similar distances traveled for COP, EVS-medial gastrocnemius (MG) EMG and EVS-APF coherence and EVS-TA EMG and EVS-MG EMG gain were elevated for multiple frequencies when standing with increased cognitive load. For the time domain, medium-latency peak amplitudes increased by 13-54% for EVS-APF and EVS-EMG relationships with the cognitive task compared to without. Peak short-latency amplitudes were unchanged. These results indicate that reliance on vestibular control of balance is enhanced when cognitive load is elevated. This augmented neural strategy may act to supplement divided cortical processing resources within the balance system and compensate for the acute neuromuscular modifications associated with increased cognitive demand.
authors.affiliation: Department of Human Physiology, University of Oregon, Eugene, OR, USA.
authors.forename: Michael A
authors.initials: MA
authors.lastname: McGeehan
authors.affiliation: Department of Human Physiology, University of Oregon, Eugene, OR, USA.
authors.forename: Marjorie H
authors.initials: MH
authors.lastname: Woollacott
authors.affiliation: Department of Human Physiology, University of Oregon, Eugene, OR, USA. brian.dalton@ubc.ca.|Faculty of Health and Social Development, School of Health and Exercise Sciences, The University of British Columbia, Okanagan Campus, ART 360 (Arts Building) 1147 Research Road, Kelowna, BC, V1V 1V7, Canada. brian.dalton@ubc.ca.
authors.forename: Brian H
authors.initials: BH
authors.lastname: Dalton
mesh_terms: D000328:Adult; D003071:Cognition / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D009483:Neuropsychological Tests; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology; D011312:Pressure; D011930:Reaction Time / Q000502:physiology; D058585:Vestibular Evoked Myogenic Potentials / Q000502:physiology*; D014722:Vestibule, Labyrinth / Q000502:physiology*; D055815:Young Adult
keywords: Electromyography; Galvanic vestibular stimulation; Posture; Sensorimotor; Stochastic