A "conscious" loss of balance: Directing attention to movement can impair the cortical response to postural perturbations

Abstract

‘Trying too hard’ is known to interfere with skilled movement, such as sports and music playing. Postural control can similarly suffer when conscious attention is directed towards it (termed ‘conscious movement processing’; CMP). However, the neural mechanisms through which CMP influences balance remain poorly understood. We explored the effects of CMP on electroencephalographic (EEG) perturbation-evoked cortical responses and subsequent balance performance. Twenty healthy young adults (age=25.1±5 years; 10 males and 10 females) stood on a force plate-embedded moveable platform whilst mobile EEG was recorded. Participants completed two blocks of 50 discrete perturbations, containing an even mix of slower (186 mm/s peak velocity) and faster (225 mm/s peak velocity) perturbations. One block was performed under conditions of CMP (i.e., instructions to consciously control balance), whilst the other was performed under ‘Control’ conditions with no additional instructions. For both slow and fast perturbations, CMP resulted in significantly smaller cortical N1 signals (a perturbation-evoked potential localised to the supplementary motor area), and lower sensorimotor beta EEG activity 200–400 ms post-perturbation. Significantly greater peak velocities of the centre of pressure (i.e., greater postural instability) were also observed during the CMP condition. Our findings provide the first evidence that disruptions to postural control during CMP may be a consequence of insufficient cortical activation relevant for balance (i.e., insufficient cortical N1 responses followed by enhanced beta suppression). We propose that conscious attempts to minimise postural instability through CMP acts as a cognitive dual-task that dampens the sensitivity of the sensorimotor system for future losses of balance.