title: The effect of a concurrent cognitive task on cortical potentials evoked by unpredictable balance perturbations.
abstract: BACKGROUND
  Although previous studies suggest that postural control requires attention and other cognitive resources, the central mechanisms responsible for this relationship remain unclear. To address this issue, we examined the effects of altered attention on cortical activity and postural responses following mechanical perturbations to upright stance. We hypothesized that cortical activity would be attenuated but not delayed when mechanical perturbations were applied during a concurrent performance of a cognitive task (i.e. when attention was directed away from the perturbation). We also hypothesized that these cortical changes would be accompanied by alterations in the postural response, as evidenced by increases in the magnitude of anteroposterior (AP) centre of pressure (COP) peak displacements and tibialis anterior (TA) muscle activity. Healthy young adults (n = 7) were instructed to continuously track (cognitive task) or not track (control task) a randomly moving visual target using a hand-held joystick. During each of these conditions, unpredictable translations of a moving floor evoked cortical and postural responses. Scalp-recorded cortical activity, COP, and TA electromyographic (EMG) measures were collected.
  
  
  RESULTS
  Results revealed a significant decrease in the magnitude of early cortical activity (the N1 response, the first negative peak after perturbation onset) during the tracking task compared to the control condition. More pronounced AP COP peak displacements and EMG magnitudes were also observed for the tracking task and were possibly related to changes in the N1 response.
  
  
  CONCLUSIONS
  Based on previous notions that the N1 response represents sensory processing of the balance disturbance, we suggest that the attenuation of the N1 response is an important central mechanism that may provide insight into the relationship between attention and postural control.
authors.affiliation: Institute of Medical Science, University of Toronto, Canada. sylvia.quant@utoronto.ca
authors.forename: Sylvia
authors.initials: S
authors.lastname: Quant
authors.forename: Allan L
authors.initials: AL
authors.lastname: Adkin
authors.forename: W Richard
authors.initials: WR
authors.lastname: Staines
authors.forename: Brian E
authors.initials: BE
authors.lastname: Maki
authors.forename: William E
authors.initials: WE
authors.lastname: McIlroy
mesh_terms: D000328:Adult; D001288:Attention / Q000502:physiology*; D002540:Cerebral Cortex / Q000502:physiology*; D003071:Cognition / Q000502:physiology*; D004569:Electroencephalography; D004576:Electromyography; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology; D006801:Humans; D008297:Male; D009038:Motion; D010775:Photic Stimulation; D004856:Postural Balance / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D013647:Task Performance and Analysis