title: Cognitive demand does not influence the responsiveness of homonymous Ia afferents pathway during postural dual task in young and elderly adults.
abstract: OBJECTIVE
  This study was designed to investigate the influence of a cognitive task on the responsiveness of the homonymous Ia afferents pathway during upright standing in young and elderly adults.
  
  
  METHODS
  Twelve young and twelve elderly adults stood upright on a foam surface positioned over a force platform, and performed a colour-naming test (cognitive task) with two cognitive loads: congruent and incongruent colour conditions. The rate of correct response in naming colour (accuracy) and associated reaction time (RT) were recorded for the cognitive task. The excursion of the centre of pressure and surface electromyogramme (EMG) of leg muscles were measured. Modulation in the efficacy of homonymous Ia afferents to discharge spinal motor neurones was assessed by means of the Hoffmann (H) reflex method.
  
  
  RESULTS
  The accuracy and RT were similar in the congruent condition between young and elderly adults (p > 0.05), and increased for both age groups in the incongruent condition, but more so for elderly adults (p = 0.014). In contrast, the H reflex amplitude did not change with the cognitive load. The excursions of the centre of pressure in the sagittal plane and muscle EMG did not vary with colour conditions in both groups (p > 0.05).
  
  
  CONCLUSIONS
  This study indicates a lack of modulation in the efficacy of group Ia afferent to activate soleus motor neurones with the cognitive demand of a concurrent task during upright standing in young and elderly adults.
authors.affiliation: Laboratory of Applied Biology and Research Unit in Neurophysiology, Faculty for Motor Sciences, ULB Neuroscience Institute, Université Libre de Bruxelles, 808, route de Lennik, CP 640, 1070, Brussels, Belgium, sbaudry@ulb.ac.be.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Baudry
authors.forename: Vinciane
authors.initials: V
authors.lastname: Gaillard
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging; D016022:Case-Control Studies; D003071:Cognition; D005260:Female; D006801:Humans; D007866:Leg / Q000294:innervation / Q000502:physiology; D008297:Male; D009046:Motor Neurons / Q000502:physiology; D018482:Muscle, Skeletal / Q000254:growth & development / Q000294:innervation / Q000502:physiology; D009475:Neurons, Afferent / Q000502:physiology*; D004856:Postural Balance; D011187:Posture; D011930:Reaction Time; D013127:Spinal Nerves / Q000254:growth & development / Q000502:physiology