title: Cortical correlates of response time slowing in older adults: ERP and ERD/ERS analyses during passive ankle movement.
abstract: OBJECTIVE
  The response time (RT) to kinesthetic perception has been used as a proprioceptive measurement, for example, in older individuals. However, the RT cannot provide information on impairments at specific stages of the respective sensorimotor processing. In the present study, electroencephalographic (EEG) signals were recorded during passive ankle movement with and without an associated perceptual task of movement detection. The main purpose was to analyze differences between young and older adults both in terms of RT and cortical responses. Putative differences in the latter were expected to point to changes in the processing associated with neural pathways or cortical regions in the older subjects.
  
  
  METHODS
  The EEG activity of nineteen older (OA, 65-76 years) and 19 young adults (YA, 21-32 years) was recorded during passive ankle movement, without motor voluntary response (NVR, sensory condition), and during a condition with voluntary motor response (VR, with measurement of the RT). Event-related potentials (ERP) and beta event-related desynchronization/synchronization (ERD/ERS) were recorded and analyzed in both experimental conditions.
  
  
  RESULTS
  The RT in OA was larger than in YA (P<0.0001). EEG analyses showed that the N1 amplitude was larger in the VR than in the NVR condition (P=0.006), whereas no difference for latency was obtained between conditions (P=0.376). Comparisons between the groups revealed attenuated (P=0.019) and delayed (P=0.001) N1 in the OA group, irrespective of the condition (no interaction group vs condition). Only OA showed correlations between RT and N1, with significant correlation for both amplitude (r=-0.603, P=0.006) and latency (r=0.703, P=0.001). The ERD/ERS analyses revealed a task-dependent group effect: in NVR, significant differences were obtained only for the ERS amplitude, which was attenuated in OA (P=0.003). In VR, larger (P=0.004) and delayed (P=0.003) ERD and attenuated (P=0.029) and delayed (P=0.017) ERS peaks were observed in the older group.
  
  
  CONCLUSIONS
  The results suggest that a larger response time to proprioceptive stimuli in older adults is associated with a weaker and delayed proprioceptive afferent inflow to the cortex. In this scenario, older adults would need a higher cognitive effort (larger ERD) to process the sensory inputs when attempting to properly perform a sensorimotor task.
  
  
  CONCLUSIONS
  ERP and ERD/ERS measurements during kinesthetic assessment provide new insights on identification of the origin of sensorimotor slowing in older adults.
authors.affiliation: Neuroscience Program and Biomedical Engineering Laboratory, University of São Paulo, EP-USP, PTC, São Paulo, Brazil. Electronic address: dianatoledo12@hotmail.com.
authors.forename: Diana R
authors.initials: DR
authors.lastname: Toledo
authors.affiliation: Division of Neurology, Federal University of São Paulo, São Paulo, Brazil.
authors.forename: Gilberto M
authors.initials: GM
authors.lastname: Manzano
authors.affiliation: Institute of Physical Activity and Sport Sciences and Graduate Program in Human Movement Sciences, Cruzeiro do Sul University, São Paulo, Brazil; Institute of Bioscience, São Paulo State University, Rio Claro, Brazil.
authors.forename: José A
authors.initials: JA
authors.lastname: Barela
authors.affiliation: Neuroscience Program and Biomedical Engineering Laboratory, University of São Paulo, EP-USP, PTC, São Paulo, Brazil.
authors.forename: André F
authors.initials: AF
authors.lastname: Kohn
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D000843:Ankle Joint / Q000502:physiology*; D001611:Beta Rhythm / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods; D003344:Cortical Synchronization / Q000502:physiology*; D004569:Electroencephalography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009068:Movement / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology*; D013003:Somatosensory Cortex / Q000502:physiology; D055815:Young Adult
keywords: Aging; Beta ERD/ERS; Event-related potential; Passive movement; Proprioception