title: Perceived Comfort and Blinding Efficacy in Randomised Sham-Controlled Transcranial Direct Current Stimulation (tDCS) Trials at 2 mA in Young and Older Healthy Adults.
abstract: BACKGROUND
  tDCS studies typically find that: lowest levels of comfort occur at stimulation-onset; young adult participants experience less comfort than older participants; and participants' blinding seems effective at low current strengths. At 2 mA conflicting results have been reported, questioning the effectiveness of blinding in sham-controlled paradigms using higher current strengths. Investigator blinding is rarely reported.
  
  
  OBJECTIVE
  Using a protocol with 30 min of 2 mA stimulation we sought to: (a) investigate the level of perceived comfort in young and older adults, ranging in age from 19 to 29 years and 63 to 76 years, respectively; (b) test investigator and participant blinding; (c) assess comfort over a longer stimulation duration; (d) add to the literature on protocols using 2 mA current strength.
  
  
  METHODS
  A two-session experiment was conducted where sham and active stimulation were administered to the frontal cortex at the F8/FP1 sites in a within-subjects manner. Levels of perceived comfort were measured, using a visual analogue scale, at the start and end of stimulation in young and older adults. Post-stimulation, participants and investigators judged whether or not active stimulation was used.
  
  
  RESULTS
  Comfort scores were lower at stimulation onset in both age groups. Older adults reported: (i) more comfort than young participants overall; (ii) comparable levels of comfort in sham and active stimulation; (iii) significantly more comfort than the young participants during active stimulation. Stimulation mode was correctly identified above chance in the second of the two sessions; 65% of all participants correctly identified the stimulation mode, resulting in a statistical trend. Similarly, the experimenter correctly identified stimulation mode significantly above chance, with 62% of all investigator judgements correct across 120 judgements.
  
  
  CONCLUSIONS
  Using 2 mA current strength over 30 minutes, tDCS stimulation comfort is lower at stimulation onset in young and older adults and, overall, lower for young participants. Investigators and participants may be able to identify active stimulation at above chance levels, although accuracy never exceeded 65% for either participants or the experimenter. Further research into blinding efficacy is recommended.
authors.affiliation: Department of Psychology and Centre for Brain Science, University of Essex, Colchester, Essex, United Kingdom.
authors.forename: Denise
authors.initials: D
authors.lastname: Wallace
authors.affiliation: Department of Psychology and Centre for Brain Science, University of Essex, Colchester, Essex, United Kingdom.
authors.forename: Nicholas R
authors.initials: NR
authors.lastname: Cooper
authors.affiliation: Department of Psychology and Centre for Brain Science, University of Essex, Colchester, Essex, United Kingdom.
authors.forename: Silke
authors.initials: S
authors.lastname: Paulmann
authors.affiliation: Monash Alfred Psychiatry Research Centre, Monash University Central Clinical School and The Alfred, Monash University, Melbourne, Australia.
authors.forename: Paul B
authors.initials: PB
authors.lastname: Fitzgerald
authors.affiliation: Department of Psychology and Centre for Brain Science, University of Essex, Colchester, Essex, United Kingdom.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Russo
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D065908:Transcranial Direct Current Stimulation / Q000009:adverse effects / Q000379:methods*