title: Perceived mental effort correlates with changes in tonic arousal during attentional tasks.
abstract: BACKGROUND
  It has been suggested that perceived mental effort reflects changes in arousal during tasks of attention. Such changes in arousal may be tonic or phasic, and may be mediated by the locus-coeruleus norepinephrine (LC-NE) system. We hypothesized that perceived mental effort during attentional tasks would correlate with tonic changes in cortical arousal, as assessed by relative electroencephalogram (EEG) band power and theta/beta ratio, and not with phasic changes in cortical arousal, assessed by P300 amplitude and latency.
  
  
  METHODS
  Forty-six healthy individuals completed tasks that engage the anterior and posterior attention networks (continuous performance task, go/no-go task, and cued target detection task). During completion of the three attentional tasks a continuous record of tonic and phasic arousal was taken. Cortical measures of arousal included frequency band power, theta/beta ratios over frontal and parietal cortices, and P300 amplitude and latency over parietal cortices. Peripheral measures of arousal included skin conductance responses, heart rate and heart rate variance. Participants reported their perceived mental effort during each of the three attentional tasks.
  
  
  RESULTS
  First, changes in arousal were seen from rest to completion of the three attentional tasks and between the attentional tasks. Changes seen between the attentional tasks being related to the task design and the attentional network activated. Second, perceived mental effort increased when demands of the task increased and correlated with left parietal beta band power during the three tasks of attention. Third, increased mental effort during the go/no-go task and the cued target detection task was inversely related to theta/beta ratios.
  
  
  CONCLUSIONS
  These results indicate that perceived mental effort reflects tonic rather than phasic changes in arousal during tasks of attention. We suggest that perceived mental effort may reflect in part tonic activity of the LC-NE system in healthy individuals.
authors.affiliation: Department of Psychiatry and Mental Health, Faculty of Health Sciences, University of Cape Town, Observatory 7925, South Africa. Fleur.Howells@uct.ac.za
authors.forename: Fleur M
authors.initials: FM
authors.lastname: Howells
authors.forename: Dan J
authors.initials: DJ
authors.lastname: Stein
authors.forename: Vivienne A
authors.initials: VA
authors.lastname: Russell
mesh_terms: D000328:Adult; D001143:Arousal / Q000502:physiology*; D001288:Attention / Q000502:physiology*; D001611:Beta Rhythm; D001921:Brain / Q000502:physiology*; D004569:Electroencephalography; D018913:Event-Related Potentials, P300; D005260:Female; D005625:Frontal Lobe / Q000502:physiology; D005712:Galvanic Skin Response / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism; D008297:Male; D008606:Mental Processes / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology; D009483:Neuropsychological Tests; D010296:Parietal Lobe / Q000502:physiology; D010507:Periodicity; D012463:Saliva / Q000378:metabolism; D013826:Theta Rhythm
chemical_list: D006854:Hydrocortisone