title: Long-term and within-day variability of working memory performance and EEG in individuals.
abstract: OBJECTIVE
  Assess individual-subject long-term and within-day variability of a combined behavioral and EEG test of working memory.
  
  
  METHODS
  EEGs were recorded from 16 adults performing n-back working memory tasks, with 10 tested in morning and afternoon sessions over several years. Participants were also tested after ingesting non-prescription medications or recreational substances. Performance and EEG measures were analyzed to derive an Overall score and three constituent sub-scores characterizing changes in performance, cortical activation, and alertness from each individual's baseline. Long-term and within-day variability were determined for each score; medication effects were assessed by reference to each individual's normal day-to-day variability.
  
  
  RESULTS
  Over the several year period, the mean Overall score and sub-scores were approximately zero with standard deviations less than one. Overall scores were lower and their variability higher in afternoon relative to morning sessions. At the group level, alcohol, diphenhydramine and marijuana produced significant effects, but there were large individual differences.
  
  
  CONCLUSIONS
  Objective working memory measures incorporating performance and EEG are stable over time and sensitive at the level of individual subjects to interventions that affect neurocognitive function.
  
  
  CONCLUSIONS
  With further research these measures may be suitable for use in individualized medical care by providing a sensitive assessment of incipient illness and response to treatment.
authors.affiliation: San Francisco Brain Research Institute & SAM Technology, San Francisco, CA 94131, United States. alan@sfbri.org
authors.forename: Alan
authors.initials: A
authors.lastname: Gevins
authors.forename: Linda K
authors.initials: LK
authors.lastname: McEvoy
authors.forename: Michael E
authors.initials: ME
authors.lastname: Smith
authors.forename: Cynthia S
authors.initials: CS
authors.lastname: Chan
authors.forename: Lita
authors.initials: L
authors.lastname: Sam-Vargas
authors.forename: Cliff
authors.initials: C
authors.lastname: Baum
authors.forename: Aaron B
authors.initials: AB
authors.lastname: Ilan
mesh_terms: D000328:Adult; D002110:Caffeine / Q000494:pharmacology; D002188:Cannabis; D002940:Circadian Rhythm / Q000502:physiology*; D003071:Cognition / Q000187:drug effects / Q000502:physiology*; D004155:Diphenhydramine / Q000494:pharmacology; D004569:Electroencephalography; D000431:Ethanol / Q000494:pharmacology; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008570:Memory, Short-Term / Q000187:drug effects / Q000502:physiology*; D008875:Middle Aged; D013647:Task Performance and Analysis; D013997:Time Factors
chemical_list: D002110:Caffeine; D000431:Ethanol; D004155:Diphenhydramine