title: Reaction time variability and related brain activity in methamphetamine psychosis.
abstract: BACKGROUND
  This study investigated the dynamics of cognitive control instability in methamphetamine (MA) abuse, as well its relationship to substance-induced psychiatric symptoms and drug use patterns.
  
  
  METHODS
  We used an ex-Gaussian reaction time (RT) distribution to examine intraindividual variability (IIV) and excessively long RTs (tau) in an individual's RT on a Stroop task in 30 currently drug-abstinent (3 months to 2 years) MA abusers compared with 27 nonsubstance-abusing control subjects. All subjects underwent functional magnetic resonance imaging while performing the Stroop task, which allowed us to measure the relationship between IIV and tau to functional brain activity.
  
  
  RESULTS
  Elevated IIV in the MA compared with the control group did not reach significance; however, when the MA group was divided into those subjects who had experienced MA-induced psychosis (MAP+) (n = 19) and those who had not (n = 11), the MAP+ group had higher average IIV compared with the other groups (p < .03). In addition, although control subjects displayed a relationship between IIV and conflict-related brain activity in bilateral prefrontal cortex such that increased IIV was associated with increased activity, the MAP+ group displayed this relationship in right prefrontal cortex only, perhaps reflecting elevated vigilance in the MAP+ group. Greater IIV did not correlate with severity of use or months MA abstinent. No group differences emerged in tau values.
  
  
  CONCLUSIONS
  These results suggest increased cognitive instability in those MA-dependent subjects who had experienced MA-induced psychosis.
authors.affiliation: Department of Psychiatry and Behavioral Sciences, University of California Davis Medical Center, Davis, California.
authors.forename: Catherine
authors.initials: C
authors.lastname: Fassbender
authors.affiliation: Department of Psychiatry and Behavioral Sciences, University of California Davis Medical Center, Davis, California.
authors.forename: Tyler A
authors.initials: TA
authors.lastname: Lesh
authors.affiliation: Department of Psychiatry and Behavioral Sciences, University of California Davis Medical Center, Davis, California.
authors.forename: Stefan
authors.initials: S
authors.lastname: Ursu
authors.affiliation: Department of Psychiatry and Behavioral Sciences, University of California Davis Medical Center, Davis, California. Electronic address: resalo@ucdavis.edu.
authors.forename: Ruth
authors.initials: R
authors.lastname: Salo
mesh_terms: D000328:Adult; D019969:Amphetamine-Related Disorders / Q000503:physiopathology* / Q000523:psychology; D001921:Brain / Q000187:drug effects / Q000503:physiopathology*; D001931:Brain Mapping; D000697:Central Nervous System Stimulants / Q000008:administration & dosage / Q000009:adverse effects*; D003071:Cognition / Q000187:drug effects / Q000502:physiology; D056344:Executive Function / Q000187:drug effects / Q000502:physiology; D005260:Female; D006801:Humans; D007206:Individuality; D008279:Magnetic Resonance Imaging; D008297:Male; D008694:Methamphetamine / Q000008:administration & dosage / Q000009:adverse effects*; D011605:Psychoses, Substance-Induced / Q000503:physiopathology* / Q000523:psychology; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology*; D057190:Stroop Test
chemical_list: D000697:Central Nervous System Stimulants; D008694:Methamphetamine
keywords: Cognitive Control; Methamphetamine; Psychosis; RT Variability; Stroop; fMRI