title: Neurocognitive intra-individual variability in mood disorders: effects on attentional response time distributions.
abstract: BACKGROUND
  Attentional impairment is a core cognitive feature of major depressive disorder (MDD) and bipolar disorder (BD). However, little is known of the characteristics of response time (RT) distributions from attentional tasks. This is crucial to furthering our understanding of the profile and extent of cognitive intra-individual variability (IIV) in mood disorders.
  
  
  METHODS
  A computerized sustained attention task was administered to 138 healthy controls and 158 patients with a mood disorder: 86 euthymic BD, 33 depressed BD and 39 medication-free MDD patients. Measures of IIV, including individual standard deviation (iSD) and coefficient of variation (CoV), were derived for each participant. Ex-Gaussian (and Vincentile) analyses were used to characterize the RT distributions into three components: mu and sigma (mean and standard deviation of the Gaussian portion of the distribution) and tau (the 'slow tail' of the distribution).
  
  
  RESULTS
  Compared with healthy controls, iSD was increased significantly in all patient samples. Due to minimal changes in average RT, CoV was only increased significantly in BD depressed patients. Ex-Gaussian modelling indicated a significant increase in tau in euthymic BD [Cohen's d = 0.39, 95% confidence interval (CI) 0.09-0.69, p = 0.011], and both sigma (d = 0.57, 95% CI 0.07-1.05, p = 0.025) and tau (d = 1.14, 95% CI 0.60-1.64, p < 0.0001) in depressed BD. The mu parameter did not differ from controls.
  
  
  CONCLUSIONS
  Increased cognitive variability may be a core feature of mood disorders. This is the first demonstration of differences in attentional RT distribution parameters between MDD and BD, and BD depression and euthymia. These data highlight the utility of applying measures of IIV to characterize neurocognitive variability and the great potential for future application.
authors.affiliation: Institute of Neuroscience,Newcastle University,Newcastle upon Tyne,UK.
authors.forename: P
authors.initials: P
authors.lastname: Gallagher
authors.affiliation: Institute of Neuroscience,Newcastle University,Newcastle upon Tyne,UK.
authors.forename: J
authors.initials: J
authors.lastname: Nilsson
authors.affiliation: Institute of Neuroscience,Newcastle University,Newcastle upon Tyne,UK.
authors.forename: A
authors.initials: A
authors.lastname: Finkelmeyer
authors.affiliation: Institute of Neuroscience,Newcastle University,Newcastle upon Tyne,UK.
authors.forename: M
authors.initials: M
authors.lastname: Goshawk
authors.affiliation: South London and Maudsley NHS Foundation Trust,London,UK.
authors.forename: K A
authors.initials: KA
authors.lastname: Macritchie
authors.affiliation: Institute of Neuroscience,Newcastle University,Newcastle upon Tyne,UK.
authors.forename: A J
authors.initials: AJ
authors.lastname: Lloyd
authors.affiliation: Institute of Neuroscience,Newcastle University,Newcastle upon Tyne,UK.
authors.forename: J M
authors.initials: JM
authors.lastname: Thompson
authors.affiliation: Department of Psychological Medicine,University of Otago,Christchurch,New Zealand.
authors.forename: R J
authors.initials: RJ
authors.lastname: Porter
authors.affiliation: King's College London,Institute of Psychiatry,Psychology and Neurosciences,London,UK.
authors.forename: A H
authors.initials: AH
authors.lastname: Young
authors.affiliation: Institute of Neuroscience,Newcastle University,Newcastle upon Tyne,UK.
authors.forename: I N
authors.initials: IN
authors.lastname: Ferrier
authors.affiliation: Institute of Neuroscience,Newcastle University,Newcastle upon Tyne,UK.
authors.forename: R H
authors.initials: RH
authors.lastname: McAllister-Williams
authors.affiliation: Institute of Neuroscience,Newcastle University,Newcastle upon Tyne,UK.
authors.forename: S
authors.initials: S
authors.lastname: Watson
mesh_terms: D000328:Adult; D001288:Attention; D001714:Bipolar Disorder / Q000523:psychology*; D016022:Case-Control Studies; D003863:Depression; D003865:Major Depressive Disorder / Q000523:psychology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D019964:Mood Disorders / Q000523:psychology*; D009483:Neuropsychological Tests; D016011:Normal Distribution; D011569:Psychiatric Status Rating Scales; D011930:Reaction Time; D012720:Severity of Illness Index; D055815:Young Adult
keywords: Attention; bipolar disorder; ex-Gaussian analyses; major depression; neuropsychology; variability