title: Verbal learning impairment in euthymic bipolar disorder: BDI v BDII.
abstract: OBJECTIVE
  Cognitive impairment is known to occur in bipolar disorder (BD), even in euthymic patients, with largest effect sizes often seen in Verbal Learning and Memory Tasks (VLT). However, comparisons between BD Type-I and Type-II have produced inconsistent results partly due to low sample sizes.
  
  
  METHODS
  This study compared the performance of 183 BDI with 96 BDII out-patients on an adapted version of the Rey Verbal Learning Task. Gender, age, years of education, mood scores and age at onset were all used as covariates. Current medication and a variety of illness variables were also investigated for potential effects on VLT performance.
  
  
  RESULTS
  BDI patients were significantly impaired relative to BDII patients on all five VLT outcome measures after controlling for the other variables [Effect Sizes=.13-.17]. The impairments seem to be unrelated to drug treatment and largely unrelated to illness variables, although age of onset affected performance on three outcome measures and number of episodes of mood elevation affected performance on one.
  
  
  CONCLUSIONS
  This study used historical healthy controls. Analysis of potential drug effects was limited by insufficient participants not being drug free. Cross-sectional nature of the study limited the analysis of the potential effect of illness variables.
  
  
  CONCLUSIONS
  This study replicates earlier findings of increased verbal learning impairment in BDI patients relative to BDII in a substantially larger sample. Such performance cannot be wholly explained by medication effects or illness variables. Thus, the cognitive impairment is likely to reflect a phenotypic difference between bipolar sub-types.
authors.affiliation: Department of Psychiatry, University of Oxford, Oxford, UK; Department of Psychology, Counselling & Psychotherapy, Newman University, Birmingham, UK. Electronic address: corin.bourne@psych.ox.ac.uk.
authors.forename: Corin
authors.initials: C
authors.lastname: Bourne
authors.affiliation: Department of Psychiatry, University of Oxford, Oxford, UK.
authors.forename: Amy
authors.initials: A
authors.lastname: Bilderbeck
authors.affiliation: Department of Psychiatry, University of Oxford, Oxford, UK.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Drennan
authors.affiliation: Department of Psychiatry, University of Oxford, Oxford, UK.
authors.forename: Lauren
authors.initials: L
authors.lastname: Atkinson
authors.affiliation: Department of Psychiatry, University of Oxford, Oxford, UK.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Price
authors.affiliation: Department of Psychiatry, University of Oxford, Oxford, UK.
authors.forename: John R
authors.initials: JR
authors.lastname: Geddes
authors.affiliation: Department of Psychiatry, University of Oxford, Oxford, UK.
authors.forename: Guy M
authors.initials: GM
authors.lastname: Goodwin
mesh_terms: D000328:Adult; D001714:Bipolar Disorder / Q000150:complications* / Q000503:physiopathology* / Q000523:psychology; D003072:Cognition Disorders / Q000150:complications / Q000503:physiopathology / Q000523:psychology; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007859:Learning Disabilities / Q000150:complications* / Q000503:physiopathology* / Q000523:psychology; D008297:Male; D008569:Memory Disorders / Q000150:complications / Q000503:physiopathology / Q000523:psychology; D010045:Outpatients; D013647:Task Performance and Analysis; D014706:Verbal Learning / Q000502:physiology*
keywords: Bipolar disorder subtypes; Cognitive impairment; Verbal learning and memory