  Background: People with bipolar disorder (BD) tend to show widespread
cognitive impairment compared to healthy controls. Impairments in processing
speed (PS), attention, and executive function (EF) may represent 'core'
impairments that have a role in wider cognitive dysfunction. Cognitive
impairments appear to relate to structural brain abnormalities in BD, but
whether core deficits are related to particular brain regions is unclear and
much of the research on brain-cognition associations is limited by univariate
analysis and small samples.
  Methods: Euthymic BD patients (n=56) and matched healthy controls (n=26)
underwent T1-weighted MRI scans and completed neuropsychological tests of PS,
attention, and EF. We utilised public datasets to develop a normative model of
cortical thickness (n=5,977) to generate robust estimations of cortical
abnormalities in patients. Canonical correlation analysis was used to assess
multivariate brain-cognition associations in BD, controlling for age, sex, and
premorbid IQ.
  Results: BD showed impairments on tests of PS, attention, and EF, and
abnormal cortical thickness in several brain regions compared to healthy
controls. Impairments in tests of PS and EF were most strongly associated with
cortical thickness in left inferior temporal, right entorhinal, and right
temporal pole areas.
  Conclusion: Impairments in PS, attention, and EF can be observed in euthymic
BD and may be related to abnormal cortical thickness in temporal regions.
Future research should continue to leverage multivariate methods to examine
complex brain-cognition associations in BD. Future research may benefit from
exploring covariance between traditional brain structural morphological metrics
such as cortical thickness, cortical volume, and surface area.
