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Introduction
Cognitive abnormalities occur in bipolar disorder (BP) (Bora, Yucel, & Pantelis, 2010), more severe in attentional and memory domains and also present in euthymic patients.
White matter pathology has been reported by using magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) predominantly in fronto-temporal areas (Bruno, Cercignani, & Ron, 2008) and less frequently gray matter loss in the anterior cingulate and dorsolateral prefrontal cortex (Bruno, Barker, Cercignani, Symms, & Ron, 2004) areas where histopathological changes are known to occur (Beasley, Cotter, & Everall, 2002). The association between cortical abnormalities and cognitive impairment in BP has received limited attention and the same applies the possibility that these associations may be different in patients with BPI who experience manic episodes and psychotic symptoms and those with BPII who do not.
We previously reported, using voxel-based morphometry (VBM) and magnetization transfer ratio (MTR) (Bruno, Papadopoulou, Cercignani, Cipolotti, & Ron, 2006), correlations between IQ change from premorbid levels and abnormalities in the superior temporal, parahippocampal gyri, uncus, and the adjacent white matter particularly in BP II patients. In this exploratory study we investigate associations between cognition and cortical parameters using surface-based morphometry (SBM) (Fischl & Dale, 2000) that measures independently cortical area and thickness. These indices share a high heritability, but are determined by different genetic mechanisms (Panizzon et al., 2009) and may respond differently to disease-related factors. We predicted that cortical thinning would be present in fronto-temporal cortex (Rimol et al., 2010) and associated with cognitive impairment. We also explored possible differences in cortico-cognitive associations in BP subgroups.
Methods
Subjects
Thirty-six patients meeting Diagnostic And Statistical Manual-IV (DSM-IV) criteria for BP were included in the study. Twenty-five were recruited from inner-London psychiatric clinics and 11 from respondents to an advertisement in the Journal of the Manic-Depressive Fellowship. Exclusion criteria were previous or current Axis I comorbidity, history of neurological or systemic disease, head injury leading to unconsciousness, and previous history of substance abuse.
Imaging and neuropsychological findings in this cohort have previously been reported (Bruno et al., 2004, 2006, 2008; Summers et al., 2006). The study was approved by the Joint Research Ethics Committee of the National Hospital for Neurology and Neurosurgery and UCL Institute of Neurology. Written informed consent...