title: Ventral striatum activity in response to reward: differences between bipolar I and II disorders.
abstract: OBJECTIVE
  Little is known about the neurobiology of bipolar II disorder. While bipolar I disorder is associated with abnormally elevated activity in response to reward in the ventral striatum, a key component of reward circuitry, no studies have compared reward circuitry function in bipolar I and bipolar II disorders. Furthermore, associations among reward circuitry activity, reward sensitivity, and striatal volume remain underexplored in bipolar and healthy individuals. The authors examined reward activity in the ventral striatum in participants with bipolar I and II disorders and healthy individuals, the relationships between ventral striatal activity and reward sensitivity across all participants, and between-group differences in striatal gray matter volume and relationships with ventral striatal activity across all participants.
  
  
  METHODS
  Twenty healthy comparison subjects and 32 euthymic bipolar I (N=17) and bipolar II (N=15) patients underwent a neuroimaging reward paradigm during functional MRI scanning, structural scanning, and completed psychometric and clinical assessments.
  
  
  RESULTS
  Region-of-interest analyses revealed significant ventral striatal activity in all participants during reward anticipation that was significantly greater in bipolar II patients compared with the other groups. Ventral striatal activity during reward anticipation correlated positively with reward sensitivity and fun seeking across all participants. Bipolar II patients had significantly greater left putamen volume than bipolar I patients, and left putamen volume correlated positively with left ventral striatal activity to reward anticipation in all participants.
  
  
  CONCLUSIONS
  Abnormally elevated ventral striatal activity during reward anticipation may be a potential biomarker of bipolar II disorder. These findings highlight the importance of adopting a dimensional approach in the study of neural mechanisms supporting key pathophysiological processes that may cut across psychiatric disorders.
authors.affiliation: MRC Center for Neuropsychiatric Genetics and Genomics, Institute of Psychological Medicine and Clinical Neurosciences, Cardiff University, UK. caserasx@cardiff.ac.uk
authors.forename: Xavier
authors.initials: X
authors.lastname: Caseras
authors.forename: Natalia S
authors.initials: NS
authors.lastname: Lawrence
authors.forename: Kevin
authors.initials: K
authors.lastname: Murphy
authors.forename: Richard G
authors.initials: RG
authors.lastname: Wise
authors.forename: Mary L
authors.initials: ML
authors.lastname: Phillips
mesh_terms: D000328:Adult; D059031:Anticipation, Psychological; D014150:Antipsychotic Agents / Q000008:administration & dosage; D001479:Basal Ganglia / Q000503:physiopathology*; D001714:Bipolar Disorder / Q000175:diagnosis / Q000473:pathology / Q000503:physiopathology*; D001931:Brain Mapping; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D006984:Hypertrophy / Q000473:pathology; D008279:Magnetic Resonance Imaging; D008297:Male; D011569:Psychiatric Status Rating Scales; D011699:Putamen / Q000473:pathology; D012201:Reward
chemical_list: D014150:Antipsychotic Agents
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