title: Hippocampal structure and function in individuals with bipolar disorder: a systematic review.
abstract: BACKGROUND
  Bipolar disorder (BD) is a psychiatric disorder accompanied by deficits in declarative memory. Given the importance of the hippocampus in declarative memory, it is not surprising that BD patients have been reported to show hippocampal abnormalities.
  
  
  OBJECTIVE
  Review evidence about structural and functional hippocampal abnormalities in BD.
  
  
  METHODS
  Systematic review of studies comparing BD patients and healthy controls with respect to hippocampal structure or function.
  
  
  RESULTS
  Twenty-five studies were included, together involving 1043 patients, 21 of which compared patients to controls. Decrease in hippocampal volume was found in four of 18 studies using adult samples, and two of three samples using adolescents. Four studies revealed localized hippocampal deficits. Meta-analysis revealed a significant but small effect with lower hippocampal volumes when comparing all BD patients with controls. Lithium treatment was associated with larger hippocampal volumes across studies. The three functional studies yielded contradictory evidence.
  
  
  CONCLUSIONS
  Studies were only cross-sectional in nature and all used MRI or fMRI to investigate hippocampal volume or function. Heterogeneous patients groups and different methodologies for hippocampal segmentation, may have contributed to difficulties when comparing the different studies.
  
  
  CONCLUSIONS
  There seems to be a small reduction in hippocampal volume in BD, which perhaps is more pronounced in early-onset BD and is counteracted by a neuroprotective effect of lithium treatment. However, how these structural abnormalities relate to functional deficits is largely unclear. Given the few functional neuroimaging studies and given the lack of congruence in these results, further investigation of especially hippocampal function in BD is recommended.
authors.affiliation: Department of Cognitive Psychology, VU University Amsterdam, Van der Boechorststraat 1, 1081BT Amsterdam, The Netherlands. Electronic address: mara.otten@vu.nl.
authors.forename: Mara
authors.initials: M
authors.lastname: Otten
authors.affiliation: Department of Cognitive Psychology, VU University Amsterdam, Van der Boechorststraat 1, 1081BT Amsterdam, The Netherlands.
authors.forename: Martijn
authors.initials: M
authors.lastname: Meeter
mesh_terms: D000293:Adolescent; D000328:Adult; D014150:Antipsychotic Agents / Q000627:therapeutic use; D001714:Bipolar Disorder / Q000188:drug therapy / Q000473:pathology* / Q000503:physiopathology* / Q000523:psychology; D003430:Cross-Sectional Studies; D059907:Functional Neuroimaging; D006624:Hippocampus / Q000187:drug effects / Q000473:pathology* / Q000503:physiopathology*; D006801:Humans; D018020:Lithium Compounds / Q000627:therapeutic use; D008279:Magnetic Resonance Imaging; D008568:Memory / Q000187:drug effects; D018696:Neuroprotective Agents / Q000627:therapeutic use; D009929:Organ Size / Q000187:drug effects
chemical_list: D014150:Antipsychotic Agents; D018020:Lithium Compounds; D018696:Neuroprotective Agents
keywords: (f)MRI; Bipolar disorder; Hippocampus; Memory