title: Hippocampal activation during associative encoding of word pairs and its relation to symptomatic improvement in depression: a functional and volumetric MRI study.
abstract: BACKGROUND
  Altered emotional memory is one of the core cognitive functions that causes and maintains depression. Although many studies have investigated the relationship between hippocampal volume, depression and treatment response, no studies have investigated the relationship for hippocampal activity. Additionally, few studies have examined the relationship between functional and structural abnormalities in depression.
  
  
  METHODS
  We conducted a functional and volumetric MRI study investigating associative encoding of positive, negative and neutral word pairs in 13 healthy controls, and 14 untreated depressives. We carried out fMRI during a memory-encoding task at baseline. Treatment response was clinically assessed six weeks after pharmacotherapy began. Then, we explored the relation between brain activation during encoding of each word pair and symptomatic improvement.
  
  
  RESULTS
  Relative to controls, depressives exhibited decreased activity in the left hippocampus during encoding positive word pairs and, in contrast, increased activity in the right hippocampus during encoding negative or neutral word pairs. Poor response to treatment was associated with smaller activation within the left hippocampus during the memory encoding of positive word pairs. Overall results were not confounded by hippocampal volume.
  
  
  CONCLUSIONS
  We could not appreciate any disease alteration during the retrieving phase.
  
  
  CONCLUSIONS
  We found qualitative differences in hippocampus functioning between depressives and healthy controls. In addition, the left hippocampus could have an effect on treatment response in depression by contributing to the dysfunctional encoding of positive information.
authors.affiliation: Department of Psychiatry and Neurosciences, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan. Electronic address: shitoki@hiroshima-u.ac.jp.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Toki
authors.forename: Yasumasa
authors.initials: Y
authors.lastname: Okamoto
authors.forename: Keiichi
authors.initials: K
authors.lastname: Onoda
authors.forename: Tomoya
authors.initials: T
authors.lastname: Matsumoto
authors.forename: Shinpei
authors.initials: S
authors.lastname: Yoshimura
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Kunisato
authors.forename: Go
authors.initials: G
authors.lastname: Okada
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Shishida
authors.forename: Makoto
authors.initials: M
authors.lastname: Kobayakawa
authors.forename: Takuji
authors.initials: T
authors.lastname: Fukumoto
authors.forename: Akihiko
authors.initials: A
authors.lastname: Machino
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Inagaki
authors.forename: Shigeto
authors.initials: S
authors.lastname: Yamawaki
mesh_terms: D000328:Adult; D000928:Antidepressive Agents / Q000627:therapeutic use; D001245:Association Learning; D016022:Case-Control Studies; D003865:Major Depressive Disorder / Q000188:drug therapy / Q000473:pathology / Q000503:physiopathology*; D005260:Female; D059907:Functional Neuroimaging; D006624:Hippocampus / Q000473:pathology / Q000503:physiopathology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008568:Memory; D012074:Remission Induction
chemical_list: D000928:Antidepressive Agents
keywords: Associative memory; Depression; Hippocampus; Pharmacotherapy; Treatment response