<b><i>Introduction:</i></b> The hippocampus is relevant to cognitive function in schizophrenia (SCZ) and mood disorder patients. Although not anatomically uniform, it is clearly divided into subfields. This study aimed to elucidate the relationship between hippocampal subfield volume and cognitive function in patients with SCZ, bipolar disorder (BP), and major depressive disorder (MDD). <b><i>Methods:</i></b> The study included 21 patients with SCZ, 22 with BP, and 21 with MDD and 25 healthy controls (HCs). Neurocognitive function was assessed using the Brief Assessment of Cognition in Schizophrenia. We obtained hippocampal subfield volumes using FreeSurfer 6.0. We compared the volumes of the hippocampal subfield between the 4 groups and ascertained correlation between the cognitive composite score and hippocampal subfield volume in each group. <b><i>Results:</i></b> The SCZ group had significantly lower cognitive composite score than the BP, MDD, and HC groups. In the SCZ group, the left and right hippocampus-amygdala transition area and right subiculum and right presubiculum volumes were significantly reduced compared to those in the HC group. The left presubiculum volumes in the SCZ group were significantly reduced compared to those in the MDD group. Subfield volumes did not significantly differ between the BP, MDD, and HC groups. Interestingly, in the SCZ group, volumes of the right CA1, right molecular layer of the hippocampus, and right granule cell and molecular layer of the dentate gyrus were significantly correlated with the cognitive composite score. <b><i>Conclusion:</i></b> Patients with SCZ had poorer cognitive function, which is related to their hippocampal pathology, than those with mood disorders.

Cognitive impairment in schizophrenia and other psychiatric disorders is a challenge to be overcome in order to maintain patients' quality of life and social function. The neurological pathogenesis of cognitive impairment requires further elucidation. In general, the hippocampus interacts between the cortical and subcortical areas for information processing and consolidation and has an important role in memory. We examined the relationship between structural connectivity of the hippocampus and cortical/subcortical areas and cognitive impairment in schizophrenia, major depressive disorder and bipolar disorder. Subjects comprised 21 healthy controls, 19 patients with schizophrenia, 20 patients with bipolar disorder and 18 patients with major depressive disorder. Diffusion-weighted tensor images data were processed using ProbtrackX2 to calculate the structural connectivity between the hippocampus and cortical/ subcortical areas. Cognitive function was assessed using the Brief Assessment of Cognition in schizophrenia composite score. Hippocampal structural connectivity index was significantly correlated with composite score in the schizophrenia

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