Loss of pattern separation performance in schizophrenia suggests dentate gyrus dysfunction

Motivated by evidence that the dentate gyrus differentially mediates the pattern separation (PS) component of declarative memory function and that dentate gyrus harbors molecular and cellular pathologies in schizophrenia, we examined whether PS performance is altered in volunteers with schizophrenia (SZV) relative to healthy volunteers (HV). In groups of well-characterized SZV (n=14) and HV (n=15), we contrasted performance on the Behavioral Pattern Separation (BPS) Task, acquiring two outcome measures, a PS parameter and a Recognition Memory (RM) parameter, as well as specific recognition data by stimulus type. The SZVs showed a significant decrement in PS performance relative to HV (mean ± SEM, SZV: 3.1 ± 2.7%; HV: 17.1 ± 5.8%; p=0.039, d'=0.86); whereas SZV and HV did not significantly differ in RM performance (SZV: 50.1 ± 8.1%; HV: 59.3 ± 5.5%; p=0.350, d'=0.36). Moreover, the SZVs showed a selective defect in correctly identifying similar lure items (SZV: 24.0 ± 3.7%; HV: 41.2 ± 4.6%; p<0.05), but demonstrated no impairment in identifying targets and novel foils. These data suggest that the dentate gyrus is dysfunctional in schizophrenia, a feature that could contribute to declarative memory impairment in the disorder and possibly to psychosis, a conclusion consistent with the considerable molecular pathology in the dentate gyrus in schizophrenia.