Hippocampus volume and episodic memory in schizophrenia

Abstract

Previous studies of schizophrenia have suggested a linkage between neuropsychological (NP) deficits and hippocampus abnormality. The relationship between hippocampus volume and NP functioning was investigated in 24 patients with chronic schizophrenia and 24 matched healthy controls. Overall intracranial, white and gray matter, and anterior (AH) and posterior (PH) hippocampus volumes were assessed from magnetic resonance images (MRI). NP domains of IQ, attention, and executive function were also evaluated with respect to volumetric measures. It was hypothesized that AH and PH volumes and episodic memory scores would be positively associated in controls and that the schizophrenia group would depart from this normative pattern. NP functioning was impaired overall and AH volume was smaller in the schizophrenia group. In the controls, the hippocampus-memory relationships involved AH and PH, and correlations were significant for verbal memory measures. In the schizophrenia group, positive correlations were constrained to PH. Negative correlations emerged between AH and verbal and visual memory measures. For both groups, cortical volume negatively correlated with age, but a negative correlation between age and hippocampus volume was found only in the schizophrenia group. In this sample of adults with schizophrenia, atypical relationships between regional hippocampus volumes and episodic memory ability were found, as was an atypical negative association between hippocampus volume and age.

Fig. 1

A pictorial representation of the steps involved in the hippocampus quantification routine. (1a) Sagittal MRI series is resliced into 1-mm coronal images. (1b) An example of cortical gray matter segmentation. (1c) Cortical mask “overlay” on T1 image. (1d) Hippocampus tissue extracted by trained rater utilizing manual editing to separate the body of the hippocampus from the cortex.

Fig. 2

Standardized representation of cognitive deficits in schizophrenia. Each bar represents mean schizophrenia group score as a z -score relative to normal control mean and standard deviation. For most tests, negative scores indicate a schizophrenia group deficit. Trails A, Trails B, and CPT Overall Deficit measures reflect schizophrenia group deficit in terms of increased time on task.

Fig. 3

The most dramatic correlational group differences were between memory test scores and right anterior and left posterior hippocampus. The scatterplots depict bivariate correlations between the variables (hippocampus volumes are in cc). Blue = control group, green = schizophrenia group.

Fig. 4

Scatterplots represent the significant correlations between age and hippocampus subregional volumes in the schizophrenia group.

Fig. 5

Schizophrenia patients taking atypical antipsychotic medications had larger anterior hippocampi and smaller posterior hippocampi than those taking typical antipsychotic medications.