Association between hippocampal volume and P300 event related potential in psychosis: support for the Kraepelinian...

Abnormalities of the P300 event related potential (ERP) and of hippocampal structure are observed in individuals with psychotic disorders and their unaffected relatives. The understanding and clinical management of psychotic disorders are largely based on the descriptive Kraepelinian distinction between 'dementia praecox' and 'manic depressive psychosis', and not dependant on any well demarcated biological underpinnings. The hippocampus is postulated to be one of the main P300 generators, yet it remains unknown whether hippocampal volume decrements are associated with P300 deficits in psychosis, and whether any association is shared across non-affective and affective psychotic disorders.

228 subjects from the Maudsley Family Psychosis Study comprising 55 patients with non-affective psychosis, 23 patients with psychotic bipolar disorder, 98 unaffected relatives, and 52 unrelated controls contributed structural MRI and ERP data. To study the relationship between hippocampal volume and P300 ERP, a seemingly unrelated regression methodology was used, accounting for whole brain volumes, clinical groups, age and gender in the analysis.

An association between left hippocampal volume and P300 latency in the combined sample comprising non-affective and affective psychotic patients, their relatives and controls was observed. There was an inverse relationship between brain structure and function in that prolongation of P300 latencies was associated with smaller left hippocampal volumes. On subdividing the sample based on Kraepelinian dichotomy, this association remained significant only for the non-affective psychosis group, comprising patients and their unaffected relatives.

Based on our findings, P300 latency, a measure of the speed of neural transmission, appears to be related to the size of the left hippocampus in schizophrenia, but not in psychotic bipolar disorder. It seems that underlying neuro-biological characteristics could help in unravelling the traditional Kraepelinian differentiation between the two major psychoses. The specificity of this brain structure-function association for schizophrenia opens the scope for further research using integration of multimodal biological data for objective categorisation of psychosis.