"Etiological commonalities are apparent between bipolar disorder and schizophrenia. For example, it is becoming clear that both populations show similar electrophysiological deficits in the auditory domain," scientists in the United States report (see also Bipolar Disorder).

"Recent studies have also shown robust visual sensory processing deficits in patients with schizophrenia using the event-related potential technique, but this has not been formally tested in those with bipolar disorder. Our goal here was to assess whether early visual sensory processing in patients with bipolar disorder, as indexed by decreased amplitude of the P1 component of the visual evoked potential (VEP), would show a similar deficit to that seen in those with schizophrenia. Since the P1 deficit has already been established as an endophenotype in schizophrenia, a finding of commonality between disorders would raise the possibility that it represents a measure of common genetic liability. We visually presented isolated-check stimuli to euthymic patients with a diagnosis of bipolar disorder and age-matched healthy controls within a simple go/no-go task and recorded VEPs using high-density (72-channel) electroencephalography. The P1 VEP amplitude was substantially reduced in patients with bipolar disorder, with an effect size of f = 0.56 (large according to Cohen's criteria). Limitations: Our sample size was relatively small and as such, did not allow for an examination of potential relations between the physiologic measures and clinical measures. This reduction in P1 amplitude among patients with bipolar disorder represents a dysfunction in early visual processing that is highly similar to that found repeatedly in patients with schizophrenia and their healthy first-degree relatives," wrote S. Yeap and colleagues, City University of New York.

The researchers concluded: "Since the P1 deficit has been related to susceptibility genes for schizophrenia, our results raise the possibility that the deficit may in fact be more broadly related to the development of psychosis and that it merits further investigation as a candidate endophenotype for bipolar disorder."

Yeap and colleagues published their study in the Journal of Psychiatry & Neuroscience (Visual sensory processing deficits in patients with bipolar disorder revealed through high-density electrical mapping. Journal of Psychiatry & Neuroscience, 2009;34(6):459-464).

For more information, contact J.J. Foxe, City University of New York, Program Cognitive Neuroscience, Dept. of Psychology, 138th St. & Convent Avenue, New York City, NY 10031, USA.

Publisher contact information for the Journal of Psychiatry & Neuroscience is: CMA-Canadian Medical Association, 1867 Alta Vista Dr., Ottawa, Ontario K1G 3Y6, Canada.