Working memory dysfunctions are considered to be promising intermediate phenotypes, i.e. biological markers, which may help to discover genetic and pathophysiological factors involved in the pathogenesis of schizophrenic and affective psychoses. However, little is known about the possible role of these brain dysfunctions for differential diagnosis, for instance between schizophrenia and bipolar affective disorder. In the present study we directly compared brain activation during verbal working memory task performance in matched groups of schizophrenic and bipolar patients as well as healthy controls.

12 schizophrenic patients, 14 bipolar patients and 14 healthy controls underwent fMRI during a delayed matching to sample task requiring the maintenance of verbal information in working memory. Data were preprocessed and statistically analyzed using standard procedures as implemented in SPM2.

Both schizophrenic and bipolar patients exhibited significantly increased activation in bilateral dorsolateral prefrontal cortex and in right intraparietal cortex. Abnormal hyperactivations that were unique to either schizophrenia or bipolar disorder were found in bilateral caudate nucleus and the right amygdala, respectively.

Compatible with findings from genetic research into the pathogenesis of schizophrenia and bipolar disorder, the present data show both similarities and significant differences between these two diagnostic categories regarding the patterns of abnormal brain activation that may underlie verbal working memory deficits in these patients.