MedWire News: Bipolar disorder and schizophrenia patients have different patterns of medial temporal lobe (MTL) activation during an emotional memory task, researchers have found.

Although bipolar disorder and schizophrenia are considered to be distinct diagnostic entities, patients may have features of both disorders, and it is not clear which, if any, have diagnostic specificity.

To investigate further, Heather Whalley, from the University of Edinburgh in the UK, and colleagues administered an emotional memory paradigm involving positive and neutral stimuli to 14 bipolar disorder patients, 15 schizophrenia patients, and 14 healthy controls, during which functional magnetic resonance imaging scans of the MTL were obtained.

There were no significant demographic differences among the groups or clinical differences between the patient groups. There were also no significant differences in performance among the three groups on the emotional memory task, or in reaction times, and all three groups showed substantial MTL activation in response to emotional stimuli.

However, bipolar disorder patients had greater increases in activation in the left hippocampus than either schizophrenia patients or controls, as well as increased activation in the right posterior cingulate, left superior temporal sulcus, and left precentral gyrus versus controls and in the left superior temporal sulcus, right inferior parietal lobule, and left cingulate gyrus versus schizophrenia patients.

In contrast, schizophrenia patients had less activation in the bilateral amygdala than controls, while bipolar disorder patients had less activation in the posterior superior temporal sulcus and calcarine sulcus versus controls.

The team notes in the journal Bipolar Disorders that there was a significant positive correlation between mania scores and anterior cingulate activation, and a significant negative correlation between depression scores and dorsolateral prefrontal cortex activation.

They conclude: “As hypothesized, this study demonstrated differential activation of MTL regions in the patient groups.

“These findings add to suggestions that there are distinct neurobiological substrates associated with each disorder.”

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