Objective: Using functional magnetic resonance imaging (fMRI) researchers in recent years have identified changes in patients with mood disorders. Brain regions known to be involved in emotional circuitry have been implicated in network dysfunction. The majority of comparisons have been conducted in relation to healthy subjects and only a handful of studies have attempted to partition unipolar and bipolar depressed patients. The aim of this study is to differentiate unipolar and bipolar patients using fMRI.

Method: 17 patients with bipolar I disorder and 15 with unipolar major depression were recruited through the CADE Clinic and through advertisement and compared with 21 age and gender matched controls. An affective word paradigm known to reliably elicit emotional changes was used to reliably induce positive and negative moods. Studies were conducted on a research-dedicated three Tesla Siemens scanner (ARCHI).

Results: Robust activations in response to emotion especially negative mood were observed in all three groups. Activations involved prefrontal and sub cortical structures implicated in emotional networks and a marked difference in responses was found with unipolar depressed patients having greater activations than healthy controls who in turn had greater activations than bipolar depressed patients.

Conclusions: The differential pattern of responsivity on fMRI across phenotypes of mood disorders is a promising preliminary finding. The different patterns of activation on fMRI in unipolar and bipolar subjects, suggests that there are functional differences in emotion processing between these phenotypes that could potentially provide diagnostic differentiation.