Principal components of the beck depression inventory and regional cerebral metabolism in unipolar and bipolar depression

Background: We determined clustering of depressive symptoms in a combined group of unipolar and patients with bipolar disorder using Principle Components Analysis of the Beck Depression Inventory. Then, comparing unipolars and bipolars, these symptom clusters were examined for interrelationships, and for relationships to regional cerebral metabolism for glucose measured by positron emission tomography. Methods: [18F]-fluoro-deoxyglucose positron emission tomography scans and Beck Depression Inventory administered to 31 unipolars and 27 bipolars, all medication-free, mildly-to-severely depressed. BDI component and total scores were correlated with global cerebral metabolism for glucose, and voxel-by-voxel with cerebral metabolism for glucose corrected for multiple comparisons. Results: In both unipolars and bipolars, the psychomotor-anhedonia symptom cluster correlated with lower absolute metabolism in right insula, claustrum, anteroventral caudate/putamen, and temporal cortex, and with higher normalized metabolism in anterior cingulate. In unipolars, the negative cognitions cluster correlated with lower absolute metabolism bilaterally in frontal poles, and in right dorsolateral frontal cortex and supracallosal cingulate. Conclusions: Psychomotor-anhedonia symptoms in unipolar and bipolar depression appear to have common, largely right-sided neural substrates, and these may be fundamental to the depressive syndrome in bipolars. In unipolars, but not bipolars, negative cognitions are associated with decreased frontal metabolism. Thus, different depressive symptom clusters may have different neural substrates in unipolars, but clusters and their substrates are convergent in bipolars.