Frontal lobe dysfunction in secondary depression

Depression is common in patients with neurological disease, particularly with diseases involving the basal ganglia. Although the mechanisms of mood disorders in these patients are poorly understood, selective neural pathways affected directly and indirectly by basal ganglia injury provide a strategy for examining these patients with functional imaging techniques. Studies of regional cerebral glucose metabolism by use of positron-emission tomography are reviewed. These studies demonstrate bilateral hypometabolism of orbital-inferior prefrontal cortex and anterior temporal cortex in depressed subjects, independent of disease etiology. This pattern is similar to that seen in patients with primary unipolar depression. These findings suggest that disruption of paralimbic pathways linking frontal cortex, temporal cortex, and striatum may contribute to both primary depression and depression associated with basal ganglia disease. The findings support the evolving concept of a neuroanatomical locus for mood regulation.