Neuroanatomical circuits in depression: implications for treatment mechanisms

We previously investigated the functional neuroanatomy of familial pure depressive disease (FPDD) using positron emission tomography (PET) measurements of regional blood flow and obtained evidence that flow is increased in the left prefrontal cortex, amygdala, and medial thalamus and is decreased in the medial caudate. These data along with other evidence suggested that circuits involving the prefrontal cortex, amygdala, and related parts of the striatum, pallidum, and medial thalamus are involved in the pathophysiology of FPDD. One of these circuits, the limbic-thalamo-cortical circuit, which includes the amygdala, the medio-dorsal thalamus, and parts of the ventral and medial prefrontal cortex, may be engaged in abnormal reverberatory activity that maintains the cognitive and emotional set of depression. Using this hypothesis as a neural model to investigate antidepressant treatment mechanisms, we review evidence that the changes in dopaminergic, serotonergic, and noradrenergic function induced by somatic antidepressant therapies may yield modulatory effects on limbic-thalamo-cortical activity. We also discuss preliminary findings of treatment-associated changes in this circuit in studies comparing PET images acquired before and during antidepressant treatment.