However, predictive biomarkers of response are unknown, and cerebral metabolism may be a good candidate. It is admitted that the depressive state is correlated with specific modifications of glucose metabolism in circuits which are involved in the neurobiology of depression. The amplitude of these changes may correlate with clinical severity or may differ with treatment type, and cerebral metabolic changes might be an additional guide to treatment. Finally, the therapeutic effect might normalize cerebral functional activity and this might be an early correlate of clinical response. However the studies using functional imaging in a therapeutic approach or in the understanding of the physiopathology of the depression are not usable in a clinical practice of routine.