Imaging strategies in depression.

Functional brain imaging in depressive disorder aims to map brain areas associated with depressive illness or to define the neurochemical correlates of the illness and its treatment. Regional deficits of functional (neural) activity has been consistently detected in the brains of subjects with ongoing affective symptoms, particularly in prefrontal areas. Understanding how these prefrontal deficits can be related to neuroanatomical circuitry, neurochemistry and normal cognitive functions is the major challenge in taking these findings forward. Although many neurochemical systems remain to be adequately imaged in vivo, significant progress has been made in the development of relevant radiotracers, particularly for select serotonin and dopamine receptor subtypes. For the future, functional brain imaging of the neurochemistry associated with core symptoms and treatment responses will be necessary for an adequate description of the pathophysiology of depressive illness.