[Are we able to measure depression?].

Etiologically and symptomatically, depression is a profoundly heterogeneous disorder. Symptoms may be classified as either emotional or cognitive. Fear, seeking and panic/grief primary emotional circuits are involved at variable intensities. Cognitive symptoms are mostly associated with executive functions' problems. Different symptoms may be linked with specific cerebral circuits dysfunctions. However, because of their heterogeneity, it seems difficult to measure depression with biological methods (cerebral imagery and evoked potentials), as if it were a one-dimensional phenomenon. Clinical impression remains the main evaluation tool for depressive patients. Psychometric scales may be useful to evaluate the efficacy of treatments and to strengthen relationship with the therapist. Hamilton Depression Scale, Montgomery and Asberg Depression Scale and Beck Depression Inventory are the most used ones. We recommend the last one, as it is reliable and easy to use in clinical settings.