Despite an exclusively biological approach to psychological phenomena proved to be useful in understanding their biological substrates and of heuristic value in finding new treatments, this approach is not to be intended as comprehensive. The psychodynamic approach allows for investigating the mechanisms of instinctual drives involved in the development of the personality of an individual, which underlies his/her behavior. These mechanisms are strongly influenced by his/her current and past experiences. The consideration and explanation of these mechanisms by purely biological approaches may be only partial and reductionist.