The neurological interest on functional or psychogenic disorders (mental or physical disturbances with no organic basis, generally unleashed by stressful situations) has been receiving increasingly more interest over the last few years. In this article we review concepts, terms and classifications of these disorders, very different over time and among different authors. Psychogenic disorders are divided into: a) dissociation (with memory, consciousness and self-identity impairment), and b) disturbances with somatizations, divided into somatoform (unconscious), factitious (voluntary search for patient's role) and malingering (searching for material gain). Special emphasis is placed on conversion or hysteria, included in somatoform disorders. New findings in functional neuroimaging are analyzed. These new data suggest an important role of unconscious and involuntary inhibition in loss of volition (similar to hypnosis and different from malingering). Normal activity in certain brain areas (motor or sensory cortex) is blocked by other areas related to emotional integration (anterior cingular and orbitofrontal cortex). The neurologist's role is important to achieve an early diagnosis of psychogenic disturbances, particularly conversive ones. This means the use of fewer economic resources and better prognosis for the patient.