Amnesia

Amnesia is a dissociative psychological disorder manifested by total or partial loss of memory and usually caused by a trauma. Unlike ordinary forgetfulness (the inability to remember a friend's telephone number), amnesia is a serious threat to a person's professional and social life. Amnesia, which depending on its cause can be either organic and psychogenic, has several types.

Global or generalized amnesia indicates the total loss of a person's identity: the individual has forgotten who she or he is. What makes this type of amnesia baffling is the fact that only personal memory is affected. The amnesiac does not remember who he or she is but displays no loss of general knowledge. A person suffering from retrograde amnesia cannot remember events that happened immediately before the trauma. In anterograde amnesia, all events following the trauma are forgotten. Finally, amnesia can also be selective, or categorical, manifested by a person's inability to remember events related to a specific incident.

The causes of amnesia can be physiological and/or psychological. Amnesia caused by physical trauma is called organic amnesia, while the term psychogenic amnesia is used in reference to amnesia caused by psychological trauma.

Organic amnesia

Examples of organic amnesia include cases of memory loss following head injuries, brain lesions, stroke, substance abuse, carbon monoxide poisoning, malnutrition, electro-convulsive therapy, surgery, and infections. Persons suffering from any kind of organic amnesia display a number of typical characteristics. Their memory loss is anterograde: events after the trauma are forgotten. In addition, they can remember the distant past well, but their grasp of the immediate past is tenuous. If treatment is unsuccessful, the amnesiac's condition can worsen, leading to progressive memory loss. In such cases, memory loss is irreversible. If therapy is successful, the patient may partially regain memories blocked by retrograde amnesia, while anterograde amnesia usually remains.

Psychogenic amnesia

The causes of psychogenic amnesia are psychological, and they include career-related stress, economic hardship, and emotional distress. Experts have maintained that psychogenic amnesia has no physiological causes, although recent research has established that emotional trauma may alter the brain physiology, thus setting the stage for the interplay of psychological and physiological factors in the etiology of amnesia. In other words, psychogenic amnesia may have secondary causes that could be defined as organic. The most enigmatic psychogenic amnesia is identity loss; the person affected by this type of amnesia loses all personal memories, while retaining his or her general (impersonal) knowledge. For example, the amnesiac may not know his or her name, but can still be able to speak an acquired second language. Furthermore, in psychogenic amnesia, there is no anterograde memory loss. Finally, although psychogenic amnesia is reversible and can end within hours or days, it is a serious condition that can be difficult to treat.