Amnestic disorders are broadly defined as a group of conditions that cause memory problems, including the inability to form new memories, loss of ability to access previously formed memories, or difficulties in learning. There are many different specific disorders contained in the category of amnestic disorders that can cause such memory problems. These disorders are further divided into sub-categories, such as anterograde amnesia and retrograde amnesia. The broad category of amnestic disorders is one of many defined in Diagnosis and Statistical Manual of Mental Health Disorders, or DSM-IV, which includes descriptions of all mental disorders recognized by the medical community at the time of each edition publication.
Amnestic disorders, generally speaking, cause amnesia of some form. Two of the main forms of amnesia are anterograde amnesia, which results in the loss or limitation of the ability to form new memories, and retrograde amnesia, which causes the loss of memories already formed. Memory is a highly complex mental process, though, so amnestic disorders need to be defined by far more than just these two categories. Such disorders may, for instance, affect one's memory of his own identity while leaving his recollection of facts and information completely intact. In other cases, an amnestic disorder may affect memories before and after the onset of the disorder, thereby making classification into one or the other of the two categories impossible.
There are many different causes of amnestic disorders, ranging from trauma or substance abuse to disease or a variety of psychological causes. Head injury often causes short-term amnesia surrounding the time of whatever caused trauma, but severe injury can result in more drastic memory problems. Sometimes, psychological rather than physical issues cause amnesia. Some people, for instance, are unable to remember traumatic parts of their childhoods, such as suffering abuse from their parents. This form of amnesia is not strictly limited to one's childhood — traumatic events in one's adult life, such as rape or other forms of violent attack, also may be forgotten in some form of amnestic psychological disorder.
Another possible cause for amnestic disorders is substance abuse. The amnesia caused by substance abuse may be acute or chronic, based on the nature of the substances used and on the duration of abuse. Consuming a great deal of alcohol in a single night, for instance, may result in a "blackout," and the individual may have difficulty recalling the events of the night. Long-term use of various drugs, on the other hand, can have more profound long-term effects on one's memory.