Memory Disorders: Amnesia, Hypermnesia, and More

Memory Disorders

Amnesia

Amnesia is the inability to retain or retrieve information, a significant memory disorder. It can stem from organic or emotional causes and may be caused by a shock to the brain.

Chronological Classification of Memory

Anterograde Amnesia

Also called amnesia of fixation, this refers to the inability to learn new information after the onset of a disorder (usually organic) causing amnesia. The patient forgets at the same pace as events unfold. By definition, it concerns recent memory. It is usually reversible, except in some post-traumatic amnesia, Korsakoff syndrome, and irreversible cases of advanced dementia.

Retrograde Amnesia

This is the inability to recall previously learned information after the onset of a disorder (usually organic) causing amnesia. Ribot's law states that memories are lost in reverse order of acquisition; the most recent memories disappear first, followed by more remote ones (childhood memories).

Lacunar Amnesia

Also called localized amnesia, this is memory loss spanning a specific period. This term often describes amnesia surrounding an episode of impaired consciousness, such as drowsiness, confusional states, or coma.

Psychogenic or Dissociative Amnesia

This involves the inability to recall important personal information; it tends to be partial and selective. Onset is sudden and often short-lived, ending abruptly within hours or days. Traumatic biographical events are often precipitants, such as situations involving physical threat or death (accidents, war) or unacceptable events (unexpected breakups, etc.). The extent and scope of amnesia often varies daily and depending on who interviews the patient, but a persistent core of unremembered information remains. Complete and generalized amnesia is rare and usually part of a broader dissociative disorder; if so, it should be classified as such. Accompanying affective states are varied but rarely severe depression. Perplexity, anxiety, and attention-seeking behaviors may be present, but sometimes there is surprisingly quiet acceptance of the disorder. Young adults are most often affected, with extreme examples seen in men under combat stress. Psychogenic dissociative states are rare in older individuals. A related disturbance is psychogenic or dissociative fugue, which adds an inability to remember one's past, along with travel away from home or work and a partial or full change of identity.

Hypermnesia

This refers to an inordinate degree of memory retention and recall.

"Idiots Savants" (wise fools)

Typically children with autism or intellectual disability who possess extraordinary memorization abilities (e.g., memorizing entire phone books or calendars).