Memory › Amnesia › Organic Amnesia

Anterograde Amnesia

Anterograde amnesia is a difficulty forming new memories for events happening after an injury or the onset of a brain disturbance, reflecting a failure to properly encode new experiences into long-term memory. During the affected period the person may seem to be interacting normally, but afterward has no memory of what took place.

This has traditionally been distinguished from retrograde amnesia purely by direction in time — retrograde affects memories formed before the injury, anterograde affects the formation of new memories afterward — and the two frequently occur together following the same event.

Also known as

Blackout

A circumscribed period of anterograde amnesia, most often experienced by people who are alcohol dependent during and after a bout of heavy drinking, but also seen in delirium.

Recognition features

• Difficulty or inability to form new, lasting memories for the period following an injury or the onset of a brain disturbance
• The person may behave and respond appropriately during the affected period, despite having no later memory of it
• Most commonly caused by accidents, but also well recognised in the setting of heavy alcohol use (blackouts) and acute confusional states
• Can vary considerably in length, from minutes to many hours

Eliciting it at interview

• Ask what the person can recall from a period known to have occurred, such as a hospital admission, and compare their account with what is documented to have happened
• Where alcohol use is relevant, ask specifically and non-judgementally about blackouts: periods of drinking they cannot recall afterward despite reportedly functioning at the time
• Assess level of consciousness and attention during the period in question, since disorders such as delirium can also underlie a blackout-like presentation

Distinguishing features

• Differs from retrograde amnesia in affecting the formation of new memories going forward rather than the retrieval of memories formed beforehand
• A blackout specifically reflects a failure of encoding during a period of impaired brain function (from alcohol or delirium), even though behaviour during that period can appear largely normal to an observer
• Reversibility is an important feature to establish: blackouts and post-injury anterograde amnesia typically indicate reversible disruption, unlike the more sustained amnestic state seen in some other organic conditions

Common misconceptions

• That a person who behaved normally during a period they cannot later recall must be lying about the memory gap; encoding failure with preserved momentary functioning is a well-recognised and genuine pattern
• That blackouts always reflect an extremely high level of intoxication; they can occur at levels of drinking below what an observer might expect

Related phenomena

Organic Amnesia · Retrograde Amnesia · Amnestic State

Practice this

Following a head injury, a woman is alert and able to hold ordinary conversations, but the following day has no memory at all of anything from the several hours immediately after regaining consciousness, despite having behaved and responded appropriately throughout that period. What is this? · A man recalls, in detail, everything that happened up to and including the moment of his accident, but has no memory of the several hours immediately afterward, during which witnesses say he was talking and behaving normally. Before revealing the answer: is this retrograde or anterograde amnesia, and what does the witnesses' account add? · A patient with a head injury has a memory gap. Before revealing the answer, decide what single question settles whether this is anterograde or retrograde amnesia. · A patient with a head injury has a memory gap. Before revealing the answer, decide what single question settles whether this is retrograde or anterograde amnesia. · You are assessing a patient shortly after a head injury and want to establish whether they have anterograde amnesia. Before revealing the answer, decide how you would assess for it. · Explain why a patient with anterograde amnesia can appear to behave completely normally during the affected period, despite having no later memory of it at all.

Illustration

A 38-year-old man is told by friends that he attended a dinner party the previous evening, held a lengthy conversation, and left without incident, none of which he has any memory of at all, though he recalls the earlier part of the evening and everything from waking the next morning onward with complete clarity.

References

• Casey, P. & Kelly, B. (2019). Fish's Clinical Psychopathology, 4th ed. Ch. 5, 'Disorders of Memory'.