Organic Amnesia
Organic amnesia is memory loss resulting from a physical disturbance of brain function, rather than a psychological process. Its presentation varies considerably depending on the nature and course of the underlying brain disturbance, ranging from the brief, circumscribed memory gaps of an acute head injury, to a persisting amnestic state following an episode of more sustained brain disease, to the slowly widening amnesia of a chronic, progressive brain disease.
This has traditionally been considered alongside the clinical course of the underlying brain disturbance — acute, subacute, or chronic — since the pattern and extent of memory loss tends to track closely with that course.
Recognition features
- A physical, identifiable disturbance of brain function underlies the memory loss
- The specific pattern (a brief gap around an injury, a persisting inability to form new memories, or a widening loss of older memories over years) reflects the nature and course of the underlying disturbance
- Personal identity is typically less affected than in dissociative amnesia, even when the memory disturbance is severe
- Often accompanied by other neurological or cognitive findings relevant to the underlying cause
Eliciting it at interview
- Establish the time course carefully: sudden onset around a specific event, a persisting inability to lay down new memories, or a gradual, progressive widening of the gap over months or years all point toward different underlying processes
- Test both the ability to recall material from before the presumed onset and the ability to learn and retain new material, since these can be affected differently
- Take a full medical and substance use history, and consider appropriate investigation, given the range of possible underlying organic causes
Distinguishing features
- Differs from dissociative amnesia in that personal identity is typically less affected, even when the memory impairment is otherwise severe
- The specific sub-type (an amnesia tied to a discrete injury, a persisting amnestic state, or a slowly progressive pattern) is distinguished mainly by its time course and the extent of what is affected
- Should not be diagnosed as a discrete amnestic state when other signs of broader cognitive impairment (as in dementia) or clouded consciousness (as in delirium) are also present
Common misconceptions
- That organic amnesia always means a progressive, worsening condition; some forms, particularly those following acute injury, can improve substantially or even resolve
- That memory loss following a head injury is always permanent; the amnestic period can shrink considerably as recovery occurs
Related phenomena
Amnesia · Retrograde Amnesia · Anterograde Amnesia · Amnestic State
Practice this
Following a significant head injury with confirmed structural brain damage, a patient has a persisting, severe difficulty forming new memories, while her sense of who she is and her social behaviour remain essentially intact and recognisable to those who know her. What is this? · A patient with no history of head injury or physical illness suddenly cannot recall her own name, family, or personal history following a traumatic event, while still being able to drive, hold a coherent conversation, and manage everyday tasks competently. Before revealing the answer: is this organic amnesia? · A patient presents with significant memory loss. Before revealing the answer, decide what distinguishes organic amnesia from dissociative amnesia. · A patient presents with memory difficulties following a known physical illness or injury. Before revealing the answer, decide how you would assess whether this is organic amnesia. · Explain why the preservation or loss of personal identity is considered such a clinically important distinguishing feature between organic and dissociative amnesia.
Illustration
Following a motorcycle accident, a 27-year-old man has no memory of the collision itself or of the several hours immediately afterward, though his memory of the weeks and years before the accident, and his memory from the following day onward, are both entirely intact.
References
- Casey, P. & Kelly, B. (2019). Fish's Clinical Psychopathology, 4th ed. Ch. 5, 'Disorders of Memory'.