Amnesias

[Raeanne Dimick]

Amnesia is partial or total inability to recall past experiences or inability to store new memories after the causative event. It may result from traumatic brain injury, degeneration, metabolic disorders, seizures, or psychologic disturbances. Diagnosis is clinical but often includes neuropsychologic testing and brain imaging (eg, CT, MRI). Treatment is directed at the cause.
Processing of memories involves the following:

Registration (taking in new information)
Encoding (forming associations, time stamps, and other processes necessary for retrieval)
Retrieval

Deficits in any of these steps can cause amnesia. Amnesia, by definition, results from impairment of memory functions, not impairment of other functions (eg, attention, motivation, reasoning, language), which may cause similar symptoms.
Amnesia can be classified as follows:

Retrograde: Amnesia for events before the causative event
Anterograde: Inability to store new memories after the causative event
Sense-specific: Amnesia for events processed by one sense—eg, visual memory

Amnesia may be

Transient (as occurs after brain trauma)
Fixed (as occurs after a serious event such as encephalitis, global ischemia, or cardiac arrest)
Progressive (as occurs with degenerative dementias, such as Alzheimer disease)

Memory deficits more commonly involve facts (declarative memory) and, less commonly, skills (procedural memory).