Retrograde amnesia

Retrograde amnesia
Classification and external resources
ICD-10	R41.2
ICD-9-CM	780.9
[]

Retrograde amnesia (RA) is a loss of memory-access to events that occurred, or information that was learned, before an injury or the onset of a disease. It tends to negatively affect episodic, autobiographical, and declarative memory while usually keeping procedural memory intact with no difficulty for learning new knowledge. RA can be temporally graded or more permanent based on the severity of its cause and is usually consistent with Ribot's Law: where subjects are more likely to lose memories closer to the traumatic incident than more remote memories. The type of information that is forgotten can be very specific, like a single event, or more general, resembling generic amnesia. It is not to be confused with anterograde amnesia, which deals with the inability to form new memories following the onset of an injury or disease.

The most commonly affected areas are associated with episodic and declarative memory such as the hippocampus, the diencephalon, and the temporal lobes.

Brain plasticity has helped explain the recovery process of brain damage induced retrograde amnesia, where neuro-structures use different neural pathways to avoid the damaged areas while still performing their tasks. Thus, the brain can learn to be independent of the impaired hippocampus, but only to a certain extent. For example, older memories are consolidated over time and in various structures of the brain, including Wernicke's area and the neocortex, making retrieval through alternate pathways possible.

As previously mentioned, RA commonly results from damage to the brain regions most closely associated with episodic and declarative memory, including autobiographical information. In extreme cases, individuals may completely forget who they are. Generally, this is a more severe type of amnesia known as global or generalized amnesia. However, memory loss can also be selective or categorical, manifested by a person's inability to remember events related to a specific incident or topic. Patients also differs in durations of RA (how long they can't recall information) and durations of what is forgotten (past time frame for which information is unavailable).

...
Wikipedia