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Concept
Retrograde amnesia
Résumé
In neurology, retrograde amnesia (RA) is the inability to access memories or information from before an injury or disease occurred. RA differs from a similar condition called anterograde amnesia (AA), which is the inability to form new memories following injury or disease onset. Although an individual can have both RA and AA at the same time, RA can also occur on its own; this 'pure' form of RA can be further divided into three types: focal, isolated, and pure RA. RA negatively affects an individual's episodic, autobiographical, and declarative memory, but they can still form new memories because RA leaves procedural memory intact. Depending on its severity, RA can result in either temporally graded or more permanent memory loss. However, memory loss usually follows Ribot's law, which states that individuals are more likely to lose recent memories than older memories. Diagnosing RA generally requires using an Autobiographical Memory Interview (AMI) and observing brain structure through magnetic resonance imaging (MRI), a computed tomography scan (CT), or electroencephalography (EEG).
Memory loss in patients with temporally graded RA strongly follows Ribot's law, meaning that one will experience more memory loss for events closer to the injury or disease onset. This type of RA is commonly triggered in individuals with Korsakoff syndrome due to a combination of long-term alcohol use and Wernicke encephalopathy. Debate has risen about why this temporal gradient forms in the first place. Initial theories proposed that the hippocampus and medial temporal lobe are not nearly as important for long-term memories compared to short-term memories. As memory processing occurs in the brain over time, neocortical regions can directly communicate with each other, so they do not rely as heavily on the hippocampus for long-term memory storage. Therefore, if an individual experiences RA that damages the hippocampus, they will lose more short-term memories according to this theory.
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