Doctors diagnose retrograde amnesia when a patient cannot recall memories that happened before the event that caused the amnesia. In most cases, memories from immediately before the event are affected, not those from years ago, meaning that childhood memories and those from decades before the event usually remain intact. Amnesia is not very well understood, and there are many theories as to what causes it.
One theory for retrograde amnesia is that memory storage has been disrupted. Older memories are more stabilized in the brain and less likely to be impacted, while those closer to the amnesic event are more vulnerable to disruption. Some studies show that when a lost memory is reactivated in retrograde amnesia, the process to reconsolidate it is similar to the original consolidation, indicating that, for someone with retrograde amnesia, making a new memory and remembering an forgotten one are similar processes.
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