Some amnesiacs fill memory gaps with confident, fluent inventions
Korsakoff syndrome, usually from severe thiamine deficiency in chronic alcoholism, wipes out the ability to form new memories. Many patients respond by confabulating: producing detailed, often implausible accounts of where they've been or what they did, and believing them completely rather than sensing any gap. First described by Sergei Korsakoff in 1889, it's one of the clearest splits between memory and the feeling of remembering.