Over several years of progressive brain disease, a patient gradually loses track of what happened even a week ago, while continuing to describe events from his childhood in vivid, accurate detail, with the gap between recent and remote memory widening steadily as the illness advances. What is this?

This is Ribot's law of memory regression: the characteristic pattern in chronic, progressive brain disease in which memory for recent events is lost before memory for the distant past, with the affected period widening gradually as the disease progresses, exactly as described. It is not an amnestic state, since Ribot's law differs from the amnestic state of Korsakoff's syndrome and similar conditions in the extent and progressive nature of the memory loss, which widens over years rather than remaining confined to the period around a single event. It is not simple retrograde amnesia, which typically refers to memory loss around a discrete injury rather than a gradually widening, progressive pattern. And it is not dementia as a whole, since Ribot's law describes one specific, named pattern of memory loss rather than the full range of cognitive impairment dementia can involve.