Anterograde Amnesia - Notable Cases

Notable Cases

The most famous case reported is that of patient Henry Molaison, known as H.M., in March 1953. Molaison's chief complaint was the persistence of severe seizures and therefore had a bilateral lobectomy (both of his MTLs were removed). As a result, Molaison had bilateral damage to both the hippocampal formation and the perirhinal cortex. Molaison had average intelligence and perceptual ability and a decent vocabulary. However, he could not learn new words or remember things that had happened more than a few minutes earlier. He could also remember anything from his childhood. If the memory was created from before his lobectomy, he still had the ability to retrieve it and remember. However, he was able to learn some new skills. He was the first well-documented case of severe anterograde amnesia, and was studied until his death in 2008.

A similar case involved Clive Wearing, an accomplished musicologist who contracted a cold virus that attacked his brain, causing herpes simplex encephalitis. As a result, Wearing developed anterograde amnesia, as well as retrograde amnesia, so he has little memory of what happened before the virus struck him in 1985, and cannot learn new declarative knowledge after the virus struck him, either. As a result of anterograde amnesia, Wearing repeatedly “wakes up” every day in 30-second intervals until his wife stops him, because his episodic memory is nonfunctional (so he does not consciously recall having woken up 30 seconds prior). Despite this, however, Wearing maintained his ability to play the piano and conduct choirs. This case is significant because it demonstrates declarative and procedural memory are separate. Therefore, despite anterograde amnesia preventing Wearing from learning new bits of information that can be explained in words (declarative memory), and also preventing him from storing new memories of events or episodes (also part of declarative memory), he has little trouble in retaining his musical abilities (procedural memory), though he has no conscious memory of having learned music.

Another case in the literature is E.P., a severely amnesic patient who was able to learn three-word sentences. He performed better on consecutive tests over a 12-week period (24 study sessions). However, when asked how confident he was about the answers, his confidence did not appear to increase. Bayley and Squire proposed his learning was similar to the process required by procedural memory tasks; E.P. could not get the answers right when one word in the three-word sentence was changed or the order of words was changed, and his ability to answer correctly, thus, became more of a "habit". Bayley and Squire claim the learning may have happened in the neocortex, and it happened without the conscious knowledge of E.P. They hypothesized the information may be acquired directly by the neocortex (to which the hippocampus projects) when there is repetition. This case illustrates the difficulty in separating procedural from declarative tasks; this adds another dimension to the complexity of anterograde amnesia.