World-famous amnesiac Henry Gustav Molaison died Tuesday of respiratory failure. Better known as “H.M.,” he had been unable to form new memories since undergoing brain surgery in 1953 at age 27. Do amnesiacs realize that they’re amnesiacs?
Yes, usually. Whether they lose their memory through physical brain damage or psychological trauma, most amnesiacs—or “amnesics,” in professional terminology—have some awareness of their condition. But it depends on how intact their brains are overall. Amnesia usually results from damage to the hippocampus, part of the brain’s medial temporal lobe, which is involved in forming new memories. * When only the hippocampus is affected, patients tend to be aware of their state. In H.M.’s case, for example, his entire hippocampus was surgically removed, but most of the rest of his brain remained functional. So when asked who the president was, he might say, “I’m sorry, but my memory isn’t very good.” (One of his amygdalae, which govern emotions, was also removed, which some experts said explained his unemotional, matter-of-fact manner.) If, however, the entire brain is damaged, a patient may be unaware of his memory loss. That’s why people who suffer from advanced Alzheimer’s, which affects the whole brain, often don’t recognize their condition.
There are two main types of amnesia: retrograde and anterograde. Retrograde means you lose your memories from before the surgery, injury, or whatever incident caused the memory loss. One famous retrograde case is Doug Bruce, the subject of the film Unknown White Male who said he “awakened” one day on the subway in New York and didn’t know who he was. Anterograde means you lose the ability to form new memories but can still recall things from before the inciting event. That was the case with H.M., who could remember scattered childhood memories.
It’s generally easier for retrograde amnesics to become aware of their condition since they can create and retain new memories, including the realization that they have a bad memory. For anterograde amnesics, awareness varies depending on the severity of their condition. In extreme cases, a patient will become aware of his amnesia only if someone brings it to his attention—but he’ll promptly forget. For example, Clive Wearing, a British musician who suffers from herpes encephalitis (an infection that attacks the brain) is in a constant state of thinking he just woke up. Nearly every entry of his journal says, in one way or another, “I am awake.” When shown past entries, he denies he wrote them. He gets upset when confronted with his condition. The professionals who tend to him are therefore trained to speak only in the immediate present, without any indication that they already know him. In less severe cases, patients will become aware of their condition on their own although it’s unclear exactly how. It may be through the brute repetition of fact. Or it may be the contrast between their current fuzziness and the richness of their pre-incident memories that helps them recognize their condition.
Got a question about today’s news? Ask the Explainer.
Explainer thanks Neal J. Cohen of the University of Illinois, Howard Eichenbaum of Boston University, Daniel Schacter of Harvard University, and Ola Selnes of Johns Hopkins University.
Correction, Dec. 11, 2008: This article originally stated that the hippocampus is responsible for short-term memory. It is believed to help convert short-term memory to long-term memory. (Return to the corrected sentence.)