YOUR MEMORIESmemory problems. This is a form of impairment known as retrograde
amnesia, as opposed to anterograde amnesia, which is the more
typical loss of ability to form new autobiographical memories. With
retrograde amnesia, the memories from before the illness or acci-
dent will usually return, gradually getting closer to the onset of the
amnesia, but falling short and leaving a permanent period of
blankness.
As well as short-term memory, another form of memory that remains
intact in amnesia is implicit memory. Psychologists have shown this
by testing the ability of amnesics to learn tricky, lab-based tasks such
as mirror drawing, which involves drawing using the mirror reflection
of your hand as a guide rather than looking straight at it. Amnesics get
better at this kind of task, just as a healthy person does, and they retain
the ability when tested at later dates. However, unlike a healthy person,
they won’t remember having performed the task before.
Patient H.M.
It’s not often that a car mechanic receives a prominent obituary in the
New York Times, but in December 2008 that’s exactly what happened
when Henry Molaison died at the age of 82. Molaison, better known
in the psychological literature as H.M., is the most studied individual
in the history of neuropsychology, having been featured in literally
hundreds of journal articles.
The interest began in the 1950s after Molaison, aged 27, awoke
from brain surgery performed to help suppress his epileptic seizures.
The surgeon, William Beecher Scoville, had removed slices from both
temporal lobes of Molaison’s brain in the region we know now is
occupied by the hippocampi. Molaison’s seizures were reduced, but so
too was his memory ability. In one of the first documented cases of “pure”
amnesia, Molaison had lost all ability to lay down new autobiographical
memories. He cooperated with psychologists amicably for the rest of
his life, working most often with Brenda Milner at McGill University and
Suzanne Corkin at MIT. They documented how he lived each experience
as if for the first time, and always greeted Milner and Corkin as if he’d
never met them before. However, he was able to learn difficult lab tasks,
such as mirror drawing, which depend on implicit, procedural memory.
Psychologists and brain scientists moved quickly to preserve
Molaison’s brain after he died, and in 2009 neuroanatomists were busy
slicing and scanning it in order to turn it into a fully searchable digital
atlas (see thebrainobservatory.ucsd.edu). Corkin is planning a memoir
of Molaison’s life based on the 45 years she spent studying him, and
Columbia Pictures has already bought the film rights.