CRF Blog

How Memory Speaks

by Bill Hayes

In How Memory Speaks for the New York Review of Books, Jerome Groopman reviews the following books on memory: I Forgot to Remember: A Memoir of Amnesia by Su Meck, with Daniel de Visé, Memory: From Mind to Molecules by Larry R. Squire and Eric R. Kandel, Madness and Memory: The Discovery of Prions — A New Biological Principle of Disease by Stanley B. Prusiner, MD, The Alzheimer Conundrum: Entanglements of Dementia and Aging by Margaret Lock, and The Answer to the Riddle Is Me: A Memoir of Amnesia by David Stuart MacLean.

Neuroscientists have gained considerable insight into memory by studying certain people who have lost it. One such person is known by the initials HM. He suffered from severe epilepsy that could not be controlled with medication. In 1953, his medial temporal lobes, parts of the brain roughly at the level of the sideburns, were removed in an experimental surgery. Although the operation succeeded in reducing the frequency and severity of HM’s seizures, it left his memory profoundly impaired.

Over the ensuing five decades, nearly one hundred studies have been conducted on him, both at the Montreal Neurological Institute and at the Massachusetts Institute of Technology. In initial studies, his neurosurgeon, William Beecher Scoville, and the psychologist Brenda Milner observed that HM could not remember articles on the front of the day’s newspaper. This inability to form new memories is called anterograde amnesia.

HM’s deficit included memories not only of new facts (semantic memory) but also of events (episodic memory). Yet he could retain a number or a visual image for a short period of time after learning it. He also remembered events from his childhood. Scoville and Milner posited that the medial temporal lobes were needed to generate recent, but not remote, memories. In later experiments, such long-term memories were discovered to be stored in the cortex, including areas that originally processed the information.

In 1962, Milner conducted a now famous experiment that yielded surprising results: despite all his deficits, HM was able to learn new motor skills. Milner asked HM to trace the outline of a star shown in a mirror. He could see only his hand, because the pencil and star were reflected in the mirror, with left and right reversed. Over the course of several days, HM performed this mirror-tracing task, and on each sequential attempt, he reduced the time it took and made fewer errors. Yet each time he began to trace the star once again, he told Milner that he had never done it before. Though he lacked “declarative memory” (that is, awareness of prior attempts), HM was able to retain his level of improved performance for as long as a year. Milner concluded that such skills, which depend on visual perception and motor ability, appear to involve brain regions outside of the medial temporal lobes.

Two luminaries in the field, Larry R. Squire, at the University of California, San Diego, and the Nobel laureate Eric R. Kandel, at Columbia University, describe these studies on HM in their elegant and engaging book, Memory. Written in accessible language for a lay reader, the authors illustrate fundamental discoveries about memory using works of art. [more]