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A half-century ago, the neuroscientist Karl Lashley wrote a paper called "In Search of the Engram," describing his frustrating attempt to find the cluster of neurons in which a rat stored its memory of a maze. After training the animal to negotiate the labyrinth, he snipped away at the brain bit by bit. While the animal became increasingly sluggish and confused, Lashley was never able to find a single location where the memory was inscribed. "I sometimes feel," Lashley ruefully wrote, "that the necessary conclusion is that learning just is not possible."
Fifty years later, memory researchers find themselves with the same mix of confusion and awe. But for all their puzzlement, they hold out hope that experiment by experiment, they are deepening their knowledge of how memory works--and inching toward a day when they can repair it when it falters.
George Johnson, a New York Times writer, is the author of In the Palaces of Memory. His most recent book is Strange Beauty: Murray Gell-Mann and the Revolution in 20th-Century Physics