The Brainiest Detective and the Brain

The incomparable Rathbone and Bruce

My earliest introduction to neuroscience came courtesy of Arthur Conan Doyle. The passage, which many readers will recognize, occurs when Watson first meets the great detective and is stunned to discover that he’s ignorant of the solar system. When Watson expresses his amazement, Holmes shares his theory of the brain:

“You appear to be astonished,” he said, smiling at my expression of surprise. “Now that I do know it I shall do my best to forget it.”

“To forget it!”

“You see,” he explained, “I consider that a man’s brain originally is like a little empty attic, and you have to stock it with such furniture as you choose. A fool takes in all the lumber of every sort that he comes across, so that the knowledge which might be useful to him gets crowded out, or at best is jumbled up with a lot of other things so that he has a difficulty in laying his hands upon it. Now the skilful workman is very careful indeed as to what he takes into his brain-attic. He will have nothing but the tools which may help him in doing his work, but of these he has a large assortment, and all in the most perfect order. It is a mistake to think that that little room has elastic walls and can distend to any extent. Depend upon it there comes a time when for every addition of knowledge you forget something that you knew before. It is of the highest importance, therefore, not to have useless facts elbowing out the useful ones.”

Recent research on the brain, however, indicates that, smart though he is, Holmes may have got this one wrong.  According to an article in Discover, our “attics” are not fixed but can expand to take in new information.  For instance, the hippocampus of London cab drivers are abnormally large:

This seahorse-shaped area lies in the core of the brain, and animal studies had linked it to memory and spatial awareness. . . . Not only did cab drivers have an unusually large hippocampus, but the size of the area matched the length of their driving careers.

But don’t lose your faith in Holmes altogether. Apparently there’s also a hitch to these bigger brains:

[Researcher Maguire] showed that a driver’s hippocampus is most active when they [sic] first plan a route. She found that the hippocampus shrinks back to a normal size once drivers retire. And she found that acquiring The Knowledge comes at a cost – taxi drivers find it more difficult to integrate new routes into their existing maps, and other aspects of their memory seemed to suffer.

Elementary, my dear Watson.

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