Gage had just filled a cavity with explosive and was tamping it down prior to detonation with a heavy metal bar - three-and-a-half- feet long, and nearly two inches across. As he did this someone called to him; he turned to see who it was - and the tamping iron struck the rock and sent a premature spark into the powder. The force of the resulting explosion jettisoned the tamping iron a clear 100 feet. En route it passed through Gage's head.
The iron entered Gage's left eye socket, continued at a slight angle through the frontal lobes of his brain and out through the top of his skull. Astonishingly he did not even pass out. And despite the hole in his head , through which his brain could be seen pulsating, Gage sat upright in an ox-cart and talked quite animatedly while he was taken to a nearby hotel to be treated by a local doctor. His cheerful indifference to his plight was probably the first sign of the extraordinary character changes that were to come.
Despite losing a great chunk of brain, Gage seemed at first to have got off lightly. He lost sight in his left eye but his speech, movement, memory and other functions were unimpaired. However, as he got better those around him found he had changed dramatically in terms of behaviour and personality. The old Gage was known as shrewd, sensible, polite, restrained and industrious. The new Gage, according to John Harlow, a physician who made a detailed report of the case, was "fitful, irreverent . . . manifesting but little deference for his fellows, impatient of restraint or advice . . . pertinaciously obstinate, yet capricious and vacillating . . . a child in his intellectual capacity . . . [but with the] animal passions of a strong man." Harlow noted that Gage was for ever making plans, and then discarding them, and was given to outbursts of bad temper and swearing such that "ladies were advised not to stay long in his presence".
Gage's life went into rapid decline. His employers would not have him back because he was so unreliable, and he was sacked or walked out of every other job he tried. The brain injury finally killed him in 1861 when he suffered a massive epileptic fit from which he never regained consciousness. There was no autopsy and Gage was buried in the normal way, along with his tamping iron.
The "Horrible Accident", as the Boston Globe described it, might have been forgotten had its consequences not been so meticulously documented by Harlow. Today neuroscientists are using brain scanners to map the functions carried out by each bit of the brain and the sorry consequences of Gage's Horrible Accident are understandable in the light of this new science.
The neurologist Hannah Damasio, of the University of Iowa recently worked out - by using computerised tomography on the skull - exactly which parts of Gage's brain were lost. They match precisely the areas now known to give us the qualities we associate with our "highest" selves - the ability to execute plans, to inhibit base urges, and to make us sensitive to other people's emotions. Gage's could not do those things after his accident because he no longer had the requisite bits of brain: part of his personality was literally blown away. His case remains one of the most persuasive demonstrations of the modular construction of the human brain.
Rita Carter is author of `Mapping the Mind' (Weidenfeld and Nicolson, pounds 25)Reuse content