Phineas P. Gage (1823–1860) was an American railroad construction foreman remembered for his improbable survival of an accident in which a large iron rod was driven completely through his head, destroying much of his brain's left frontal lobe, and for that injury's reported effects on his personality and behavior over the remaining 12 years of his life‍ —‌ effects sufficiently profound (for a time at least) that friends saw him as "no longer Gage."

Long known as the "American Crowbar Case"‍—‌once termed "the case which more than all others is calculated to excite our wonder, impair the value of prognosis, and even to subvert our physiological doctrines"  —‌ Phineas Gage influenced 19th-century discussion about the mind and brain, particularly debate on cerebral localization, and was perhaps the first case to suggest the brain's role in determining personality, and that damage to specific parts of the brain might induce specific mental changes.

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