Hat size, brain size, intelligence, and dementia
What morphometry can tell us about brain function and disease
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Hat sizes—6-3/8 to 7-7/8—seem a peculiar array of fractional numbers with which to identify hats, from small to extra-large, to fit the full range of human heads. These arcane numbers are the diameters in inches of perfect circles whose circumferences match the heads on which the hats fit. You can determine your cranial circumference in inches from your hat size by multiplying by π or in centimeters by multiplying by 7.98.
“Normal” cranial circumference for adults is about 50 to 60 cm (although Nellhaus’ age 18 figures ±2 SD give a somewhat narrower range1), with microcephaly at one end of the range and macrocephaly at the other. This range of normal describes only the capacity of the cranium and not its contents; not everyone outside the range is abnormal, and not everyone within it has normal brain function. The great French author, Anatole France, who won the Nobel Prize in 1921 for his literary genius, was known to have an extremely small head.
Twenty-three hundred years ago Herophilus understood that the “brain was the organ of mind,” but for centuries exactly how the structure related to the functions was unclear. In the late 18th century, Gall articulated the concept that behavioral functions were related to specific anatomical locations in the brain. Limited (by …
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