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No. 42: Nov-Dec 1985

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Left-handers have larger interbrain connections

The two halves of the human brain are connected by a bundle of nerve fibers called the corpus callosum. The corpus callosum is thought to help integrate the activities of the right and left brains which, for reasons unknown, seem to specialize in different kinds of mental operations. Studies of the corpus callosum reveal that it is about 11% larger in left-handers than in right-handers. In terms of interconnecting nerve fibers this comes to 25,000,000 more for the left-handers. Just what sort of information flows along these myriad pathways is not known, although we do know that left-handers have greater bihemispheric representation of cognitive functions; i.e., the brain functions are not so specialized in each half of the brain. But why should left-handers and right-handers be different at all? Are they born with unequal corpus callosa? Or are these nerve highways equal are birth and atrophy in right-handers ? (Witelson, Sandra F.; "The Brain Connection: The Corpus Callosum is Larger in Left-Handers, " Science, 229:665, 1985. )

From Science Frontiers #42, NOV-DEC 1985. 1985-2000 William R. Corliss