Scientists in California and Finland have done what may be the first study that provides estimates of the strength of genetic influences on the size and shape of different parts of the brain. The study, which compared brain images of identical and fraternal twins, shows very high hereditary incidence for areas associated with intelligent quotient (IQ) and verbal skills. Cognitive tests also showed a "highly significant" relation between IQ and grey matter volume in the frontal cortex. The scientists did brain scans of 20 pairs of adult twins, half of them identical. They found that the volume of grey matter (which contains the nerve cell bodies) in frontal lobes and in the language areas of the temporal lobes was virtually the same in identical twins but differed substantially in fraternal pairs. This means that it is largely governed by genetic factors (Science, Vol 294, no 5546, November 16, 2001).
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