Asymmetry of Chimpanzee Planum Temporale: Humanlike Pattern of Wernicke's Brain Language Area Homolog

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Abstract
The anatomic pattern and left hemisphere size predominance of the planum temporale, a language area of the human brain, are also present in chimpanzees (Pan troglodytes). The left planum temporale was significantly larger in 94 percent (17 of 18) of chimpanzee brains examined. It is widely accepted that the planum temporale is a key component of Wernicke's receptive language area, which is also implicated in human communication-related disorders such as schizophrenia and in normal variations such as musical talent. However, anatomic hemispheric asymmetry of this cerebrocortical site is clearly not unique to humans, as is currently thought. The evolutionary origin of human language may have been founded on this basal anatomic substrate, which was already lateralized to the left hemisphere in the common ancestor of chimpanzees and humans 8 million years ago.