Volume of Temporal Lobe White Matter

The human temporal lobe has evolved a relatively large amount of underlying white matter. Comparative MRI studies have shown that the human brain has a significantly greater amount of white matter underneath the temporal cortex than predicted by allometric expectations for an ape of a human-sized temporal lobe (Rilling and Seligman 2002). Schenker et al. (2005) showed that humans have relatively more white matter directly underneath gyri in the temporal lobe than expected for an ape with the same temporal lobe “core” white matter. Additionally, the arcuate fasciculus in humans has greater connectivity in the middle temporal gyrus than in chimpanzees or macaque monkeys (Rilling et al., 2008). Hence, the enlargement of temporal lobe white matter in human evolution may be related to specializations of language circuits.