Planum temporale

The planum temporale is the cortical area just posterior to the auditory cortex (Heschl's gyrus) within the Sylvian fissure. It is a triangular region which forms the heart of Wernicke's area, one of the most important functional areas for language.

The planum temporale shows a significant asymmetry. In 65% of all individuals the left planum temporale appears to be more developed, while the right planum temporale is more developed in only 10%. In some people’s brains, the planum temporale is more than five times larger on the left than on the right, making it the most asymmetrical structure in the brain.

This greater size of the left planum temporale compared with the right is already present in the foetus, where it can be observed starting from the 31st week of gestation. This observation strengthens the hypothesis of a genetic predisposition for brain asymmetry.

Functions
The planum temporale is a highly lateralized brain structure involved with language and with music. Although the planum temporale is found to have an asymmetry in the normal population, having a leftward bias in right-handed individuals, people who possess absolute pitch have an increased leftward asymmetry of the planum temporale. This is due to a smaller than average volume of the right planum temporale and not a larger than average volume of the left. The planum temporale may also play an important role in auditory processing with recent research suggesting that the region is responsible for representing the location of sounds in space.

Other than Humans
Although the brain area was thought to be unique to humans, almost like the anatomic version of the linguistic "language organ" of Noam Chomsky, it was shown to be similarly leftward asymmetric in chimpanzees and other great apes but not other primates, ; as was a related, rightward asymmetric, brain region the planum parietale that is implicated with dyslexia in humans. Monkeys show cellular asymmetry but not gross anatomic asymmetry of the planum temporale. Brain Research, 2008. The question still remains open; what are great apes or monkeys using this "non-human primate language area" for?