300px|thumb|Diagram labeling planum temporale in green
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. Original studies on this area found that the planum temporale was one of the most asymmetric regions in the brain, larger in the left cerebral hemisphere than the right.
Location
The planum temporale makes up the superior surface of the superior temporal gyrus to the parietal lobe. The posterior extent of the planum temporale has been variably defined, which has led to disputes to estimates of size and degree of asymmetry.
This greater size of the left planum temporale compared with the right is already present in the fetus, where it can be observed starting from the 31st week of gestation. This observation strengthens the hypothesis of a genetic predisposition for brain asymmetry, however the effect of fetal experience has not been ruled out. Leftward asymmetry, however, does not directly relate to asymmetry of language processing in all individuals.
Recent evidence can be used to support the idea that differences between males and females in planum temporale asymmetry begin to develop and show early in development, potentially during prenatal stages. Gender based asymmetry may be the result of environmental factors occurring in-utero, such as levels of testosterone.
Certain studies have found differences within the planum temporale on a microscopic level, finding greater cell packing density in females, as well as a reduction of micro-structural asymmetry. Females have also been found to display asymmetry in grey matter volume.
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.
There have also been many studies that show the asymmetry of the planum temporale to be related to handedness of subjects. There have been reports of decreased asymmetry displayed on the left side of the planum temporale in those that are dominantly left handed. This reduced lateralization correlates with more severe positive symptoms, such as hallucinations, as measured by the PANSS.
Non-human brains
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?
Hemispheric differences
{| class="wikitable"
|+Summary Table
!Left Hemisphere
!Right Hemisphere
|-
|Normal development- larger in size and surface area
|Normal development- smaller in size and surface area
|Damage can lead to impaired ability to decode phonemes
|}
Additional images
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File:Planum temporale.gif|3D visualization of the planum temporale in an average human brain
File:Planum temporale coronal sections.gif|Planum temporale highlighted in green on coronal T1 MRI images
File:Planum temporale sagittal sections.gif|Planum temporale highlighted in green on sagittal T1 MRI images
File:Planum temporale transversal sections.gif|Planum temporale highlighted in green on transversal T1 MRI images
</gallery>