Planum temporale
The planum temporale is the cortical area just posterior to the auditory cortex (Heschl's gyrus) within the Sylvian fissure.<ref>Template:Cite book</ref> It is a triangular region which forms the heart of Wernicke's area, one of the most important functional areas for language.<ref name=mcgill>The Brain From Top To Bottom</ref> 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.<ref name="Becker2002">Template:Cite book</ref>
LocationEdit
The planum temporale makes up the superior surface of the superior temporal gyrus to the parietal lobe.<ref name="ClarkBoutros2010">Template:Cite book</ref> The posterior extent of the planum temporale has been variably defined, which has led to disputes to estimates of size and degree of asymmetry.<ref name="ClarkBoutros2010" />
AsymmetryEdit
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 11%. 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. Evidence for this asymmetry has also been seen in great apes.<ref>Template:Cite journal</ref>
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.<ref name=mcgill>The Brain From Top To Bottom</ref><ref>Template:Cite journal</ref> Leftward asymmetry, however, does not directly relate to asymmetry of language processing in all individuals.<ref name="ClarkBoutros2010" />
Gender based asymmetryEdit
Imaging has repeatedly suggested gender marked differences in planum temporale surface area asymmetry. There have been multiple findings suggesting a greater leftward surface area asymmetry in male subjects, with no significant difference as mediated by gender of the right part of the planum temporale.<ref>Template:Cite journal</ref>
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.<ref name=":0">Template:Cite journal</ref>
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.<ref name=":0" />
Due to the novel nature of these findings, researchers have yet to discern how to interpret these sex-based differences on brain function.<ref name=":1">Template:Cite journal</ref>
FunctionsEdit
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.<ref>Template:Cite journal</ref> 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.<ref>Template:Cite news</ref>
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.<ref name=":1" />
Atypical developmentEdit
The planum temporale seems to be symmetrical in individuals with dyslexia, which may indicate that their low specialization in the left hemisphere is a cause of their disability. This symmetry also holds for people who stutter, although it is also possible to see a larger right planum temporale in stutters. It is thought that this bias for right hemisphere could be interrupting or impeding information flow between Wernickes and Broca's, which are on the left hemisphere.
MRI studies have shown that the planum temporale in schizophrenics is more symmetrical.<ref name="Ritsner2009">Template:Cite book</ref> This reduced lateralization correlates with more severe positive symptoms, such as hallucinations, as measured by the PANSS.<ref name="Ritsner2009" />
Sexual dimorphism has shown to play an important role on planum temporale studies within schizophrenia. These findings have highlighted the relevance and importance of sex/gender as a plays a key role on PT in schizophrenia, underlying the importance of gender as a key component of brain morphology and the specialized brain structure and function for schizophrenia.<ref>Template:Cite journal</ref>
Non-human brainsEdit
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,<ref>Template:Cite journal</ref> as was a related, rightward asymmetric, brain region the planum parietale that is implicated with dyslexia in humans.<ref>Template:Cite journal</ref> Monkeys show cellular asymmetry but not gross anatomic asymmetry of the planum temporale.<ref>Template:Cite journal</ref> (Brain Research, 2008). The question still remains open; what are great apes or monkeys using this "non-human primate language area" for?<ref>Template:Cite news</ref><ref>Chimps Like Us / We're Like Chimps</ref><ref>Template:Cite book</ref><ref>Sciencenews 1998 PDF Template:WebarchiveTemplate:Full citation needed</ref>
Hemispheric differencesEdit
| Left Hemisphere | Right Hemisphere |
|---|---|
| Normal development- larger in size and surface area<ref name=":2">Binder J. R., Frost J. A., Hammeke T. A., Rao S. M., Cox R. W. (1996). Function of the left planum temporale in auditory and linguistic processing. Brain 119 1239–1247. 10.1093/brain/119.4.1239</ref> | Normal development- smaller in size and surface area<ref name=":2" /> |
| Decrease in size leads to difficulty with word recognition<ref name=":2" /> | ------- |
| main}}</ref> | Damage can lead to impaired ability to decode phonemes<ref name=":3" /> |
| Decrease in size can lead to dyslexia<ref name=":3" /> | Increase in size can lead to dyslexia<ref name=":3" /> |
| Lesions result in difficulty of speech recognition<ref name=":2" /> | ------- |
| ------- | main}}</ref> |
Additional imagesEdit
- Planum temporale.gif
3D visualization of the planum temporale in an average human brain
- Planum temporale coronal sections.gif
Planum temporale highlighted in green on coronal T1 MRI images
- Planum temporale sagittal sections.gif
Planum temporale highlighted in green on sagittal T1 MRI images
- Planum temporale transversal sections.gif
Planum temporale highlighted in green on transversal T1 MRI images