Planum temporale

The planum temporale makes up the superior surface of the superior temporal gyrus to the parietal lobe.{{cite book|author1=David L. Clark|author2=Nash N. Boutros|author3=Mario F. Mendez|title=The Brain and Behavior: An Introduction to Behavioral Neuroanatomy|url=https://books.google.com/books?id=32Ucobqp97EC&pg=PA62|access-date=4 January 2013|date=20 May 2010|publisher=Cambridge University Press|isbn=978-0-521-14229-8|pages=62–}} The posterior extent of the planum temporale has been variably defined, which has led to disputes to estimates of size and degree of asymmetry.

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.{{cite journal|last=Carroll|first=S. B.|title=Genetics and the Making of Homo sapiens|journal=Nature|year=2003|volume=422|issue=6934|pages=849–857|pmid=12712196|doi=10.1038/nature01495|s2cid=4333307}}

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.[http://thebrain.mcgill.ca/flash/i/i_10/i_10_cr/i_10_cr_lan/i_10_cr_lan.html The Brain From Top To Bottom]{{cite journal |vauthors=Dorsaint-Pierre R, Penhune VB, Watkins KE, etal |title=Asymmetries of the planum temporale and Heschl's gyrus: relationship to language lateralization |journal=Brain |volume=129 |issue=Pt 5 |pages=1164–76 |date=May 2006 |pmid=16537567 |doi=10.1093/brain/awl055 |doi-access=free }} Leftward asymmetry, however, does not directly relate to asymmetry of language processing in all individuals.

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.{{cite journal |doi=10.1006/brln.1997.1825 |pmid=9344480 |title=The Relation of Planum Temporale Asymmetry and Morphology of the Corpus Callosum to Handedness, Gender, and Dyslexia: A Review of the Evidence |journal=Brain and Language |volume=60 |issue=2 |pages=255–322 |year=1997 |last1=Beaton |first1=Alan A |s2cid=17560377 }}

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.{{cite journal |doi=10.1002/hbm.22579 |pmid=25044828 |title=Planum temporale asymmetry in developmental dyslexia: Revisiting an old question |journal=Human Brain Mapping |volume=35 |issue=12 |pages=5717–35 |year=2014 |last1=Altarelli |first1=Irene |last2=Leroy |first2=François |last3=Monzalvo |first3=Karla |last4=Fluss |first4=Joel |last5=Billard |first5=Catherine |last6=Dehaene-Lambertz |first6=Ghislaine |author6-link=Ghislaine Dehaene-Lambertz |last7=Galaburda |first7=Albert M |author-link7=Albert Galaburda|last8=Ramus |first8=Franck |pmc=6869664 }}

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.

Due to the novel nature of these findings, researchers have yet to discern how to interpret these sex-based differences on brain function.{{cite journal |doi=10.1006/nimg.2001.0857 |pmid=11506541 |title=Cerebral Asymmetry and the Effects of Sex and Handedness on Brain Structure: A Voxel-Based Morphometric Analysis of 465 Normal Adult Human Brains |journal=NeuroImage |volume=14 |issue=3 |pages=685–700 |year=2001 |last1=Good |first1=Catriona D |last2=Johnsrude |first2=Ingrid |last3=Ashburner |first3=John |last4=Henson |first4=Richard N.A |last5=Friston |first5=Karl J |last6=Frackowiak |first6=Richard S.J |s2cid=16235256 }}

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.{{cite journal |doi=10.1006/nimg.2001.0925 |pmid=11707095 |title=Absolute Pitch and Planum Temporale |journal= NeuroImage |volume=14 |issue=6 |pages=1402–8 |year=2001 |last1=Keenan |first1=Julian Paul |last2=Thangaraj |first2=Ven |last3=Halpern |first3=Andrea R |last4=Schlaug |first4=Gottfried |s2cid=8886472 |url=https://digitalcommons.bucknell.edu/cgi/viewcontent.cgi?article=1340&context=fac_journ |url-access=subscription }} 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.{{cite news|work=Science Daily|date=22 September 2007|url=https://www.sciencedaily.com/releases/2007/09/070919121602.htm |title=Brain Center For 'Sound Space' Identified |access-date=22 September 2007}}

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.

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.{{cite book|author=Michael S. Ritsner|title=The Handbook of Neuropsychiatric Biomarkers, Endophenotypes and Genes|url=https://books.google.com/books?id=H03fPRQiz6YC&pg=PA101|access-date=4 January 2013|date=1 January 2009|publisher=Springer|isbn=978-1-4020-9831-4|pages=101–}} This reduced lateralization correlates with more severe positive symptoms, such as hallucinations, as measured by the PANSS.

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.{{cite journal |doi=10.1016/j.eurpsy.2017.01.1621 |title=Sexual-dimorphism of the planum temporale in schizophrenia: An MRI study |journal=European Psychiatry |volume=41 |pages=S828 |year=2017 |last1=Pigoni |first1=A |last2=Delvecchio |first2=G |last3=Perlini |first3=C |last4=Barillari |first4=M |last5=Ruggeri |first5=M |last6=Altamura |first6=C |last7=Bellani |first7=M |last8=Brambilla |first8=P |s2cid=149395883 }}

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,{{cite journal |vauthors=Gannon PJ, Holloway RL, Broadfield DC, Braun AR |title=Asymmetry of chimpanzee planum temporale: humanlike pattern of Wernicke's brain language area homolog |journal=Science |volume=279 |issue=5348 |pages=220–2 |date=January 1998 |pmid=9422693 |doi=10.1126/science.279.5348.220|bibcode=1998Sci...279..220G }} as was a related, rightward asymmetric, brain region the planum parietale that is implicated with dyslexia in humans.{{cite journal |vauthors=Gannon PJ, Kheck N, Hof PR |title=Leftward interhemispheric asymmetry of macaque monkey temporal lobe language area homolog is evident at the cytoarchitectural, but not gross anatomic level |journal=Brain Res. |volume=1199 |pages=62–73 |date=March 2008 |pmid=18262172 |doi=10.1016/j.brainres.2007.12.041 |s2cid=20325315 }} Monkeys show cellular asymmetry but not gross anatomic asymmetry of the planum temporale.{{cite journal |vauthors=Gannon PJ, Kheck NM, Braun AR, Holloway RL |title=Planum parietale of chimpanzees and orangutans: a comparative resonance of human-like planum temporale asymmetry |journal=Anat Rec A |volume=287 |issue=1 |pages=1128–41 |date=November 2005 |pmid=16215971 |doi=10.1002/ar.a.20256 |doi-access=free }} (Brain Research, 2008).

The question still remains open; what are great apes or monkeys using this "non-human primate language area" for?{{cite news |author=Blakeslee S |title=Brain of Chimpanzee Sheds Light on Mystery of Language |url=http://www.uwm.edu/~wash/brainlg.htm |work=The New York Times |date=1998-01-13 }}[https://web.archive.org/web/19991002202809/http://www.geocities.com/RainForest/Vines/4451/ChimpsLikeUs.html Chimps Like Us / We're Like Chimps]{{cite book |author1=Gibson, Kathleen Rita |author2=Falk, Dean |title=Evolutionary anatomy of the primate cerebral cortex |publisher=Cambridge University Press |location=Cambridge, UK |year=2001 |isbn=0-521-64271-X |url=https://books.google.com/books?id=zE7GXRg7dNQC&q=gannon+language&pg=PA216 |page=216}}[http://www.sciencenews.org/pages/pdfs/data/1998/153-02/15302-08.pdf Sciencenews 1998 PDF] {{webarchive|url=https://web.archive.org/web/20110524095138/http://www.sciencenews.org/pages/pdfs/data/1998/153-02/15302-08.pdf |date=2011-05-24 }}{{full citation needed|date=December 2017}}

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

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Category:Cerebral cortex