The planum temporale is the cortical area just posterior to the auditory cortex (

Heschl's gyrus The transverse temporal gyri, also called Heschl's gyri () or Heschl's convolutions, are gyri found in the area of primary auditory cortex buried within the lateral sulcus of the human brain, occupying Brodmann areas 41 and 42. Transverse tempo ...

) within the

Sylvian fissure In neuroanatomy, the lateral sulcus (also called Sylvian fissure, after Franciscus Sylvius, or lateral fissure) is one of the most prominent features of the human brain. The lateral sulcus is a deep fissure in each hemisphere that separates th ...

. It is a triangular region which forms the heart of

Wernicke's area Wernicke's area (; ), also called Wernicke's speech area, is one of the two parts of the cerebral cortex that are linked to speech, the other being Broca's area. It is involved in the comprehension of written and spoken language, in contrast to B ...

, one of the most important functional areas for language.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, with this area being up to ten times larger in the left cerebral hemisphere than the right.

Location

The planum temporale makes up the superior surface of the

superior temporal gyrus The superior temporal gyrus (STG) is one of three (sometimes two) gyri in the temporal lobe of the human brain, which is located laterally to the head, situated somewhat above the external ear. The superior temporal gyrus is bounded by: * the l ...

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.

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. This greater size of the left planum temporale compared with the right is already present in the

fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal dev ...

, where it can be observed starting from the 31st week of

gestation Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pr ...

. This observation strengthens the hypothesis of a genetic predisposition for brain asymmetry, however the effect of fetal experience has not been ruled out.The Brain From Top To Bottom
/ref> Leftward asymmetry, however, does not directly relate to asymmetry of language processing in all individuals. In addition, more and more research is suggesting that the apparent asymmetries in this region are the result of old techniques and criteria used to identify the planum temporale. When new imaging is used that takes into account asymmetries in the curvatures of lateral fissures, the hemispheric asymmetries of the planum temporale become negligible. This newer imaging would indicate that the size of the region would not explain the higher faculties of language in the left hemisphere, but would instead require an analysis of the neural circuitry.

Gender based asymmetry

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. 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. Due to the novel nature of these findings, researchers have yet to discern how to interpret these sex-based differences on brain function.

Functions

The planum temporale is a highly lateralized

brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...

structure involved with

language Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by which humans communicate, and may be conveyed through a variety of ...

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 Absolute pitch (AP), often called perfect pitch, is a rare ability of a person to identify or re-create a given musical note without the benefit of a reference tone. AP may be demonstrated using linguistic labeling ("naming" a note), associating ...

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.

Atypical development

The planum temporale seems to be symmetrical in individuals with

dyslexia Dyslexia, also known until the 1960s as word blindness, is a disorder characterized by reading below the expected level for one's age. Different people are affected to different degrees. Problems may include difficulties in spelling words, r ...

, 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

schizophrenic Schizophrenia is a mental disorder characterized by continuous or relapsing episodes of psychosis. Major symptoms include hallucinations (typically hearing voices), delusions, and disorganized thinking. Other symptoms include social w ...

s is more symmetrical. This reduced lateralization correlates with more severe positive symptoms, such as

hallucination A hallucination is a perception in the absence of an external stimulus that has the qualities of a real perception. Hallucinations are vivid, substantial, and are perceived to be located in external objective space. Hallucination is a combinati ...

s, 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.

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 Avram Noam Chomsky (born December 7, 1928) is an American public intellectual: a linguist, philosopher, cognitive scientist, historian, social critic, and political activist. Sometimes called "the father of modern linguistics", Chomsky i ...

, 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?Sciencenews 1998 PDF

Hemispheric differences

Additional images

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

References

{{Authority control Cerebral cortex