Planum temporale
Encyclopedia
The planum temporale is an area of the human brain. It 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. 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
, where it can be observed starting from the 31st week of gestation
. This observation strengthens the hypothesis of a genetic predisposition for brain asymmetry.
The planum temporale seems to be symmetrical in dyslexics, which may indicate that their low specialization in the left hemisphere is a cause of their disability. This symmetry also holds for stutterers, 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.
However, 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.
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.
, 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?
Wernicke's area
Wernicke's area is one of the two parts of the cerebral cortex linked since the late nineteenth century to speech . It is involved in the understanding of written and spoken language...
, 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. 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
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
, where it can be observed starting from the 31st week of gestation
Gestation
Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....
. This observation strengthens the hypothesis of a genetic predisposition for brain asymmetry.
The planum temporale seems to be symmetrical in dyslexics, which may indicate that their low specialization in the left hemisphere is a cause of their disability. This symmetry also holds for stutterers, 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.
However, 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.
Functions
The planum temporale is a highly lateralizedLateralization of brain function
A longitudinal fissure separates the human brain into two distinct cerebral hemispheres, connected by the corpus callosum. The sides resemble each other and each hemisphere's structure is generally mirrored by the other side. Yet despite the strong anatomical similarities, the functions of each...
brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
structure involved with language
Language
Language may refer either to the specifically human capacity for acquiring and using complex systems of communication, or to a specific instance of such a system of complex communication...
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
Absolute pitch , widely referred to as perfect pitch, is the ability of a person to identify or re-create a given musical note without the benefit of an external reference.-Definition:...
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 ChomskyNoam Chomsky
Avram Noam Chomsky is an American linguist, philosopher, cognitive scientist, and activist. He is an Institute Professor and Professor in the Department of Linguistics & Philosophy at MIT, where he has worked for over 50 years. Chomsky has been described as the "father of modern linguistics" and...
, 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?