Language center
Encyclopedia
The term language center (or more accurately centers, e.g. Broca's area
and Wernicke's area
) refers to the areas of the brain which serve a particular function for speech processing and production.
and fMRI
have allowed researchers to generate pictures showing which areas of a living brain are active at a given time. In the past, research was primarily based on observations of loss of ability resulting from damage to the cerebral cortex
. Indeed, medical imaging has represented a radical step forward for research on speech processing. Since then, a whole series of relatively large areas of the brain have been found to be involved in speech processing. In more recent research, subcortical regions (those lying below the cerebral cortex such as the putamen
and the caudate nucleus
) as well as the pre-motor areas (BA 6
) have received increased attention. It is now generally assumed that the following structures of the cerebral cortex near the primary and secondary auditory cortexes
play a fundamental role in speech processing:
The left hemisphere is usually dominant in right-handed people, although bilateral activations are not uncommon in the area of syntactic processing. It is now accepted that the right hemisphere plays an important role in the processing of suprasegmental acoustic features like prosody
.
Most areas of speech processing develop in the second year of life in the dominant half (hemisphere
) of the brain, which often (though not necessarily) corresponds to the opposite of the dominant hand
. 98 percent of right-handed people are left-hemisphere dominant, and the majority of left-handed people as well.
The differentiation of speech production into only two large sections of the brain (i.e. Broca's and Wernicke's areas), accepted long before the advent of medical imaging techniques, is now considered outdated. Broca's Area was first suggested to play a role in speech function by the French neurologist and anthropologist Paul Broca in 1861. The basis for this discovery was analysis of speech problems resulting from injuries to this region of the brain, located in the inferior frontal gyrus. Lesions to Broca's Area resulted primarily in disruptions to speech production. Damage to Wernicke's Area, which is located in the lower part of the temporal lobe
, lead mainly to disruptions in speech reception. This area was named for German doctor Carl Wernicke, who discovered it in 1874 in the course of his research into aphasias
(loss of ability to speak).
Broca's Area is today still considered an important language center, playing a central role in processing syntax, grammar, and sentence structure.
In summary, these early research efforts demonstrated that semantic and structural speech production takes place in different areas of the brain.
Broca's area
Broca's area is a region of the hominid brain with functions linked to speech production.The production of language has been linked to the Broca’s area since Pierre Paul Broca reported impairments in two patients. They had lost the ability to speak after injury to the posterior inferior frontal...
and Wernicke's area
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...
) refers to the areas of the brain which serve a particular function for speech processing and production.
Current scientific consensus
New medical imaging techniques such as PETPositron emission tomography
Positron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
and fMRI
Functional magnetic resonance imaging
Functional magnetic resonance imaging or functional MRI is a type of specialized MRI scan used to measure the hemodynamic response related to neural activity in the brain or spinal cord of humans or other animals. It is one of the most recently developed forms of neuroimaging...
have allowed researchers to generate pictures showing which areas of a living brain are active at a given time. In the past, research was primarily based on observations of loss of ability resulting from damage to the cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
. Indeed, medical imaging has represented a radical step forward for research on speech processing. Since then, a whole series of relatively large areas of the brain have been found to be involved in speech processing. In more recent research, subcortical regions (those lying below the cerebral cortex such as the putamen
Putamen
The putamen is a round structure located at the base of the forebrain . The putamen and caudate nucleus together form the dorsal striatum. It is also one of the structures that comprises the basal ganglia. Through various pathways, the putamen is connected to the substantia nigra and globus pallidus...
and the caudate nucleus
Caudate nucleus
The caudate nucleus is a nucleus located within the basal ganglia of the brains of many animal species. The caudate nucleus is an important part of the brain's learning and memory system.-Anatomy:...
) as well as the pre-motor areas (BA 6
Brodmann area 6
- Human :Brodmann area 6 is part of the frontal cortex in the human brain. Situated just anterior to the primary motor cortex , it is composed of the premotor cortex and, medially, the supplementary motor area, or SMA...
) have received increased attention. It is now generally assumed that the following structures of the cerebral cortex near the primary and secondary auditory cortexes
Primary auditory cortex
The primary auditory cortex is the region of the brain that is responsible for the processing of auditory information. Corresponding roughly with Brodmann areas 41 and 42, it is located on the temporal lobe, and performs the basics of hearing—pitch and volume...
play a fundamental role in speech processing:
- Superior temporal gyrusSuperior temporal gyrusThe superior temporal gyrus is one of three 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 lateral sulcus above;...
(STG): morphosyntactic processing (anterior section), integration of syntacticSyntaxIn linguistics, syntax is the study of the principles and rules for constructing phrases and sentences in natural languages....
and semanticSemanticsSemantics is the study of meaning. It focuses on the relation between signifiers, such as words, phrases, signs and symbols, and what they stand for, their denotata....
information (posterior section) - Inferior frontal gyrusInferior frontal gyrusThe inferior frontal gyrus is a gyrus of the frontal lobe . It is labelled gyrus frontalis inferior, its Latin name...
(IFG, Brodmann areaBrodmann areaA Brodmann area is a region of the cerebral cortex defined based on its cytoarchitectonics, or structure and organization of cells.-History:...
(BA) 45Brodmann area 45Brodmann area 45 , is part of the frontal cortex in the human brain. Situated on the lateral surface, inferior to BA9 and adjacent to BA46.This area is also known as pars triangular ...
/47Brodmann area 47Brodmann area 47, or BA47, is part of the frontal cortex in the human brain. Curving from the lateral surface of the frontal lobe into the ventral frontal cortex. It is below areas BA10 and BA45, and beside BA11....
): syntactic processing, working memoryWorking memoryWorking memory has been defined as the system which actively holds information in the mind to do verbal and nonverbal tasks such as reasoning and comprehension, and to make it available for further information processing... - Inferior frontal gyrusInferior frontal gyrusThe inferior frontal gyrus is a gyrus of the frontal lobe . It is labelled gyrus frontalis inferior, its Latin name...
(IFG, BA 44Brodmann area 44Brodmann area 44, or BA44, is part of the frontal cortex in the human brain. Situated just anterior to premotor cortex and on the lateral surface, inferior to BA9....
): syntactic processing, working memory - Middle temporal gyrusMiddle temporal gyrusMiddle temporal gyrus is a gyrus in the brain on the Temporal lobe. It is located between the superior temporal gyrus and inferior temporal gyrus. Its exact function is unknown, but it has been connected with processes as different as contemplating distance, recognition of known faces, and...
(MTG): lexical semanticLexical semanticsLexical semantics is a subfield of linguistic semantics. It is the study of how and what the words of a language denote . Words may either be taken to denote things in the world, or concepts, depending on the particular approach to lexical semantics.The units of meaning in lexical semantics are...
processing
The left hemisphere is usually dominant in right-handed people, although bilateral activations are not uncommon in the area of syntactic processing. It is now accepted that the right hemisphere plays an important role in the processing of suprasegmental acoustic features like prosody
Prosody (linguistics)
In linguistics, prosody is the rhythm, stress, and intonation of speech. Prosody may reflect various features of the speaker or the utterance: the emotional state of the speaker; the form of the utterance ; the presence of irony or sarcasm; emphasis, contrast, and focus; or other elements of...
.
Most areas of speech processing develop in the second year of life in the dominant half (hemisphere
Cerebral hemisphere
A cerebral hemisphere is one of the two regions of the eutherian brain that are delineated by the median plane, . The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres has an outer layer of grey matter called the cerebral cortex that is...
) of the brain, which often (though not necessarily) corresponds to the opposite of the dominant hand
Handedness
Handedness is a human attribute defined by unequal distribution of fine motor skills between the left and right hands. An individual who is more dexterous with the right hand is called right-handed and one who is more skilled with the left is said to be left-handed...
. 98 percent of right-handed people are left-hemisphere dominant, and the majority of left-handed people as well.
Older models
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
, lead mainly to disruptions in speech reception. This area was named for German doctor Carl Wernicke, who discovered it in 1874 in the course of his research into aphasias
Aphasia
Aphasia is an impairment of language ability. This class of language disorder ranges from having difficulty remembering words to being completely unable to speak, read, or write....
(loss of ability to speak).
Broca's Area is today still considered an important language center, playing a central role in processing syntax, grammar, and sentence structure.
In summary, these early research efforts demonstrated that semantic and structural speech production takes place in different areas of the brain.
Further reading
- Donald Loritz: How the Brain evolved Language, Oxford University Press 1999, ISBN 0-19-511874-X (hardcover), ISBN 0-19-515124-0 (paperback)
- Friederici, A.D.: Towards a neural basis of auditory sentence processing. Trends in Cognitive Sciences, 6:78, 2002.
- Kaan, E. and Swaab, T.Y.: The brain circuitry of syntactic comprehension. Trends in Cognitive Sciences, 6:350, 2002.
- Dronkers, N.F., Pinker, S. & Damasio, A.: Language and the Aphasias. In: Kandel, E.R., Schwartz, J.H. & Jessel, T.M. (eds.) Principles of Neuroscience, Fourth Edition, New York: McGraw-Hill, 2000, 1169-1187