A
cerebral hemisphere is one of the two regions of the
eutheriaEutheria is a group of mammals consisting of placental mammals plus all extinct mammals that are more closely related to living placentals than to living marsupials . They are distinguished from noneutherians by various features of the feet, ankles, jaws and teeth...
n
brainThe 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,...
that are delineated by the median plane, (
medial longitudinal fissureThe great longitudinal fissure is the deep groove which separates the two hemispheres of the vertebrate brain....
). 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 matterGrey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil , glial cells and capillaries. Grey matter contains neural cell bodies, in contrast to white matter, which does not and mostly contains myelinated axon tracts...
called the
cerebral cortexThe 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...
that is supported by an inner layer of
white matterWhite matter is one of the two components of the central nervous system and consists mostly of myelinated axons. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color is due to...
. The hemispheres are linked by the
corpus callosumThe corpus callosum , also known as the colossal commissure, is a wide, flat bundle of neural fibers beneath the cortex in the eutherian brain at the longitudinal fissure. It connects the left and right cerebral hemispheres and facilitates interhemispheric communication...
, a very large bundle of nerve fibers, and also by other smaller commissures, including the
anterior commissureThe anterior commissure is a bundle of nerve fibers , connecting the two cerebral hemispheres across the midline, and placed in front of the columns of the fornix...
,
posterior commissureThe posterior commissure is a rounded band of white fibers crossing the middle line on the dorsal aspect of the upper end of the cerebral aqueduct. It is important in the bilateral pupillary light reflex....
, and hippocampal commissure. These commissures transfer information between the two hemispheres to coordinate localized functions.
A
cerebral hemisphere is one of the two regions of the
eutheriaEutheria is a group of mammals consisting of placental mammals plus all extinct mammals that are more closely related to living placentals than to living marsupials . They are distinguished from noneutherians by various features of the feet, ankles, jaws and teeth...
n
brainThe 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,...
that are delineated by the median plane, (
medial longitudinal fissureThe great longitudinal fissure is the deep groove which separates the two hemispheres of the vertebrate brain....
). 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 matterGrey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil , glial cells and capillaries. Grey matter contains neural cell bodies, in contrast to white matter, which does not and mostly contains myelinated axon tracts...
called the
cerebral cortexThe 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...
that is supported by an inner layer of
white matterWhite matter is one of the two components of the central nervous system and consists mostly of myelinated axons. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color is due to...
. The hemispheres are linked by the
corpus callosumThe corpus callosum , also known as the colossal commissure, is a wide, flat bundle of neural fibers beneath the cortex in the eutherian brain at the longitudinal fissure. It connects the left and right cerebral hemispheres and facilitates interhemispheric communication...
, a very large bundle of nerve fibers, and also by other smaller commissures, including the
anterior commissureThe anterior commissure is a bundle of nerve fibers , connecting the two cerebral hemispheres across the midline, and placed in front of the columns of the fornix...
,
posterior commissureThe posterior commissure is a rounded band of white fibers crossing the middle line on the dorsal aspect of the upper end of the cerebral aqueduct. It is important in the bilateral pupillary light reflex....
, and hippocampal commissure. These commissures transfer information between the two hemispheres to coordinate localized functions.
Macroscopically the hemispheres are roughly mirror images of each other, with only subtle differences (e.g.
Yakovlevian torqueYakovlevian torque is the tendency of the right side of the human brain to be warped slightly forward relative to the left. This is responsible for certain asymmetries, such as how the lateral sulcus of the human brain is often longer and less curved on the left side of the brain relative to the...
). On a microscopic level, the
architectureThe cytoarchitectonics of the cerebral cortex is the study of neuronal cell bodies cytoarchitecture in the cerebral cortex of the brain.-History:...
, types of cells, types of
neurotransmitterNeurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...
s and
receptorIn biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...
subtypes are markedly asymmetrical between the two hemispheres. However, while some of these hemispheric distribution differences are consistent across human beings, or even across some species, many observable distribution differences vary from individual to individual within a given species.
Embryological development
The
cerebral hemispheres are derived from the
telencephalonThe cerebrum or telencephalon, together with the diencephalon, constitutes the forebrain. The cerebrum is the most anterior region of the vertebrate central nervous system. Telencephalon refers to the embryonic structure, from which the mature cerebrum develops...
. They arise five weeks after conception as bilateral invaginations of the walls.
The hemispheres grow round in a C-shape and then back again, pulling all structures internal to the hemispheres (such as the
ventriclesThe ventricular system is a set of structures containing cerebrospinal fluid in the brain. It is continuous with the central canal of the spinal cord.-Components:The system comprises four ventricles:* right and left lateral ventricles* third ventricle...
) with them.
The interventricular foramen (sometimes called the interventricular foramena of munro) allows communication with the lateral ventricle.
The
choroid plexusThe choroid plexus is a structure in the ventricles of the brain where cerebrospinal fluid is produced...
is formed from ependymal cells and vascular
mesenchymeMesenchyme, or mesenchymal connective tissue, is a type of undifferentiated loose connective tissue that is derived mostly from mesoderm, although some are derived from other germ layers; e.g. some mesenchyme is derived from neural crest cells and thus originates from the ectoderm...
.
Hemisphere lateralization
Broad generalizations are often made in
popular psychologyThe term popular psychology refers to concepts and theories about human mental life and behavior that are purportedly based on psychology and that attain popularity among the general population...
about certain functions (e.g. logic, creativity) being lateralized, that is, located in the right or left side of the brain. These claims are often inaccurate, as most brain functions are actually distributed across both hemispheres. Most scientific evidence for asymmetry relates to low-level perceptual functions rather than the higher-level functions popularly discussed (e.g. subconscious processing of grammar, not "logical thinking" in general).
The best evidence of lateralization for one specific ability is
languageLanguage 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...
. Both of the major areas involved in language skills,
Broca's areaBroca'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 areaWernicke'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...
, are in the left hemisphere.
Perceptual informationPerception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs...
is processed in both hemispheres, but is laterally partitioned: information from each side of the body is sent to the opposite hemisphere (visual information is partitioned Optic radiation, but still lateralized). Similarly, motor control signals sent out to the body also come from the hemisphere on the opposite side. Thus,
Hand preferenceHandedness 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...
(which hand someone prefers to use) is also related to hemisphere lateralization.
NeuropsychologistsNeuroscience is the scientific study of the nervous system. Traditionally, neuroscience has been seen as a branch of biology. However, it is currently an interdisciplinary science that collaborates with other fields such as chemistry, computer science, engineering, linguistics, mathematics,...
(e.g. Roger Sperry,
Michael GazzanigaMichael S. Gazzaniga is a professor of psychology at the University of California, Santa Barbara, where he heads the new SAGE Center for the Study of the Mind. He is one of the leading researchers in cognitive neuroscience, the study of the neural basis of mind...
) have studied
split-brainSplit-brain is a lay term to describe the result when the corpus callosum connecting the two hemispheres of the brain is severed to some degree. The surgical operation to produce this condition is called corpus callosotomy and is usually used as a last resort to treat otherwise intractable epilepsy...
patients to better understand lateralization. Sperry pioneered the use of lateralized
tachistoscopeA tachistoscope is a device that displays an image for a specific amount of time. It can be used to increase recognition speed, to show something too fast to be consciously recognized, or to test which elements of an image are memorable. Actual tachistoscopes use a slide or transparency projector...
s to present visual information to one hemisphere or the other. Scientists have also studied people born without a
corpus callosumThe corpus callosum , also known as the colossal commissure, is a wide, flat bundle of neural fibers beneath the cortex in the eutherian brain at the longitudinal fissure. It connects the left and right cerebral hemispheres and facilitates interhemispheric communication...
to determine specialization of brain hemispheres.
The magnocellular pathway of the visual system sends more information to the right hemisphere, while the parvocellular pathway sends more information to the left hemisphere.
In some respects, the hemispheres are asymmetrical. There are higher levels of the neurotransmitter
norepinephrineNorepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...
on the right and higher levels of
dopamineDopamine is a catecholamine neurotransmitter present in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this substituted phenethylamine functions as a neurotransmitter, activating the five known types of dopamine receptors—D1, D2, D3, D4, and D5—and their...
on the left. There is more white matter (longer axons) on right and more grey matter (cell bodies) on the left.
LinearIn mathematics, a linear map or function f is a function which satisfies the following two properties:* Additivity : f = f + f...
reasonReason is a term that refers to the capacity human beings have to make sense of things, to establish and verify facts, and to change or justify practices, institutions, and beliefs. It is closely associated with such characteristically human activities as philosophy, science, language, ...
ing functions of
languageLanguage 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...
such as grammar and word production are often lateralized to the left hemisphere of the brain. In contrast, holistic
reasonReason is a term that refers to the capacity human beings have to make sense of things, to establish and verify facts, and to change or justify practices, institutions, and beliefs. It is closely associated with such characteristically human activities as philosophy, science, language, ...
ing functions of
languageLanguage 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...
such as intonation and emphasis are often lateralized to the right hemisphere of the brain. Other integrative functions such as intuitive or
heuristicHeuristic refers to experience-based techniques for problem solving, learning, and discovery. Heuristic methods are used to speed up the process of finding a satisfactory solution, where an exhaustive search is impractical...
arithmetic, binaural sound localization,
emotionEmotion is a complex psychophysiological experience of an individual's state of mind as interacting with biochemical and environmental influences. In humans, emotion fundamentally involves "physiological arousal, expressive behaviors, and conscious experience." Emotion is associated with mood,...
s, etc. seem to be more bilaterally controlled.
| Left hemisphere functions |
Right hemisphere functions |
numerical computation (exact calculation, numerical comparison, estimation)
left hemisphere only: direct fact retrieval |
numerical computation (approximate calculation, numerical comparison, estimation) |
| language: grammar/vocabulary, literal |
language: intonation/accentuation, prosody 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...
, pragmatic, contextual |
See also
- Michael Gazzaniga
Michael S. Gazzaniga is a professor of psychology at the University of California, Santa Barbara, where he heads the new SAGE Center for the Study of the Mind. He is one of the leading researchers in cognitive neuroscience, the study of the neural basis of mind...
- Paul Broca
Pierre Paul Broca was a French physician, surgeon, anatomist, and anthropologist. He was born in Sainte-Foy-la-Grande, Gironde. He is best known for his research on Broca's area, a region of the frontal lobe that has been named after him. Broca’s Area is responsible for articulated language...
- Manas K. Mandal
Manas Kumar Mandal, is a scientist and psychologist who is the director of the Defence Institute of Psychological Research, Delhi, India since January 5, 2004.Manas Mandal VDO , Rajakata , Ranibandh , Bankura , Westbengal , India-Research areas:...
- Hemispherectomy
Hemispherectomy is a very rare surgical procedure where one cerebral hemisphere is removed or disabled. This procedure is used to treat a variety of seizure disorders where the source of the epilepsy is localized to a broad area of a single hemisphere of the brain...
- Elkhonon Goldberg
Elkhonon Goldberg is a neuropsychologist and cognitive neuroscientist known for his work in hemispheric specialization and the "novelty-routinization" theory.- Biography :...