Lateralization of brain function
Encyclopedia
A longitudinal fissure separates the human brain
into two distinct cerebral hemisphere
s, 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 cortical
hemisphere are managed differently. For example, the lateral sulcus
generally is longer in the left hemisphere than in the right hemisphere.
Broad generalizations are often made in popular psychology about one side or the other having characteristic labels such as "logical" or "creative". These labels need to be treated carefully; although a lateral dominance is measurable, these characteristics are in fact existent in both sides, and
experimental evidence provides little support for correlating the structural differences between the sides with functional differences.
The extent of any modularity, or specialization of brain function by area, remains under investigation. If a specific region of the brain or even an entire hemisphere is either injured or destroyed, its functions can sometimes be assumed by a neighboring region, even in the opposite hemisphere, depending upon the area damaged and the patient's age. When injury interferes with pathways from one area to another, alternative (indirect) connections may come to exist to communicate information with detached areas, despite the inefficiencies.
While functions are lateralized, these are only a tendency. They trend across the many individuals may also vary significantly as to how any specific function is implemented. The areas of exploration of this causal or effectual difference of a particular brain function includes its gross anatomy, dendritic structure, and neurotransmitter distribution. The structural and chemical variance of a particular, brain function, between the two hemispheres of one brain or between the same hemisphere of two different brains is still being studied. Short of having undergone a hemispherectomy
(removal of a cerebral hemisphere), no one is a "left-brain only" or "right-brain only" person.
Brain function lateralization is evident in the phenomena of right- or left-handedness and of right or left ear preference, but a person's preferred hand is not a clear indication of the location of brain function. Although 95% of right-handed people have left-hemisphere dominance for language, only 18.8% of left-handed people have right-hemisphere dominance for language function. Additionally, 19.8% of the left-handed have bilateral language functions. Even within various language functions (e.g., semantics, syntax, prosody), degree (and even hemisphere) of dominance may differ.
reason
ing and language
functions such as grammar and vocabulary often are lateralized to the left hemisphere of the brain. Dyscalculia
is a neurological
syndrome associated with damage to the left temporo
-parietal
junction. This syndrome is associated with poor numeric manipulation, poor mental arithmetic
skill, and the inability to either understand or apply mathematical concepts.
In contrast, prosodic
language functions, such as intonation
and accent
uation, often are lateralized to the right hemisphere of the brain. The processing of visual and audiological stimuli, spatial manipulation, facial perception
, and artistic ability seem to be functions of the right hemisphere. Depression is linked with a hyperactive right hemisphere, with evidence of selective involvement in "processing negative emotions, pessimistic thoughts and unconstructive thinking styles", as well as vigilance, arousal and self-reflection, and a relatively hypoactive left hemisphere, "specifically involved in processing pleasurable experiences" and "relatively more involved in decision-making processes". Additionally, "left hemisphere lesions result in an omissive response bias or error pattern whereas right hemisphere lesions result in a commissive response bias or error pattern." The delusional misidentification syndrome
s reduplicative paramnesia
and Capgras delusion
are also often the result of right hemisphere lesions. There is evidence that the right hemisphere is more involved in processing novel situations, while the left hemisphere is most involved when routine or well rehearsed processing is called for.
Other integrative functions, including arithmetic, binaural sound localization, and emotions (lateralization of emotion
), seem more bilaterally controlled.
); "tan" was one of the few words he could articulate, hence his nickname. In Tan's autopsy
, Broca determined he had a syphilitic lesion
in the left cerebral hemisphere. This left frontal lobe
brain area (Broca's area
) is an important speech production region. The motor aspects of speech production deficits caused by damage to Broca’s area are known as Broca's aphasia. In clinical assessment of this aphasia, it is noted that the patient cannot clearly articulate the language being employed.
physician
Karl Wernicke
continued in the vein of Broca's research by studying language deficits unlike Broca's aphasia. Wernicke noted that not every deficit was in speech production; some were linguistic. He found that damage to the left posterior
, superior temporal
gyrus
(Wernicke's area
) caused language comprehension deficits rather than speech production deficits, a syndrome known as Wernicke's aphasia.
comparison of the hemispheres in healthy subjects. Particularly, magnetic resonance imaging
(MRI) and positron emission tomography
(PET) are important because of their high spatial resolution and ability to image subcortical brain structures.
fiber tract, the arcuate fasciculus
. This axon
al tract allows the neurons in the two areas to work together in creating vocal language. In more than 95% of right-handed men, and more than 90% of right-handed women, language and speech are subserved by the brain's left hemisphere. In left-handed people, the incidence of left-hemisphere language dominance has been reported as 73% and 61%.
There are ways of determining hemispheric dominance in a person. The Wada Test
introduces an anesthetic to one hemisphere of the brain via one of the two carotid arteries
. Once the hemisphere is anesthetized, a neuropsychological
examination is effected to determine dominance for language production, language comprehension, verbal memory
, and visual memory functions. Less invasive (sometimes costlier) techniques, such as functional magnetic resonance imaging
and Transcranial magnetic stimulation
, also are used to determine hemispheric dominance; usage remains controversial for being experimental.
based neurosurgeon
Wilder Penfield
and his neurologist
colleague Herbert Jasper
developed a technique of brain mapping to help reduce side effect
s caused by surgery
to treat epilepsy
. They stimulated motor
and somatosensory cortices of the brain with small electrical currents to activate discrete brain regions. They found that stimulation of one hemisphere's motor cortex produces muscle
contraction on the opposite side of the body. Furthermore, the functional map of the motor and sensory
cortices is fairly consistent from person to person; Penfield and Jasper's famous pictures of the motor and sensory homunculi
were the result.
and Roger Wolcott Sperry
in the 1960s on split-brain
patients led to an even greater understanding of functional laterality. Split-brain patients are patients who have undergone corpus callosotomy
(usually as a treatment for severe epilepsy), a severing of a large part of the corpus callosum
. The corpus callosum connects the two hemispheres of the brain and allows them to communicate. When these connections are cut, the two halves of the brain have a reduced capacity to communicate with each other. This led to many interesting behavior
al phenomena that allowed Gazzaniga and Sperry to study the contributions of each hemisphere to various cognitive and perceptual processes. One of their main findings was that the right hemisphere was capable of rudimentary language processing, but often has no lexical or grammatical abilities. Eran Zaidel, however, also studied such patients and found some evidence for the right hemisphere having at least some syntactic ability.
For example: Patients with brain damage from surgery, stroke or infection sometimes develop a syndrome in which they can feel sensations in their hand, but they don't feel responsible for nor able to control its movements. In patients with a corpus callostomy, alien hand syndrome
most often manifests as uncontrolled but purposeful movements of the nondominant hand.
states that the research on brain lateralization is valid as a research program, though commercial promoters have applied it to promote subjects and products far outside the implications of the research. For example, the implications of the research have no bearing on psychological interventions such as EMDR and neurolinguistic programming, brain training equipment, or management training.
, frogs, reptile
s, bird
s and mammal
s with the left hemisphere being specialized to categorize information and control everyday, routine behavior, with the right hemisphere responsible for responses to novel events and behavior in emergencies including the expression of intense emotions. An example of a routine left hemisphere behavior is feeding behavior whereas as a right hemisphere is escape from predators and attacks from conspecifics.
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
into two distinct cerebral 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...
s, connected by the corpus callosum
Corpus callosum
The 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...
. 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 cortical
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...
hemisphere are managed differently. For example, the lateral sulcus
Lateral sulcus
-External links:* * * http://www.uams.edu/radiology/education/residency/diagnostic/pdf/sylvian_cistern_RSNA2003.pdf...
generally is longer in the left hemisphere than in the right hemisphere.
Broad generalizations are often made in popular psychology about one side or the other having characteristic labels such as "logical" or "creative". These labels need to be treated carefully; although a lateral dominance is measurable, these characteristics are in fact existent in both sides, and
experimental evidence provides little support for correlating the structural differences between the sides with functional differences.
The extent of any modularity, or specialization of brain function by area, remains under investigation. If a specific region of the brain or even an entire hemisphere is either injured or destroyed, its functions can sometimes be assumed by a neighboring region, even in the opposite hemisphere, depending upon the area damaged and the patient's age. When injury interferes with pathways from one area to another, alternative (indirect) connections may come to exist to communicate information with detached areas, despite the inefficiencies.
While functions are lateralized, these are only a tendency. They trend across the many individuals may also vary significantly as to how any specific function is implemented. The areas of exploration of this causal or effectual difference of a particular brain function includes its gross anatomy, dendritic structure, and neurotransmitter distribution. The structural and chemical variance of a particular, brain function, between the two hemispheres of one brain or between the same hemisphere of two different brains is still being studied. Short of having undergone a hemispherectomy
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...
(removal of a cerebral hemisphere), no one is a "left-brain only" or "right-brain only" person.
Brain function lateralization is evident in the phenomena of right- or left-handedness and of right or left ear preference, but a person's preferred hand is not a clear indication of the location of brain function. Although 95% of right-handed people have left-hemisphere dominance for language, only 18.8% of left-handed people have right-hemisphere dominance for language function. Additionally, 19.8% of the left-handed have bilateral language functions. Even within various language functions (e.g., semantics, syntax, prosody), degree (and even hemisphere) of dominance may differ.
Left vs. right
LinearLinear
In mathematics, a linear map or function f is a function which satisfies the following two properties:* Additivity : f = f + f...
reason
Reason
Reason 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 and 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...
functions such as grammar and vocabulary often are lateralized to the left hemisphere of the brain. Dyscalculia
Dyscalculia
Dyscalculia is a specific learning disability involving innate difficulty in learning or comprehending simple arithmetic. It is akin to dyslexia and includes difficulty in understanding numbers, learning how to manipulate numbers, learning maths facts, and a number of other related symptoms...
is a neurological
Neurology
Neurology is a medical specialty dealing with disorders of the nervous system. Specifically, it deals with the diagnosis and treatment of all categories of disease involving the central, peripheral, and autonomic nervous systems, including their coverings, blood vessels, and all effector tissue,...
syndrome associated with damage to the left temporo
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....
-parietal
Parietal lobe
The parietal lobe is a part of the Brain positioned above the occipital lobe and behind the frontal lobe.The parietal lobe integrates sensory information from different modalities, particularly determining spatial sense and navigation. For example, it comprises somatosensory cortex and the...
junction. This syndrome is associated with poor numeric manipulation, poor mental arithmetic
Arithmetic
Arithmetic or arithmetics is the oldest and most elementary branch of mathematics, used by almost everyone, for tasks ranging from simple day-to-day counting to advanced science and business calculations. It involves the study of quantity, especially as the result of combining numbers...
skill, and the inability to either understand or apply mathematical concepts.
In contrast, prosodic
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...
language functions, such as intonation
Intonation (linguistics)
In linguistics, intonation is variation of pitch while speaking which is not used to distinguish words. It contrasts with tone, in which pitch variation does distinguish words. Intonation, rhythm, and stress are the three main elements of linguistic prosody...
and accent
Accent (linguistics)
In linguistics, an accent is a manner of pronunciation peculiar to a particular individual, location, or nation.An accent may identify the locality in which its speakers reside , the socio-economic status of its speakers, their ethnicity, their caste or social class, their first language In...
uation, often are lateralized to the right hemisphere of the brain. The processing of visual and audiological stimuli, spatial manipulation, facial perception
Face perception
Face perception is the process by which the brain and mind understand and interpret the face, particularly the human face.The human face's proportions and expressions are important to identify origin, emotional tendencies, health qualities, and some social information. From birth, faces are...
, and artistic ability seem to be functions of the right hemisphere. Depression is linked with a hyperactive right hemisphere, with evidence of selective involvement in "processing negative emotions, pessimistic thoughts and unconstructive thinking styles", as well as vigilance, arousal and self-reflection, and a relatively hypoactive left hemisphere, "specifically involved in processing pleasurable experiences" and "relatively more involved in decision-making processes". Additionally, "left hemisphere lesions result in an omissive response bias or error pattern whereas right hemisphere lesions result in a commissive response bias or error pattern." The delusional misidentification syndrome
Delusional misidentification syndrome
Delusional misidentification syndrome is an umbrella term, introduced by Christodoulou for a group of delusional disorders that occur in the context of mental or neurological illness. They all involve a belief that the identity of a person, object or place has somehow changed or has been altered...
s reduplicative paramnesia
Reduplicative paramnesia
Reduplicative paramnesia is the delusional belief that a place or location has been duplicated, existing in two or more places simultaneously, or that it has been 'relocated' to another site...
and Capgras delusion
Capgras delusion
The Capgras delusion theory is a disorder in which a person holds a delusion that a friend, spouse, parent, or other close family member has been replaced by an identical-looking impostor...
are also often the result of right hemisphere lesions. There is evidence that the right hemisphere is more involved in processing novel situations, while the left hemisphere is most involved when routine or well rehearsed processing is called for.
Other integrative functions, including arithmetic, binaural sound localization, and emotions (lateralization of emotion
Emotional lateralization
Emotional lateralization is the asymmetrical representation of emotional control and processing in the brain. There is evidence for the lateralization of other brain functions too....
), seem 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, pragmatic, contextual |
Broca
One of the first indications of brain function lateralization resulted from the research of French physician Pierre Paul Broca, in 1861. His research involved the male patient nicknamed "Tan", who suffered a speech deficit (aphasiaAphasia
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....
); "tan" was one of the few words he could articulate, hence his nickname. In Tan's autopsy
Autopsy
An autopsy—also known as a post-mortem examination, necropsy , autopsia cadaverum, or obduction—is a highly specialized surgical procedure that consists of a thorough examination of a corpse to determine the cause and manner of death and to evaluate any disease or injury that may be present...
, Broca determined he had a syphilitic lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
in the left cerebral hemisphere. This left frontal lobe
Frontal lobe
The frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...
brain area (Broca's area
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...
) is an important speech production region. The motor aspects of speech production deficits caused by damage to Broca’s area are known as Broca's aphasia. In clinical assessment of this aphasia, it is noted that the patient cannot clearly articulate the language being employed.
Wernicke
GermanGermany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
physician
Physician
A physician is a health care provider who practices the profession of medicine, which is concerned with promoting, maintaining or restoring human health through the study, diagnosis, and treatment of disease, injury and other physical and mental impairments...
Karl Wernicke
Karl Wernicke
Carl Wernicke was a German physician, anatomist, psychiatrist and neuropathologist. He earned his medical degree at the University of Breslau...
continued in the vein of Broca's research by studying language deficits unlike Broca's aphasia. Wernicke noted that not every deficit was in speech production; some were linguistic. He found that damage to the left posterior
Anatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
, superior temporal
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....
gyrus
Gyrus
A gyrus is a ridge on the cerebral cortex. It is generally surrounded by one or more sulci .-Notable gyri:* Superior frontal gyrus, lat. gyrus frontalis superior* Middle frontal gyrus, lat. gyrus frontalis medius...
(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...
) caused language comprehension deficits rather than speech production deficits, a syndrome known as Wernicke's aphasia.
Advance in imaging technique
These seminal works on hemispheric specialization were done on patients and/or postmortem brains, raising questions about the potential impact of pathology on the research findings. New methods permit the in vivoIn vivo
In vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...
comparison of the hemispheres in healthy subjects. Particularly, magnetic resonance imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
(MRI) and positron emission tomography
Positron 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...
(PET) are important because of their high spatial resolution and ability to image subcortical brain structures.
Handedness and language
Broca's Area and Wernicke’s Area are linked by a white matterWhite matter
White 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...
fiber tract, the arcuate fasciculus
Arcuate fasciculus
The arcuate fasciculus is the neural pathway connecting the posterior part of the temporoparietal junction with the frontal cortex in the brain and is now considered as part of the superior longitudinal fasciculus..-Neuroanatomy:...
. This axon
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....
al tract allows the neurons in the two areas to work together in creating vocal language. In more than 95% of right-handed men, and more than 90% of right-handed women, language and speech are subserved by the brain's left hemisphere. In left-handed people, the incidence of left-hemisphere language dominance has been reported as 73% and 61%.
There are ways of determining hemispheric dominance in a person. The Wada Test
Wada test
The Wada test, named after Canadian neurologist and epileptologist Juhn Atsushi Wada, also known as the "intracarotid sodium amobarbital procedure" , is used to establish cerebral language and memory representation of each hemisphere.-Method:...
introduces an anesthetic to one hemisphere of the brain via one of the two carotid arteries
Carotid artery
Carotid artery can refer to:* Common carotid artery* External carotid artery* Internal carotid artery...
. Once the hemisphere is anesthetized, a neuropsychological
Neuropsychology
Neuropsychology studies the structure and function of the brain related to specific psychological processes and behaviors. The term neuropsychology has been applied to lesion studies in humans and animals. It has also been applied to efforts to record electrical activity from individual cells in...
examination is effected to determine dominance for language production, language comprehension, verbal memory
Verbal memory
Verbal memory is a term used in Cognitive Psychology that refers to memory of words and other abstractions involving language.-Verbal Encoding:Verbal Encoding refers to the interpretation of verbal stimuli...
, and visual memory functions. Less invasive (sometimes costlier) techniques, such as functional magnetic resonance imaging
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...
and Transcranial magnetic stimulation
Transcranial magnetic stimulation
Transcranial magnetic stimulation is a noninvasive method to cause depolarization or hyperpolarization in the neurons of the brain...
, also are used to determine hemispheric dominance; usage remains controversial for being experimental.
Movement and sensation
In the 1940s, American born, MontrealMontreal
Montreal is a city in Canada. It is the largest city in the province of Quebec, the second-largest city in Canada and the seventh largest in North America...
based neurosurgeon
Neurosurgery
Neurosurgery is the medical specialty concerned with the prevention, diagnosis, treatment, and rehabilitation of disorders which affect any portion of the nervous system including the brain, spine, spinal cord, peripheral nerves, and extra-cranial cerebrovascular system.-In the United States:In...
Wilder Penfield
Wilder Penfield
Wilder Graves Penfield, OM, CC, CMG, FRS was an American born Canadian neurosurgeon. During his life he was called "the greatest living Canadian"...
and his neurologist
Neurologist
A neurologist is a physician who specializes in neurology, and is trained to investigate, or diagnose and treat neurological disorders.Neurology is the medical specialty related to the human nervous system. The nervous system encompasses the brain, spinal cord, and peripheral nerves. A specialist...
colleague Herbert Jasper
Herbert Jasper
Herbert Henri Jasper, was a Canadian psychologist, physiologist, anatomist, chemist and neurologist.Born in La Grande, Oregon, he attended Reed College in Portland, Oregon and received his PhD in psychology from the University of Iowa in 1931 and earned a Doctor of Science degree from the...
developed a technique of brain mapping to help reduce side effect
Adverse effect (medicine)
In medicine, an adverse effect is a harmful and undesired effect resulting from a medication or other intervention such as surgery.An adverse effect may be termed a "side effect", when judged to be secondary to a main or therapeutic effect. If it results from an unsuitable or incorrect dosage or...
s caused by surgery
Surgery
Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...
to treat epilepsy
Epilepsy
Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...
. They stimulated motor
Motor cortex
Motor cortex is a term that describes regions of the cerebral cortex involved in the planning, control, and execution of voluntary motor functions.-Anatomy of the motor cortex :The motor cortex can be divided into four main parts:...
and somatosensory cortices of the brain with small electrical currents to activate discrete brain regions. They found that stimulation of one hemisphere's motor cortex produces muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
contraction on the opposite side of the body. Furthermore, the functional map of the motor and sensory
Somatosensory system
The somatosensory system is a diverse sensory system composed of the receptors and processing centres to produce the sensory modalities such as touch, temperature, proprioception , and nociception . The sensory receptors cover the skin and epithelia, skeletal muscles, bones and joints, internal...
cortices is fairly consistent from person to person; Penfield and Jasper's famous pictures of the motor and sensory homunculi
Cortical homunculus
A cortical homunculus is a pictorial representation of the anatomical divisions of the primary motor cortex and the primary somatosensory cortex , i.e., the portion of the human brain directly responsible for the movement and exchange of sense and motor information of the rest of the body.There...
were the result.
Split-brain patients
Research by Michael GazzanigaMichael 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...
and Roger Wolcott Sperry
Roger Wolcott Sperry
Roger Wolcott Sperry was a neuropsychologist, neurobiologist and Nobel laureate who, together with David Hunter Hubel and Torsten Nils Wiesel, won the 1981 Nobel Prize in Medicine for his work with split-brain research....
in the 1960s on split-brain
Split-brain
Split-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 led to an even greater understanding of functional laterality. Split-brain patients are patients who have undergone corpus callosotomy
Corpus callosotomy
Corpus callosotomy is a surgical procedure that disconnects the cerebral hemispheres, resulting in a condition called split-brain....
(usually as a treatment for severe epilepsy), a severing of a large part of the corpus callosum
Corpus callosum
The 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...
. The corpus callosum connects the two hemispheres of the brain and allows them to communicate. When these connections are cut, the two halves of the brain have a reduced capacity to communicate with each other. This led to many interesting behavior
Behavior
Behavior or behaviour refers to the actions and mannerisms made by organisms, systems, or artificial entities in conjunction with its environment, which includes the other systems or organisms around as well as the physical environment...
al phenomena that allowed Gazzaniga and Sperry to study the contributions of each hemisphere to various cognitive and perceptual processes. One of their main findings was that the right hemisphere was capable of rudimentary language processing, but often has no lexical or grammatical abilities. Eran Zaidel, however, also studied such patients and found some evidence for the right hemisphere having at least some syntactic ability.
For example: Patients with brain damage from surgery, stroke or infection sometimes develop a syndrome in which they can feel sensations in their hand, but they don't feel responsible for nor able to control its movements. In patients with a corpus callostomy, alien hand syndrome
Alien hand syndrome
Alien hand syndrome is a neurological disorder in which the afflicted person's hand appears to take on a mind of its own...
most often manifests as uncontrolled but purposeful movements of the nondominant hand.
Exaggeration
Terence HinesTerence Hines
-Career:*Adjunct Professor of Neurology at New York Medical College.*Professor of Psychology at Pace University, Pleasantville, New York.- Works :*1987 Pseudoscience and the Paranormal; ISBN 0879754125...
states that the research on brain lateralization is valid as a research program, though commercial promoters have applied it to promote subjects and products far outside the implications of the research. For example, the implications of the research have no bearing on psychological interventions such as EMDR and neurolinguistic programming, brain training equipment, or management training.
Nonhuman brain lateralization
Specialization of the two hemispheres is general in vertebrates including fishFish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
, frogs, reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s, bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s and mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s with the left hemisphere being specialized to categorize information and control everyday, routine behavior, with the right hemisphere responsible for responses to novel events and behavior in emergencies including the expression of intense emotions. An example of a routine left hemisphere behavior is feeding behavior whereas as a right hemisphere is escape from predators and attacks from conspecifics.
See also
- AmbidexterityAmbidexterityAmbidexterity is the state of being equally adept in the use of both left and right appendages . It is one of the most famous varieties of cross-dominance. People that are naturally ambidextrous are rare, with only one out of one hundred people being naturally ambidextrous...
- BicameralismBicameralism (psychology)Bicameralism is a hypothesis in psychology that argues that the human brain once assumed a state in which cognitive functions were divided between one part of the brain which appears to be "speaking", and a second part which listens and obeys—a bicameral mind...
- Brain asymmetryBrain asymmetryBrain asymmetry can refer to at least two quite distinct findings:* Neuroanatomical differences between the left and right sides of the brain* Lateralized functional differences: Lateralization of brain function...
- Cross-dominanceCross-dominanceCross-dominance, also known as mixed-handedness, mixed dominance, or hand-confusion, is a motor skill manifestation where a person favors one hand for some tasks and the other hand for others. For example, a cross-dominant person might write with the left hand but throw primarily with the right...
- Dual brain theoryDual brain theoryThe dual brain theory claims that the two cerebral hemispheres of the brain may sense and react to the environment independently from one another and that as a result of traumatic experience, one half may dominate the other in order to reduce the traumatized hemisphere's exposure to harm.This...
- HandednessHandednessHandedness 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...
- LateralityLateralityLaterality is the preference that most humans show for one side of their body over the other. Examples include right-handedness or left-footedness. It may also apply to other animals, or to plants.- Human laterality :...
- Left brain interpreterLeft brain interpreterIn neuropsychology the left brain interpreter refers to the construction of explanations by the left brain in order to make sense of the world by reconciling new information with what was known before...
Bookmarks
- Lateralization of Brain Function bookmarks on Faviki, the tagging engine that uses DBPediaDBpediaDBpedia is a project aiming to extract structured content from the information created as part of the Wikipedia project. This structured information is then made available on the World Wide Web. DBpedia allows users to query relationships and properties associated with Wikipedia resources,...
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