The human brain is separated by a longitudinal fissure, separating the brain into two distinct cerebral hemispheres by the corpus callosum. The two sides of the brain are similar in appearance, and every structure in each hemisphere is generally mirrored on the other side. Despite these strong similarities, the functions of each cortical hemisphere are different. The human brain controls the central nervous system (CNS), by way of the cranial nerves and spinal cord, the peripheral nervous system (PNS) and regulates virtually all human activity. ... The longitudinal fissure is the fissure (groove) that runs from the rostral to caudal portion of the brain, that serves to separate the left and right hemispheres. ... For other uses, see Brain (disambiguation). ... The human brain as viewed from above, showing the cerebral hemispheres. ... The corpus callosum is a structure of the mammalian brain in the longitudal fissure that connects the left and right cerebral hemispheres. ... Location of the cerebral cortex Slice of the cerebral cortex, ca. ...

Broad generalizations are often made in popular psychology about certain function (eg. logic, creativity) being lateralised, that is, located in the right or left side of the brain. These ideas need to be treated carefully because the popular lateralizations are often distributed across both sides.^[1] However, there is some division of mental processing. Probably most fundamental to brain lateralization is the fact that the lateral sulcus is generally longer in the left hemisphere than in the right hemisphere. Researchers have been investigating to what extent areas of the brain are specialized for certain functions. If a specific region of the brain is injured or destroyed, their functions can sometimes be recovered by neighboring brain regions - even opposite hemispheres. This depends more on the age and the damage occurred than anything else. This does not cite its references or sources. ... Lateral sulcus The lateral sulcus (also called Sylvian fissure or lateral fissure) is one of the most prominent structures of the human brain. ...

It is important to note that—while functions are indeed lateralized—these lateralizations are trends and do not apply to every person in every case. Short of having undergone a hemispherectomy (the removal of an entire cerebral hemisphere) there are no "left-brained only" or "right-brained only" people. Hemispherectomy is a medical procedure where one hemisphere (half) of the brain is removed. ...

Lateralization of brain functions is evident in the phenomena of right- or left-handedness, -earedness and -eyedness. But the handedness of a person is by no means a clear indication of location of brain function. While 95% of right handers have their language functions in the left hemisphere, only 18.8% of left-handers have their language function lateralized in the right hemisphere. Additionally, 19.8% of left-handers even have bilateral language functions.^[2]

Which side?

Linear reasoning functions of language such as grammar and word production are often lateralized to the left hemisphere of the brain. Dyscalculia is a neurological syndrome associated with damage to the left temporal-parietal junction^[3]. This syndrome is associated with poor number manipulation, poor mental arithmetic, and an inability to understand or apply mathematical concepts.^[4] For other uses, see Linear (disambiguation). ... For other uses, see Reason (disambiguation). ... This article or section is in need of attention from an expert on the subject. ... Neurology is a branch of medicine dealing with disorders of the nervous system. ... The temporal lobes are part of the cerebrum. ... The parietal lobe is a lobe in the brain. ... Arithmetic tables for children, Lausanne, 1835 Arithmetic or arithmetics (from the Greek word αριθμός = number) 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. ...

In contrast, holistic reasoning functions of language such as intonation and emphasis are often lateralized to the right hemisphere of the brain. Functions such as the transduction of visual and musical stimuli such as spatial manipulation, facial perception, and artistic ability also seem to be lateralized to the right hemisphere. Holism (from holon, a Greek word meaning entity) is the idea that the properties of a system cannot be determined or explained by the sum of its components alone. ... For other uses, see Reason (disambiguation). ... For other uses, see Music (disambiguation). ... Face perception is the process by which the brain and mind understand and interpret the face, particularly the human face. ...

Other integrative functions such as intuitive or heuristic arithmetic, binaural sound localization, emotions, etc. seem to be more bilaterally controlled.^[5] Look up Heuristic in Wiktionary, the free dictionary. ... For other uses, see Emotion (disambiguation). ...

^[6] For other uses, see Linear (disambiguation). ... Holism (from holon, a Greek word meaning entity) is the idea that the properties of a system cannot be determined or explained by the sum of its components alone. ... Euclid, Greek mathematician, 3rd century BC, as imagined by by Raphael in this detail from The School of Athens. ... Euclid, Greek mathematician, 3rd century BC, as imagined by by Raphael in this detail from The School of Athens. ...

History

Speech and language

Speech consists of the mechanical process required for vocalizations, such as articulation and phonation. Language is the set of arbitrary symbols used for communication, often in the form of words strung together following syntactical rules. In linguistics, manner of articulation describes how the tongue, lips, and other speech organs involved in making a sound make contact. ... In linguistics, manner of articulation describes how the tongue, lips, and other speech organs involved in making a sound make contact. ... In phonetics, phonation is the use of the laryngeal system to generate an audible source of acoustic energy, i. ... Communication is a process that allows organisms to exchange information by several methods. ... For other uses, see Word (disambiguation). ... For other uses, see Syntax (disambiguation). ...

Broca

One of the first indications of brain function laterality arose from research by French physician Paul Broca in 1861. Broca's research involved a patient nicknamed "Tan", who had a speech deficit (aphasia). One of the few words this patient could clearly articulate was "tan", leading to his nickname. Broca performed a post-mortem autopsy and determined that Tan had a lesion, caused by syphilis, in the left cerebral hemisphere. This brain area—in the left frontal lobe—is known as Broca's area and is an important region for speech production. Deficits in speech production caused by damage to Broca’s area are known as Broca's aphasia. In clinical assessment of this condition, it is noted that the patient lacks clear articulation of the language being employed. For other uses, see Doctor. ... Paul Pierre Broca (June 28, 1824 - July 9, 1880) was a French physician, anatomist and anthropologist. ... Year 1861 (MDCCCLXI) was a common year starting on Tuesday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Sunday of the 12-day slower Julian calendar). ... Look up aphasia in Wiktionary, the free dictionary. ... Post-mortem, postmortem and post mortem redirect here. ... Skin lesions caused by Chickenpox A lesion is any abnormal tissue found on or in an organism, usually damaged by disease or trauma. ... Syphilis is a sexually transmitted disease caused by Treponema pallidum. ... The frontal lobe is an area in the brain of mammals. ... Brocas area is the section of the human brain (in the opercular and triangular sections of the inferior frontal gyrus of the frontal lobe of the cortex) that is involved in language processing, speech production and comprehension. ... Expressive aphasia, known as Brocas aphasia in clinical neuropsychology and agrammatic aphasia in cognitive neuropsychology, is an aphasia caused by damage to Brocas area in the brain. ...

Wernicke

German physician Karl Wernicke followed up on the work done by Broca by studying language deficits unlike those shown by Broca's aphasics. Wernicke noticed that not all deficits were in speech production, but rather linguistic. He found that damage to the left posterior, superior temporal gyrus resulted in deficits in language comprehension rather than speech production. This region is now referred to as Wernicke's area, and the associated syndrome is known as Wernicke's aphasia. For other uses, see Doctor. ... Carl Wernicke -- 1848-1905. ... In sciences dealing with the anatomy of animals, precise anatomical terms of location are necessary for a variety of reasons. ... The temporal lobes are part of the cerebrum. ... Grays FIG. 726– Lateral surface of left cerebral hemisphere, viewed from the side. ... Wernickes area is a part of the human brain that forms part of the cortex, on the left posterior section of the superior temporal gyrus, encircling the auditory cortex, on the Sylvian fissure (part of the brain where the temporal lobe and parietal lobe meet). ... Receptive aphasia, also known as Wernickes aphasia in clinical neuropsychology and neologistic jargonaphasia in cognitive neuropsychology, is a type of aphasia caused by neurological damage to Wernickes area in the brain. ...

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 vivo 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. In vivo (Latin for (with)in the living). ... “MRI” redirects here. ... Image of a typical positron emission tomography (PET) facility Positron emission tomography (PET) is a nuclear medicine medical imaging technique which produces a three-dimensional image or map of functional processes in the body. ...

Handedness and language

Broca's area and Wernicke’s area are linked by a white matter fiber tract called the arcuate fasciculus. This axonal tract allows the neurons in these two areas to work together to create vocal language. In more than 95% of right-handed males and more than 90% of right-handed females, language and speech are subserved by the left hemisphere of the brain. In left-handed people, the incidence of left-hemisphere language dominance is 73% ^[7] or 61%^[2], depending on the studies. White matter is one of the two main solid components of the central nervous system. ... Figure one illustrates significant language areas of the brain. ... An axon or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ... Drawing by Santiago Ramón y Cajal of neurons in the pigeon cerebellum. ... A person who is right-handed is more dextrous with their right hand than with their left hand: they will write with their right hand, and probably also use this hand for tasks such as personal care, cooking, and so on. ... This article is about the Male sex. ... Look up Female in Wiktionary, the free dictionary. ... People who are left-handed are more dextrous with their left hand than with their right hand: they will probably also use their left hand for tasks such as personal care, cooking, and so on. ...

There are several ways of determining hemisphere dominance in a living human. The Wada test involves introducing an anesthetic into one hemisphere of the brain through one of the two carotid arteries. Once one hemisphere is anesthetized, a neuropsychological exam is performed to determine dominance for such functions as language production and comprehension, verbal memory, and visual memory. More modern, less invasive and, in some cases, costlier techniques, such as functional magnetic resonance imaging and transcranial magnetic stimulation, can also be used to determine dominance, but their use is controversial and still considered experimental. This article is about modern humans. ... The Wada test, also known as the intracarotid sodium amobarbital procedure (ISAP), is used to establish which cerebral functions are localised to which hemisphere. ... Anesthesia (AE), also anaesthesia (BE), is the process of blocking the perception of pain and other sensations. ... In human anatomy, the carotid artery is a major artery of the head and neck. ... Neuropsychology is a branch of psychology and neurology that aims to understand how the structure and function of the brain relate to specific psychological processes and overt behaviors. ... Functional magnetic resonance imaging (fMRI) is the use of MRI to measure the haemodynamic response related to neural activity in the brain or spinal cord of humans or other animals. ... Transcranial magnetic stimulation (TMS) is the use of powerful rapidly changing magnetic fields to induce electric fields in the brain by electromagnetic induction without the need for surgery or external electrodes. ...

Sensory and motor homunculi at the London Natural History Museum

Image File history File linksMetadata Download high resolution version (2048x1536, 1392 KB) Sensory and motor homunculi Photograph taken at the London Natural History Museum. ... Image File history File linksMetadata Download high resolution version (2048x1536, 1392 KB) Sensory and motor homunculi Photograph taken at the London Natural History Museum. ... The concept of a homunculus (Latin for little man, sometimes spelled homonculus, plural homunculi) is often used to illustrate the functioning of a system. ...

Movement and sensation

In the 1940s, Canadian neurosurgeon Wilder Penfield and his neurologist colleague Herbert Jasper developed a technique of brain mapping to help reduce side effects 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 could produce 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. This article does not cite any references or sources. ... Insertion of an electrode during neurosurgery for Parkinsons disease. ... Dr Wilder Graves Penfield, CC, OM, CMG, MD, FRS (January 25/26, 1891 – April 5, 1976) was a American-born Canadian neurosurgeon. ... Neurology is the branch of medicine that deals with the nervous system and disorders affecting it. ... Herbert Henri Jasper (July 27, 1906 – March 11, 1999) was a Canadian psychologist, physiologist, anatomist, chemist and neurologist. ... Adverse effect, in medicine, is an abnormal, harmful, undesired and/or unintended side-effect, although not necessarily unexpected, which is obtained as the result of a therapy or other medical intervention, such as drug/chemotherapy, physical therapy, surgery, medical procedure, use of a medical device, etc. ... “Surgeon” redirects here. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... The lateral postcentral gyrus is a prominent structure in the parietal lobe of the human brain and an important landmark. ... A top-down view of skeletal muscle Muscle (from Latin musculus little mouse [1]) is contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. ... Somatic sensation consists of the various sensory receptors that trigger the experiences labelled as touch or pressure, temperature (warm or cold), pain (including itch and tickle), and the sensations of muscle movement and joint position including posture, movement, and facial expression (collectively also called proprioception). ... The concept of a homunculus (Latin for little man, sometimes spelled homonculus, plural homunculi) is often used to illustrate the functioning of a system. ...

Split-brain patients

Research by Michael Gazzaniga 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 behavioral 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^[8]. Michael Gazzaniga is the David T. McLaughlin Distinguished University Professor at Dartmouth, where he is also Director of the Center for Cognitive Neuroscience. ... Image:Roger W Sperry. ... The 1960s decade refers to the years from 1960 to 1969, inclusive. ... Split-brain is the condition where the corpus callosum connecting the two halves of the brain is severed to some degree. ... The corpus callosum is a structure of the mammalian brain in the longitudal fissure that connects the left and right cerebral hemispheres. ... This article does not cite any references or sources. ...

Pseudoscientific exaggeration of the research

Hines (1987) 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 out of the implications of the research. For example, the implications of the research have no bearing on psychological interventions such as EMDR, brain training equipment, or management training. One explanation for being so prone to exaggeration and false application is that the left-right brain dichotomy is an easy-to-understand notion, yet is often grossly oversimplified and misused for promotion in the guise of science (Sala et al 1999). This is often known as right-brain mythology, and is associated with occult notions such as yin/yang, righteous and sinister, and day and night. The research on lateralization of brain functioning is ongoing, and its implications are always tightly delineated, whereas the pseudoscientific applications are exaggerated, and applied to an extremely wide range of situations. Niall Casey is great. Eye Movement Desensitisation and Reprocessing , also known by its abreviation EMDR, claims to relieve the symptoms of Post traumatic stress disorder (PTSD) and other mental health problems using originally only movements of the eyes similar to those which occur naturally in REM sleep. ...

See also

• Ambidexterity
• Cross-dominance
• Dual brain theory
• Eye dominance
• Handedness
• Laterality
• Left-handed
• Right-handed

Ambidexterity is the ability of being equally adept with each hand (or, to a limited degree, feet). ... Cross-dominance, also known as mixed-handedness, is a motor skill manifestation where a person favors one hand for some tasks and the other hand for others, while not necessarily being ambidextrous (two-handed), such as someone that writes with a left hand and grabs with the right. ... A theory 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 hemispheres exposure to harm. ... Eye dominance (sometimes called eyedness) refers to the tendency to use one eye more than the other in certain tasks involving precise hand-eye coordination and a reasonably distant target. ... For other uses, see Handedness (disambiguation). ... This does not adequately cite its references or sources. ... People who are left-handed are more dextrous with their left hand than with their right hand: they will probably also use their left hand for tasks such as personal care, cooking, and so on. ... A person who is right-handed is more dextrous with their right hand than with their left hand: they will write with their right hand, and probably also use this hand for tasks such as personal care, cooking, and so on. ...

References

• Goulven Josse, Nathalie Tzourio-Mazoyer (2003) Review: Hemispheric specialization for language. Brain Research Reviews 44 1–12.

• Hines, Terence (1987). Left Brain/Right Brain Mythology and Implications for Management and Training. The Academy of Management Review, 12:4, 600–606.
• Sala, (1999). Mind Myths: Exploring Popular Assumptions about the Mind and Brain. New York; Wiley

Further reading

• A.R. Luria, Higher cortical functions in man, Basic Books, 1966.
• Kandel E, Schwartz J, Jessel T. Principles of Neural Science. 4th ed. New York: McGraw-Hill; 2000. ISBN 0-8385-7701-6
• Gazzaniga, M.S., Ivry, R., & Mangun Eat Mushrooms, G.R. Fundamentals of Cognitive Neuroscience. 2nd ed. W.W. Norton, 2002. ISBN 0-393-97777-3
• Betty Edwards, The New Drawing on the Right Side of the Brain, revised & expanded edition. New York: Tarcher; August 30, 1999. ISBN 0-87477-424-1