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{{BioPsy}}
 
{{BioPsy}}
The [[human brain]] is separated by a [[longitudinal fissure]], separating the [[brain]] into two distinct [[cerebral hemisphere]]s ([[left hemisphere]] and [[right hemisphere]]) connected 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 [[cerebral cortex|cortical]] hemisphere are different.
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{{About|specialization of function between the left and right hemispheres of the brain|specialization of brain function generally| Functional specialization (brain)}}
   
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.<ref name="Western 2006">Western et al. 2006 "Psychology: Austraian and New Zealand edition" John Wiley p.107</ref> 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.
 
   
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.
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{{Image|Cerebral lobes.png|thumb|right|alt=Diagram of the human brain.|The human brain is divided into two hemispheres&ndash;left and right. Scientists continue to explore how some cognitive functions tend to be dominated by one side or the other; that is, how they are ''lateralized''.}}
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The [[longitudinal fissure]] separates the [[human brain]] into two distinct [[cerebral hemisphere]]s, connected by the [[corpus callosum]]. The hemispheres exhibit strong, but not complete, [[symmetry in biology#bilateral symmetry|bilateral symmetry]] in both structure and function. For example, structurally, the [[lateral sulcus]] generally is longer in the left hemisphere than in the right hemisphere, and functionally, [[Broca's area]] and [[Wernicke's area]] are present only in the left hemisphere in greater than 95% of the population.
   
Lateralization of brain functions is evident in the phenomena of [[handedness]] (right- or left-handedness), [[aural dominance]] - (earedness) and [[Ocular dominance]] - (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.<ref name="psycho2">Taylor, Insep and Taylor, M. Martin (1990) "Psycholinguistics: Learning and using Language". page 362</ref>
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Broad generalizations are often made in popular psychology about one side ''or'' the other having characteristic labels, such as "logical" for the left side or "creative" for the right. These labels are not supported by studies on lateralization, as lateralization does not add specialized usage from either hemisphere. <ref name = Nielsen>Nielsen, Jared A., Brandon A. Zielinski, Michael A. Ferguson, Janet E. Lainhart, and Jeffrey S. Anderson. [http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0071275 "An Evaluation of the Left-Brain vs. Right-Brain Hypothesis with Resting State Functional Connectivity Magnetic Resonance Imaging."] PLOS ONE, 14 Aug. 2013. Web. 30 Aug. 2013.</ref> Both hemispheres contribute to both kinds of processes.<ref name="Westen 2006">Westen et al. 2006 ''Psychology: Australian and New Zealand edition''. John Wiley p.107</ref> and experimental evidence provides little support for correlating the structural differences between the sides with such broadly-defined functional differences.<ref>{{cite PMID|12511860}}</ref>
   
==Which side? ==
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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 in the ipsilateral hemisphere or a corresponding region in the contralateral hemisphere, depending upon the area damaged and the patient's age.<ref>{{Cite PMID|15009226}}</ref> When injury interferes with pathways from one area to another, alternative (indirect) connections may develop to communicate information with detached areas, despite the inefficiencies.
[[Linear]] [[reason]]ing functions of [[language]] such as grammar and word production are often lateralized to the left hemisphere of the brain. [[Dyscalculia]] is a [[neurology|neurological]] syndrome associated with damage to the left [[temporal lobe|temporal]]-[[parietal lobe|pariet]] junction<ref name="Levy_1">Levy LM, Reis IL, Grafman J. Metabolic abnormalities detected by 1H-MRS in dyscalculia and dysgraphia. ''Neurology''. 1999 Aug 11;53(3):639-41. PMID 10449137</ref>. This syndrome is associated with poor number manipulation, poor mental [[arithmetic]], and an inability to understand or apply mathematical concepts.<ref name="Dyscalculia">[http://www.dyscalculia.org/calc.html Dyscalculia Symtoms]</ref>
 
   
In contrast, [[holistic]] [[reason]]ing 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 [[music]]al stimuli such as spatial manipulation, [[face perception|facial perception]], and artistic ability also seem to be lateralized to the right hemisphere.
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Brain function lateralization is evident in the phenomena of right- or left-handedness<ref>{{Cite PMID|11099452}}</ref> and of right or left ear preference,<ref>{{Cite PMID|16190905}}</ref> but a person's preferred hand is not a clear indication of the location of brain function. Although 95% of [[Right-handedness|right-handed]] people have left-hemisphere dominance for language, 18.8% of [[Left-handedness|left-handed]] people have right-hemisphere dominance for language function. Additionally, 19.8% of the left-handed have bilateral language functions.<ref name="psycho2">Taylor, Insep and Taylor, M. Martin (1990) "Psycholinguistics: Learning and using Language". page 362</ref> Even within various language functions (e.g., semantics, syntax, [[prosody]]), degree (and even hemisphere) of dominance may differ.<ref>Regarding different languages: http://www.bbc.co.uk/news/health-11181457</ref>
   
Other integrative functions such as intuitive or [[heuristic]] arithmetic, binaural sound localization, [[emotion]]s, etc. seem to be more bilaterally controlled.<ref name="Dehaene_1">Dehaene S, Spelke E, Pinel P, Stanescu R, Tsivkin S. Sources of mathematical thinking: behavioral and brain-imaging evidence. Science. 1999 May 7;284(5416):970-4. PMID 10320379.</ref>
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Additionally, although some functions are lateralized, these are only a tendency. The trend across 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 include 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.<ref>{{cite journal | author = Goswami U | year = 2006 | title = Neuroscience and education: from research to practice? | url = | journal = Nat Rev Neurosci | volume = 7 | issue = 5| pages = 406–11 | doi = 10.1038/nrn1907 | pmid = 16607400 }}</ref>
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==Left vs. Right==
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[[Linear]] [[reason]]ing<ref name="processing">[http://frank.mtsu.edu/~studskl/hd/LRBrain.html Left/Right Processing.]</ref> and [[language]] functions such as grammar and vocabulary<ref>[http://webspace.ship.edu/cgboer/speechbrain.html Dr. C. George Boeree. Speech and the Brain.]</ref> often are lateralized to the left hemisphere of the brain. [[Dyscalculia]] is a [[neurology|neurological]] syndrome associated with damage to the left [[temporal lobe|temporo]]-[[parietal lobe|parietal]] junction.<ref name="Levy_1">Levy LM, Reis IL, Grafman. J. Metabolic abnormalities detected by 1H-MRS in dyscalculia and dysgraphia. ''Neurology''. 1999 Aug 11;53(3):639-41. PMID 10449137</ref> This syndrome is associated with poor numeric manipulation, poor mental [[arithmetic]] skill, and the inability to either understand or apply mathematical concepts.<ref name="Dyscalculia">[http://www.dyscalculia.org/calc.html Dyscalculia Symptoms]</ref>
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In contrast, [[prosody (linguistics)|prosodic]] language functions, such as intonation and accentuation, often are lateralized to the right hemisphere of the brain.<ref>{{cite journal |author=Ross ED, Monnot M |title=Neurology of affective prosody and its functional-anatomic organization in right hemisphere |journal=Brain Lang. |volume=104 |issue=1 |pages=51–74 |year=2008 |month=January |pmid=17537499 |doi= 10.1016/j.bandl.2007.04.007|url=}}</ref><ref>{{cite journal |author=George MS, Parekh PI, Rosinsky N, Ketter TA, Kimbrell TA, Heilman KM, Herscovitch P, Post RM |title=Understanding Emotional Prosody Activates Right Hemisphere Regions |journal= Arch Neurol. |volume=53 |issue=7 |pages=665–670 |year=1996 |month=July |pmid=8929174 |doi= |url=}}</ref> Functions such as the processing of visual and audiological stimuli, spatial manipulation, [[face perception|facial perception]], and artistic ability seem to be functions of the right hemisphere.
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Other integrative functions, including arithmetic,<ref name=Dehaene2>Dehaene S, Spelke E, Pinel P, Stanescu R, Tsivkin S. Sources of mathematical thinking: behavioral and brain-imaging evidence. Science. 1999 May 7;284(5416):970-4. PMID 10320379.</ref><ref name = Dehaene2003>Stanislas Dehaene, Manuela Piazza, Philippe Pinel, and Laurent Cohen. Three parietal circuits for number processing. Cognitive Neuropsychology, 20:487-506</ref> binaural sound localization, and emotions, seem more bilaterally controlled.
 
{| class="wikitable"
 
{| class="wikitable"
|'''Left brain functions'''
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|'''Left hemisphere functions'''
|'''Right brain functions'''
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|'''Right hemisphere functions'''
|----
 
| sequential
 
| simultaneous
 
|----
 
| analytical
 
| holistic
 
 
|----
 
|----
| verbal
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| analytical<ref name="psychology">[http://psychology.jrank.org/pages/545/Right-Brain-Hemisphere.html Right-Brain Hemisphere]</ref>
| imagistic
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| holistic<ref name="processing" /><ref name="psychology" />
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|----
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| verbal<ref name="processing" /><ref name="psychology" /><ref name="handness">[http://www.indiana.edu/~primate/brain.html Handedness and Brain Lateralization.]</ref>
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| [[prosodic]]<ref name="handness" />
 
|----
 
|----
| logical
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| logical<ref name="processing" /><ref name="psychology" />
| intuitive
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| intuitive<ref name="processing" /><ref name="psychology" /><ref>[http://academic.cuesta.edu/acasupp/AS/312.HTM Converting Words into Pictures--Reading Comprehension Guide--Academic Support]</ref>
 
|----
 
|----
| [[linear]] algorithmic processing
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| numerical computation (exact calculation, numerical comparison, estimation) <br>left hemisphere only: direct fact retrieval<ref name=Dehaene2/><ref name = Dehaene2003/>
| [[holistic]]al algorithmic processing
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| numerical computation (approximate calculation, numerical comparison, estimation)<ref name=Dehaene2/><ref name = Dehaene2003/>
 
|----
 
|----
| [[mathematics]]: perception of counting/measurement
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| language: grammar/vocabulary, literal<ref name = Talyor>Taylor, Insep, and Taylor, M. Martin (1990) "Psycholinguistics: Learning and using Language". p. 367</ref>
| [[mathematics]]: perception of shapes/motions{{Fact|date=June 2007}}
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| language: intonation/accentuation, prosody, pragmatic, contextual<ref name = Talyor/>
|----
 
| present and past
 
| present and future{{Fact|date=June 2007}}
 
|----
 
| [[language]]: grammar/words, literal
 
| [[language]]: intonation/emphasis, prosody, pragmatic, contextual
 
 
|}
 
|}
<ref>except the mathematics and time claims, which are both unreferenced, all from Taylor, Insep and Taylor, M. Martin (1990) "Psycholinguistics: Learning and using Language". page 367</ref>
 
   
==Assessment of lateral dominance==
 
A niumber of techniques are used to explore lateral dominance. These include:
 
*[[Dichhaptic technique]]
 
*[[Dichotic listening]]
 
   
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==History of research on lateralization==
   
==History==
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===Broca===
===Speech and language===
 
[[Manner of articulation|Speech]] consists of the mechanical process required for vocalizations, such as [[Manner of articulation|articulation]] and [[phonation]]. Language is the set of arbitrary [[symbol]]s used for [[communication]], often in the form of [[word]]s strung together following [[syntax|syntactical]] rules.
 
   
====Broca====
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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 ([[aphasia]]); "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 [[Expressive aphasia]]. In clinical assessment of this aphasia, it is noted that the patient cannot clearly articulate the language being employed.
One of the first indications of brain function laterality arose from research by [[France|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.
 
   
====Wernicke====
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===Wernicke===
[[Germany|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 some were linguistic. He found that damage to the left [[Anatomical terms of location|posterior]], superior [[temporal lobe|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]].
 
   
====Advance in imaging technique====
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German physician [[Karl Wernicke]] continued in the vein of Broca's research by studying language deficits unlike expressive aphasia. Wernicke noted that not every deficit was in speech production; some were linguistic. He found that damage to the left [[Anatomical terms of location|posterior]], superior [[temporal lobe|temporal]] [[gyrus]] ([[Wernicke's area]]) caused language comprehension deficits rather than speech production deficits, a syndrome known as [[Receptive aphasia]].
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.
 
   
===Handedness and language===
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===Advance in imaging technique===
Broca's area and Wernicke’s area are linked by a [[white matter]] fiber tract called the [[arcuate fasciculus]]. This [[axon]]al tract allows the [[neuron]]s in these two areas to work together to create vocal language. In more than 95% of [[right-handed]] [[male]]s and more than 90% of right-handed [[female]]s, 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% <ref name="Knecht_1">Knecht S, Dräger B, Deppe M, Bobe L, Lohmann H, Flöel A, Ringelstein EB, Henningsen H. Handedness and hemispheric language dominance in healthy humans. ''Brain''. 2000;123(12):2512-2518. http://brain.oxfordjournals.org/cgi/content/full/123/12/2512</ref> or 61%<ref name="psycho2" />, depending on the studies.
 
   
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 artery|carotid arteries]]. Once one hemisphere is anesthetized, a [[neuropsychology|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.
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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.
   
[[Image:Sensory and motor homunculi.jpg|thumb|Sensory and motor [[Homunculus|homunculi]] at the London Natural History Museum]]
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==Lateralization of functions==
   
 
===Movement and sensation===
 
===Movement and sensation===
In the [[1940s]], [[Canada|Canadian]] [[neurosurgery|neurosurgeon]] [[Wilder Penfield]] and his [[neurologist]] colleague [[Herbert Jasper]] developed a technique of brain mapping to help reduce [[Adverse effect (medicine)|side effect]]s caused by [[surgery]] to treat [[epilepsy]]. They stimulated [[motor cortex|motor]] and [[somatosensory cortex|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 [[Somatosensory system|sensory]] cortices is fairly consistent from person to person; Penfield and Jasper's famous pictures of the motor and sensory [[cortical homunculus|homunculi]] were the result.
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In the 1940s, American born, [[Montreal]] based [[neurosurgery|neurosurgeon]] [[Wilder Penfield]] and his [[neurologist]] colleague [[Herbert Jasper]] developed a technique of [[cortical stimulation mapping|brain mapping]] to help reduce [[Adverse effect (medicine)|side effect]]s caused by [[surgery]] to treat [[epilepsy]]. They stimulated [[motor cortex|motor]] and [[somatosensory cortex|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 [[Somatosensory system|sensory]] cortices is fairly consistent from person to person; Penfield and Jasper's famous pictures of the motor and sensory [[cortical homunculus|homunculi]] were the result.
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==Gender differences==
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In the past it was believed that there were lateralization differences between men and women, and that these differences led to hemisphere specialization of cognitive function. <ref>{{cite book|last=Maccoby|first=Eleanor|title=The Psychology of Sex Differences|year=1974|publisher=Stanford University Press|location=Stanford, California|isbn=0804709742}}</ref> This was an inaccurate understanding based on studies done of localized areas of each hemisphere. Male brains are no more lateralized than female brains. Neither men or women are biased by specialized usage from either hemisphere of their brain through lateralization. <ref name=Nielsen />
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==Lateralized cognitive processes==
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[[Language]] functions such as grammar, vocabulary and literal meaning<ref name = Boeree>{{cite web | author = Boeree, C.G. | year = 2004 | title = Speech and the Brain | url = http://webspace.ship.edu/cgboer/speechbrain.html | accessdate = February 17, 2012 }}</ref><ref name = Talyor>{{cite book | author = Taylor, I. & Taylor, M. M. | year = 1990 | title = Psycholinguistics: Learning and using Language | publisher = Pearson | isbn = 978-0-13-733817-7}} p. 367</ref> are typically lateralized to the left hemisphere, especially in right handed individuals.<ref name = Talyor /> While language production is left-lateralized in up to 90% of right-handed subjects, it is more bilateral, or even right lateralized in approximately 50% of left-handers.<ref name = Beaumont>{{cite book|author = Beaumont, J.G. | year = 2008 | title = Introduction to Neuropsychology, Second Edition | location = | publisher = The Guilford Press | isbn = 978-1-59385-068-5}} Chapter 7</ref> In contrast, [[prosody (linguistics)|prosodic]] language functions, such as [[intonation (linguistics)|intonation]] and [[stress (linguistics)|accent]]uation, often are lateralized to the right hemisphere of the brain.<ref>{{cite journal |author=Ross ED, Monnot M |title=Neurology of affective prosody and its functional-anatomic organization in right hemisphere |journal=Brain Lang. |volume=104 |issue=1 |pages=51–74 |year=2008 |month=January |pmid=17537499 |doi= 10.1016/j.bandl.2007.04.007|url=}}</ref><ref>{{cite journal |author=George MS, Parekh PI, Rosinsky N, Ketter TA, Kimbrell TA, Heilman KM, Herscovitch P, Post RM |title=Understanding Emotional Prosody Activates Right Hemisphere Regions |journal= Arch Neurol. |volume=53 |issue=7 |pages=665–670 |year=1996 |month=July |pmid=8929174 |doi= 10.1001/archneur.1996.00550070103017|url=}}</ref>
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The processing of visual and auditory stimuli, spatial manipulation, [[face perception|facial perception]], and artistic ability are represented bilaterally, but may show a right hemisphere superiority.<ref name = Beaumont /> Numerical estimation, comparison and online calculation depend on bilateral parietal regions<ref name=Dehaene2>{{cite journal | volume=284 | issue=5416 | title=Sources of mathematical thinking: behavioral and brain-imaging evidence | year=1999 | month=May | author=[[Stanislas Dehaene|Dehaene S]], Spelke E, Pinel P, Stanescu R, Tsivkin S | journal=Science | pages=970–4 | doi=10.1126/science.284.5416.970 | pmid = 10320379 | url = http://www.unicog.org/publications/DehaeneSpelke_ExactApprox_Science1999.pdf}}</ref><ref name = Dehaene2003>{{cite journal | author = Dehaene, S.., Piazza, M., Pinel, P. & Cohen, L. | year = 2003 | title = Three parietal circuits for number processing | journal = Cognitive Neuropsychology | volume = 20 | doi = 10.1080/02643290244000239 | pmid = 20957581 | url = http://www.unicog.org/publications/DehaeneEtAl_3parietalCircuits_CogNeuropsy2003.pdf | issue = 3–6 | pages = 487–506}}</ref> while exact calculation and fact retrieval are associated with left parietal regions, perhaps due to their ties to linguistic processing.<ref name=Dehaene2/><ref name = Dehaene2003/> [[Dyscalculia]] is a [[neurology|neurological]] syndrome associated with damage to the left [[temporal lobe|temporo]]-[[parietal lobe|parietal]] junction.<ref name="Levy_1">{{cite journal | pmid = 10449137 | volume=53 | issue=3 | title=Metabolic abnormalities detected by 1H-MRS in dyscalculia and dysgraphia | year=1999 | month=August | author=Levy LM, Reis IL, Grafman J | journal=Neurology | pages=639–41 | doi = 10.1212/WNL.53.3.639}}</ref> This syndrome is associated with poor numeric manipulation, poor mental [[arithmetic]] skill, and the inability to either understand or apply mathematical concepts.<ref name="Dyscalculia">[http://www.dyscalculia.org/calc.html Dyscalculia Symptoms]</ref>
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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".<ref>{{cite journal | doi = 10.1016/j.neures.2010.06.013 | pmid = 20603163 | volume=68 | issue=2 | title=Depression and the hyperactive right-hemisphere | year=2010 | month=October | author=Hecht D | journal=Neurosci. Res. | pages=77–87}}</ref> 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."<ref>{{cite journal | doi = 10.1080/13576500802328613 | pmid = 18991140 | volume=14 | issue=2 | title=Post unilateral lesion response biases modulate memory: crossed double dissociation of hemispheric specialisations | year=2009 | month=March | author=Braun CM, Delisle J, Guimond A, Daigneault R | journal=Laterality | pages=122–64}}</ref> The [[delusional misidentification syndrome]]s, [[reduplicative paramnesia]] and [[Capgras delusion]] are also often the result of right hemisphere lesions.<ref>{{cite journal | doi = 10.1212/01.wnl.0000338625.47892.74 | pmid = 19122035 | volume=72 | issue=1 | title=Delusional misidentifications and duplications: right brain lesions, left brain delusions | year=2009 | month=January | author=Devinsky O | journal=Neurology | pages=80–7}}</ref><ref>{{cite journal | pmid = 20387212 | volume=50 | issue=7 | title=[Capgras delusion: a review of aetiological theories] | year=2010 | month=April | author=Madoz-G&uacute;rpide A, Hillers-Rodr&iacute;guez R | journal=Rev Neurol | pages=420–30}}</ref> There is evidence<ref>{{cite book | author = [[Elkhonon Goldberg|Goldberg, E.]] | year = 2009 | title = The New Executive Brain: Frontal Lobes in a Complex World | location = New York, NY | publisher = Oxford University Press | isbn = 978-0-19-532940-7}}</ref> 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.
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===Handedness and language===
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Broca's area and Wernicke's area are linked by a [[white matter]] fiber tract, the [[arcuate fasciculus]] {{Dubious|Talk: Lateralization of brain function#Connection between Broca's and Wiernecke's|date=May 2010}}. 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, the left hemisphere is dominant in certain aspects of language and speech processing. In left-handed people, the incidence of left-hemisphere language dominance has been reported as 73%<ref name="Knecht_1">{{cite journal |last=Knecht |first=S. |last2=Dräger |first2=B. |last3=Deppe |first3=M. |last4=Bobe |first4=L. |last5=Lohmann |first5=H. |last6=Flöel |first6=A. |last7=Ringelstein |first7=E. B. |last8=Henningsen |first8=H. |title=Handedness and hemispheric language dominance in healthy humans |journal=Brain |year=2000 |volume=123 |issue=12 |pages=2512&ndash;2518 |doi=10.1093/brain/123.12.2512 }}</ref> and 61%,<ref name="psycho2" /> suggesting left handed people tend to be less lateralized than right-handed people. In general, however, [[neuroimaging]] methods such as [[functional magnetic resonance imaging]] and [[magnetoencephalography]] show involvement of both hemispheres in many aspects of language processing, and the "dominance" of one hemisphere just refers to more brain activation relative to the other hemisphere (or better performance by that hemisphere on [[psycholinguistics|psycholinguistic]] tasks such as [[dichotic listening]]); it is not the case that language is "localized" in any one hemisphere.
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==Research methods==
 
===Split-brain patients===
 
===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 [[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<ref name="Kandel_1">Kandel E, Schwartz J, Jessel T. ''Principles of Neural Science''. 4th ed. p1182. New York: McGraw-Hill; 2000. ISBN 0-8385-7701-6</ref>.
+
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 [[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.<ref name="Kandel_1">Kandel E, Schwartz J, Jessel T. ''Principles of Neural Science''. 4th ed. p1182. New York: McGraw&ndash;Hill; 2000. ISBN 0-8385-7701-6</ref> Eran Zaidel, however, also studied such patients and found some evidence for the right hemisphere having at least some syntactic ability.
   
==Pseudoscientific exaggeration of the research==
+
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 callosotomy, [[alien hand syndrome]] most often manifests as uncontrolled but purposeful movements of the nondominant hand.{{Citation needed|date=May 2010}}
   
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.<ref>Sala, (1999). ''Mind Myths: Exploring Popular Assumptions about the Mind and Brain.'' New York; Wiley</ref> 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.
+
  +
There are ways of determining hemispheric dominance in a person. The [[wada test|Wada Test]] introduces an anesthetic to one hemisphere of the brain via one of the two [[carotid artery|carotid arteries]]. Once the hemisphere is anesthetized, a [[neuropsychology|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.
  +
  +
==Exaggeration of the lateralization concept==
  +
[[Terence Hines]] 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.<ref name=Hines>{{cite journal |authorlink = Terence Hines |last=Hines |first=Terence |year=1987 |title=Left Brain/Right Brain Mythology and Implications for Management and Training |journal=The Academy of Management Review |volume=12 |issue=4 |pages=600–606 |doi=10.2307/258066 |jstor=258066 }}</ref> For example, the implications of the research have no bearing on psychological interventions such as [[EMDR]] and [[neurolinguistic programming]],<ref>{{cite journal |last=Drenth |first=J. D. |year=2003 |title=Growing anti-intellectualism in Europe; a menace to science |journal=Studia Psychologica |volume=45 |issue=1 |pages=5–13 |doi= }}, available in [http://www.allea.org/Pages/ALL/4/881.bGFuZz1FTkc.pdf ''ALLEA Annual Report 2003''], pp. 61–72</ref> brain training equipment, or management training.<ref>{{cite book |last=Sala |first=Sergio Della |year=1999 |title=Mind Myths: Exploring Popular Assumptions about the Mind and Brain |location=New York |publisher=Wiley |isbn=0-471-98303-9 }}</ref>
  +
  +
==Nonhuman brain lateralization==
  +
Specialization of the two hemispheres is general in vertebrates including [[fish]], [[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.<ref>{{Cite pmid|16209828}}</ref>
  +
  +
==Advantages of brain lateralization==
  +
The widespread lateralization of many vertebrate animals indicates an evolutionary advantage associated with the specialization of each hemisphere.<ref name="Halpern 2005">{{cite journal | author = Halpern ''et al.'' | year = 2005 | title = Lateralization of the Vertebrate Brain: Taking the Side of Model Systems | url = | journal = The Journal of Neuroscience | volume = 25 | issue = 45| pages = 10351–10357 }}</ref> In one experiment, baby chicks were lateralized before hatching by exposing their eggs to light.<ref name="Rogers 1990">{{cite journal | author = Rogers | year = 1990 | title = Light Input and the Reversal of Functional Lateralization in the Chicken Brain | url = | journal = Behav Brain Res | volume = 38 | issue = 3| pages = 211–21 }}</ref> These chicks were set to a task of picking out food from a bed of pebbles. Neither the lateralized, nor the non-lateralized chicks had a problem with this task, but the lateralized chicks only used the eye on the side of which they were lateralized to pick up the pebbles. When presented with a second task of watching for a cutout of a predatory hawk, the discrepancy between lateralized and non-lateralized chicks became evident. Lateralized chicks could pick food out of the pebbles with one eye and one half of the brain<ref name="Deng and Rogers 1997">{{cite journal | author = Deng , Rogers | year = 1997 | title = Differential Contributions of the Two Visual Pathways to Functional Lateralization in Chicks | url = | journal = Behav Brain Res | volume = 87 | issue = 2| pages = 173–82 }}</ref> while using the other eye and other half of their brain to monitor the skies for predators.<ref name="Rogers 2000">{{cite journal | author = Rogers | year = 2000 | title = Evolution of Hemispheric Specialization: Advantages and Disadvantages | url = | journal = Brain Lang | volume = 73 | issue = 2| pages = 236–53 }}</ref> Not only could non-lateralized chicks not complete the two tasks simultaneously, but their performance of the single task deteriorated. This suggests that the evolutionary advantage of lateralization comes from the capacity to perform separate parallel tasks in each hemisphere of the brain.<ref name="Halpern 2005"/>
   
 
==See also==
 
==See also==
 
*[[Ambidexterity]]
 
*[[Ambidexterity]]
  +
*[[Bicameralism]]
  +
*[[Cerebral dominance]]
 
*[[Cross-dominance]]
 
*[[Cross-dominance]]
 
*[[Dual brain theory]]
 
*[[Dual brain theory]]
*[[Functional specialization (brain)]]
+
*[[Emotional lateralization]]
 
*[[Eye dominance]]
 
*[[Eye dominance]]
  +
*[[Functional specialization (brain)]]
 
*[[Handedness]]
 
*[[Handedness]]
  +
*[[Hemispherectomy]]
  +
*[[Interhemispheric interaction]]
 
*[[Laterality]]
 
*[[Laterality]]
  +
*[[Lateralization of bird song]]
 
*[[Left brain]]
 
*[[Left brain]]
  +
*[[Left brain interpreter]]
 
*[[Left-handed]]
 
*[[Left-handed]]
 
*[[Ocular dominance]]
 
*[[Ocular dominance]]
Line 86: Line 89:
 
*[[Michael Gazzaniga|Gazzaniga, M.S.]], Ivry, R., & Mangun, G.R. ''Fundamentals of Cognitive Neuroscience.'' 2nd ed. W.W. Norton, 2002. ISBN 0-393-97777-3
 
*[[Michael Gazzaniga|Gazzaniga, M.S.]], Ivry, R., & Mangun, 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
 
*[[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
+
*[[Iain McGilchrist]] (2009) [[The Master and His Emissary]]
   
 
[[Category:Cerebral dominanace]]]
 
[[Category:Cerebral dominanace]]]

Latest revision as of 10:32, November 24, 2013

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Template:Image The longitudinal fissure separates the human brain into two distinct cerebral hemispheres, connected by the corpus callosum. The hemispheres exhibit strong, but not complete, bilateral symmetry in both structure and function. For example, structurally, the lateral sulcus generally is longer in the left hemisphere than in the right hemisphere, and functionally, Broca's area and Wernicke's area are present only in the left hemisphere in greater than 95% of the population.

Broad generalizations are often made in popular psychology about one side or the other having characteristic labels, such as "logical" for the left side or "creative" for the right. These labels are not supported by studies on lateralization, as lateralization does not add specialized usage from either hemisphere. [1] Both hemispheres contribute to both kinds of processes.[2] and experimental evidence provides little support for correlating the structural differences between the sides with such broadly-defined functional differences.[3]

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 in the ipsilateral hemisphere or a corresponding region in the contralateral hemisphere, depending upon the area damaged and the patient's age.[4] When injury interferes with pathways from one area to another, alternative (indirect) connections may develop to communicate information with detached areas, despite the inefficiencies.

Brain function lateralization is evident in the phenomena of right- or left-handedness[5] and of right or left ear preference,[6] 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, 18.8% of left-handed people have right-hemisphere dominance for language function. Additionally, 19.8% of the left-handed have bilateral language functions.[7] Even within various language functions (e.g., semantics, syntax, prosody), degree (and even hemisphere) of dominance may differ.[8]

Additionally, although some functions are lateralized, these are only a tendency. The trend across 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 include 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.[9]

Left vs. RightEdit

Linear reasoning[10] and language functions such as grammar and vocabulary[11] often are lateralized to the left hemisphere of the brain. Dyscalculia is a neurological syndrome associated with damage to the left temporo-parietal junction.[12] This syndrome is associated with poor numeric manipulation, poor mental arithmetic skill, and the inability to either understand or apply mathematical concepts.[13]

In contrast, prosodic language functions, such as intonation and accentuation, often are lateralized to the right hemisphere of the brain.[14][15] Functions such as the processing of visual and audiological stimuli, spatial manipulation, facial perception, and artistic ability seem to be functions of the right hemisphere.

Other integrative functions, including arithmetic,[16][17] binaural sound localization, and emotions, seem more bilaterally controlled.

Left hemisphere functions Right hemisphere functions
analytical[18] holistic[10][18]
verbal[10][18][19] prosodic[19]
logical[10][18] intuitive[10][18][20]
numerical computation (exact calculation, numerical comparison, estimation)
left hemisphere only: direct fact retrieval[16][17]
numerical computation (approximate calculation, numerical comparison, estimation)[16][17]
language: grammar/vocabulary, literal[21] language: intonation/accentuation, prosody, pragmatic, contextual[21]


History of research on lateralizationEdit

BrocaEdit

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 (aphasia); "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 Expressive aphasia. In clinical assessment of this aphasia, it is noted that the patient cannot clearly articulate the language being employed.

WernickeEdit

German physician Karl Wernicke continued in the vein of Broca's research by studying language deficits unlike expressive 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 Receptive aphasia.

Advance in imaging techniqueEdit

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.


Lateralization of functionsEdit

Movement and sensationEdit

In the 1940s, American born, Montreal based 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 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.

Gender differencesEdit

In the past it was believed that there were lateralization differences between men and women, and that these differences led to hemisphere specialization of cognitive function. [22] This was an inaccurate understanding based on studies done of localized areas of each hemisphere. Male brains are no more lateralized than female brains. Neither men or women are biased by specialized usage from either hemisphere of their brain through lateralization. [1]

Lateralized cognitive processesEdit

Language functions such as grammar, vocabulary and literal meaning[23][21] are typically lateralized to the left hemisphere, especially in right handed individuals.[21] While language production is left-lateralized in up to 90% of right-handed subjects, it is more bilateral, or even right lateralized in approximately 50% of left-handers.[24] In contrast, prosodic language functions, such as intonation and accentuation, often are lateralized to the right hemisphere of the brain.[25][26]

The processing of visual and auditory stimuli, spatial manipulation, facial perception, and artistic ability are represented bilaterally, but may show a right hemisphere superiority.[24] Numerical estimation, comparison and online calculation depend on bilateral parietal regions[16][17] while exact calculation and fact retrieval are associated with left parietal regions, perhaps due to their ties to linguistic processing.[16][17] Dyscalculia is a neurological syndrome associated with damage to the left temporo-parietal junction.[12] This syndrome is associated with poor numeric manipulation, poor mental arithmetic skill, and the inability to either understand or apply mathematical concepts.[13]

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".[27] 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."[28] The delusional misidentification syndromes, reduplicative paramnesia and Capgras delusion are also often the result of right hemisphere lesions.[29][30] There is evidence[31] 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.

Handedness and languageEdit

Broca's area and Wernicke's area are linked by a white matter fiber tract, the arcuate fasciculus [dubious]. This axonal 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, the left hemisphere is dominant in certain aspects of language and speech processing. In left-handed people, the incidence of left-hemisphere language dominance has been reported as 73%[32] and 61%,[7] suggesting left handed people tend to be less lateralized than right-handed people. In general, however, neuroimaging methods such as functional magnetic resonance imaging and magnetoencephalography show involvement of both hemispheres in many aspects of language processing, and the "dominance" of one hemisphere just refers to more brain activation relative to the other hemisphere (or better performance by that hemisphere on psycholinguistic tasks such as dichotic listening); it is not the case that language is "localized" in any one hemisphere.


Research methodsEdit

Split-brain patientsEdit

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.[33] 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 callosotomy, alien hand syndrome most often manifests as uncontrolled but purposeful movements of the nondominant hand.[citation needed]


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.

Exaggeration of the lateralization conceptEdit

Terence Hines 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.[34] For example, the implications of the research have no bearing on psychological interventions such as EMDR and neurolinguistic programming,[35] brain training equipment, or management training.[36]

Nonhuman brain lateralizationEdit

Specialization of the two hemispheres is general in vertebrates including fish, frogs, reptiles, birds and mammals 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.[37]

Advantages of brain lateralizationEdit

The widespread lateralization of many vertebrate animals indicates an evolutionary advantage associated with the specialization of each hemisphere.[38] In one experiment, baby chicks were lateralized before hatching by exposing their eggs to light.[39] These chicks were set to a task of picking out food from a bed of pebbles. Neither the lateralized, nor the non-lateralized chicks had a problem with this task, but the lateralized chicks only used the eye on the side of which they were lateralized to pick up the pebbles. When presented with a second task of watching for a cutout of a predatory hawk, the discrepancy between lateralized and non-lateralized chicks became evident. Lateralized chicks could pick food out of the pebbles with one eye and one half of the brain[40] while using the other eye and other half of their brain to monitor the skies for predators.[41] Not only could non-lateralized chicks not complete the two tasks simultaneously, but their performance of the single task deteriorated. This suggests that the evolutionary advantage of lateralization comes from the capacity to perform separate parallel tasks in each hemisphere of the brain.[38]

See alsoEdit

ReferencesEdit

  • Goulven Josse, Nathalie Tzourio-Mazoyer (2003) Review: Hemispheric specialization for language. Brain Research Reviews 44 1–12.
  1. 1.0 1.1 Nielsen, Jared A., Brandon A. Zielinski, Michael A. Ferguson, Janet E. Lainhart, and Jeffrey S. Anderson. "An Evaluation of the Left-Brain vs. Right-Brain Hypothesis with Resting State Functional Connectivity Magnetic Resonance Imaging." PLOS ONE, 14 Aug. 2013. Web. 30 Aug. 2013.
  2. Westen et al. 2006 Psychology: Australian and New Zealand edition. John Wiley p.107
  3. PMID 12511860 (PMID 12511860)
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  4. PMID 15009226 (PMID 15009226)
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  5. PMID 11099452 (PMID 11099452)
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  6. PMID 16190905 (PMID 16190905)
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  7. 7.0 7.1 Taylor, Insep and Taylor, M. Martin (1990) "Psycholinguistics: Learning and using Language". page 362
  8. Regarding different languages: http://www.bbc.co.uk/news/health-11181457
  9. Goswami U (2006). Neuroscience and education: from research to practice?. Nat Rev Neurosci 7 (5): 406–11.
  10. 10.0 10.1 10.2 10.3 10.4 Left/Right Processing.
  11. Dr. C. George Boeree. Speech and the Brain.
  12. 12.0 12.1 Levy LM, Reis IL, Grafman. J. Metabolic abnormalities detected by 1H-MRS in dyscalculia and dysgraphia. Neurology. 1999 Aug 11;53(3):639-41. PMID 10449137
  13. 13.0 13.1 Dyscalculia Symptoms
  14. Ross ED, Monnot M (January 2008). Neurology of affective prosody and its functional-anatomic organization in right hemisphere. Brain Lang. 104 (1): 51–74.
  15. George MS, Parekh PI, Rosinsky N, Ketter TA, Kimbrell TA, Heilman KM, Herscovitch P, Post RM (July 1996). Understanding Emotional Prosody Activates Right Hemisphere Regions. Arch Neurol. 53 (7): 665–670.
  16. 16.0 16.1 16.2 16.3 16.4 Dehaene S, Spelke E, Pinel P, Stanescu R, Tsivkin S. Sources of mathematical thinking: behavioral and brain-imaging evidence. Science. 1999 May 7;284(5416):970-4. PMID 10320379.
  17. 17.0 17.1 17.2 17.3 17.4 Stanislas Dehaene, Manuela Piazza, Philippe Pinel, and Laurent Cohen. Three parietal circuits for number processing. Cognitive Neuropsychology, 20:487-506
  18. 18.0 18.1 18.2 18.3 18.4 Right-Brain Hemisphere
  19. 19.0 19.1 Handedness and Brain Lateralization.
  20. Converting Words into Pictures--Reading Comprehension Guide--Academic Support
  21. 21.0 21.1 21.2 21.3 Taylor, Insep, and Taylor, M. Martin (1990) "Psycholinguistics: Learning and using Language". p. 367
  22. Maccoby, Eleanor (1974). The Psychology of Sex Differences, Stanford, California: Stanford University Press.
  23. Boeree, C.G. (2004). Speech and the Brain. URL accessed on February 17, 2012.
  24. 24.0 24.1 Beaumont, J.G. (2008). Introduction to Neuropsychology, Second Edition, The Guilford Press. Chapter 7
  25. Ross ED, Monnot M (January 2008). Neurology of affective prosody and its functional-anatomic organization in right hemisphere. Brain Lang. 104 (1): 51–74.
  26. George MS, Parekh PI, Rosinsky N, Ketter TA, Kimbrell TA, Heilman KM, Herscovitch P, Post RM (July 1996). Understanding Emotional Prosody Activates Right Hemisphere Regions. Arch Neurol. 53 (7): 665–670.
  27. Hecht D (October 2010). Depression and the hyperactive right-hemisphere. Neurosci. Res. 68 (2): 77–87.
  28. Braun CM, Delisle J, Guimond A, Daigneault R (March 2009). Post unilateral lesion response biases modulate memory: crossed double dissociation of hemispheric specialisations. Laterality 14 (2): 122–64.
  29. Devinsky O (January 2009). Delusional misidentifications and duplications: right brain lesions, left brain delusions. Neurology 72 (1): 80–7.
  30. Madoz-Gúrpide A, Hillers-Rodríguez R (April 2010). [Capgras delusion: a review of aetiological theories]. Rev Neurol 50 (7): 420–30.
  31. Goldberg, E. (2009). The New Executive Brain: Frontal Lobes in a Complex World, New York, NY: Oxford University Press.
  32. Knecht, S. (2000). Handedness and hemispheric language dominance in healthy humans. Brain 123 (12): 2512–2518.
  33. Kandel E, Schwartz J, Jessel T. Principles of Neural Science. 4th ed. p1182. New York: McGraw–Hill; 2000. ISBN 0-8385-7701-6
  34. Hines, Terence (1987). Left Brain/Right Brain Mythology and Implications for Management and Training. The Academy of Management Review 12 (4): 600–606.
  35. Drenth, J. D. (2003). Growing anti-intellectualism in Europe; a menace to science. Studia Psychologica 45 (1): 5–13., available in ALLEA Annual Report 2003, pp. 61–72
  36. Sala, Sergio Della (1999). Mind Myths: Exploring Popular Assumptions about the Mind and Brain, New York: Wiley.
  37. PMID 16209828 (PMID 16209828)
    Citation will be completed automatically in a few minutes. Jump the queue or expand by hand
  38. 38.0 38.1 Halpern et al. (2005). Lateralization of the Vertebrate Brain: Taking the Side of Model Systems. The Journal of Neuroscience 25 (45): 10351–10357.
  39. Rogers (1990). Light Input and the Reversal of Functional Lateralization in the Chicken Brain. Behav Brain Res 38 (3): 211–21.
  40. Deng , Rogers (1997). Differential Contributions of the Two Visual Pathways to Functional Lateralization in Chicks. Behav Brain Res 87 (2): 173–82.
  41. Rogers (2000). Evolution of Hemispheric Specialization: Advantages and Disadvantages. Brain Lang 73 (2): 236–53.
  • Hines, Terence (1987). Left Brain/Right Brain Mythology and Implications for Management and Training. The Academy of Management Review, 12:4, 600–606.

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