A longitudinal fissure separates the human brain The human brain is the center of the human nervous system and is a highly complex organ. Enclosed in the cranium, it has the same general structure as the brains of other mammals, but is over three times as large as the brain of a mammal with an equivalent body size. Most of the expansion comes from the cerebral cortex, a convoluted layer of into two distinct cerebral hemispheres A cerebral hemisphere is defined as one of the two regions of the brain that are delineated by the body's median plane, (medial longitudinal fissure). 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 supported by, connected by the corpus callosum The corpus callosum is a structure of the mammalian brain in the longitudinal fissure that connects the left and right cerebral hemispheres. It also facilitates communication between the two hemispheres. It is the largest white matter structure in the brain, consisting of 200-250 million contralateral axonal projections. It is a wide, flat bundle. The sides resemble each other and each hemisphere's structure is generally mirrored by the other side. Yet despite the strong similarities, the functions of each cortical The cerebral cortex is a structure within the brain that plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It constitutes the outermost layer of the cerebrum. In preserved brains, it has a grey color, hence the name "grey matter". Grey matter is formed by neurons and their unmyelinated hemisphere are different.

Popular psychology The term popular psychology refers to concepts and theories about human mental life and behaviour that are purportedly based on psychology and that attain popularity among the general population. The concept is closely related to the human potential movement of the 1950s and '60s tends to make broad and sometimes pseudoscientific generalizations about certain functions (e.g. logic, creativity) being lateral, that is, located in either the right or the left side of the brain. Researchers often criticize popular psychology for this, because the popular lateralizations often are distributed across both hemispheres, [1] although mental processing is divided between them.[citation needed]

Many differences between the hemispheres have been observed, from the gross anatomical level to differences in dendritic structure or neurotransmitter distribution. For example, the lateral sulcus It divides the frontal lobe and parietal lobe above from the temporal lobe below. It is in both hemispheres of the brain but is longer in the left hemisphere. The lateral sulcus is one of the earliest-developing sulci of the human brain. It first appears around the fourteenth gestational week generally is longer in the left hemisphere than in the right hemisphere. However, experimental evidence provides little, if any, consistent support for correlating such structural differences with functional differences.[2] The extent of specialized brain function by area remains under investigation. If a specific region of the brain 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. Injury may also interfere with a pathway from one area to another. In this case, alternative (indirect) connections may exist which can be used to transmit the information to the target area. Such transmission may not be as efficient as the original pathway.

While functions are lateralized, the lateralizations are functional trends, which differ across individuals and specific function. Short of having undergone a hemispherectomy Hemispherectomy is a 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. It is solely reserved for extreme cases in which the seizures have not responded to (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 Being right-handed is the form of handedness characterized by greater coordination in the right hand and arm, and strong preference, in one-handed tasks, for using the right rather than left limb people have left-hemisphere dominance for language, only 18.8% of left-handed Left-handedness is the preference for the left hand over the right for everyday activities such as writing. Most left-handed people exhibit some degree of ambidexterity. Left-handedness is relatively uncommon; 90 to 93 percent of the adult population is right-handed people have right-hemisphere dominance for language function. Additionally, 19.8% of the left-handed have bilateral language functions.[3] Even within various language functions (e.g., semantics, syntax, prosody), degree (and even hemisphere) of dominance may differ.

Contents

Left vs. Right

Linear The word linear comes from the Latin word linearis, which means created by lines. In mathematics, a linear map or function f is a function which satisfies the following two properties.. reasoning Reason, as used in this article, refers to mental faculties that generate or affirm propositions, by activities of the mind such as judging, predicting, inferring, generalizing, and comparing[4] and language A language is a system for encoding information. In its most common use, the term refers to so-called "natural languages" — the forms of communication considered peculiar to humankind. In linguistics the term is extended to refer to the human cognitive facility of creating and using language. Essential to both meanings is the functions such as grammar and vocabulary[5] often are lateralized to the left hemisphere of the brain. Dyscalculia Dyscalculia or math disability is a specific learning disability involving innate difficulty in learning or comprehending mathematics is a neurological 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, such as muscle. The corresponding surgical specialty syndrome associated with damage to the left temporo The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both the left and right hemispheres of the brain-parietal The parietal lobe is a lobe in the brain. It is positioned above the occipital lobe and behind (posterior to) the frontal lobe junction.[6] This syndrome is associated with poor numeric manipulation, poor mental 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. In common usage, the word refers to a branch of (or the forerunner of) mathematics which records elementary properties of certain operations on skill, and the inability to either understand or apply mathematical concepts.[7]

In contrast, prosodic In linguistics, prosody is the rhythm, stress, and intonation of connected speech (as opposed to smaller elements like syllables or words). Prosody may reflect various features of the speaker or the utterance: the emotional state of a speaker; whether an utterance is a statement, a question, or a command; whether the speaker is being ironic or language functions, such as intonation and accentuation, often are lateralized to the right hemisphere of the brain.[8][9] Functions such as the processing of visual and audiological stimuli, spatial manipulation, facial perception Face perception is the process by which the brain and mind understand and interpret the face, particularly the human face, and artistic ability seem to be functions of the right hemisphere.

Other integrative functions, including arithmetic,[10][11] binaural sound localization, and emotions, seem more bilaterally controlled.

Left hemisphere functions Right hemisphere functions
analytical[12] holistic[4][12]
verbal[4][12][13] prosodic In linguistics, prosody is the rhythm, stress, and intonation of connected speech (as opposed to smaller elements like syllables or words). Prosody may reflect various features of the speaker or the utterance: the emotional state of a speaker; whether an utterance is a statement, a question, or a command; whether the speaker is being ironic or[13]
logical[4][12] intuitive[4][12][14]
numerical computation (exact calculation, numerical comparison, estimation) left hemisphere only: direct fact retrieval[10][11] numerical computation (approximate calculation, numerical comparison, estimation)[10][11]
language: grammar/vocabulary, literal[15] language: intonation/accentuation, prosody, pragmatic, contextual[15]

History

Speech and language

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 (aphasia Aphasia is a language disorder in which there is an impairment (but not loss) of speech and of comprehension of speech. The term dysphasia has also been used, although in modern times aphasia is used much more commonly, particularly in the field of speech and language pathology, to avoid confusion with the swallowing disorder dysphagia); "tan" was one of the few words he could articulate, hence his nickname. In Tan's autopsy An autopsy, also known as a post-mortem examination, necropsy , autopsia cadaverum, or obduction, is a medical 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. It is usually performed by a specialized medical doctor called a, Broca determined he had a syphilitic lesion Lesions are caused by any process that damages tissues. A cancerous tumor is an example of a lesion, however the surrounding tissue damaged by a tumor is also a lesion. Trauma, including electrocution and chemical burns can also cause lesions. Certain diseases present lesions, for example the skin deformities caused by chicken pox. Lesions can in the left cerebral hemisphere. This left frontal lobe The frontal lobe is an area in the brain of mammals. It is located at the front of each cerebral hemisphere and positioned anterior to the parietal lobes and above and anterior to the temporal lobes. It is separated from the parietal lobe by the primary motor cortex, which controls voluntary movements of specific body parts associated with the brain area (Broca's Area The importance of Broca’s area in producing language has been recognized since Paul Pierre Broca reported impairments in two patients he encountered. They had lost the ability to speak after injury to the posterior inferior frontal gyrus of the brain. Since then, the approximate region he identified has become known as Broca’s area, and the) 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

German Germany (pronounced /ˈdʒɜrməni/ ), officially the Federal Republic of Germany (German: Bundesrepublik Deutschland, pronounced [ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant] ( listen)), is a country in Central Europe. It is bordered to the north by the North Sea, Denmark, and the Baltic Sea; to the east by Poland and the Czech Republic; to the south physician A physician, medical practitioner, doctor of medicine, or medical doctor practices medicine, and is concerned with maintaining or restoring human health through the study, diagnosis, and treatment of disease and injury. This is accomplished through a detailed knowledge of anatomy, physiology, diseases and treatment — the science of medicine — Karl Wernicke Carl Wernicke was a German physician, anatomist, psychiatrist and neuropathologist. He earned his medical degree at the University of Breslau (1870). He died in Germany due to injuries suffered during a bicycle accident continued in the vein of Broca's research by studying language deficits unlike Broca aphasias. Wernicke noted that not every deficit was in speech production; some were linguistic. He found that damage to the left posterior Standard anatomical terms of location are employed in sciences which deal with the anatomy of animals to avoid ambiguities which might otherwise arise. They are not language-specific, and thus require no translation. They are universal terms that may be readily understood by zoologists who speak any language, superior temporal The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both the left and right hemispheres of the brain gyrus A gyrus is a ridge on the cerebral cortex. It is generally surrounded by one or more sulci (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 traditionally considered to consist of the posterior section of the superior temporal gyrus in the dominant cerebral hemisphere (which is the left hemisphere in about 90% of people)) 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 vivo In vivo refers to 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. In vivo testing is often employed over in vitro because it is better suited for observing the overall effects of an experiment on a comparison of the hemispheres in healthy subjects. Particularly, magnetic resonance imaging Magnetic Resonance Imaging , or nuclear magnetic resonance imaging (NMRI), is primarily a medical imaging technique most commonly used in radiology to visualize the internal structure and function of the body. MRI provides much greater contrast between the different soft tissues of the body than computed tomography (CT) does, making it especially (MRI) and positron emission tomography Positron emission tomography is a nuclear medicine imaging technique which 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 (tracer), which is introduced into the body on a biologically active molecule. Images of tracer (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 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 of myelin is composed largely of lipid and a few percent of capillaries. Its white color is due to its usual preservation in formaldehyde. A 20 fiber tract, the arcuate fasciculus. This axonal An axon or nerve fiber is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma 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% [16] and 61%[3].

There are ways of determining hemispheric dominance in a person. The Wada Test The Wada test, also known as the "intracarotid sodium amobarbital procedure" , is used to establish which cerebral functions are localized to which hemisphere introduces an anesthetic to one hemisphere of the brain via one of the two carotid arteries The common carotid artery is a paired structure, meaning that there are two in the body, one for each half. The left and right common carotid arteries follow the same course with the exception of their origin. The right common carotid originates in the neck from the brachiocephalic trunk. The left arises from the aortic arch in the thoracic region. Once the hemisphere is anesthetized, a neuropsychological Neuropsychology is the basic scientific discipline that studies the structure and function of the brain related to specific psychological processes and overt 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 higher 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 Functional MRI or functional Magnetic Resonance Imaging is a type of specialized MRI scan. It measures the haemodynamic 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. Since the early 1990s, fMRI has come to dominate the brain mapping field and Transcranial magnetic stimulation Transcranial magnetic stimulation is a noninvasive method to excite neurons in the brain: weak electric currents are induced in the tissue by rapidly changing magnetic fields (electromagnetic induction). This way, brain activity can be triggered with minimal discomfort, and the functionality of the circuitry and connectivity of the brain can be, also are used to determine hemispheric dominance; usage remains controversial for being experimental.

Movement and sensation

In the 1940s, Canadian Canada is a country occupying most of upper North America, extending from the Atlantic Ocean in the east to the Pacific Ocean in the west and northward into the Arctic Ocean. It is the world's second largest country by total area and shares the world's longest common border with the United States to the south and northwest neurosurgeon Neurosurgery is the surgical discipline focused on treating those central and peripheral nervous systems and spinal column diseases amenable to surgical intervention. In the United States there are only about 3,000 neurosurgeons.[citation needed] 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."[citation needed] He devoted much thinking to the functionings of the mind, and continued until his death to contemplate whether there was any scientific basis for the existence of the human and his neurologist 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, such as muscle. The corresponding surgical specialty colleague Herbert Jasper developed a technique of brain mapping to help reduce side effects 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, and may result from an unsuitable or incorrect dosage or procedure, which could be due to medical caused by surgery Surgery is a 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, to help improve bodily function or appearance, or sometimes for some other reason. An act of performing surgery may be called a surgical procedure, operation, or simply to treat epilepsy Epilepsy is a common chronic neurological disorder characterized by recurrent unprovoked seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or synchronous neuronal activity in the brain. About 50 million people worldwide have epilepsy, with almost 90% of these people being in developing countries. Epilepsy is more. They stimulated motor Motor cortex is a term that describes regions of the cerebral cortex involved in the planning, control, and execution of voluntary motor functions 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.

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[17]. 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

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 and neurolinguistic programming (Drenth 2003:53), brain training equipment, or management training. One explanation for why research on lateralization is so prone to exaggeration and false application is that the left-right brain dichotomy is an easy-to-understand notion, which can be oversimplified and misused for promotion in the guise of science.[18] 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.

See also

References

  1. ^ Western et al. 2006 "Psychology: Austraian and New Zealand edition" John Wiley p.107
  2. ^ Toga AW, Thompson PM. (2003). Mapping brain asymmetry. Nat Rev Neurosci. 4(1):37-48.PubMed
  3. ^ a b Taylor, Insep and Taylor, M. Martin (1990) "Psycholinguistics: Learning and using Language". page 362
  4. ^ a b c d e Left/Right Processing.
  5. ^ Dr. C. George Boeree. Speech and the Brain.
  6. ^ 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
  7. ^ Dyscalculia Symptoms
  8. ^ Ross ED, Monnot M (January 2008). "Neurology of affective prosody and its functional-anatomic organization in right hemisphere". Brain Lang. 104 (1): 51–74. doi:10.1016/j.bandl.2007.04.007. PMID 17537499.
  9. ^ 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. PMID 8929174.
  10. ^ a b c 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.
  11. ^ a b c Stanislas Dehaene, Manuela Piazza, Philippe Pinel, and Laurent Cohen. Three parietal circuits for number processing. Cognitive Neuropsychology, 20:487-506
  12. ^ a b c d e Right-Brain Hemisphere
  13. ^ a b Handedness and Brain Lateralization.
  14. ^ Converting Words into Pictures--Reading Comprehension Guide--Academic Support
  15. ^ a b Taylor, Insep, and Taylor, M. Martin (1990) "Psycholinguistics: Learning and using Language". p. 367
  16. ^ 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
  17. ^ Kandel E, Schwartz J, Jessel T. Principles of Neural Science. 4th ed. p1182. New York: McGraw-Hill; 2000. ISBN 0-8385-7701-6
  18. ^ Sala, (1999). Mind Myths: Exploring Popular Assumptions about the Mind and Brain. New York; Wiley

Sources

Further reading

Categories: Neuropsychology | Cerebrum

 

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