Brain
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226176490
2008-07-17T04:33:20Z
Someguy1221
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Reverted edits by [[Special:Contributions/60.241.82.45|60.241.82.45]] to last version by MER-C (using [[WP:HG|Huggle]])
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[[Image:Brain 090407.jpg|thumb|right|238px|[[Human brain]]]]
In animals, the '''brain''' is the control center of the [[central nervous system]], responsible for [[behavior]]. In mammals, the brain is located in the head, protected by the [[skull]] and close to the primary sensory apparatus of [[Visual perception|vision]], [[Hearing (sense)|hearing]], [[equilibrioception]] (balance), sense of [[taste]], and [[olfaction]] (smell).
While all [[vertebrate]]s have a brain, most [[invertebrate]]s have either a centralized brain or collections of individual [[ganglion|ganglia]]. Some animals such as [[cnidarian]]s and [[echinoderm]]s do not have a centralized brain, and instead have a decentralized nervous system, while animals such as [[sponge]]s lack both a brain and nervous system entirely.
Brains can be extremely complex. For example, the [[human brain]] contains roughly 100 billion [[neuron]]s, each linked to as many as 10,000 other neurons.
==History==
{{main|History of the brain}}
Early views on the function of the brain regarded it as little more than cranial stuffing. In [[Ancient Egypt]], from the late [[Middle Kingdom]] onwards, in preparation for [[mummification]], the brain was regularly removed, for it was the [[heart]] that was assumed to be the seat of intelligence. According to [[Herodotus]], during the first step of mummification, "The most perfect practice is to extract as much of the brain as possible with an iron hook, and what the hook cannot reach is mixed with drugs." Over the next five-thousand years, this view came to be reversed; the brain is now known to be seat of intelligence, although [[idiom]]atic variations of the former remain, as in "memorizing something by heart".<ref>{{ cite book | last=Hendrickson | first=Robert | title=The Facts on File Encyclopedia of Word and Phrase Origins | publisher=Facts on File | location=New York | year=2000 | month=April | ISBN=978-0816040889 | quote=The ancient Greeks believed that the heart, the most noticeable internal organ, was the seat of intelligence and memory as well as emotion. This belief was passed on down the ages and became the basis for the English expression 'learn by heart,' which is used by Chaucer (1374) and must have been proverbial long before that. 'To record' reminds us again of this ancient belief in the heart as the seat of the mind. When writing wasn't a simple act, things had to be memorized; thus we have the word 'record,' formed from the Latin 're,' 'again,' and 'cor,' 'heart,' which means exactly the same as 'learn by heart.' }}</ref>
The first thoughts on the field of [[psychology]] came from [[Ancient philosophy|ancient philosophers]], such as [[Aristotle]]. As thinkers became more in tune with [[biomedical research]] over time, as was the case with [[Early Muslim sociology#Neuroscience and Psychology|medieval psychologists]] such as [[Ibn al-Haytham|Alhazen]] and [[Avicenna]] for example, the concepts of [[experimental psychology]] and [[clinical psychology]] began emerging. From that point, different branches of psychology emerged with different individuals creating new ideas, with modern [[psychologist]]s such as [[Sigmund Freud|Freud]] and [[Carl Jung|Jung]] contributing to the field.
==Mind and brain==
{{Unreferencedsection|date=June 2008}}
{{portalpar|Mind and Brain}}
The [[mind-body problem]] is one of the central problems in the history of [[philosophy]]. The brain is the physical and biological [[matter]] contained within the [[skull]], responsible for electrochemical neuronal processes. The ''mind'', in contrast, consists in mental attributes, such as [[belief]]s, [[desire]]s, [[perception]]s, and so on. There are scientifically demonstrable correlations between mental events and neuronal events; the philosophical question is whether these phenomena are identical, at least partially distinct, or related in some other way.
Philosophical positions on the mind-body problem fall into two main categories. The first category is '''[[Dualism (philosophy of mind)|dualism]]''', according to which the mind exists independently of the brain. Dualist theories are further divided into [[substance dualism]] and [[property dualism]]. [[René Descartes]] is perhaps the most prominent substance dualist, while property dualism is more popular among contemporary dualists like [[David Chalmers]]. Dualism requires admitting non-physical substances or properties into [[ontology]], which is in apparent conflict with the [[scientific world view]]. The second category is '''[[materialism]]''', according to which mental phenomena are identical to neuronal phenomena. A third category of view, '''[[idealism (philosophy)|idealism]]''', claims that only mental substances and phenomena exist. This view, most prominently held by 18th century Irish philosopher [[George Berkeley|Bishop George Berkeley]], has few contemporary adherents.
==Comparative anatomy==
[[Image:Mouse brain.jpg|thumb|right|238px|A mouse brain.]]
Three groups of animals have notably complex brains: the [[arthropod]]s ([[insect]]s, [[crustacean]]s, [[arachnid]]s, and others), the [[cephalopod]]s ([[octopus]]es, [[squid]]s, and similar [[mollusk]]s), and the [[craniata|craniates]] ([[vertebrate]]s and [[hagfish]]).<ref name="butler">{{cite journal | last = Butler | first = Ann B. | title = Chordate Evolution and the Origin of Craniates: An Old Brain in a New Head | journal = The Anatomical Record | year = 2000 | volume = 261 | pages = 111–125 | doi = 10.1002/1097-0185(20000615)261:3<111::AID-AR6>3.0.CO;2-F }}</ref> The brain of arthropods and cephalopods arises from twin parallel nerve cords that extend through the body of the animal. Arthropods have a central brain with three divisions and large ''optical lobes'' behind each [[eye]] for visual processing.<ref name="butler"/>
The brain of craniates develops from the [[anatomical terms of location|anterior]] section of a single dorsal [[neural tube|nerve cord]], which later becomes the [[spinal cord]].<ref name="kandel">{{cite book | authorlink = Eric R. Kandel | last = Kandel | first = ER | coauthors = Schwartz JH, Jessell TM | title = [[Principles of Neural Science]] | edition = 4th ed. | publisher = McGraw-Hill | location = New York | year = 2000 | id = ISBN 0-8385-7701-6 }}</ref> In craniates, the brain is protected by the [[bone]]s of the [[skull]].
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In vertebrates, increasing [[complexity]] in the [[cerebral cortex]] correlates with height on the [[phylogenetic tree|phylogenetic]] and [[evolutionary tree]]. Primitive vertebrates such as [[fish]], [[reptile]]s, and [[amphibian]]s have fewer than six layers of neurons in the outer layer of their brains. This cortical configuration is called the [[allocortex]] (or heterotypic cortex).<ref name="martin">{{cite book | last = Martin | first = John H. | title = Neuroanatomy: Text and Atlas | edition = Second Edition | publisher = McGraw-Hill | location = New York | year = 1996 | id = ISBN 0-07-138183-X }}</ref>
[This is probably utterly outdated if not outright bullshit. At least the wording needs to be revised - there is no "high" and "low" in phylogeny except for Intelligent Design advocates and other teleologists]
-->
[[Mammal]]s have a six-layered [[neocortex]] (or homotypic cortex, neopallium), in addition to having some parts of the brain that are allocortex.<ref name="kandel"/> In mammals, increasing convolutions of the brain are characteristic of animals with more advanced brains. These convolutions provide a larger surface area for a greater number of neurons while keeping the volume of the brain compact enough to fit inside the skull. The folding allows more grey matter to fit into a smaller volume. The folds are called [[Sulcus (neuroanatomy)|sulci]], while the spaces between the folds are called [[gyrus|gyri]].
In [[bird]]s, the part of the brain that functionally corresponds to the neocortex is called [[nidopallium]] and derives from a different part of the brain. Some birds (like [[corvid]]s and [[parrot]]s), are thought by some to have high intelligence, but even in these, the brain region that forms the mammalian neocortex is in fact almost entirely absent.
Although the general [[histology]] of the brain is similar from person to person, the structural anatomy can differ. Apart from the gross [[embryology|embryological]] divisions of the brain, the location of specific gyri and sulci, primary sensory regions, and other structures differs between species.
===Insects===
In insects, the brain has four parts, the [[optical lobes]], the [[protocerebrum]], the [[deutocerebrum]], and the [[tritocerebrum]]. The optical lobes are behind each eye and process visual stimuli.<ref name="butler"/> The protocerebrum contains the [[mushroom bodies]], which respond to [[olfaction|smell]], and the central body complex. In some [[species]] such as [[bee]]s, the mushroom body receives input from the visual pathway as well. The deutocerebrum includes the [[antennal lobe]]s, which are similar to the mammalian [[olfactory bulb]], and the mechanosensory [[neuropil]]s which receive information from [[Somatosensory system|touch]] receptors on the head and [[antenna (biology)|antennae]]. The antennal lobes of [[fly|flies]] and [[moth]]s are quite complex.
===Cephalopods===
In cephalopods, the brain has two regions: the supraesophageal mass and the subesophageal mass,<ref name="butler"/> separated by the [[esophagus]]. The supra- and subesophageal masses are connected to each other on either side of the esophagus by the basal lobes and the dorsal magnocellular lobes.<ref name="butler"/> The large optic lobes are sometimes not considered to be part of the brain, as they are anatomically separate and are joined to the brain by the optic stalks. However, the optic lobes perform much visual processing, and so functionally are part of the brain.
===Mammals and other vertebrates===
The [[telencephalon]] (cerebrum) is the largest region of the mammalian brain. This is the structure that is most easily visible in brain specimens, and is what most people associate with the "brain". In humans and several other animals, the fissures (sulci) and convolutions (gyri) give the brain a wrinkled appearance. In non-mammalian vertebrates with no cerebrum, the [[metencephalon]] is the highest center in the brain. Because humans walk upright, there is a flexure, or bend, in the brain between the [[brain stem]] and the cerebrum. Other vertebrates do not have this flexure. Generally, comparing the locations of certain brain structures between humans and other vertebrates often reveals a number of differences.
Behind (or in humans, below) the cerebrum is the cerebellum. The cerebellum is known to be involved in the control of movement,<ref name="kandel"/> and is connected by thick white matter fibers (cerebellar peduncles) to the [[pons]].<ref name="martin">{{cite book | last = Martin | first = John H. | title = Neuroanatomy: Text and Atlas | edition = Second Edition | publisher = McGraw-Hill | location = New York | year = 1996 | id = ISBN 0-07-138183-X }}</ref> The cerebrum has two [[cerebral hemispheres]]. The [[cerebellum]] also has hemispheres. The telencephalic hemispheres are connected by the [[corpus callosum]], another large white matter tract. An outgrowth of the telencephalon called the [[olfactory bulb]] is a major structure in many animals, but in humans and other primates it is relatively small.
Vertebrate nervous systems are distinguished by [[symmetry (biology)#Bilateral symmetry|bilaterally symmetrical]] [[encephalization]]. Encephalization refers to the tendency for more complex organisms to gain larger brains through evolutionary time. Larger vertebrates develop a complex, layered and interconnected neuronal circuitry. In modern species most closely related to the first vertebrates, brains are covered with gray matter that has a three-layer structure (allocortex). Their brains also contain deep brain nuclei and fiber tracts forming the white matter. Most regions of the human cerebral cortex have six layers of neurons (neocortex).<ref name="martin" />
====Vertebrate brain regions====
(''See related article at [[List of regions in the human brain]]'')
[[Image:EmbryonicBrain.svg|thumb|right|238px|Diagram depicting the main subdivisions of the [[embryogenesis|embryonic]] vertebrate brain. These regions will later differentiate into forebrain, midbrain and hindbrain structures.]]
According to the hierarchy based on embryonic and evolutionary development, [[chordate]] brains are composed of the three regions that later develop into five total divisions:
*[[Rhombencephalon]] (hindbrain)
**[[Myelencephalon]]
**[[Metencephalon]]
*[[Mesencephalon]] (midbrain)
*[[Prosencephalon]] (forebrain)
**[[Diencephalon]]
**[[Telencephalon]]
The brain can also be classified according to function, including divisions such as:
*[[Limbic system]]
*[[Sensory system]]s
**[[Visual system]]
**[[Olfactory system]]
**[[Gustatory system]]
**[[Auditory system]]
**[[Somatosensory system]]
*[[Muscle|Motor system]]
*[[cerebral cortex|Associative areas]]
In recent years it was realized that certain [[bird]]s have developed high intelligence entirely [[convergent evolution|convergently]] from [[mammals]] such as humans. Hence, the functional areas of the avian brain have been redefined by the [[Avian Brain Nomenclature Consortium]]. See also [[Bird intelligence]].
====Humans====
{{Unreferencedsection|date=June 2008}}
[[Image:Brain animated color nevit.gif|thumb|238px|Human brain with color coded lobes]]
{{main|Human brain}}
The structure of the human brain differs from that of other animals in several important ways. These differences allow for many abilities over and above those of other animals, such as advanced cognitive skills. Human encephalization is especially pronounced in the [[neocortex]], the most complex part of the [[cerebral cortex]]. The proportion of the human brain that is devoted to the neocortex—especially to the [[prefrontal cortex]]—is larger than in all other [[mammal]]s (indeed larger than in all animals, although only in mammals has the neocortex evolved to fulfill this kind of function).
Humans have unique neural capacities, but much of their brain structure is similar to that of other mammals. Basic systems that alert the nervous system to stimulus, that sense events in the environment, and monitor the condition of the body are similar to those of even non-mammalian vertebrates. The neural circuitry underlying human consciousness includes both the advanced neocortex and prototypical structures of the [[brainstem]]. The human brain also has a massive number of synaptic connections allowing for a great deal of [[parallel processing]].
The human brain is also the largest organ in the Nervous System.
==Neurobiology==
{{Unreferencedsection|date=June 2008}}
The brain is composed of two broad classes of cells, [[neuron]]s and [[glia]], both of which contain several different cell types which perform different functions. Interconnected neurons form [[neural network]]s (or [[neural ensemble]]s). These networks are similar to man-made [[electrical circuit]]s in that they contain circuit elements (neurons) connected by biological wires (nerve fibers). These do not form simple one-to-one electrical circuits like many man-made circuits, however. Typically neurons connect to at least a thousand other neurons.<ref>{{cite book | title = Basic Histology: Text and Atlas | edition = 10th ed. | first = L.C. | last = Junqueira | coauthors = J. Carneiro }} (Statistic from page 161)</ref> These highly specialized circuits make up systems which are the basis of [[perception]], different types of action, and higher cognitive function.
===Structure===
{{Neuron map|[[Neuron]]}}
Neurons are the cells that convey information to other cells; these constitute the essential class of brain cells.
In addition to neurons, the brain contains [[glial cell]]s in a roughly 10:1 proportion to neurons. Glial cells ("glia" is Greek for “glue”) form a support system for neurons. They create the insulating myelin, provide structure to the neuronal network, manage waste, and clean up neurotransmitters. Most types of glia in the brain are present in the entire [[nervous system]]. Exceptions include the [[oligodendrocyte]]s which myelinate neural [[axon]]s (a role performed by [[Schwann cell]]s in the peripheral nervous system). The myelin in the oligodendrocytes insulates the axons of some neurons. [[White matter]] in the brain is myelinated neurons, while [[grey matter]] contains mostly cell [[soma (biology)|soma]], [[dendrite]]s, and unmyelinated portions of axons and glia. The space between neurons is filled with dendrites as well as unmyelinated segments of axons; this area is referred to as the [[neuropil]].
In mammals, the brain is surrounded by [[connective tissue]]s called the [[meninges]], a system of [[membrane]]s that separate the skull from the brain. This three-layered covering is composed of (from the outside in) the [[dura mater]], [[arachnoid mater]], and [[pia mater]]. The arachnoid and pia are physically connected and thus often considered as a single layer, the pia-arachnoid. Below the arachnoid is the subarachnoid space which contains [[cerebrospinal fluid]], a substance that protects the nervous system. [[Blood vessel]]s enter the central nervous system through the perivascular space above the pia mater. The cells in the blood vessel walls are joined tightly, forming the [[blood-brain barrier]] which protects the brain from [[toxin]]s that might enter through the blood.
The brain is bathed in [[cerebrospinal fluid]] (CSF), which circulates between layers of the meninges and through cavities in the brain called [[Ventricular system|ventricle]]s. It is important both chemically for [[metabolism]] and mechanically for shock-prevention. For example, the human brain weighs about 1-1.5 kg or about 2-3 [[pound (mass)|lb]]. The [[mass]] and [[density]] of the brain are such that it will begin to collapse under its own weight if unsupported by the CSF. The CSF allows the brain to float, easing the physical [[stress (physics)|stress]] caused by the brain’s mass.
===Function===
Vertebrate brains receive signals through nerves arriving from the sensors of the organism. These signals are then processed throughout the central nervous system; reactions are formulated based upon reflex and learned experiences. A similarly extensive nerve network delivers signals from a brain to control important muscles throughout the body. Anatomically, the majority of afferent and efferent nerves (with the exception of the [[cranial nerves]]) are connected to the spinal cord, which then transfers the signals to and from the brain.
Sensory input is processed by the brain to recognize danger, find food, identify potential mates, and perform more sophisticated functions. [[Visual perception|Visual]], touch, and [[hearing (sense)|auditory]] sensory pathways of vertebrates are routed to specific nuclei of the [[thalamus]] and then to regions of the cerebral cortex that are specific to each [[sensory system]], the [[visual system]], the [[auditory system]], and the [[somatosensory system]]. Olfactory pathways are routed to the olfactory bulb, then to various parts of the [[olfactory system]]. [[Taste]] is routed through the brainstem and then to other portions of the [[gustatory system]].
To control movement the brain has several parallel systems of muscle control. The motor system controls voluntary muscle movement, aided by the [[motor cortex]], [[cerebellum]], and the [[basal ganglia]]. The system eventually projects to the spinal cord and then out to the muscle effectors. Nuclei in the brain stem control many involuntary muscle functions such as heart rate and breathing. In addition, many automatic acts (simple reflexes, locomotion) can be controlled by the spinal cord alone.
Brains also produce a portion of the body's [[hormone]]s that can influence organs and glands elsewhere in a body—conversely, brains also react to hormones produced elsewhere in the body. In mammals, the hormones that regulate hormone production throughout the body are produced in the brain by the structure called the [[pituitary gland]].
Evidence strongly suggests that developed brains derive consciousness from the complex interactions between the numerous systems within the brain. Cognitive processing in mammals occurs in the cerebral cortex but relies on midbrain and [[limbic system|limbic]] functions as well. Among "younger" (in an evolutionary sense) vertebrates, advanced processing involves progressively rostral (forward) regions of the brain.
Hormones, incoming sensory information, and cognitive processing performed by the brain determine the brain state. Stimulus from any source can trigger a general arousal process that focuses cortical operations to processing of the new information. This focusing of cognition is known as [[attention]]. Cognitive priorities are constantly shifted by a variety of factors such as hunger, fatigue, belief, unfamiliar information, or threat. The simplest dichotomy related to the processing of threats is the [[fight-or-flight response]] mediated by the [[amygdala]] and other limbic structures.
====Neurotransmitter systems====
{{Main|Neurotransmitter systems}}
Neurons expressing certain types of neurotransmitters sometimes form distinct systems, where activation of the system causes effects in large volumes of the brain, called ''volume transmission''.
The major neurotransmitter systems are the [[noradrenaline]] (norepinephrine) system, the [[dopamine]] system, the [[serotonin]] system and the [[cholinergic]] system.
Drugs targeting the neurotransmitter of such systems affects the whole system, which explains the mode of action of many drugs;
* [[Cocaine]], for example, blocks the reuptake of [[dopamine]], leaving these neurotransmitters in the [[synapse|synaptic gap]] longer.
* [[Prozac]] is a [[serotonin reuptake inhibitor|selective serotonin reuptake inhibitor]] (SSRI), hence potentiating the effect of naturally released serotonin.
* [[AMPT]] prevents the conversion of tyrosine to [[L-DOPA]], the precursor to dopamine; [[reserpine]] prevents dopamine storage within [[vesicles]]; and [[deprenyl]] inhibits [[monoamine oxidase]] (MAO)-B and thus increases dopamine levels.
Diseases may affect specific neurotransmitter systems. For example, [[Parkinson's disease]] is at least in part related to failure of dopaminergic cells in [[deep-brain nuclei]], for example the [[substantia nigra]]. Treatments potentiating the effect of dopamine precursors have been proposed and effected, with moderate success.
A brief comparison of the major neurotransmitter systems follows:
{| class="wikitable"
|+Neurotransmitter systems
|-
! System !! Origin!!<ref name=Rang> {{cite book |author=Rang, H. P. |title=Pharmacology |publisher=Churchill Livingstone |location=Edinburgh |year=2003 |pages= page 474 for noradrenaline system, page 476 for dopamine system, page 480 for serotonin system and page 483 for cholinergic system. |isbn=0-443-07145-4 |doi=}} </ref> Effects<ref name=Rang/>
|-
!rowspan=2| Noradrenaline system
| [[locus coeruleus]]
|rowspan=2|
*arousal
*reward
|-
| [[lateral tegmental field]]
|-
! Dopamine system
|| [[dopamine]] [[neural pathway|pathways]]:
* [[mesocortical pathway]]
* [[mesolimbic pathway]]
* [[nigrostriatal pathway]]
* [[tuberoinfundibular pathway]]
|| [[motor system]], reward, [[cognition]], [[endocrine]], [[nausea]]
|-
!rowspan=2| Serotonin system
| caudal [[dorsal raphe nucleus]]
|rowspan=2| Increase [[extraversion and introversion|introversion]], [[Mood (psychology)|mood]], [[satiety]], [[body temperature]] and [[sleep]], while decreasing [[nociception]].
|-
| rostral [[dorsal raphe nucleus]]
|-
!rowspan=3| Cholinergic system
| ''pontomesencephalotegmental complex''
|rowspan=3|
*[[learning]]
*[[Memory#Short-term|short-term memory]]
*arousal
*reward
|-
| [[basal optic nucleus of Meynert]]
|-
| medial [[septal nucleus]]
|}
===Origin===
Since even unicellular organisms can have, at least, photosensitive [[eyespot apparatus|eyespot]]s and react to tactile stimuli, it is hypothesized that sensory organs developed before the brain did.<ref>{{cite journal | last = Gehring | first = W. J. | date = 13 January 2005 | title = New Perspectives on Eye Development and the Evolution of Eyes and Photoreceptors: The Evolution of Eyes and Brain | journal = Journal of Heredity | volume = 96 | issue = 3 | pages = 171–184 | publisher = Oxford Journals | doi = 10.1093/jhered/esi027 | url = http://jhered.oxfordjournals.org/cgi/content/full/96/3/171 | format = Full text | accessdate = 2008-04-26 | quote = | pmid = 15653558 }}</ref> The brain is an information-processing organ and its evolution is dependent on the presence of information accessed into sensory organs, sensory input, and the need to process this information and transmit it.
===Pathology===
[[Image:Frontotemporal degeneration.png|right|thumb|238px|A [[human brain]] showing [[frontotemporal lobar degeneration]] causing frontotemporal dementia.]]
Clinically, [[death]] is defined as an absence of brain activity as measured by [[EEG]]. Injuries to the brain tend to affect large areas of the organ, sometimes causing major deficits in intelligence, memory, and movement. Head trauma caused, for example, by vehicle or industrial accidents, is a leading cause of death in youth and middle age. In many cases, more damage is caused by resultant [[edema]] than by the impact itself. [[Stroke]], caused by the blockage or rupturing of blood vessels in the brain, is another major cause of death from brain damage.
Other problems in the brain can be more accurately classified as diseases rather than injuries. [[Neurodegenerative disease]]s, such as [[Alzheimer's disease]], [[Parkinson's disease]], [[motor neurone disease]], and [[Huntington's disease]] are caused by the gradual death of individual neurons, leading to decrements in movement control, memory, and cognition. Currently only the symptoms of these diseases can be treated. [[Mental illness]]es, such as [[clinical depression]], [[schizophrenia]], [[bipolar disorder]], and [[post-traumatic stress disorder]] are brain disorders that impact [[Wiktionary:personality|personality]] and, typically, other aspects of mental and somatic function. These disorders may be treated by [[psychiatry|psychiatric therapy]], [[medication|pharmaceutical]] intervention, or through a combination of treatments; therapeutic effectiveness varies significantly among individuals.
Some infectious diseases affecting the brain are caused by [[virus]]es and [[bacteria]]. Infection of the [[meninges]], the membrane that covers the brain, can lead to [[meningitis]]. [[Bovine spongiform encephalopathy]] (also known as mad cow disease), is deadly in [[cattle]] and humans and is linked to [[prion]]s. [[Kuru (disease)|Kuru]] is a similar prion-borne degenerative brain disease affecting humans. Both are linked to the ingestion of neural tissue, and may explain the tendency in some species to avoid [[cannibalism]]. Viral or bacterial causes have been reported in [[multiple sclerosis]] and [[Parkinson's disease]], and are established causes of [[encephalopathy]], and [[encephalomyelitis]].
Many brain disorders are [[congenital disorder|congenital]]. [[Tay-Sachs disease]], [[Fragile X syndrome]], and [[Down syndrome]] are all linked to [[gene]]tic and [[chromosome|chromosomal]] errors. Many other syndromes, such as the intrinsic [[circadian rhythm]] disorders, are suspected to be congenital as well. Malfunctions in the embryonic [[neural development|development]] of the brain can be caused by genetic factors, [[drug use]], [[nutritional deficiencies]], and [[infectious diseases]] during [[pregnancy]].
Certain brain disorders are treated by brain [[neurosurgeon]]s while others are treated by neurologists and psychiatrists.
==Study of the brain==
===Fields of study===
[[Neuroscience]] seeks to understand the nervous system, including the brain, from a biological and [[computational neuroscience|computational]] perspective. [[Psychology]] seeks to understand behavior and the brain. [[Neurology]] refers to the [[medicine|medical]] applications of neuroscience. The brain is also one of the most important organs studied in [[psychiatry]], the branch of medicine which exists to study, prevent, and treat [[mental disorders]].<ref name=Storrow1>Storrow, H.A. (1969). ''Outline of Clinical Psychiatry''. New York: Appleton-Century-Crofts, p. 1. ISBN 978-0-39-085075-1</ref><ref name=Lyness3>Lyness, J.M. (1997). ''Psychiatric Pearls''. Philadelphia: F.A. Davis Company, p. 3. ISBN 978-0-80-360280-9</ref><ref name=Guze4>Guze, S.B. (1992). ''Why Psychiatry Is a Branch of Medicine''. New York: Oxford University Press, p. 4. ISBN 978-0-19-507420-8</ref> [[Cognitive science]] seeks to unify neuroscience and psychology with other fields that concern themselves with the brain, such as [[computer science]] ([[artificial intelligence]] and similar fields) and [[philosophy]].
===Methods of observation===
{{main|neuroimaging}}
Each method for observing activity in the brain has its advantages and drawbacks.
====Electrophysiology====
Electrophysiology allows scientists to record the electrical activity of individual neurons or groups of neurons.
====EEG====
By placing electrodes on the scalp one can record the summed electrical activity of the cortex in a technique known as [[electroencephalography]] (EEG). EEG measures the mass changes in electrical current from the cerebral cortex, but can only detect changes over large areas of the brain with very little sub-cortical activity.
====MEG====
Apart from measuring the electric field around the skull it is possible to measure the magnetic field directly in a technique known as [[magnetoencephalography]] (MEG). This technique has the same temporal resolution as EEG but much better spatial resolution, although admittedly not as good as fMRI. The main advantage over fMRI is a direct relationship between neural activation and measurement.
====fMRI and PET====
[[Image:FMRI.jpg|thumb|238px|A scan of the brain using fMRI]]
Functional magnetic resonance imaging (fMRI) measures changes in [[blood flow]] in the brain, but the activity of neurons is not directly measured, nor can it be distinguished whether this activity is inhibitory or excitatory. fMRI is a noninvasive, indirect method for measuring neural activity that is based on '''BOLD'''; '''B'''lood '''O'''xygen '''L'''evel '''D'''ependent changes. The changes in blood flow that occur in capillary beds in specific regions of the brain are thought to represent various neuronal activities ([[metabolism]] of synaptic reuptake). Similarly, a [[Positron emission tomography| positron emission tomography]] (PET), is able to monitor [[glucose]] and [[oxygen]] metabolism as well as neurotransmitter activity in different areas within the brain which can be correlated to the level of activity in that region.
====Behavioral====
Behavioral tests can measure symptoms of disease and mental performance, but can only provide indirect measurements of brain function and may not be practical in all animals. In humans however, a neurological exam can be done to determine the location of any trauma, [[lesion]], or [[tumor]] within the brain, brain stem, or spinal cord.
====Anatomical====
[[post-mortem|Autopsy]] analysis of the brain allows for the study of anatomy and [[protein]] expression patterns, but is only possible after the human or animal is dead. [[Magnetic resonance imaging]] (MRI) can be used to study the anatomy of a living creature and is widely used in both research and medicine.
===Other studies===
[[computer science|Computer scientists]] have produced simulated "[[artificial neural network]]s" loosely based on the structure of neuron connections in the brain. Some [[artificial intelligence]] research seeks to replicate brain function—although not necessarily brain mechanisms—but as yet has been met with limited success.
Creating [[algorithm]]s to mimic a biological brain is very difficult because the brain is not a static arrangement of circuits, but a network of vastly interconnected neurons that are constantly changing their connectivity and sensitivity. More recent work in both neuroscience and artificial intelligence models the brain using the [[mathematics|mathematical]] tools of [[chaos theory]] and [[dynamical system]]s. Current research has also focused on recreating the neural structure of the brain with the aim of producing human-like cognition and artificial intelligence.
==As food== <!--Brain dish redirects here-->
<!--[[Image:Porkbrain.jpg|right|thumb|238px|Pork brain, ready to be cooked]]-->
[[Image:GoatBrain.jpg|thumb|Goat brain prior to being cooked]]
Like most other internal organs, the brain can serve as nourishment. For example, in the [[Southern United States]] canned [[pork]] brain in [[gravy]] can be purchased for consumption as food. This form of brain is often fried with [[scrambled eggs]] to produce the famous "[[Eggs and brains|Eggs n' Brains]]".<ref>{{cite web | author = Lukas, Paul | title = Inconspicuous Consumption: Mulling Brains | work = New York magazine | url = http://www.bozosoft.com/mike/meat/brains-article.html | accessdaymonth = 14 October | accessyear = 2005 }}</ref> The brain of animals also features in [[French cuisine]] such as in the dish ''tête de veau'', or ''head of calf''. Although it sometimes consists only of the outer meat of the skull and [[jaw]], the full meal includes the brain, [[tongue]], and [[gland]]s. Similar delicacies from around the world include [[Mexico|Mexican]] ''[[taco]]s de sesos'' made with cattle brain as well as [[squirrel]] brain in the US South.<ref>{{cite web | url = http://www.weird-food.com/weird-food-mammal.html | work = Weird-Food.com | title = Weird Foods: Mammal | accessdaymonth = 14 October | accessyear = 2005 }}</ref> The Anyang tribe of [[Cameroon]] practiced a tradition in which a new [[tribal chief]] would consume the brain of a hunted [[gorilla]] while another senior member of the [[tribe]] would eat the heart.<ref>{{cite web | url = http://www.berggorilla.de/english/gjournal/texte/18culture.html | author = Meder, Angela | title = Gorillas in African Culture and Medicine | work = Gorilla Journal | accessdaymonth = 14 October | accessyear = 2005 }}</ref> [[Indonesia]]n cuisine specialty in [[Minangkabau]] cuisine also served beef brain in a gravy coconut milk named [[gulai otak]] (beef brain curry). Roasted or fried goat brain is eaten in south India and some parts of north India. Norwegian cuisine includes [[smalahove]] where a singed lamb's head, including the brain, tongue and eye, serves two people.
Consuming the brain and other nerve tissue of animals is not without risks. The first problem is that the makeup of the brain is 60% fat due to large quantities of [[myelin]] (which itself is 70% fat) insulating the axons of neurons.<ref>{{cite web | url = http://www.autisminfo.com/dorfman.htm | title = Nutritional Summary: Notes Taken From a Recent Autism Society Meeting | author = Dorfman, Kelly | work = Diet and Autism | accessdaymonth = 14 October | accessyear = 2005 }}</ref> As an example, a 140 g can of "pork brains in milk gravy", a single serving, contains 3500 milligrams of [[cholesterol]], 1170% of our recommended daily intake.<ref>{{cite web | url = http://thewvsr.com/porkbrains.htm | title = Pork Brains in Milk Gravy | accessdaymonth = 14 October | accessyear = 2005 }}</ref>
Brain consumption can result in contracting fatal [[Transmissible spongiform encephalopathy|transmissible spongiform encephalopathies]] such as Variant [[Creutzfeldt-Jakob disease]] and other [[prion]] diseases in humans and [[Bovine spongiform encephalopathy|mad cow disease]] in cattle.<ref>{{cite journal | last = Collinge | first = John | date = 2001 | title = Prion diseases of humans and animals: their causes and molecular basis | journal = Annual Review of Neuroscience | volume = 24 | pages = 519–50 | url = http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11283320 | doi = 10.1146/annurev.neuro.24.1.519 <!--Retrieved from URL by DOI bot--> | pmid = 11283320 }}</ref> Another prion disease called [[Kuru (disease)|kuru]] has been traced to a funerary ritual among the [[Fore (people)|Fore]] people of [[Papua New Guinea]] in which those close to the dead would eat the brain of the deceased to create a sense of [[immortality]].<ref>{{cite journal | last = Collins | first = S | coauthors = McLean CA, Masters CL | date = 2001 | title = Gerstmann-Straussler-Scheinker syndrome,fatal familial insomnia, and kuru: a review of these less common human transmissible spongiform encephalopathies | journal = Journal of Clinical Neuroscience | volume = 8 | issue = 5 | ages = 387–97 | url = http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11535002 | pmid = 11535002 }}</ref> Some [[archaeology|archaeological]] evidence suggests that the mourning rituals of [[Europe]]an [[Neanderthal]]s also involved the consumption of the brain.<ref>{{cite book | url = http://search.barnesandnoble.com/booksearch/isbninquiry.asp?ean=9781582432533&displayonly=CHP | title = The Aztec Treasure House | last = Connell | first = Evan S. | publisher = Counterpoint Press | year = 2001 | id = ISBN 1-58243-162-0 }}</ref> Because of the risk of being infected by prions one should always wear gloves when handling brains.
It is also well-known in the hunting community that the brain of wild animals should not be consumed, due to the risk of [[chronic wasting disease]]. The brain is still useful to hunters, in that most animals have enough brain matter for use in the [[tanning]] of their own hides.
==Brain energy consumption==
[[Image:PET-image.jpg|thumb|right|200px|[[Positron emission tomography|PET]] Image of the human brain showing energy consumption]]
Although the brain represents only 2% of the body weight, it receives 15% of the cardiac output, 20% of total body oxygen consumption, and 25% of total body glucose utilization. The energy consumption for the brain to simply survive is 0.1 Calories per minute, while this value can be as high as 1.5 Calories per minute during crossword puzzle-solving.<ref name="popular">{{ cite web | last = Calderone | first = Melissa A. | title = Mental Workout: Do you use more energy when you're thinking really hard? | url = http://www.popsci.com/popsci/science/61994314e58fb010vgnvcm1000004eecbccdrcrd.html | year = 2006 | month = July | accessdate = 2007-06-03 }}</ref> The demands of the brain limit its size in many species. [[Molossid]] bats and the [[Vespertilionid]] ''[[Nyctalus]] spp.'' have brains that have been reduced from the ancestral form to invest in wing-size for the sake of maneuverability. This contrasts with [[fruit bat]]s, which require more advanced neural structures and do not pursue their prey.<ref>Safi, K., M.A. Seid & D.K.N. Dechmann. (2005) "Bigger is not always better: when brains get smaller." ''[[Biol. Lett.]]'' '''1'''(3): 283-6.</ref>
== See also ==
*[[Traumatic brain injury]]
==References==
{{reflist}}
{{Refimprove|date=April 2008}}
==Further reading==
{{portalpar|Neuroscience|Neuro logo.png}}
*{{cite book|author=Junqueira, L.C., and J. Carneiro|title=Basic Histology: Text and Atlas, Tenth Edition|publisher=Lange Medical Books McGraw-Hill|year=2003|id=ISBN 0-07-121565-4}}
* Kinseher Richard, Geborgen in Liebe und Licht – Gemeinsame Ursache von Intuition, Déjà-vu-, Schutzengel-, und Nahtod-Erlebnissen, BoD, 2006, ISBN 3-8334-51963, German language: (A new theory: A LIVE-scan of the episodic memory, can be observed during near-death-experiences. The stored experiences are then judged by the topical intellect.)
*{{cite book|author=Sala, Sergio Della, editor.|title=Mind myths: Exploring popular assumptions about the mind and brain|publisher=J. Wiley & Sons, New York|year=1999|id=ISBN 0-471-98303-9}}
*{{cite book|author=Vander, A., J. Sherman, D. Luciano|title=Human Physiology: The Mechanisms of Body Function|publisher=McGraw Hill Higher Education|year=2001|id=ISBN 0-07-118088-5}}
*{{cite book |author= [[Piero Scaruffi|Scaruffi, Piero]]|title=The Nature of Consciousness |publisher=Omniware |year= |isbn=0-9765531-1-2 |doi=}}
==External links==
{{commonscat|Brain}}
* [http://www.howstuffworks.com/Brain.htm How Your Brain Works] at [[HowStuffWorks]]
* [http://www.stanford.edu/group/hopes/basics/braintut/ab0.html The HOPES Brain Tutorial] at [http://hopes.stanford.edu/ hopes.stanford.edu]
* [http://brainmuseum.org/ Comparative Mammalian Brain Collection]
* [http://www.sciencedaily.com/news/mind_brain/ Brain Research News from ScienceDaily]
* [http://braininfo.rprc.washington.edu BrainInfo for Neuroanatomy]
* [http://faculty.washington.edu/chudler/neurok.html Neuroscience for kids]
* [http://www.newscientist.com/channel/being-human/brain Everything you wanted to know about the brain] – Provided by ''[[New Scientist]]''.
* [http://www.biaq.com.au/ Fact sheets on brain injury - causes, effects and coping strategies]
* [http://purl.net/net/neurowiki Neuroscience wiki].
* [http://www.brainmaps.org/ BrainMaps.org], interactive high-resolution digital brain atlas based on scanned images of serial sections of both primate and non-primate brains
* [http://www.sciam.com/article.cfm?chanID=sa006&articleID=000AF67F-28CD-1F30-9AD380A84189F2D7&pageNumber=1&catID=2 Scientific American Magazine (September 2003 Issue) Ultimate Self-Improvement]
* [http://cerebralhealth.com/neuroscienceresearch.php Brain Research and Information Network B.R.A.I.N.]
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{{Mesencephalon}}
{{Rhombencephalon}}
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