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kkkkkkFor other uses of the term brain see brain (disambiguation). For information on the human brain specifically, please see its article.
Comparative brain sizesIn animals, the brain, or encephalon (Greek for "in the head"), is the control center of the central nervous system. In most animals, the brain is located in the head close to the primary sensory apparatus and the mouth. While all vertebrate nervous systems have a brain, invertebrate nervous systems have either a centralized brain or collections of individual ganglia. The brain is extremely complex; the human brain contains 100 billion or more neurons, each linked to as many as 10,000 others[1]. This enormous number of interconnections, however, does not indicate intelligence.
Contents [hide]
1 History
2 Overview
3 Mind and brain
4 Comparative anatomy
4.1 Invertebrates
4.2 Vertebrates
4.2.1 Vertebrate brain regions
4.2.2 Humans
5 Neurobiology
5.1 Histology
5.2 Function
5.3 Brain pathology
6 The study of the brain
6.1 Fields of study
6.2 Methods of observation
6.2.1 Electrophysiology
6.2.2 EEG
6.2.3 fMRI and PET
6.2.4 Behavioral
6.2.5 Anatomical
6.2.6 Other methods
6.3 Other matters
7 Brain as food
8 See also
9 Further reading
9.1 References
10 External links
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History
Main article: History of the brain
Early views on the function of the brain regarded it to be a form of “cranial stuffing” of sorts. In 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 the seat of intelligence, although colloquial variations of the former remain as in “memorizing something by heart”.
[edit]
Overview
The brain is not only important as the site of reason and intelligence, it is also the source of cognition, emotion, memory, and motor, and other forms of learning, and it controls and coordinates most sensory systems, movement, behavior, but it also controls homeostatic body functions such as heart rate, blood pressure, fluid balance, and body temperature. Some behaviors such as simple reflexes and basic locomotion, can be executed under spinal cord control alone.
Most brains exhibit a visible distinction between grey matter and white matter. Grey matter consists of the cell bodies of the neurons, while white matter consists of the fibers (axons) that connect neurons. The axons are surrounded by a fatty insulating sheath called myelin, giving the white matter its distinctive color. The outer, visible layers of the brain are the cortex, and consist mainly of grey matter.
The study of the brain is known as neuroscience, a field of biology aimed at understanding the functions of the brain at every level, from the molecular up to the psychological.
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Mind and brain
Mind and Brain Portal
A distinction is often made in the philosophy of mind between the mind and the brain, and there is some controversy as to their exact relationship, leading to the mind-body problem. The brain is defined as the physical, biological matter contained within the skull, responsible for all electrochemical neuronal processes. The mind, however, is seen in terms of mental attributes, such as beliefs or desires. Some suggest that the mind exists in some way independently of the brain, such as in a soul or epiphenomenon. Others, such as strong AI theorists, say that the mind is directly analogous to computer software and the brain to hardware.
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Comparative anatomy
A mouse brain.Three groups of animals have notably complex brains: the arthropods (insects and crustaceans), the cephalopods (octopi, squids, and similar mollusks), and the craniates (vertebrates)[2]. 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.[2]
The brain of craniates develops from the anterior section of a single dorsal nerve cord, which later becomes the spinal cord[3]. In craniates, the brain is protected by the bones of the skull. In vertebrates, increasing complexity in the cerebral cortex correlates with height on the phylogenetic and evolutionary tree. Primitive vertebrates such as fish, reptiles, and amphibians have fewer than six layers of neurons in the outer layer of their brains. This cortical configuration is called the allocortex (or heterotypic cortex)[4].
More complex vertebrates such as mammals have a six-layered neocortex (or homotypic cortex, neopallium), in addition to having some parts of the brain that are allocortex.[4] 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, similar to a really long slinky being able to fit into a tiny box when completely pushed together. The folds are called gyri, while the spaces between the folds are called sulci.
Although the general histology of the brain is similar from person to person, the structural anatomy can differ. Apart from the gross embryological divisions of the brain, the location of specific gyri and sulci, primary sensory regions, and other structures differs between species.
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Invertebrates
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.[2] The protocerebrum contains the mushroom bodies, which respond to smell, and the central body complex. In some species such as bees, the mushroom body receives input from the visual pathway as well. The deutocerebrum includes the antennal lobes, which are similar to the mammalian olfactory bulb, and the mechanosensory neuropils which receive information from touch receptors on the head and antennae. The antennal lobes of flies and moths are quite complex.
In cephalopods, the brain has two regions: the supraesophageal mass and the subesophageal mass,[2] 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.[2] 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.
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Vertebrates
The lobes of the cerebral cortex include the frontal (red), temporal (green), occipital (yellow), and parietal lobes (orange). The cerebellum (blue) is not part of the telencephalon. In vertebrates a gross division into three major parts is used.The telencephalon (cerebrum) is the largest region of the mammalian brain. This is the structure that is most easily visible, and is what most people associate with the "brain". In humans, 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, and so comparing the locations of certain brain structures between humans and other vertebrates can be confusing.
Behind (or in humans, below) the cerebrum is the cerebellum. The cerebellum is mainly involved in the control of movement [5], and is connected by thick white matter fibers (cerebellar peduncles) to the pons.[4] The cerebrum and the cerebellum each have two 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 encephalization and bilateral symmetry. 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).[4]
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Vertebrate brain regions
(See related article at List of regions in the human brain)
Diagram depicting the main subdivisions of the 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 systems
Visual system
Olfactory system
Gustatory system
Auditory system
Somatosensory system
Motor system
Associative areas
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Humans
Main article: 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 animals.
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 insensitive to pain. A headache comes from the muscles and nerves lining it, not the organ itself.
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Neurobiology
The brain is composed of two broad classes of cells, neurons and glia both of which contain several different cell types which perform different functions. Interconnected neurons form neural networks (or neural ensembles). These networks are similar to man-made electrical circuits 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[6]. These highly specialized circuits make up systems which are the basis of perception, action, and higher cognitive function.
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Histology
Diagram of basic features of a neuron.Neurons are the cells that generate action potentials and convey information to other cells; these constitute the essential class of brain cells.
In addition to neurons, the brain contains glial cells 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 oligodendrocytes which myelinate neural axons (a role performed by Schwann cells 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, dendrites, 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 also contains connective tissue called the meninges, a system of membranes that separate the skull from the brain. This three-layered covering is made of, from the outside in, 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 vessels 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 toxins 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 ventricles. It is important both chemically for metabolism and mechanically for shock-prevention. For example, the human brain weighs about 1-1.5 kg. The mass and density of the brain are such that it will begin to collapse under its own weight. The CSF allows the brain to float, easing the stress caused by the brain’s mass.
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Function
Vertebrate brains receive signals through nerves arriving from the sensors of the organism. These signals are then interpreted 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 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, touch, and 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 hormones that can influence organs and glands elsewhere in a body—conversely, brains also react to hormones produced elsewhere in the body. In mammals, most of these hormones are released into the circulatory system by a structure called the pituitary gland.
It is hypothesized 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 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.
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Brain pathology
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 and industrial accidents, is a leading cause of death in youth and middle age. In many cases, more damage is caused by resultant swelling (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 diseases, 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 illnesses, such as clinical depression, schizophrenia, bipolar disorder, and post-traumatic stress disorder are brain diseases that impact the personality and typically on other aspects of mental and somatic function. These disorders may be treated by psychiatric therapy, pharmaceutical intervention, or through a combination of treatments; therapeutic effectiveness varies significantly among individuals.
Some infectious diseases affecting the brain are caused by viral and bacterial infection(s). 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 is linked to prions. 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 substantiated in multiple sclerosis, Parkinson's disease, Lyme disease, encephalopathy, and encephalomyelitis.
Some brain disorders are congenital. Tay-Sachs disease, Fragile X syndrome, and Down syndrome are all linked to genetic and chromosomal errors. Malfunctions in the embryonic development of the brain can be caused by genetic factors, by drug use, and disease during a mother's pregnancy.
Certain brain disorders are treated by brain surgeons (neurosurgeons) while others are treated by neurologists and psychiatrists.
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The study of the brain
[edit]
Fields of study
Neuroscience seeks to understand the nervous system, including the brain, from a biological and computational perspective. Psychology seeks to understand behavior and the brain. The terms neurology and psychiatry usually refer to medical applications of neuroscience and psychology respectively. 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.
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Methods of observation
Main article: neuroimaging
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Electrophysiology
Each method for observing activity in the brain has its advantages and drawbacks. Electrophysiology allows scientists to record the electrical activity of individual neurons or groups of neurons.
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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.
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fMRI and PET
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. Similarly, a positron emission tomography (PET), is able to monitor glucose metabolism in different areas within the brain which can be correlated to the level of activity in that region.
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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.
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Anatomical
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.
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Other methods
Attempts have also been made to directly "read" the brain, which has been accomplished in a rudimentary manner through a brain-computer interface. Brain activity can be detected by implanted electrodes, raising the possibility of direct mind-computer interface. The reverse method has been successfully demonstrated: brain implants have been used to generate artificial hearing and (crude and experimental) artificial vision for deaf and blind people. Brain pacemakers are now commonly used to regulate brain activity in conditions such as Parkinson's disease.
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Other matters
Computer scientists have produced simulated neural networks loosely based on the structure of neuron connections in the brain. Artificial intelligence seeks to replicate brain function—although not necessarily brain mechanisms—but as yet has been met with limited success.
Creating algorithms 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 mathematical tools of chaos theory and dynamical systems. Current research has also focused on recreating the neural structure of the brain with the aim of producing human-like cognition and artificial intelligence.
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Brain as food
Pork brain, ready to be cookedLike 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. The form of brain is often fried with scrambled eggs to produce the famous "Eggs n' Brains".[7] The brain of animals also features in French cuisine such as in the dish [tête de veau], or head of calf. Although it might consist only of the outer meat of the skull and jaw, the full meal includes the brain, tongue, and glands, with the latter form being the favorite food of French President Jacques Chirac.[8] Similar delicacies from around the world include Mexican tacos de sesos made with cattle brain as well as squirrel brain in the US South.[9] 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.[10]
Consuming the brain and other nerve tissue of animals is not without risks. The first problem is that the brain is made up of 60% fat due to the myelin (which itself is 70% fat) insulating the axons of neurons and glia.[11] 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.[12]
Brain consumption can also result in contracting fatal transmissible spongiform encephalopathies such as Variant Creutzfeldt-Jakob disease and other prion diseases in humans and mad cow disease in cattle.[13]. Another prion disease called kuru has been traced to a funerary ritual among the 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.[14] Some archaeological evidence suggests that the mourning rituals of European Neanderthals also involved the consumption of the brain.[15]
It is not only humans who eat the brains of other animals. The two species of chimpanzee, though generally vegetarian, are known to eat the brains of monkeys to obtain fat in their diet.[citation needed]
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See also
Nervous system
Central nervous system
Neuroscience
Neurology
A/S ratio
Brain damage
Brain-computer interface
Human brain
Regions in the human brain
Traumatic brain injury
[edit]
Further reading
Junqueira, L.C., and J. Carneiro (2003). Basic Histology: Text and Atlas, Tenth Edition. Lange Medical Books McGraw-Hill. ISBN 0071215654.
Sala, Sergio Della, editor. (1999). Mind myths: Exploring popular assumptions about the mind and brain. J. Wiley & Sons, New York. ISBN 0471983039.
Vander, A., J. Sherman, D. Luciano (2001). Human Physiology: The Mechanisms of Body Function. McGraw Hill Higher Education. ISBN 0071180885.
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References
^ Chudler, Eric H. (2006). Brain Facts and Figures. Neuroscience for Kids. Retrieved on May 19, 2006.
^ a b c d e Butler, Ann B. (2000). "Chordate Evolution and the Origin of Craniates: An Old Brain in a New Head". The Anatomical Record 261: 111–125.
^ Kandel, ER; Schwartz JH, Jessell TM (2000). Principles of Neural Science, 4th ed., New York: McGraw-Hill. ISBN 0838577016.
^ a b c d Martin, John H. (1996). Neuroanatomy: Text and Atlas, Second Edition, New York: McGraw-Hill. ISBN 007138183X.
^ Kandel, ER; Schwartz JH, Jessell TM (2000). Principles of Neural Science, 4th ed., New York: McGraw-Hill. ISBN 0838577016.
^ Junqueira, L.C.; J. Carneiro. Basic Histology: Text and Atlas, 10th ed.. (Statistic from page 161)
^ Lukas, Paul. Inconspicuous Consumption: Mulling Brains. New York magazine. Retrieved on 14 October 2005.
^ Glover, William. Tales from the Loir: Tête de Veau. Cave Life in France. Retrieved on 14 October 2005.
^ Weird Foods: Mammal. Weird-Food.com. Retrieved on 14 October 2005.
^ Meder, Angela. Gorillas in African Culture and Medicine. Gorilla Journal. Retrieved on 14 October 2005.
^ Dorfman, Kelly. Nutritional Summary: Notes Taken From a Recent Autism Society Meeting. Diet and Autism. Retrieved on 14 October 2005.
^ Pork Brains in Milk Gravy. Retrieved on 14 October 2005.
^ Collinge, John (2001). "Prion diseases of humans and animals: their causes and molecular basis". Annual Review of Neuroscience 24: 519–50. PMID 11283320.
^ Collins, S, McLean CA, Masters CL (2001). "Gerstmann-Straussler-Scheinker syndrome,fatal familial insomnia, and kuru: a review of these less common human transmissible spongiform encephalopathies". Journal of Clinical Neuroscience 8 (5). PMID 11535002.
^ Connell, Evan S. (2001). The Aztec Treasure House. Counterpoint Press. ISBN 1582431620.
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External links
Brain Tutorial
Comparative Mammalian Brain Collection
RMCybernetics - The Brain and Artificial Intelligence
BrainInfo for Neuroanatomy
Neuroscience for kids
Everything you wanted to know about the brain — Provided by New Scientist.
neuroscience wiki
BrainMaps.org, interactive high-resolution digital brain atlas based on scanned images of
For other uses, see Mind (disambiguation).
Mind and Brain Portal
Mind refers to the collective aspects of intellect and consciousness which are manifest in some combination of thought, perception, emotion, will, memory, and imagination.
There are many theories of what the mind is and how it works, dating back to Plato, Aristotle and other Ancient Greek philosophers. Pre-scientific theories, which were rooted in theology, concentrated on the relationship between the mind and the soul, the supposed supernatural or divine essence of the human person. Modern theories, based on a scientific understanding of the brain, see the mind as a phenomenon of psychology, and the term is often used more or less synonymously with consciousness.
The question of which human attributes make up the mind is also much debated. Some argue that only the "higher" intellectual functions constitute mind: particularly reason and memory. In this view the emotions - love, hate, fear, joy - are more "primitive" or subjective in nature and should be seen as different in nature or origin to the mind. Others argue that the rational and the emotional sides of the human person cannot be separated, that they are of the same nature and origin, and that they should all be considered as part of the individual mind.
Contents [hide]
1 Thought
2 Nature of the mind
3 History of the philosophy of the mind
4 Current research
5 See also
6 External links
[edit]
Thought
In popular usage mind is frequently synonymous with thought: It is that private conversation with ourselves that we carry on "inside our heads" during every waking moment of our lives. Thus we "make up our minds," "change our minds" or are "of two minds" about something. One of the key attributes of the mind in this sense is that it is a private sphere. No-one else can "know our mind." They can only know what we communicate.
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Nature of the mind
Both philosophers and psychologists remain divided about the nature of the mind. Some take what is known as the substantial view, and argue that the mind is a single entity, perhaps having its base in the brain but distinct from it and having an autonomous existence. This view ultimately derives from Plato, and was absorbed from him into Christian thought. In its most extreme form, the substantial view merges with the theological view that the mind is an entity wholly separate from the body, in fact a manifestation of the soul, which will survive the body's death and return to God, its creator.
Others take what is known as the functional view, ultimately derived from Aristotle, which holds that the mind is a term of convenience for a variety of mental functions which have little in common except that humans are conscious of their existence. Functionalists tend to argue that the attributes which we collectively call the mind are closely related to the functions of the brain and can have no autonomous existence beyond the brain, nor can they survive its death. In this view mind is a subjective manifestation of consciousness: the human brain's ability to be aware of its own existence. The concept of the mind is therefore a means by which the conscious brain understands its own operations.
If we follow the pantheistic view, Mind is synonymous with Soul, and emanates (since it is non-dimensional, or trans-dimensional) from the Spirit (the essence that can manifest itself through any level in pantheistic hierarchy/holarchy - as a mind/soul of a single cell (with very primitive, elemental consciousness), a human or animal mind/soul (with consciousness on a level of organic synergy of an individual human or animal), or a (superior) mind/soul with synergetically extremely complex and sophisticated consciousness of whole galaxies involving all sub-levels. Spirit (essence) manifests as - Soul/Mind. And the (non-physical) Soul/Mind is a 'driver' of the body. Therefore, the body, including the brain, is just a 'vehicle' for the physical world (if we, for example, have a whole planet as a 'body' then its brain is the synergetic super-brain that involves all the brains of species with a brain on that planet).
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History of the philosophy of the mind
According to Neo-Platonism, nondual Spirit manifests as Soul or Mind. Mind is synonymous with Soul, and emanates from the Spirit (the essence that can manifest itself through any level in the cosmic hierarchy/holarchy, from the mind/soul of a single cell (with prehension – very primitive, elemental consciousness), a human or animal mind/soul (with consciousness on a level of an individual human/animal), or an oversoul, with consciousness of whole galaxies involving all sub-levels. And the (non-physical) Soul/Mind is a 'driver' of the body. Therefore, the body, including the brain, is just a vehicle for the physical world.
A leading exponent of the substantial view was George Berkeley, an 18th century Anglican bishop and philosopher. Berkeley argued that there is no such thing as matter and what humans see as the material world is nothing but an idea in God's mind, and that therefore the human mind is purely a manifestation of the soul or spirit or similar. This type of belief is also common in certain types of spiritual non-dualistic belief, but outside this field few philosophers take an extreme view today. However, the view that the human mind is of a nature or essence somehow different from, and higher than, the mere operations of the brain, continues to be widely held.
Berkeley's views were attacked, and in the eyes of many philosophers demolished, by T.H. Huxley, a 19th century biologist and disciple of Charles Darwin, who agreed that the phenomena of the mind were of a unique order, but argued that they can only be explained in reference to events in the brain. Huxley drew on a tradition of materialist thought in British philosophy dating to Thomas Hobbes, who argued in the 17th century that mental events were ultimately physical in nature, although with the biological knowledge of his day he could not say what their physical basis was. Huxley blended Hobbes with Darwin to produce the modern materialist or functional view.
Huxley's view was reinforced by the steady expansion of knowledge about the functions of the human brain. In the 19th century it was not possible to say with certainty how the brain carried out such functions as memory, emotion, perception and reason. This left the field open for substantialists to argue for an autonomous mind, or for a metaphysical theory of the mind. But each advance in the study of the brain during the 20th century made this harder, since it became more and more apparent that all the components of the mind have their origins in the functioning of the brain.
Huxley's rationalism, however, was disturbed in the early 20th century by the ideas of Sigmund Freud, who developed a theory of the unconscious mind, and argued that those mental processes of which humans are subjectively aware are only a small part of their total mental activity. Freudianism was in a sense a revival of the substantial view of the mind in a secular guise. Although Freud did not deny that the mind was a function of the brain, he held the mind has, as it were, a mind of its own, of which we are not conscious, which we cannot control, and which can be accessed only though psychoanalysis (particularly the interpretation of dreams). Freud's theory of the unconscious, although impossible to prove empirically, has been widely accepted and has greatly influenced the popular understanding of the mind.
More recently, Douglas Hofstadter's 1979 Pulitzer Prize-winning book "Gödel, Escher, Bach - an eternal Golden Braid", is a tour de force on the subject of mind, and how it might arise from the neurology of the brain. Amongst other biological and cybernetic phenomena, Hofstadter places tangled loops and recursion at the center of Self, Self-awareness, and perception of oneself, and thus at the heart of Mind and thinking. Likewise philosopher Ken Wilber posits that Mind is the interior dimension of the brain holon. That is, that mind is what a brain looks like internally, when it looks at itself.
Quantum physicist David Bohm had a theory of mind that is most comparable to Neo-Platonic theories. "Thought runs you. Thought, however, gives false info that you are running it, that you are the one who controls thought. Whereas actually thought is the one which controls each one of us..."(Thought as a System, D. Bohm, 1992)
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Current research
The debate about the nature of the mind is relevant to the development of artificial intelligence. If the mind is indeed a thing separate from or higher than the functioning of the brain, then presumably it will not be possible for any machine, no matter how sophisticated, to duplicate it. If on the other hand the mind is no more than the aggregated functions of the brain, then it will be possible, at least in theory, to create a machine with a mind.
The Mind/Brain/Behavior Interfaculty Initiative (MBB) at Harvard University aims to elucidate the structure, function, evolution, development, and pathology of the nervous system in relation to human behavior and mental life. It draws on the departments of psychology, neurobiology, neurology, molecular and cellular biology, radiology, psychiatry, organismic and evolutionary biology, history of science, and linguistics.
the human brain compared to the world brain..
human brain-The human brain is the anteriormost part of the central nervous system in humans as well as the primary control center for the peripheral nervous system.
The brain controls "lower" or involuntary activities such as heartbeat, respiration, and digestion - these are known as autonomic functions. The brain also controls "higher" order, conscious activities, such as thought, reasoning, and abstraction. The human brain is generally regarded as more capable of these higher order activities than any other species.
Contents [hide]
1 Overview
2 Anatomy
3 Function
4 Study of the brain
5 Popular misconceptions
6 Brain enhancement
7 Comparison of the brain and a computer
8 See also
9 References
9.1 Notes
9.2 Books
10 External links
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Overview
Human encephalization is especially pronounced in the neocortex, the most complex portion of the cerebral cortex. Singular among those of all animals, the human brain possesses the largest and most massive neocortex. Humans thus enjoy unique neural capacities despite the fact that much of the human neuroarchitecture resembles that of more primitive species. Basic systems that alert the nervous system to stimuli, sense events in the environment, and monitor and maintain the internal environment of the body (homeostasis) are similar in some ways to those of the most basic vertebrates. Human consciousness involves both the extended capacity of the modern neocortex in particular as well as profoundly developed prototypical structures of the brain stem. But the human brain is unique, in part, because it relies on some million billion synaptic connections, making it an extremely intricate and densely connected neural network.
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Anatomy
Sagittal slice from a MRI scan of a human brain. See an animated sequence of slices.The normal adult human brain typically weighs between 1 and 1.5 kg (3 lb) and has an average volume of 1,600 cm³. An average male brain has approximately 4% more cells and 100 grams more brain tissue than an average female brain. However, both sexes have similar brain weight to body weight ratios (She Brains - He Brains)[1]. The mature brain consumes some 20% of the energy used by the body, while the developing brain of an infant consumes around 60%. Such heavy energy usage generates large quantities of heat, which must be continually removed to prevent brain damage.
A bulbous cerebral cortex is composed of convoluted grey matter internally supported by deep brain white matter. The two hemispheres of the brain are separated by a prominent central fissure and connect to each other at the corpus callosum. A well-developed cerebellum is visible at the back of the brain. Brain stem structures are almost completely enveloped by the cerebellum and telencephalon, with only the medulla oblongata visible as it merges with the spinal cord.
The blood supply to the brain involves several arteries that enter the brain and communicate in a circle called the circle of Willis. Blood is then drained from the brain through a network of sinuses that drain into the right and left internal jugular veins.
The brain is suspended in cerebrospinal fluid (CSF) which also fills spaces called ventricles inside it. The dense fluid protects the brain and spinal cord from shock; a brain that weighs 1,500 g in air weighs only 50 g when suspended in CSF (Livingston, 1965). Fluid movement within the brain is limited by the blood-brain barrier and the blood-cerebrospinal fluid barrier.
The brain is easily damaged by compression, so the fluid surrounding the central nervous system must be maintained at a constant volume. Humans are estimated to produce about 500 ml or more of cerebrospinal fluid each day, with only about 15 percent of the body's estimated 150 ml of CSF at any given time located in the ventricles of the brain. The remainder fills the subarachnoid space which separates the soft tissues of the brain and spinal cord from the hard surrounding bones (skull and vertebrae). Elevated levels of CSF are associated with traumatic brain injury and a pediatric disease known as hydrocephalus. Increased fluid pressure can result in permanent brain injury and death.
The exceptional size of the human brain resulted in some anatomical compromises. At birth, an infant's skull is as large as it can be without causing undue peril to the mother and child. However, prior to the intervention of modern medicine, childbirth was a dangerous event that frequently resulted in the death of the mother. The difficulty experienced by humans in giving birth is nearly unique in the animal kingdom. Female humans have large pelvic openings to accommodate the birth of large-headed children, but the larger this opening, the more the ability of the mother to run is compromised.
At birth, the human skull is rather soft, and it deforms somewhat during its passage through the birth canal, then recovers its shape. This allows it to expand to make room for the brain, which continues to grow, at the same rate as that of an unborn fetus, for an additional year. In all other animals the growth rate of the brain slows significantly at birth.
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Function
A human brain color-coded to show the four cerebral lobes and cerebellum.The human brain is the source of the conscious, cognitive mind. The mind is the set of cognitive processes related to perception, interpretation, imagination, and memories, of which a person may or may not be aware. Beyond cognitive functions, the brain regulates autonomic processes related to essential body functions such as respiration and heartbeat.
Extended neocortical capacity allows humans some control over emotional behavior, but neural pathways between emotive centers of the brain stem and cerebral motor control areas are shorter than those connecting complex cognitive areas in the neocortex with incoming sensory information from the brain stem. Powerful emotional pathways can modulate spontaneous emotive expression regardless of attempts at cerebral self-control. Emotive stability in humans is associated with planning, experience, and an environment that is both stable and stimulating, especially during early developmental years.
The 19th century discovery of the primary motor cortex mapped to correspond with regions of the body led to popular belief that the brain was organized around a homunculus. A distorted figure drawn to represent the body's motor map in the prefrontal cortex was popularly recognized as the brain's homunculus, but function of the human brain is far more complex.
The human brain appears to have no localized center of conscious control. The brain seems to derive consciousness from interaction among numerous systems within the brain. Executive functions rely on cerebral activities, especially those of the frontal lobes, but redundant and complementary processes within the brain result in a diffuse assignment of executive control that can be difficult to attribute to any single locale.
Midbrain functions include routing, selecting, mapping, and cataloguing information, including information perceived from the environment and information that is remembered and processed throughout the cerebral cortex. Endocrine functions housed in the midbrain play a leading role in modulating arousal of the cortex and of autonomic systems.
Nerves from the brain stem complex where autonomic functions are modulated join nerves routing messages to and from the cerebrum in a bundle that passes through the spinal column to related parts of a body. Twelve pairs of cranial nerves, including some that innervate parts of the head, follow pathways from the medulla oblongata outside the spinal cord.
A definite description of the biological basis for consciousness so far eludes the best efforts of the current generation of researchers. But reasonable assumptions based on observable behaviors and on related internal responses have provided the basis for general classification of elements of consciousness and of likely neural regions associated with those elements. Researchers know people lose consciousness and regain it, they have identified partial losses of consciousness associated with particular neuropathologies and they know that certain conscious activities are impossible without particular neural structures.
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Study of the brain
Picture of a human brain generated from MRI dataAlthough folklore would have it that about 90% of the human brain is dormant, this has proven scientifically unfounded; researchers until the mid 1990s focused on only a small portion of the brain in efforts to understand its computational capacity.
Grey matter, the thin layer of cells covering the cerebrum, was believed by most scholars to be the primary center of cognitive and conscious processing. White matter, the mass of glial cells that support the cerebral grey matter, was assumed to primarily provide nourishment, physical support, and connective pathways for the more functional cells on the cerebral surface. But research fueled by the interest of Dr. Marian Diamond in the glial structure of Albert Einstein's brain led to a line of research that offered strong evidence that glial cells serve a computational role beyond merely transmitting processed signals between more functional parts of the brain. In 2004, Scientific American published an article suggesting scientists in the early 21st century are only beginning to study the "other half of the brain."
For many millennia the function of the brain was unknown. Ancient Egyptians threw the brain away prior to the process of mummification. Ancient thinkers such as Aristotle imagined that mental activity took place in the heart. Greek scholars assumed correctly that the brain serves a role in cooling the body, but incorrectly presumed the brain to function as a sort of radiator, rather than as a thermostat as is now understood. The Alexandrian biologists Herophilos and Erasistratus were among the first to conclude that the brain was the seat of intelligence. Galen's theory that the brain's ventricles were the sites of thought and emotion prevailed until the work of the Renaissance anatomist Vesalius.
A slice of an MRI scan of the brain. See an animation of the scan from top to bottom.The modern study of the brain and its functions is known as neuroscience. Psychology is the scientific study of the mind and behavior. Neurology and psychiatry are both medical approaches to the study of the mind and its pathology or mental illness respectively.
The brain is now thought to be the organ responsible for the phenomena of consciousness and thought. It also integrates and controls (together with the central nervous system) allostatic balance and autonomic functions in the body, regulates as well as directly producing many hormones, and performs processing, recognition, cognition and integration related to emotion. Studies of brain damage resulting from accidents led to the identification of specialized areas of the brain devoted to functions such as the processing of vision and audition.
Neuroimaging has allowed the function of the living brain to be studied in detail without damaging the brain. New imaging techniques allowed blood flow within the brain to be studied in detail during a wide range of psychological tests. Functional neuroimaging such as functional magnetic resonance imaging and positron emission tomography allows researchers to monitor activities of the brain as they occur (see also history of neuroimaging).
Molecular analysis of the brain has provided insight into some aspects of what the brain does as an organ, but not how it functions in higher-level processes. Further, the molecular and cell biological examination of brain pathology is hindered by the scarcity of appropriate samples for study, the (usual) inability to biopsy the brain from a living person suffering from a malady, and an incomplete description of the brain's microanatomy. With respect to the normal brain, comparative transcriptome analysis between the human and chimpanzee brain and between brain and liver (a common molecular baseline organ) has revealed specific and consistent differences in gene expression between human and chimpanzee brain and a general increase in the gene expression of many genes in humans as compared to chimpanzees. Furthermore, variations in gene expression in the cerebral cortex between individuals in either species is greater than between sub-regions of the cortex of a single individual[2].
In addition to pathological and imaging studies, the study of computational networks, largely in computer science, provided another means through which to understand neural processes. A body of knowledge developed for the production of electronic, mathematical computation of systems provided a basis for researchers to develop and refine hypotheses about the computational function of biological neural networks. The study of neural networks now involves study of both biological and artificial neural networks.
A new discipline of cognitive science has started to fuse the results of these investigations with observations from psychology, philosophy, linguistics, and computer science.
Recently the brain was used in bionics by several groups of researchers. In a particular example, a joint team of United States Navy researchers and Russian scientists from Nizhny Novgorod State University worked to develop an artificial analogue of olivocerebellar circuit, a part of the brain responsible for balance and limb movement. The researchers plan to use it to control Autonomous Underwater Vehicles.
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Popular misconceptions
The following are some commonly held misconceptions of the mind and brain perpetuated through urban legends, mass media, and the promotion of dubious products to consumers (Sala, 1999). A number of practitioners of pseudoscience, New Age philosophies, and mystical or occult practices are known to use some of these ideas as a part of their belief systems (also see popular psychology).
The human brain is firm and grey: The fresh/living brain is actually very soft, jelly-like and deep red. They do not become firm and grey until they have been preserved with various chemicals/resins.
Humans use only 10% or less of their brain: Even though some mysteries of brain function persist, every part of the brain has a known function.[1][2][3]
This misconception most likely arose from a misunderstanding (or misrepresentation in an advertisement) of neurological research in the late 1800s or early 1900s when researchers discovered that only about 10% of the neurons in the brain are firing at any given time.
Another possible origin of the myth is that only 10% of the cells in the brain are neurons; the rest are glial cells that, despite being involved in learning, do not "think" in the same way that neurons do.
If all of a person's neurons began firing at once he would not become smarter, but would instead suffer a seizure. In fact, studies have shown that the brains of more intelligent people are less active than the brains of less intelligent people when working on the same problems.
Some psychics continue to propagate this myth by asserting that the "unused" ninety percent of the human brain is capable of exhibiting psychic powers and can be trained to perform psychokinesis and extra-sensory perception.
A less literal interpretation of the statement is valid. It can be reasonably claimed that most people only use a very small fraction of the cognitive potential of their brain, even though all individual brain neurons are busily working. Various cultural inventions enable humans to better utilize their cognitive potential, such as reading, education, problem solving, critical thinking, etc.
Mental abilities are separated into the left and right cerebral hemispheres: Some mental functions such as speech and language tend to be localized to specific areas in one hemisphere. If one hemisphere is damaged at a very early age however, these functions can often be recovered in part or even in full by the other hemisphere. Other abilities such as motor control, memory, and general reasoning are spread equally across the two hemispheres. See lateralization of brain function.
Creativity can be easily developed using simple brainstorming/lateral thinking techniques.
Learning can be achieved more powerfuly through subliminal techniques: Technically, information that is entirely subliminal cannot be perceived at all. The extent to which subliminal techniques can influence learning depends largely on what level of perception the techniques affect.
Hypnosis can lead to perfect recall of details: Not only is this not entirely true, an incompetent or deceptive hypnotist can actually implant (deliberately or unintentionally by leading questions) false memories of events that never occurred. This is because memory is not stored as "facts", but as impressions, and emotions, and is often reinterpreted as people mature or change.
New neurons cannot be created, they only die as one ages. In fact, new neurons can grow within the mature adult brain, this process is known as neurogenesis. Regardless of neuron growth or death, brain function and capabilities can be learned and developed throughout life.
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Brain enhancement
Various methods have been proposed to improve the cognitive performance of the human brain including pharmacological methods (nootropic drugs), electric stimulation (direct current polarization) and surgery. More advanced methods of brain enhancement may be possible in the future, perhaps including direct brain-computer interfaces. These proposed enhancements are a major focus of Transhumanism.
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Comparison of the brain and a computer
Much interest has been focused on comparing the brain with computers. A variety of obvious analogies exist: for example, individual neurons can be compared to transistors on a microchip, and the specialised parts of the brain can be compared with graphics cards and other system components. However, such comparisons are fraught with difficulties. Perhaps the most fundamental difference between brains and computers are that today's computers operate by performing often sequential instructions from an input program, while no clear analogy of a program appears in human brains. The closest equivalent would be the idea of a logical process, but the nature and existence of such entities are subjects of philosophical debate. Given Turing's model of computation, the Turing machine (which shows that any computation that can be performed by a parallel computer can be done by a sequential computer), this may be a functional, not fundamental, distinction. However, Maass and Markram have recently argued that "in contrast to Turing machines, generic computations by neural circuits are not digital, and are not carried out on static inputs, but rather on functions of time" (the Turing machine computes recursive functions). Ultimately, computers were not designed to be models of the brain, though subjects like neural networks attempt to abstract the behavior of the brain in a way that can be simulated computationally.
In addition to the technical differences, other key differences exist. The brain is massively parallel and interwoven, whereas programming of this kind is extremely difficult for computer software writers (most parallel systems run semi-independently, for example each working on a small separate 'chunk' of a problem). The human brain is also mediated by chemicals and analog processes, many of which are only understood at a basic level and others of which may not yet have been discovered, so that a full description is not yet available in science. Finally, and perhaps most significantly, the human brain appears hard-wired with certain abilities, such as the ability to learn language, to interact with experienced and not chosen emotions, and usually develops within a culture.
Nevertheless, there have been numerous attempts to quantify differences in capability between the human brain and computers. According to Hans Moravec, by extrapolating from known capabilities of the retina to process image inputs, a brain has a processing capacity of 100 trillion instructions per second, and is likely to be surpassed
world brain-In 1938, aged 72, English writer H. G. Wells published a little book of essays and speeches titled World Brain.
One essay titled "The Idea of a Permanent World Encyclopaedia" is remarkable in presenting a vision very similar to Wikipedia. This essay first appeared in the new Encyclopédie française, August, 1937.
The essay "The Brain Organization of the Modern World" lays out Wells' vision for "...a sort of mental clearing house for the mind, a depot where knowledge and ideas are received, sorted, summarized, digested, clarified and compared." (p. 49) Wells felt that technological advances such as microfilm could be utilized towards this end so that "any student, in any part of the world, will be able to sit with his projector in his own study at his or her convenience to examine any book, any document, in an exact replica." (p. 54) A similar view of an automated system for making all of humanity's knowledge available to all had been proposed a few years earlier by Paul Otlet, one of the founders of information science.
Wells had been involved with the socialist Fabian Society, the League of Nations, and the International PEN, and his intent for World Brain was no less than helping to solve what he termed the World Problem, i.e. the possibility of the mutual destruction of nations in a World War. Wells has been both praised for envisioning an educational knowledge network (not unlike the Internet and World Wide Web) and criticized for proposing what to some amounts to a New World Order. His concept of a "world brain" has more recently been revived by others in the guise of the global brain.
dual brain theriree-The dual brain theory claims that the two cerebral hemispheres of the brain may sense and react to the environment independently from one another and that as a result of traumatic experience, one half may dominate the other in order to reduce the traumatized hemisphere's exposure to harm.
This theory is an extension of split-brain studies of epileptic patients having the corpus callosum severed in order to reduce seizures. These studies indicated the existence of two intact autonomous minds.
Studies of healthy people with intact corpus callosums also indicate differing abilities or emotional responses associated with the two hemispheres. Studies using the Wada test and others are cited. In addition the theory draws upon research by Werner Wittling, Stuart Dimond, Roger Drake, Patrizio Tessoldi, Edward Fouty and Steve Levick.
Dr. Fredric Schiffer purports to have experimented with lateralizing glasses which restrict patients to one side of the visual field or the other, in turn stimulating the associated hemisphere. This allowed some patients to experience the world through the more submissive or immature self and to compare differing experiences and changes in emotional moods, simply by switching between glasses. The glasses are fabricated simply by taping over the right or left halves of both lenses of typical safety glasses. The glasses function according the properties of the optic tract, whereby the left (right) half of the retina of both eyes are each connected to the right (left) hemisphere, via optic nerves, which partially cross at the optic chiasm. The patient could then relativize experience and escape from a single viewpoint or life experience. In this manner a patient, through counseling, might begin a rapport between hemispheres in order to lead a more balanced and fruitful life.