Neuroglia

From Wikipedia, the free encyclopedia

Neuroglia
Illustration of the four different types of glial cells found in the central nervous system: ependymal cells (light pink), astrocytes (green), microglial cells (dark red), and oligodendrocytes (light blue).
Details
Precursor	Neuroectoderm for macroglia, and hematopoietic stem cells for microglia
System	Nervous system
Identifiers
MeSH	D009457
TA	A14.0.00.005
TH	H2.00.06.2.00001
FMA	54541
Anatomical terms of microanatomy

Neuroglia, also called glial cells or simply glia, are non-neuronal cells in the central nervous system (brain and spinal cord) and the peripheral nervous system. They maintain homeostasis, form myelin, and provide support and protection for neurons.^[1] In the central nervous system, glial cells include oligodendrocytes, astrocytes, ependymal cells, and microglia, and in the peripheral nervous system glial cells include Schwann cells and satellite cells. They have four main functions: (1) To surround neurons and hold them in place (2) To supply nutrients and oxygen to neurons (3) To insulate one neuron from another (4) To destroy pathogens and remove dead neurons. They also play a role in neurotransmission and synaptic connections,^[2] and in physiological processes like breathing.^[3][4] .

Glia were discovered in 1856, by the pathologist Rudolf Virchow in his search for a "connective tissue" in the brain.^[5] The term derives from Greek γλία and γλοία "glue"(/ˈɡliːə/ or /ˈɡlaɪə/), and suggests the original impression that they were the glue of the nervous system.

Types

Neuroglia of the brain shown by Golgi's method

Astrocytes can be identified in culture because, unlike other mature glia, they express glial fibrillary acidic protein (GFAP)

Glial cells in a rat brain stained with an antibody against GFAP

Different types of neuroglia

Macroglia

Derived from ectodermal tissue.

Location	Name	Description
CNS	Astrocytes	The most abundant type of macroglial cell in the CNS,[6] astrocytes (also called astroglia) have numerous projections that link neurons to their blood supply while forming the blood-brain barrier. They regulate the external chemical environment of neurons by removing excess potassium ions, and recycling neurotransmitters released during synaptic transmission. Astrocytes may regulate vasoconstriction and vasodilation by producing substances such as arachidonic acid, whose metabolites are vasoactive. Astrocytes signal each other using ATP. The gap junctions (also known as electrical synapses) between astrocytes allow the messenger molecule IP3 to diffuse from one astrocyte to another. IP3 activates calcium channels on cellular organelles, releasing calcium into the cytoplasm. This calcium may stimulate the production of more IP3 and cause release of ATP through channels in the membrane made of pannexins. The net effect is a calcium wave that propagates from cell to cell. Extracellular release of ATP, and consequent activation of purinergic receptors on other astrocytes, may also mediate calcium waves in some cases. In general, there are two types of astrocytes, protoplasmic and fibrous, similar in function but distinct in morphology and distribution. Protoplasmic astrocytes have short, thick, highly branched processes and are typically found in gray matter. Fibrous astrocytes have long, thin, less branched processes and are more commonly found in white matter. It has recently been shown that astrocyte activity is linked to blood flow in the brain, and that this is what is actually being measured in fMRI.[7] They also have been involved in neuronal circuits playing an inhibitory role after sensing changes in extracellular calcium.[8]
CNS	Oligodendrocytes	Oligodendrocytes are cells that coat axons in the central nervous system (CNS) with their cell membrane, forming a specialized membrane differentiation called myelin, producing the myelin sheath. The myelin sheath provides insulation to the axon that allows electrical signals to propagate more efficiently.[9]
CNS	Ependymal cells	Ependymal cells, also named ependymocytes, line the spinal cord and the ventricular system of the brain. These cells are involved in the creation and secretion of cerebrospinal fluid (CSF) and beat their cilia to help circulate the CSF and make up the blood-CSF barrier. They are also thought to act as neural stem cells.[10]
CNS	Radial glia	Radial glia cells arise from neuroepithelial cells after the onset of neurogenesis. Their differentiation abilities are more restricted than those of neuroepithelial cells. In the developing nervous system, radial glia function both as neuronal progenitors and as a scaffold upon which newborn neurons migrate. In the mature brain, the cerebellum and retina retain characteristic radial glial cells. In the cerebellum, these are Bergmann glia, which regulate synaptic plasticity. In the retina, the radial Müller cell is the glial cell that spans the thickness of the retina and, in addition to astroglial cells,[11] participates in a bidirectional communication with neurons.[12]
PNS	Schwann cells	Similar in function to oligodendrocytes, Schwann cells provide myelination to axons in the peripheral nervous system (PNS). They also have phagocytotic activity and clear cellular debris that allows for regrowth of PNS neurons.[13]
PNS	Satellite cells	Satellite glial cells are small cells that surround neurons in sensory, sympathetic, and parasympathetic ganglia.[14] These cells help regulate the external chemical environment. Like astrocytes, they are interconnected by gap junctions and respond to ATP by elevating intracellular concentration of calcium ions. They are highly sensitive to injury and inflammation, and appear to contribute to pathological states, such as chronic pain.[15]
PNS	Enteric glial cells	Are found in the intrinsic ganglia of the digestive system. They are thought to have many roles in the enteric system, some related to homeostasis and muscular digestive processes.[16]

Microglia

Microglia are specialized macrophages capable of phagocytosis that protect neurons of the central nervous system.^[17] They are derived from the earliest wave of mononuclear cells that originate in yolk sac blood islands early in development, and colonize the brain shortly after the neural precursors begin to differentiate.^[18]

These cells are found in all regions of the brain and spinal cord. Microglial cells are small relative to macroglial cells, with changing shapes and oblong nuclei. They are mobile within the brain and multiply when the brain is damaged. In the healthy central nervous system, microglia processes constantly sample all aspects of their environment (neurons, macroglia and blood vessels). In a healthy brain, microglia direct the immune response to brain damage and play an important role in the inflammation that accompanies the damage. Many diseases and disorders are associated with deficient microglia, such as Alzheimer's disease, Parkinson's disease, and ALS.

Other

Pituicytes from the posterior pituitary are glia cells with characteristics in common to astrocytes.^[19] Tanycytes in the median eminence of the hypothalamus are a type of ependymal cell that descend from radial glia and line the base of the third ventricle.^[20]

Total number

In general, neuroglial cells are smaller than neurons; there are about 86 billion neurons and 85 billion "non-neuronal" (glia) cells in the human male brain. Glial cells make up about half the total volume of the brain and spinal cord.^[21][22]^ The ratio varies from one part of the brain to another. The glia/neuron ratio in the cerebral cortex is 3.72 (60.84 billion glia (72%); 16.34 billion neurons), while that of the cerebellum is only 0.23 (16.04 billion glia; 69.03 billion neurons). The ratio in the cerebral cortex gray matter is 1.48, with 3.76 for the gray and white matter combined.^[21] The ratio of the basal ganglia, diencephalon and brainstem combined is 11.35.^[21]

Most cerebral cortex glia are oligodendrocytes (75.6%); astrocytes account for 17.3% and microglia for 6.5%.^[23]

Development

23-week fetal brain culture astrocyte

Most glia are derived from ectodermal tissue of the developing embryo, in particular the neural tube and crest. The exception is microglia, which are derived from hemopoietic stem cells. In the adult, microglia are largely a self-renewing population and are distinct from macrophages and monocytes, which infiltrate the injured and diseased CNS.

In the central nervous system, glia develop from the ventricular zone of the neural tube. These glia include the oligodendrocytes, ependymal cells, and astrocytes. In the peripheral nervous system, glia derive from the neural crest. These PNS glia include Schwann cells in nerves and satellite glial cells in ganglia.

Current research involving glial cells in the human cochlea proposes that these cells are the common precursor to both mature Schwann cells and satellite glial cells. Additionally, the peripheral glial cells located along the peripheral processes expressed NGFR, indicating a phenotype distinct from the peripheral glial cells located along the central processes.^[24]

Capacity to divide

Glia retain the ability to undergo cell division in adulthood, whereas most neurons cannot. The view is based on the general deficiency of the mature nervous system in replacing neurons after an injury, such as a stroke or trauma, while very often there is a profound proliferation of glia, or gliosis near or at the site of damage. However, detailed studies found no evidence that 'mature' glia, such as astrocytes or oligodendrocytes, retain the ability of mitosis. Only the resident oligodendrocyte precursor cells seem to keep this ability after the nervous system matures. On the other hand, there are a few regions in the mature nervous system, such as the dentate gyrus of the hippocampus and the subventricular zone, where generation of new neurons can be observed.^[25]

Glial cells are known to be capable of mitosis. By contrast, scientific understanding of whether neurons are permanently post-mitotic,^[26] or capable of mitosis,^[27][28][29] is still developing. In the past, glia had been considered^{[by whom?]} to lack certain features of neurons. For example, glial cells were not believed to have chemical synapses or to release transmitters. They were considered to be the passive bystanders of neural transmission. However, recent studies have shown this to be untrue.^[30]

Functions

Some glial cells function primarily as the physical support for neurons. Others regulate the internal environment of the brain, especially the fluid surrounding neurons and their synapses, and nutrify neurons. During early embryogenesis, glial cells direct the migration of neurons and produce molecules that modify the growth of axons and dendrites.

Neuron repair and development

Glia are also crucial in the development of the nervous system and in processes such as synaptic plasticity and synaptogenesis. Glia have a role in the regulation of repair of neurons after injury. In the central nervous system (CNS), glia suppress repair. Glial cells known as astrocytes enlarge and proliferate to form a scar and produce inhibitory molecules that inhibit regrowth of a damaged or severed axon. In the peripheral nervous system (PNS), glial cells known as Schwann cells promote repair. After axonal injury, Schwann cells regress to an earlier developmental state to encourage regrowth of the axon. This difference between the CNS and the PNS, raises hopes for the regeneration of nervous tissue in the CNS. For example, a spinal cord may be able to be repaired following injury or severance. Schwann cells are also known as neuri-lemmocytes. These cells envelop nerve fibers of the PNS by winding repeatedly around a nerve fiber with the nucleus inside of it. This process creates a myelin sheath, which not only aids in conductivity but also assists in the regeneration of damaged fibers.

Myelin sheath creation

Oligodendrocytes are another type of glial cell of the CNS. These dendrocytes resemble an octopus bulbous body and contain up to fifteen arm-like processes. Each “arm” reaches out to a nerve fiber and spirals around it, creating a myelin sheath. This myelin sheath insulates the nerve fiber from the extracellular fluid as well as speeds up the signal conduction in the nerve fiber.^[31]

Neurotransmission

Recent research indicates that glial cells of the hippocampus and cerebellum participate in synaptic transmission, regulate the clearance of neurotransmitters from the synaptic cleft, and release gliotransmitters such as ATP, which modulate synaptic function.^[32]

Astrocytes are crucial in clearance of neurotransmitters from within the synaptic cleft, which provides distinction between arrival of action potentials and prevents toxic build-up of certain neurotransmitters such as glutamate (excitotoxicity). It is also thought that glia play a role in many neurological diseases, including Alzheimer's disease.^[33] Furthermore, at least in vitro, astrocytes can release gliotransmitter glutamate in response to certain stimulation. Another unique type of glial cell, the oligodendrocyte precursor cells or OPCs, have very well-defined and functional synapses from at least two major groups of neurons.^[34] The only notable differences between neurons and glial cells are neurons' possession of axons and dendrites, and capacity to generate action potentials.

Clinical significance

Neoplastic glial cells stained with an antibody against GFAP (brown), from a brain biopsy

While glial cells in the PNS frequently assist in regeneration of lost neural functioning, loss of neurons in the CNS does not result in a similar reaction from neuroglia.^[13] In the CNS, regrowth will only happen if the trauma was mild, and not severe.^[35] When severe trauma presents itself, the survival of the remaining neurons becomes the optimal solution. However, some studies investigating the role of glial cells in Alzheimer's Disease are beginning to contradict the usefulness of this feature, and even claim it can "exacerbate" the disease.^[36] In addition to impacting the potential repair of neurons in Alzheimer's Disease, scarring and inflammation from glial cells have been further implicated in the degeneration of neurons caused by Amyotrophic lateral sclerosis.^[37]

In addition to neurodegenerative diseases, a wide range of harmful exposure, such as hypoxia, or physical trauma, can lead to the end result of physical damage to the CNS.^[35] Generally, when damage occurs to the CNS, glial cells cause Apoptosis among the surrounding cellular bodies.^[35] Then, there is a large amount of microglial activity, which results in inflammation, and finally, there is a heavy release of growth inhibiting molecules.^[35]

History

Glia were first described in 1856 by the pathologist Rudolf Virchow in a comment to his 1846 publication on connective tissue. A more detailed description of glial cells was provided in the 1858 book Cellular Pathology by the same author.^[38]

When markers for different types of cells were analyzed, Einstein's brain was discovered to contain significantly more glia than normal brains in the left angular gyrus, an area thought to be responsible for mathematical processing and language.^[39]

The ratio of glia to neurons increases with our definition of intelligence. Not only does the ratio of glia to neurons increase through evolution, but so does the size of the glia. Astroglial cells in the human have a volume 27 times greater than the same cells in the mouse's brain.^[40]

These important scientific findings may begin to shift the neuron-specific perspective into a more holistic view of the brain which encompasses the glial cells as well. The glia's importance is becoming ever more clear as time goes on and new research is conducted. For most of the last century, scientists had written off glial cells as being nothing more than the structure and foundations that hold the neurons in place. But now, there is direct evidence that correlates the number of glial cells in the brain with the amount of intelligence that any given species possesses.^[41] Future research will begin to shed light on the mysterious, yet increasingly crucial, role of glial cells.

Reductionism

From Wikipedia, the free encyclopedia

Descartes claimed that non-human animals could be explained reductively as automata — De homine, 1662.

Reductionism is any of several related philosophical ideas regarding the associations between phenomena which can be described in terms of other simpler or more fundamental phenomena.^[1]

The Oxford Companion to Philosophy suggests that reductionism is "one of the most used and abused terms in the philosophical lexicon" and suggests a three part division:^[2]

1. Ontological reductionism: a belief that the whole of reality consists of a minimal number of parts.
2. Methodological reductionism: the scientific attempt to provide explanation in terms of ever smaller entities.
3. Theory reductionism: the suggestion that a newer theory does not replace or absorb an older one, but reduces it to more basic terms. Theory reduction itself is divisible into three parts: translation, derivation and explanation.^[3]

Reductionism can be applied to any phenomenon, including objects, explanations, theories, and meanings.^{[3][4] [5]}

For the sciences, application of methodological reductionism attempts explanation of entire systems in terms of their individual, constituent parts and their interactions. For example, the temperature of a gas is reduced to nothing but the average kinetic energy of its molecules in motion. Thomas Nagel speaks of psychophysical reductionism (the attempted reduction of psychological phenomena to physics and chemistry), as do others and physico-chemical reductionism (the attempted reduction of biology to physics and chemistry), again as do others.^[6] In a very simplified and sometimes contested form, such reductionism is said to imply that a system is nothing but the sum of its parts.^[4][7] However, a more nuanced opinion is that a system is composed entirely of its parts, but the system will have features that none of the parts have.^[8] "The point of mechanistic explanations is usually showing how the higher level features arise from the parts."^[7]

Other definitions are used by other authors. For example, what John Polkinghorne terms conceptual or epistemological reductionism^[4] is the definition provided by Simon Blackburn^[9] and by Jaegwon Kim:^[10] that form of reductionism concerning a program of replacing the facts or entities entering statements claimed to be true in one type of discourse with other facts or entities from another type, thereby providing a relationship between them. Such an association is provided where the same idea can be expressed by "levels" of explanation, with higher levels reducible if need be to lower levels. This use of levels of understanding in part expresses our human limitations in remembering detail. However, "most philosophers would insist that our role in conceptualizing reality [our need for an hierarchy of "levels" of understanding] does not change the fact that different levels of organization in reality do have different properties."^[8]

Reductionism strongly represents a certain perspective of causality. In a reductionist framework, the phenomena that can be explained completely in terms of relations between other more fundamental phenomena, are termed epiphenomena. Often there is an implication that the epiphenomenon exerts no causal agency on the fundamental phenomena that explain it. The epiphenomena are sometimes said to be "nothing but" the outcome of the workings of the fundamental phenomena, although the epiphenomena might be more clearly and efficiently described in very different terms. There is a tendency to avoid considering an epiphenomenon as being important in its own right. This attitude may extend to cases where the fundamentals are not obviously able to explain the epiphenomena, but are expected to by the speaker. In this way, for example, morality can be deemed to be "nothing but" evolutionary adaptation, and consciousness can be considered "nothing but" the outcome of neurobiological processes.

Reductionism should be distinguished from eliminationism: reductionists do not deny the existence of phenomena, but explain them in terms of another reality; eliminationists deny the existence of the phenomena themselves. For example, eliminationists deny the existence of life by their explanation in terms of physical and chemical processes.

Reductionism also does not preclude the existence of what might be termed emergent phenomena, but it does imply the ability to understand those phenomena completely in terms of the processes from which they are composed. This reductionist understanding is very different from emergentism, which intends that what emerges in "emergence" is more than the sum of the processes from which it emerges.^[11]

Types

Most philosophers delineate three types of reductionism and anti-reductionism.^[2]

Ontological reductionism

Ontological reductionism is the belief that reality is composed of a minimum number of kinds of entities or substances. This claim is usually metaphysical, and is most commonly a form of monism, in effect claiming that all objects, properties and events are reducible to a single substance. (A dualist who is an ontological reductionist would believe that everything is reducible to two substances — as one possible example, a dualist might claim that reality is composed of "matter" and "spirit".)

Richard Jones divides ontological reductionism into two: the reductionism of substances (e.g., the reduction of mind to matter) and the reduction of the number of structures operating in nature (e.g., the reduction of one physical force to another). This permits scientists and philosophers to affirm the former while being anti-reductionists regarding the latter.^[12]

Nancey Murphy has claimed that there are two species of ontological reductionism: one that denies that wholes are anything more than their parts; and the stronger thesis of atomist reductionism that wholes are not "really real". She admits that the phrase "really real" is apparently senseless but nonetheless has tried to explicate the supposed difference between the two.^[13]

Ontological reductionism denies the idea of ontological emergence, and claims that emergence is an epistemological phenomenon that only exists through analysis or description of a system, and does not exist fundamentally.^[14]

Ontological reductionism takes two different forms: token ontological reductionism and type ontological reductionism.

Token ontological reductionism is the idea that every item that exists is a sum item. For perceivable items, it affirms that every perceivable item is a sum of items with a lesser degree of complexity. Token ontological reduction of biological things to chemical things is generally accepted.

Type ontological reductionism is the idea that every type of item is a sum type of item, and that every perceivable type of item is a sum of types of items with a lesser degree of complexity. Type ontological reduction of biological things to chemical things is often rejected.^[15]

Michael Ruse has criticized ontological reductionism as an improper argument against vitalism.^[16]

Methodological reductionism

Methodological reductionism is the position that the best scientific strategy is to attempt to reduce explanations to the smallest possible entities. Methodological reductionism would thus include the claim that the atomic explanation of a substance's boiling point is preferable to the chemical explanation, and that an explanation based on even smaller particles (quarks and leptons, perhaps) would be even better.^{[citation needed]} Methodological reductionism, therefore, is the opinion that all scientific theories either can or should be reduced to a single super~theory through the process of theoretical reduction.

Theory reductionism

Theory reduction is the process by which one theory absorbs another. For example, both Kepler's laws of the motion of the planets and Galileo's theories of motion formulated for terrestrial objects are reducible to Newtonian theories of mechanics because all the explanatory power of the former are contained within the latter. Furthermore, the reduction is considered to be beneficial because Newtonian mechanics is a more general theory—- that is, it explains more events than Galileo's or Kepler's. Theoretical reduction, therefore, is the reduction of one explanation or theory to another—- that is, it is the absorption of one of our ideas about a particular item into another idea.

In science

Reductionist thinking and methods form the basis for many of the well-developed topics of modern science, including much of physics, chemistry and cell biology. Classical mechanics in particular is seen as a reductionist framework, and statistical mechanics can be considered as a reconciliation of macroscopic thermodynamic laws with the reductionist method of explaining macroscopic properties in terms of microscopic components.

In science, reductionism implies that certain topics of study are based on areas that study smaller spatial scales or organizational units. While it is commonly accepted that the foundations of chemistry are based in physics, and molecular biology is based on chemistry, similar statements become controversial when one considers less rigorously defined intellectual pursuits. For example, claims that sociology is based on psychology, or that economics is based on sociology and psychology would be met with reservations. These claims are difficult to substantiate even though there are obvious associations between these topics (for instance, most would agree that psychology can affect and inform economics). The limit of reductionism's usefulness stems from emergent properties of complex systems, which are more common at certain levels of organization. For example, certain aspects of evolutionary psychology and sociobiology are rejected by some who claim that complex systems are inherently irreducible and that a holistic method is needed to understand them.

Some strong reductionists believe that the behavioral sciences should become "genuine" scientific disciplines based on genetic biology, and on the systematic study of culture (see Richard Dawkins's concept of memes). In his book The Blind Watchmaker, Dawkins introduced the term "hierarchical reductionism"^[17] to describe the opinion that complex systems can be described with a hierarchy of organizations, each of which is only described in terms of objects one level down in the hierarchy. He provides the example of a computer, which using hierarchical reductionism is explained in terms of the operation of hard drives, processors, and memory, but not on the level of logic gates, or on the even simpler level of electrons in a semiconductor medium.

Others argue that inappropriate use of reductionism limits our understanding of complex systems. In particular, ecologist Robert Ulanowicz says that science must develop techniques to study ways in which larger scales of organization influence smaller ones, and also ways in which feedback loops create structure at a given level, independently of details at a lower level of organization. He advocates (and uses) information theory as a framework to study propensities in natural systems.^[18] Ulanowicz attributes these criticisms of reductionism to the philosopher Karl Popper and biologist Robert Rosen.^[19]

The idea that phenomena such as emergence and work within the topic of complex systems theory pose limits to reductionism has been advocated by Stuart Kauffman.^[20] Emergence is especially relevant when systems exhibit historicity.^[21] Emergence is strongly related to nonlinearity.^[22] The limits of the application of reductionism are claimed to be especially evident at levels of organization with higher amounts of complexity, including living cells,^[23] neural networks, ecosystems, society, and other systems formed from assemblies of large numbers of diverse components linked by multiple feedback loops.^[23][24]

Nobel laureate Philip Warren Anderson used the idea that symmetry breaking is an example of an emergent phenomenon in his 1972 Science paper "More is different" to make an argument about the limitations of reductionism.^[25] One observation he made was that the sciences can be arranged roughly in a linear hierarchy — particle physics, solid state physics, chemistry, molecular biology, cellular biology, physiology, psychology, social sciences — in that the elementary entities of one science obeys the principles of the science that precedes it in the hierarchy; yet this does not imply that one science is just an applied version of the science that precedes it. He writes that "At each stage, entirely new laws, concepts and generalizations are necessary, requiring inspiration and creativity to just as great a degree as in the previous one. Psychology is not applied biology nor is biology applied chemistry."

Disciplines such as cybernetics and systems theory imply non-reductionism, sometimes to the extent of explaining phenomena at a given level of hierarchy in terms of phenomena at a higher level, in a sense, the opposite of reductionism.^[26]

In mathematics

In mathematics, reductionism can be interpreted as the philosophy that all mathematics can (or ought to) be based on a common foundation, which for modern mathematics is usually axiomatic set theory.

Ernst Zermelo was one of the major advocates of such an opinion; he also developed much of axiomatic set theory. It has been argued that the generally accepted method of justifying mathematical axioms by their usefulness in common practice can potentially weaken Zermelo's reductionist claim.^[27]

Jouko Väänänen has argued for second-order logic as a foundation for mathematics instead of set theory,^[28] whereas others have argued for category theory as a foundation for certain aspects of mathematics.^[29][30]

The incompleteness theorems of Kurt Gödel, published during 1931, caused doubt about the attainability of an axiomatic foundation for all of mathematics. Any such foundation would have to include axioms powerful enough to describe the arithmetic of the natural numbers (a subset of all mathematics). Yet Gödel proved that for any self-consistent recursive axiomatic system powerful enough to describe the arithmetic of the natural numbers, there are propositions about the natural numbers that cannot be proved from the axioms, but which we can prove in the natural language with which we described the axioms. Such propositions are known as formally undecidable propositions. For example, the continuum hypothesis is undecidable in the Zermelo-Fraenkel set theory as shown by Cohen.

In religion

Religious reductionism generally attempts to explain religion by explaining it in terms of nonreligious causes. A few examples of reductionistic explanations for the presence of religion are: that religion can be reduced to humanity's conceptions of right and wrong, that religion is fundamentally a primitive attempt at controlling our environments, that religion is a way to explain the existence of a physical world, and that religion confers an enhanced survivability for members of a group and so is reinforced by natural selection.^[31] Anthropologists Edward Burnett Tylor and James George Frazer employed some religious reductionist arguments.^[32] Sigmund Freud held that religion is nothing more than an illusion, or even a mental illness, and Marx claimed that religion is "the sigh of the oppressed," and the opium of the people providing only "the illusory happiness of the people," thus providing two influential examples of reductionistic views against the idea of religion.

In linguistics

Linguistic reductionism is the idea that everything can be described or explained by a language with a limited number of concepts, and combinations of those concepts.^[33] An example is the language Toki Pona.

In philosophy

The concept of downward causation poses an alternative to reductionism within philosophy. This opinion is developed by Peter Bøgh Andersen, Claus Emmeche, Niels Ole Finnemann, and Peder Voetmann Christiansen, among others. These philosophers explore ways in which one can talk about phenomena at a larger-scale level of organization exerting causal influence on a smaller-scale level, and find that some, but not all proposed types of downward causation are compatible with science. In particular, they find that constraint is one way in which downward causation can operate.^[34] The notion of causality as constraint has also been explored as a way to shed light on scientific concepts such as self-organization, natural selection, adaptation, and control.^[35]

Free will

Philosophers of the Enlightenment worked to insulate human free will from reductionism. Descartes separated the material world of mechanical necessity from the world of mental free will. German philosophers introduced the concept of the "noumenal" realm that is not governed by the deterministic laws of "phenomenal" nature, where every event is completely determined by chains of causality.^[36] The most influential formulation was by Immanuel Kant, who distinguished between the causal deterministic framework the mind imposes on the world—- the phenomenal realm—- and the world as it exists for itself, the noumenal realm, which included free will. To insulate theology from reductionism, 19th century post-Enlightenment German theologians, especially Friedrich Schleiermacher and Albrecht Ritschl, used the Romantic method of basing religion on the human spirit, so that it is a person's feeling or sensibility about spiritual matters that comprises religion.^[37]

Antireductionism

The anti-reductionist considers as minimum requirement upon the reductionist: "At the very least the anti-reductionist is owed an account of why the intuitions arise if they are not accurate."^[38]

A contrast to reductionism is holism or emergentism. Holism is the idea that items can have properties, (emergent properties), as a whole that are not explainable from the sum of their parts. The principle of holism was summarized concisely by Aristotle in the Metaphysics: "The whole is more than the sum of its parts".

Alternatives

The development of systems thinking has provided methods for describing issues in a holistic rather than a reductionist way, and many scientists use a holistic paradigm.^[39] When the terms are used in a scientific context, holism and reductionism refer primarily to what sorts of models or theories offer valid explanations of the natural world; the scientific method of falsifying hypotheses, checking empirical data against theory, is largely unchanged, but the method guides which theories are considered. The conflict between reductionism and holism in science is not universal—- it usually concerns whether or not a holistic or reductionist method is appropriate in the context of studying a specific system or phenomenon.

In many cases (such as the kinetic theory of gases), given a good understanding of the components of the system, one can predict all the important properties of the system as a whole. In other systems, emergent properties of the system are said to be almost impossible to predict from knowledge of the parts of the system. Complexity theory studies systems and properties of the latter type.

Alfred North Whitehead's metaphysics opposed reductionism. He refers to this as the "fallacy of the misplaced concreteness". His scheme was to frame a rational, general understanding of phenomena, derived from our reality.

Sven Erik Jorgensen, an ecologist, states both theoretical and practical arguments for a holistic method in certain topics of science, especially ecology. He argues that many systems are so complex that it will not ever be possible to describe all their details. Making an analogy to the Heisenberg uncertainty principle in physics, he argues that many interesting and relevant ecological phenomena cannot be replicated in laboratory conditions, and thus cannot be measured or observed without influencing and changing the system in some way. He also indicates the importance of interconnectedness in biological systems. His opinion is that science can only progress by outlining what questions are unanswerable and by using models that do not attempt to explain everything in terms of smaller hierarchical levels of organization, but instead model them on the scale of the system itself, taking into account some (but not all) factors from levels both higher and lower in the hierarchy.^[40]

Criticism

Fragmentalism is an alternative term for ontological reductionism,^[41] although fragmentalism is frequently used in a pejorative sense.^[42] Anti-realists use the term fragmentalism in arguments that the world does not exist of separable entities, instead consisting of wholes. For example, advocates of this idea claim that:

The linear deterministic approach to nature and technology promoted a fragmented perception of reality, and a loss of the ability to foresee, to adequately evaluate, in all their complexity, global crises in ecology, civilization and education.^[43]

The term "fragmentalism" is usually applied to reductionist modes of thought, frequently with the related pejorative term of scientism. This usage is popular amongst some ecological activists:

There is a need now to move away from scientism and the ideology of cause-and-effect determinism toward a radical empiricism, such as William James proposed, as an epistemology of science.^[44]

These perspectives are not new and during the early twentieth century, William James noted that rationalist science emphasized what he termed fragmentation and disconnection.^[45]

Such opinions also motivate many criticisms of the scientific method:

The scientific method only acknowledges monophasic consciousness. The method is a specialized system that emphasizes studying small and distinctive parts in isolation, which results in fragmented knowledge.^[45]

An alternative usage of this term is in cognitive psychology. Here, George Kelly developed "constructive alternativism" as a form of personal construct psychology, this provided an alternative to what he considered "accumulative fragmentalism". For this theory, knowledge is seen as the construction of successful mental models of the exterior world, rather than the accumulation of independent "nuggets of truth".^[46]

Holism

From Wikipedia, the free encyclopedia

Holism (from Greek ὅλος holos "all, whole, entire") is the idea that systems (physical, biological, chemical, social, economic, mental, linguistic) and their properties should be viewed as wholes, not just as a collection of parts.^[1][2]

The term holism was coined by J. C. Smuts in Holism and Evolution.^[3][4] It was Smuts' opinion that holism is a concept that represents all of the wholes in the universe, and these wholes are the real factors in the universe. Further, that Holism also denoted a theory of the universe in the same vein as Materialism and Spiritualism.^{[3]:120–121}

Synopsis of Holism and Evolution

After identifying the need for reform in the fundamental concepts of matter, life and mind (chapter 1) Smuts examines the reformed concepts (as of 1926) of space and time (chapter 2), matter (chapter 3) and biology (chapter 4) and concludes that the close approach to each other of the concepts of matter, life and mind, and the partial overflow of each other's domain, implies that there is a fundamental principle (Holism) of which they are the progressive outcome.^[3]:86 Chapters 5 and 6 provide the general concept, functions and categories of Holism; chapters 7 and 8 address Holism with respect to Mechanism and Darwinism, chapters 9-11 make a start towards demonstrating the concepts and functions of Holism for the metaphysical categories (mind, personality, ideals) and the book concludes with a chapter that argues for the universal ubiquity of Holism and its place as a monistic ontology.

The following is an overview of Smuts' opinions regarding the general concept, functions, and categories of Holism; like the definition of Holism, other than the idea that the whole is greater than the sum of its parts, the editor is unaware of any authoritative secondary sources corroborating Smuts' opinions.

Structure

Wholes are composites which have an internal structure, function or character which clearly differentiates them from mechanical additions, aggregates, and constructions, such as science assumes on the mechanical hypothesis.^[3]:106 The concept of structure is not confined to the physical domain (e.g. chemical, biological and artifacts); it also applies to the metaphysical domain (e.g. mental structures, properties, attributes, values, ideals, etc.)^[3]:161

Field

The field of a whole is not something different and additional to it, it is the continuation of the whole beyond its sensible contours of experience.^[3]:113 The field characterizes a whole as a unified and synthesised event in the system of Relativity, that includes not only its present but also its past—and also its future potentialities.^[3]:89 As such, the concept of field entails both activity and structure.^[3]:115

Variation

Darwin's theory of organic descent placed primary emphasis on the role of natural selection but there would be nothing to select if not for variation. Variations that are the result of mutations in the biological sense and variations that are the result of individually acquired modifications in the personal sense are attributed by Smuts to Holism; further it was his opinion that because variations appear in complexes and not singly, evolution is more than the outcome of individual selections, it is holistic.^{[3]:190–192}

Regulation

The whole exhibits a discernible regulatory function as it relates to cooperation and coordination of the structure and activity of parts, and to the selection and deselection of variations. The result is a balanced correlation of organs and functions. The activities of the parts are directed to central ends; co-operation and unified action instead of the separate mechanical activities of the parts.^[3]:125

Creativity

It is the intermingling of fields which is creative or causal in nature. This is seen in matter, where if not for its dynamic structural creative character matter could not have been the mother of the universe. This function, or factor of creativity is even more marked in biology where the protoplasm of the cell is vitally active in an ongoing process of creative change where parts are continually being destroyed and replaced by new protoplasm. With minds the regulatory function of Holism acquires consciousness and freedom, demonstrating a creative power of the most far-reaching character. Holism is not only creative but self-creative, and its final structures are far more holistic than its initial structures.^{[3]:18, 37, 67–68, 88–89}

Causality

As it relates to causality Smuts makes reference to A. N. Whitehead, and indirectly Baruch Spinoza; the Whitehead premise is that organic mechanism is a fundamental process which realizes and actualizes individual syntheses or unities. Holism (the factor) exemplifies this same idea while emphasizing the holistic character of the process. The whole completely transforms the concept of Causality; results are not directly a function of causes. The whole absorbs and integrates the cause into its own activity; results appear as the consequence of the activity of the whole.^{[3]:121–124,126} Note that this material relating to Whitehead's influence as it relates to causality was added in the second edition and, of course, will not be found in reprints of the first edition; nor is it included in the most recent Holst edition. It is the second edition of Holism and Evolution (1927) that provides the most recent and definitive treatment by Smuts.

The whole is greater than the sum of its parts

The fundamental holistic characters as a unity of parts which is so close and intense as to be more than the sum of its parts; which not only gives a particular conformation or structure to the parts, but so relates and determines them in their synthesis that their functions are altered; the synthesis affects and determines the parts, so that they function towards the whole; and the whole and the parts, therefore reciprocally influence and determine each other, and appear more or less to merge their individual characters: the whole is in the parts and the parts are in the whole, and this synthesis of whole and parts is reflected in the holistic character of the functions of the parts as well as of the whole.^[3]:88

Progressive grading of wholes

A "rough and provisional" summary of the progressive grading of wholes that comprise holism is as follows:^[3]:109

1. Material structure e.g. a chemical compound
2. Functional structure in living bodies
3. Animals, which exhibit a degree of central control that is-primarily implicit and unconscious
4. Personality, characterized as conscious central control
5. States and similar group organizations characterized by central control that involves many people.
6. Holistic Ideals, or absolute Values, distinct from human personality that are creative factors in the creation of a spiritual world, for example Truth, Beauty and Goodness.

Indications of holism in philosophy

In philosophy, any doctrine that emphasizes the priority of a whole over its parts is holism. Some suggest that such a definition owes its origins to a non-holistic view of language and places it in the reductivist camp. Alternately, a 'holistic' definition of holism denies the necessity of a division between the function of separate parts and the workings of the 'whole'. Effectively this means that the concept of a part has no absolute foundation in observation, but is rather a result of a materialist structuring of reality based on the necessity of logical and distinct units as a means to deriving information through comparative analysis. It suggests that the key recognizable characteristic of a concept of 'true' holism is a sense of the fundamental truth of any particular experience. This exists in contradistinction to what is perceived as the reductivist reliance on inductive method as the key to verification of its concept of how the parts function within the whole. Equally the potential for recognising the clarity of holistic experience within the logical terms of maths is limited by the abstract nature of numbers. In terms of real life measurements numbers have no scale or dimensional properties so have to rely on experimentally verified units (e.g. inches, volts, calories etc.), to describe reality. It is this reliance on the holistic integrity of experience which leads to the recognition that intuitive perception rather than mathematical calculation is the source of the truth of effective theories. (See references Holism, 2016.)

Philosophy of language

In the philosophy of language this becomes the claim, called semantic holism, that the meaning of an individual word or sentence can only be understood in terms of its relations to a larger body of language, even a whole theory or a whole language. In the philosophy of mind, a mental state may be identified only in terms of its relations with others. This is often referred to as "content holism" or "holism of the mental". This notion involves the philosophies of such figures as Frege, Wittgenstein, and Quine.^[5]

Epistemological and confirmation holism

Epistemological and confirmation holism are mainstream ideas in contemporary philosophy.

Ontological holism

Ontological holism was espoused by David Bohm in his theory^[6] on the implicate and explicate order.

Spinoza

The concept of holism played a pivotal role in Baruch Spinoza's philosophy.^[7][8]

Hegel

Hegel rejected "the fundamentally atomistic conception of the object," (Stern, 38) arguing that "individual objects exist as manifestations of indivisible substance-universals, which cannot be reduced to a set of properties or attributes; he therefore holds that the object should be treated as an ontologically primary whole." (Stern, 40) In direct opposition to Kant, therefore, "Hegel insists that the unity we find in our experience of the world is not constructed by us out of a plurality of intuitions." (Stern, 40) In "his ontological scheme a concrete individual is not reducible to a plurality of sensible properties, but rather exemplifies a substance universal." (Stern, 41) His point is that it is "a mistake to treat an organic substance like blood as nothing more than a compound of unchanging chemical elements, that can be separated and united without being fundamentally altered." (Stern, 103) In Hegel's view, a substance like blood is thus "more of an organic unity and cannot be understood as just an external composition of the sort of distinct substances that were discussed at the level of chemistry." (Stern, 103) Thus in Hegel's view, blood is blood and cannot be successfully reduced to what we consider are its component parts; we must view it as a whole substance entire unto itself. This is most certainly a fundamentally holistic view.^[9]

Indications of holism in physical science

Agriculture

There are several newer methods in agricultural science such as permaculture and holistic planned grazing (holistic management) that integrate ecology and social sciences with food production. Organic farming is sometimes considered a holistic approach.

Chaos and complexity

In the latter half of the 20th century, holism led to systems thinking and its derivatives. Systems in biology, psychology, or sociology are frequently so complex that their behavior is, or appears, "new" or "emergent": it cannot be deduced from the properties of the elements alone.^[10]

Holism has thus been used as a catchword. This contributed to the resistance encountered by the scientific interpretation of holism, which insists that there are ontological reasons that prevent reductive models in principle from providing efficient algorithms for prediction of system behavior in certain classes of systems.^{[citation needed]}

Scientific holism holds that the behavior of a system cannot be perfectly predicted, no matter how much data is available. Natural systems can produce surprisingly unexpected behavior, and it is suspected that behavior of such systems might be computationally irreducible, which means it would not be possible to even approximate the system state without a full simulation of all the events occurring in the system. Key properties of the higher level behavior of certain classes of systems may be mediated by rare "surprises" in the behavior of their elements due to the principle of interconnectivity, thus evading predictions except by brute force simulation.

Complexity theory (also called "science of complexity") is a contemporary heir of systems thinking. It comprises both computational and holistic, relational approaches towards understanding complex adaptive systems and, especially in the latter, its methods can be seen as the polar opposite to reductive methods. General theories of complexity have been proposed, and numerous complexity institutes and departments have sprung up around the world. The Santa Fe Institute is arguably the most famous of them.

Ecology

The Earth seen from Apollo 17.

Holistic thinking is often applied to ecology, combining biological, chemical, physical, economic, ethical, and political insights. The complexity grows with the area, so that it is necessary to reduce the characteristic of the view in other ways, for example to a specific time of duration.

John Muir, Scots born early American conservationist,^[11] wrote "When we try to pick out anything by itself we find it hitched to everything else in the Universe".

More information is to be found in the field of systems ecology, a cross-disciplinary field influenced by general systems theory.

Medicine

In primary care the term "holistic," has been used to describe approaches that take into account social considerations and other intuitive judgements.^[12] The term holism, and so-called approaches, appear in psychosomatic medicine in the 1970s, when they were considered one possible way to conceptualize psychosomatic phenomena. Instead of charting one-way causal links from psyche to soma, or vice versa, it aimed at a systemic model, where multiple biological, psychological and social factors were seen as interlinked.^[13]

Other, alternative approaches in the 1970s were psychosomatic and somatopsychic approaches, which concentrated on causal links only from psyche to soma, or from soma to psyche, respectively.^[13] At present it is commonplace in psychosomatic medicine to state that psyche and soma cannot really be separated for practical or theoretical purposes.^{[citation needed]} A disturbance on any level—somatic, psychic, or social—will radiate to all the other levels, too. In this sense, psychosomatic thinking is similar to the biopsychosocial model of medicine.^{[citation needed]}

Many alternative medicine practitioners claim a holistic approach to healing.

Neurology

A lively debate has run since the end of the 19th century regarding the functional organization of the brain. The holistic tradition (e.g., Pierre Marie) maintained that the brain was a homogeneous organ with no specific subparts whereas the localizationists (e.g., Paul Broca) argued that the brain was organized in functionally distinct cortical areas which were each specialized to process a given type of information or implement specific mental operations. The controversy was epitomized with the existence of a language area in the brain, nowadays known as the Broca's area.^[14]

Indications of holism in social science

Architecture

Architecture is often argued by design academics and those practicing in design to be a holistic enterprise.^[15] Used in this context, holism tends to imply an all-inclusive design perspective. This trait is considered exclusive to architecture, distinct from other professions involved in design projects.

Branding

A holistic brand (also holistic branding) is considering the entire brand or image of the company. For example, a universal brand image across all countries, including everything from advertising styles to the stationery the company has made, to the company colours.

Economics

With roots in Schumpeter, the evolutionary approach might be considered the holist theory in economics. They share certain language from the biological evolutionary approach. They take into account how the innovation system evolves over time. Knowledge and know-how, know-who, know-what and know-why are part of the whole business economics. Knowledge can also be tacit, as described by Michael Polanyi. These models are open, and consider that it is hard to predict exactly the impact of a policy measure. They are also less mathematical.

Education reform

The Taxonomy of Educational Objectives identifies many levels of cognitive functioning, which can be used to create a more holistic education. In authentic assessment, rather than using computers to score multiple choice tests, a standards based assessment uses trained scorers to score open-response items using holistic scoring methods.^[16] In projects such as the North Carolina Writing Project, scorers are instructed not to count errors, or count numbers of points or supporting statements. The scorer is instead instructed to judge holistically whether "as a whole" is it more a "2" or a "3". Critics question whether such a process can be as objective as computer scoring, and the degree to which such scoring methods can result in different scores from different scorers.

Psychology

Psychology of perception

A major holist movement in the early twentieth century was gestalt psychology. The claim was that perception is not an aggregation of atomic sense data but a field, in which there is a figure and a ground. Background has holistic effects on the perceived figure. Gestalt psychologists included Wolfgang Koehler, Max Wertheimer, Kurt Koffka. Koehler claimed the perceptual fields corresponded to electrical fields in the brain. Karl Lashley did experiments with gold foil pieces inserted in monkey brains purporting to show that such fields did not exist. However, many of the perceptual illusions and visual phenomena exhibited by the gestaltists were taken over (often without credit) by later perceptual psychologists. Gestalt psychology had influence on Fritz Perls' gestalt therapy, although some old-line gestaltists opposed the association with counter-cultural and New Age trends later associated with gestalt therapy. Gestalt theory was also influential on phenomenology. Aron Gurwitsch wrote on the role of the field of consciousness in gestalt theory in relation to phenomenology. Maurice Merleau-Ponty made much use of holistic psychologists such as work of Kurt Goldstein in his "Phenomenology of Perception."

Teleological psychology

Alfred Adler believed that the individual (an integrated whole expressed through a self-consistent unity of thinking, feeling, and action, moving toward an unconscious, fictional final goal), must be understood within the larger wholes of society, from the groups to which he belongs (starting with his face-to-face relationships), to the larger whole of mankind. The recognition of our social embeddedness and the need for developing an interest in the welfare of others, as well as a respect for nature, is at the heart of Adler's philosophy of living and principles of psychotherapy.

Edgar Morin, the French philosopher and sociologist, can be considered a holist based on the transdisciplinary nature of his work.

Mel Levine, M.D., author of A Mind at a Time,^[17] and co-founder (with Charles R. Schwab) of the not-for-profit organization All Kinds of Minds, can be considered a holist based on his view of the 'whole child' as a product of many systems and his work supporting the educational needs of children through the management of a child's educational profile as a whole rather than isolated weaknesses in that profile.

Anthropology

There is an ongoing dispute as to whether anthropology is intrinsically holistic. Supporters of this concept consider anthropology holistic in two senses. First, it is concerned with all human beings across times and places, and with all dimensions of humanity (evolutionary, biophysical, sociopolitical, economic, cultural, psychological, etc.) Further, many academic programs following this approach take a "four-field" approach to anthropology that encompasses physical anthropology, archeology, linguistics, and cultural anthropology or social anthropology.^[18]

Some leading anthropologists disagree, and consider anthropological holism to be an artifact from 19th century social evolutionary thought that inappropriately imposes scientific positivism upon cultural anthropology.^[19]

The term "holism" is additionally used within social and cultural anthropology to refer to an analysis of a society as a whole which refuses to break society into component parts. One definition says: "as a methodological ideal, holism implies ... that one does not permit oneself to believe that our own established institutional boundaries (e.g. between politics, sexuality, religion, economics) necessarily may be found also in foreign societies."^[20]

Émile Durkheim

Émile Durkheim developed a concept of holism which he set as opposite to the notion that a society was nothing more than a simple collection of individuals. In more recent times, Louis Dumont^[21] has contrasted "holism" to "individualism" as two different forms of societies. According to him, modern humans live in an individualist society, whereas ancient Greek society, for example, could be qualified as "holistic", because the individual found identity in the whole society. Thus, the individual was ready to sacrifice himself or herself for his or her community, as his or her life without the polis had no sense whatsoever.

Cosmomorphism

The French Protestant missionary Maurice Leenhardt coined the term "cosmomorphism" to indicate the state of perfect symbiosis with the surrounding environment which characterized the culture of the Melanesians of New Caledonia. For these people, an isolated individual is totally indeterminate, indistinct, and featureless until he can find his position within the natural and social world in which he is inserted. The confines between the self and the world are annulled to the point that the material body itself is no guarantee of the sort of recognition of identity which is typical of our own culture.^[22][23]

Theology

Holistic concepts are strongly represented within the thoughts expressed within Logos (per Heraclitus), Panentheism and Pantheism.^{[citation needed]}

In theological anthropology, which belongs to theology and not to anthropology, holism is the belief that body, soul and spirit are not separate components of a person, but rather facets of a united whole.^[24]