Stochastic

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https://en.wikipedia.org/wiki/Stochastic

Stochastic (/stəˈkæstɪk/; from Ancient Greek στόχος (stókhos) 'aim, guess') refers to the property of being well-described by a random probability distribution. Although stochasticity and randomness are distinct in that the former refers to a modeling approach and the latter refers to phenomena themselves, these two terms are often used synonymously. Furthermore, in probability theory, the formal concept of a stochastic process is also referred to as a random process.

Stochasticity is used in many different fields, including the natural sciences such as biology, chemistry, ecology, neuroscience, and physics, as well as technology and engineering fields such as image processing, signal processing, information theory, computer science, cryptography, and telecommunications. It is also used in finance, due to seemingly random changes in financial markets as well as in medicine, linguistics, music, media, colour theory, botany, manufacturing, and geomorphology.

Etymology

The word stochastic in English was originally used as an adjective with the definition "pertaining to conjecturing", and stemming from a Greek word meaning "to aim at a mark, guess", and the Oxford English Dictionary gives the year 1662 as its earliest occurrence. In his work on probability Ars Conjectandi, originally published in Latin in 1713, Jakob Bernoulli used the phrase "Ars Conjectandi sive Stochastice", which has been translated to "the art of conjecturing or stochastics". This phrase was used, with reference to Bernoulli, by Ladislaus Bortkiewicz, who in 1917 wrote in German the word Stochastik with a sense meaning random. The term stochastic process first appeared in English in a 1934 paper by Joseph Doob. For the term and a specific mathematical definition, Doob cited another 1934 paper, where the term stochastischer Prozeß was used in German by Aleksandr Khinchin, though the German term had been used earlier in 1931 by Andrey Kolmogorov.

Mathematics

In the early 1930s, Aleksandr Khinchin gave the first mathematical definition of a stochastic process as a family of random variables indexed by the real line. Further fundamental work on probability theory and stochastic processes was done by Khinchin as well as other mathematicians such as Andrey Kolmogorov, Joseph Doob, William Feller, Maurice Fréchet, Paul Lévy, Wolfgang Doeblin, and Harald Cramér. Decades later Cramér referred to the 1930s as the "heroic period of mathematical probability theory".

In mathematics, the theory of stochastic processes is an important contribution to probability theory, and continues to be an active topic of research for both theory and applications.

The word stochastic is used to describe other terms and objects in mathematics. Examples include a stochastic matrix, which describes a stochastic process known as a Markov process, and stochastic calculus, which involves differential equations and integrals based on stochastic processes such as the Wiener process, also called the Brownian motion process.

Natural science

One of the simplest continuous-time stochastic processes is Brownian motion. This was first observed by botanist Robert Brown while looking through a microscope at pollen grains in water.

Physics

The Monte Carlo method is a stochastic method popularized by physics researchers Stanisław Ulam, Enrico Fermi, John von Neumann, and Nicholas Metropolis. The use of randomness and the repetitive nature of the process are analogous to the activities conducted at a casino. Methods of simulation and statistical sampling generally did the opposite: using simulation to test a previously understood deterministic problem. Though examples of an "inverted" approach do exist historically, they were not considered a general method until the popularity of the Monte Carlo method spread.

Perhaps the most famous early use was by Enrico Fermi in 1930, when he used a random method to calculate the properties of the newly discovered neutron. Monte Carlo methods were central to the simulations required for the Manhattan Project, though they were severely limited by the computational tools of the time. Therefore, it was only after electronic computers were first built (from 1945 on) that Monte Carlo methods began to be studied in depth. In the 1950s they were used at Los Alamos for early work relating to the development of the hydrogen bomb, and became popularized in the fields of physics, physical chemistry, and operations research. The RAND Corporation and the U.S. Air Force were two of the major organizations responsible for funding and disseminating information on Monte Carlo methods during this time, and they began to find a wide application in many different fields.

Uses of Monte Carlo methods require large amounts of random numbers, and it was their use that spurred the development of pseudorandom number generators, which were far quicker to use than the tables of random numbers which had been previously used for statistical sampling.

Biology

Stochastic resonance: In biological systems, introducing stochastic "noise" has been found to help improve the signal strength of the internal feedback loops for balance and other vestibular communication. It has been found to help diabetic and stroke patients with balance control. Many biochemical events also lend themselves to stochastic analysis. Gene expression, for example, has a stochastic component through the molecular collisions—as during binding and unbinding of RNA polymerase to a gene promoter—via the solution's Brownian motion.

Creativity

Simonton (2003, Psych Bulletin) argues that creativity in science (of scientists) is a constrained stochastic behaviour such that new theories in all sciences are, at least in part, the product of a stochastic process.

Computer science

Stochastic ray tracing is the application of Monte Carlo simulation to the computer graphics ray tracing algorithm. "Distributed ray tracing samples the integrand at many randomly chosen points and averages the results to obtain a better approximation. It is essentially an application of the Monte Carlo method to 3D computer graphics, and for this reason is also called Stochastic ray tracing."

Stochastic forensics analyzes computer crime by viewing computers as stochastic steps.

In artificial intelligence, stochastic programs work by using probabilistic methods to solve problems, as in simulated annealing, stochastic neural networks, stochastic optimization, genetic algorithms, and genetic programming. A problem itself may be stochastic as well, as in planning under uncertainty.

Finance

The financial markets use stochastic models to represent the seemingly random behaviour of various financial assets, including the random behavior of the price of one currency compared to that of another (such as the price of US Dollar compared to that of the Euro), and also to represent random behaviour of interest rates. These models are then used by quantitative analysts to value options on stock prices, bond prices, and on interest rates, see Markov models. Moreover, it is at the heart of the insurance industry.

Geomorphology

Main article: Meander § Stochastic theory

The formation of river meanders has been analyzed as a stochastic process.

Language and linguistics

Non-deterministic approaches in language studies are largely inspired by the work of Ferdinand de Saussure, for example, in functionalist linguistic theory, which argues that competence is based on performance. This distinction in functional theories of grammar should be carefully distinguished from the langue and parole distinction. To the extent that linguistic knowledge is constituted by experience with language, grammar is argued to be probabilistic and variable rather than fixed and absolute. This conception of grammar as probabilistic and variable follows from the idea that one's competence changes in accordance with one's experience with language. Though this conception has been contested, it has also provided the foundation for modern statistical natural language processing and for theories of language learning and change.

Manufacturing

Manufacturing processes are assumed to be stochastic processes. This assumption is largely valid for either continuous or batch manufacturing processes. Testing and monitoring of the process is recorded using a process control chart which plots a given process control parameter over time. Typically a dozen or many more parameters will be tracked simultaneously. Statistical models are used to define limit lines which define when corrective actions must be taken to bring the process back to its intended operational window.

This same approach is used in the service industry where parameters are replaced by processes related to service level agreements.

Media

The marketing and the changing movement of audience tastes and preferences, as well as the solicitation of and the scientific appeal of certain film and television debuts (i.e., their opening weekends, word-of-mouth, top-of-mind knowledge among surveyed groups, star name recognition and other elements of social media outreach and advertising), are determined in part by stochastic modeling. A recent attempt at repeat business analysis was done by Japanese scholars and is part of the Cinematic Contagion Systems patented by Geneva Media Holdings, and such modeling has been used in data collection from the time of the original Nielsen ratings to modern studio and television test audiences.

Medicine

See also: Stochastic theory of hematopoiesis

Stochastic effect, or "chance effect" is one classification of radiation effects that refers to the random, statistical nature of the damage. In contrast to the deterministic effect, severity is independent of dose. Only the probability of an effect increases with dose.

Music

In music, mathematical processes based on probability can generate stochastic elements.

Stochastic processes may be used in music to compose a fixed piece or may be produced in performance. Stochastic music was pioneered by Iannis Xenakis, who coined the term stochastic music. Specific examples of mathematics, statistics, and physics applied to music composition are the use of the statistical mechanics of gases in Pithoprakta, statistical distribution of points on a plane in Diamorphoses, minimal constraints in Achorripsis, the normal distribution in ST/10 and Atrées, Markov chains in Analogiques, game theory in Duel and Stratégie, group theory in Nomos Alpha (for Siegfried Palm), set theory in Herma and Eonta, and Brownian motion in N'Shima. Xenakis frequently used computers to produce his scores, such as the ST series including Morsima-Amorsima and Atrées, and founded CEMAMu. Earlier, John Cage and others had composed aleatoric or indeterminate music, which is created by chance processes but does not have the strict mathematical basis (Cage's Music of Changes, for example, uses a system of charts based on the I-Ching). Lejaren Hiller and Leonard Issacson used generative grammars and Markov chains in their 1957 Illiac Suite. Modern electronic music production techniques make these processes relatively simple to implement, and many hardware devices such as synthesizers and drum machines incorporate randomization features. Generative music techniques are therefore readily accessible to composers, performers, and producers.

Social sciences

Stochastic social science theory is similar to systems theory in that events are interactions of systems, although with a marked emphasis on unconscious processes. The event creates its own conditions of possibility, rendering it unpredictable if simply for the number of variables involved. Stochastic social science theory can be seen as an elaboration of a kind of 'third axis' in which to situate human behavior alongside the traditional 'nature vs. nurture' opposition. See Julia Kristeva on her usage of the 'semiotic', Luce Irigaray on reverse Heideggerian epistemology, and Pierre Bourdieu on polythetic space for examples of stochastic social science theory.

The term stochastic terrorism has come into frequent use with regard to lone wolf terrorism. The terms "Scripted Violence" and "Stochastic Terrorism" are linked in a "cause <> effect" relationship. "Scripted violence" rhetoric can result in an act of "stochastic terrorism". The phrase "scripted violence" has been used in social science since at least 2002.

Author David Neiwert, who wrote the book Alt-America, told Salon interviewer Chauncey Devega:

Scripted violence is where a person who has a national platform describes the kind of violence that they want to be carried out. He identifies the targets and leaves it up to the listeners to carry out this violence. It is a form of terrorism. It is an act and a social phenomenon where there is an agreement to inflict massive violence on a whole segment of society. Again, this violence is led by people in high-profile positions in the media and the government. They're the ones who do the scripting, and it is ordinary people who carry it out.

Think of it like Charles Manson and his followers. Manson wrote the script; he didn't commit any of those murders. He just had his followers carry them out.

Subtractive color reproduction

When color reproductions are made, the image is separated into its component colors by taking multiple photographs filtered for each color. One resultant film or plate represents each of the cyan, magenta, yellow, and black data. Color printing is a binary system, where ink is either present or not present, so all color separations to be printed must be translated into dots at some stage of the work-flow. Traditional line screens which are amplitude modulated had problems with moiré but were used until stochastic screening became available. A stochastic (or frequency modulated) dot pattern creates a sharper image.

Reboot (fiction)

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The Godzilla film franchise, which began in 1954, has been rebooted numerous times. Pictured here is a promotional still for Godzilla Raids Again (1955).

In serial fiction, the term "reboot" signifies a new start to an established fictional universe, work, or series. A reboot discards continuity to re-create its characters, plotlines and backstory from the beginning. It has been described as a way to "rebrand" or "restart an entertainment universe that has already been established".

Another definition of a reboot is a remake which is part of an established film series or other media franchise. The term has been criticized for being a vague and "confusing" "buzzword", and a neologism for remake, a concept which has been losing popularity since the 2010s. William Proctor proposes that there is a distinction between reboots, remakes and retcons.

Origin

The term is thought to originate from the computing term reboot, meaning to restart a computer system. There is a change in meaning: the computing term refers to restarting the same program unaltered, while the term discussed here refers to revising a narrative from the beginning. The first known use of reboot applied to an entertainment franchise was in a 1994 Usenet posting.

Types

Say you've had 187 issues of 'The Incredible Hulk' and you decide you're going to introduce a new Issue 1. You pretend like those first 187 issues never happened, and you start the story from the beginning and the slate is wiped clean, and no one blinks. One of the reasons they do that is after 10 years of telling the same story, it gets stale and times change. So we did the cinematic equivalent of a reboot, and by doing that, setting it at the beginning, you're instantly distancing yourself from anything that's come before.

— David S. Goyer, on Batman Begins

Reboots cut out non-essential elements associated with a pre-established franchise and start it anew, distilling it down to the core elements that made the source material popular. For audiences, reboots allow easier entry for newcomers unfamiliar with earlier titles in a series.

Comic books

In comic books, a long-running title may have its continuity erased to start over from the beginning, enabling writers to redefine characters and open up new story opportunities, allowing the title to bring in new readers. Comic books sometimes use an in-universe explanation for a reboot, such as merging parallel worlds and timelines together, or destroying a fictional universe and recreating it from the beginning.

Film

With reboots, filmmakers revamp and reinvigorate a film series to attract new fans and stimulate revenue. A reboot can renew interest in a series that has grown stale. Reboots act as a safe project for a studio, since a reboot with an established fanbase is less risky (in terms of expected profit) than an entirely original work, while at the same time allowing the studio to explore new demographics.

A soft reboot is a reboot which acts as a sequel but is almost, if not identical to the original predecessor.

Television

See also: Revival (television)

A television series can return to production after cancellation or a long hiatus. Whereas a reboot disregards the previous continuity of a work, the term has also been used as a "catch all" phrase to categorize sequel series or general remakes due to the rise of such productions in the late 2010s.

A related concept is retooling, which is used to substantially change the premise of a series while keeping some of the core characters. Retools are usually part of an effort to forestall cancellation of a still running production.

Video games

Reboots and remakes are common in the video game industry. Remakes in video games are used to refresh the storyline and elements of the game and to take advantage of technology and features not available at the time of earlier entries.

Soft reboot

A soft reboot is a reboot that shares some continuity with the original series, but that changes the style, tone, or intent.

Origin myth

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An origin myth is a type of myth that explains the beginnings of a natural or social aspect of the world. One specific kind of origin myth is the creation or cosmogonic myth, which narrates the formation of the universe. However, numerous cultures have stories that take place after the initial origin. These stories aim to explain the origins of natural phenomena or human institutions within an already existing world. In Graeco-Roman scholarship, the terms etiological myth and aition (derived from the Ancient Greek word αἴτιον, meaning "cause") are occasionally used to describe a myth that clarifies an origin, particularly how an object or custom came into existence.

Nature of origin myths

Origin myths are narratives that explain how a particular reality came into existence.They often serve to justify the established order by attributing its establishment to sacred forces (see Social function section below). The line between cosmogonic myths (which describe the origin of the world) and origin myths is not always clear. A myth about the origin of a specific part of the world assumes the existence of the world itself, which often relies on a cosmogonic myth. Therefore, origin myths can be seen as expanding upon and building upon their cultures' cosmogonic myths. In traditional cultures, it is common for the recitation of an origin myth to be preceded by the recitation of a cosmogonic myth.

Within academic circles, the term "myth" is often used specifically to refer to origin and cosmogonic myths. Folklorists, for example, reserve the term "myth" for stories that describe creation. Stories that do not primarily focus on origins are categorized as "legend" or "folk tale," which are distinct from myths according to folklorists. Mircea Eliade, a historian, argues that in many traditional cultures, almost every sacred story can be considered an origin myth. Traditional societies often pattern their behavior after sacred events and view their lives as a cyclical return to a mythical age. As a result, nearly every sacred story portrays events that establish a new framework for human behavior, making them essentially stories of creation.

Social function

See also: Myth and ritual and Eternal return (Eliade)

An origin myth often functions to justify the current state of affairs. In traditional cultures, the entities and forces described in origin myths are often considered sacred. Thus, by attributing the state of the universe to the actions of these entities and forces, origin myths give the current order an aura of sacredness: "Myths reveal that the World, man, and life have a supernatural origin and history, and that this history is significant, precious, and exemplary." Many cultures instil the expectation that people take mythical gods and heroes as their role models, imitating their deeds and upholding the customs they established:

When the missionary and ethnologist C. Strehlow asked the Australian Arunta why they performed certain ceremonies, the answer was always: "Because the ancestors so commanded it." The Kai of New Guinea refused to change their way of living and working, and they explained: "It was thus that the Nemu (the Mythical Ancestors) did, and we do likewise." Asked the reason for a particular detail in a ceremony, a Navaho chanter answered: "Because the Holy People did it that way in the first place." We find exactly the same justification in the prayer that accompanies a primitive Tibetan ritual: "As it has been handed down from the beginning of the earth’s creation, so must we sacrifice. … As our ancestors in ancient times did—so do we now."

Founding myths unite people and tend to include mystical events along the way to make "founders" seem more desirable and heroic. Ruling monarchs or aristocracies may allege descent from mythical founders/gods/heroes in order to legitimate their control. For example: Julius Caesar and his relatives claimed Aeneas (and through Aeneas, the goddess Venus) as an ancestor.

Founding myth

The Dispute of Minerva and Neptune (c. 1689 or 1706) by René-Antoine Houasse, depicting the founding myth of Athens

A "founding myth" or etiological myth (Greek aition) explains either:

• the origins of a ritual or of the founding of a city
• the ethnogenesis of a group presented as a genealogy with a founding father and thus of a nation (natio, 'birth')
• the spiritual origins of a belief, philosophy, discipline, or idea – presented as a narrative

Beginning in protohistorical times many civilizations and kingdoms adopted some version of a heroic model national origin myth, including the Hittites and Zhou dynasty in the Bronze Age; the Scythians, Wusun, Romans and Goguryeo in Antiquity; Turks and Mongols during the Middle Ages; and the Dzungar Khanate in the late Renaissance.

In the founding myth of the Zhou dynasty in China, Lady Yuan makes a ritual sacrifice to conceive, then becomes pregnant after stepping into the footprint of the King of Heaven. She gives birth to a son, Hou Ji, whom she leaves alone in dangerous places where he is protected by sheep, cattle, birds, and woodcutters. Convinced that he is a supernatural being, she takes him back and raises him. When he grows to adulthood, he takes the position of Master of Horses in the court of Emperor Yao, and becomes successful at growing grains, gourds and beans. According to the legend, he becomes founder of the Zhou dynasty after overthrowing the evil ruler of Shang.

Like other civilizations, the Scythians also claimed descent from the son of the god of heaven. One day, the daughter of the god of the Dnieper River stole a young man's horses while he was herding his cattle, and forced him to lie with her before returning them. From this union, she conceived three sons, giving them their father's greatbow when they came of age. The son who could draw the bow would become king. All tried, but only the youngest was successful. On his attempt, three golden objects fell from the sky: a plow and yoke, a sword, and a cup. When the eldest two tried to pick them up, fire prevented them. After this, it was decided the youngest son, Scythes, would become king, and his people would be known as Scythians.

The Torah (or Pentateuch, as biblical scholars sometimes call it) is the collective name for the first five books of the Bible: Genesis, Exodus, Leviticus, Numbers, and Deuteronomy. It forms the charter myth of Israel, the story of the people's origins and the foundations of their culture and institutions, and it is a fundamental principle of Judaism that the relationship between God and his chosen people was set out on Mount Sinai through the Torah, though many stories are adapted from older religions.

A founding myth may serve as the primary exemplum, as the myth of Ixion was the original Greek example of a murderer rendered unclean by his crime, who needed cleansing (catharsis) of his impurity.

Founding myths feature prominently in Greek mythology. "Ancient Greek rituals were bound to prominent local groups and hence to specific localities", Walter Burkert has observed, "i.e. the sanctuaries and altars that had been set up for all time". Thus Greek and Hebrew founding myths established the special relationship between a deity and local people, who traced their origins from a hero and authenticated their ancestral rights through the founding myth. Greek founding myths often embody a justification for the ancient overturning of an older, archaic order, reformulating a historical event anchored in the social and natural world to valorize current community practices, creating symbolic narratives of "collective importance" enriched with metaphor in order to account for traditional chronologies, and constructing an etiology considered to be plausible among those with a cultural investment.

In the Greek view, the mythic past had deep roots in historic time, its legends treated as facts, as Carlo Brillante has noted, its heroic protagonists seen as links between the "age of origins" and the mortal, everyday world that succeeded it. A modern translator of Apollonius' Argonautica has noted, of the many aitia embedded as digressions in that Hellenistic epic, that "crucial to social stability had to be the function of myths in providing explanations, authorization or empowerment for the present in terms of origins: this could apply, not only to foundations or charter myths and genealogical trees (thus supporting family or territorial claims) but also to personal moral choices." In the period after Alexander the Great expanded the Hellenistic world, Greek poetry—Callimachus wrote a whole work simply titled Aitia—is replete with founding myths. Simon Goldhill employs the metaphor of sedimentation in describing Apollonius' laying down of layers "where each object, cult, ritual, name, may be opened... into a narrative of origination, and where each narrative, each event, may lead to a cult, ritual, name, monument."

A notable example is the myth of the foundation of Rome—the tale of Romulus and Remus, which Virgil in turn broadens in his Aeneid with the odyssey of Aeneas and his razing of Lavinium, and his son Iulus's later relocation and rule of the famous twins' birthplace Alba Longa, and their descent from his royal line, thus fitting perfectly into the already established canon of events. Similarly, the Old Testament's story of the Exodus serves as the founding myth for the community of Israel, telling how God delivered the Israelites from slavery and how they therefore belonged to him through the Covenant of Mount Sinai.

During the Middle Ages, founding myths of the medieval communes of northern Italy manifested the increasing self-confidence of the urban population and the will to find a Roman origin, however tenuous and legendary. In 13th-century Padua, when each commune looked for a Roman founder – and if one was not available, invented one—a legend had been current in the city, attributing its foundation to the Trojan Antenor.

Larger-than-life heroes continue to bolster the origin-myths of many newer nations and societies. In modern-era colonial contexts, waves of individuals and groups come to the fore in popular history as shaping and exemplifying the ideals of a group: explorers followed by conquerors followed by developers/exploiters. Note for example the conquistadors of the Iberian empires, the bandeirantes in Brazil, the coureurs des bois in Canada, the Cossacks and the promyshlenniki in Siberia and in Alaska, the bands of pioneers in the central and western United States, and the voortrekkers in Southern Africa.

Foundation stories

Foundational stories are accounts of the development of cities and nations. A foundational story represents the view that the creation of the city is a human achievement. Human control and the removal of wild, uncontrolled nature is underlined. There are two versions of foundational stories: civilization story and degradation story.

Civilization stories take a view of nature as dangerous and wild. The development of the city is seen as a successful distancing of humans from nature. Nature is locked out, and humans take pride in doing so successfully. In 1984 the geographer Yi-Fu Tuan suggested ranking cities according to their distance to natural rhythms and cycles.

Degradation stories (also called pollution stories) take a different stance. The city is seen as spoiling the landscape of the ecological relations that existed before the city was established. There is a sense of guilt for degrading the intact system of nature. In degradation stories true nature only exists outside the city.

Mood disorder

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Mood_disorder 

 

Mood disorder
Other names	mental disorder
A depressive man standing by a country pond in the pouring rain
Specialty	Psychiatry
Types	Bipolar disorder, cyclothymia, disruptive mood dysregulation disorder, dysthymia, major depressive disorder, premenstrual dysphoric disorder, seasonal affective disorder
Causes	Family history, previous diagnosis of a mood disorder, trauma, stress or major life changes in the case of depression, physical illness or use of certain medications. Depression has been linked to major diseases such as cancer, diabetes, Parkinson’s disease and heart disease, Brain structure and function in the case of bipolar disorder.
Medication	Antidepressants, mood stabilizers, antipsychotics

A mood disorder, also known as an affective disorder, is any of a group of conditions of mental and behavioral disorder where a disturbance in the person's mood is the main underlying feature. The classification is in the Diagnostic and Statistical Manual of Mental Disorders (DSM) and International Classification of Diseases (ICD).

Mood disorders fall into seven groups, including; abnormally elevated mood, such as mania or hypomania; depressed mood, of which the best-known and most researched is major depressive disorder (MDD) (alternatively known as clinical depression, unipolar depression, or major depression); and moods which cycle between mania and depression, known as bipolar disorder (BD) (formerly known as manic depression). There are several sub-types of depressive disorders or psychiatric syndromes featuring less severe symptoms such as dysthymic disorder (similar to MDD, but longer lasting and more persistent, though often milder) and cyclothymic disorder (similar to but milder than BD).

In some cases, more than one mood disorder can be present in an individual, like bipolar disorder and depressive disorder. If a mood disorder and schizophrenia are both present in an individual, this is known as schizoaffective disorder. Mood disorders may also be substance induced, or occur in response to a medical condition.

English psychiatrist Henry Maudsley proposed an overarching category of affective disorder. The term was then replaced by mood disorder, as the latter term refers to the underlying or longitudinal emotional state, whereas the former refers to the external expression observed by others.

Classification

Depressive disorders

• Major depressive disorder (MDD), commonly called major depression, unipolar depression, or clinical depression, wherein a person has one or more major depressive episodes. After a single episode, Major Depressive Disorder (single episode) would be diagnosed. After more than one episode, the diagnosis becomes Major Depressive Disorder (Recurrent). Depression without periods of mania is sometimes referred to as unipolar depression because the mood remains at the bottom "pole" and does not climb to the higher, manic "pole" as in bipolar disorder.

Individuals with a major depressive episode or major depressive disorder are at increased risk for suicide. Seeking help and treatment from a health professional dramatically reduces the individual's risk for suicide. Studies have demonstrated that asking if a depressed friend or family member has thought of committing suicide is an effective way of identifying those at risk, and it does not "plant" the idea or increase an individual's risk for suicide in any way. Epidemiological studies carried out in Europe suggest that, at this moment, roughly 8.5 percent of the world's population have a depressive disorder. No age group seems to be exempt from depression, and studies have found that depression appears in infants as young as 6 months old who have been separated from their mothers.

• Depressive disorder is frequent in primary care and general hospital practice but is often undetected. Unrecognized depressive disorder may slow recovery and worsen prognosis in physical illness, therefore it is important that all doctors be able to recognize the condition, treat the less severe cases, and identify those requiring specialist care.

Diagnosticians recognize several subtypes or course specifiers:

• Atypical depression (AD) is characterized by mood reactivity (paradoxical anhedonia) and positivity, significant weight gain or increased appetite ("comfort eating"), excessive sleep or somnolence (hypersomnia), a sensation of heaviness in limbs known as leaden paralysis, and significant social impairment as a consequence of hypersensitivity to perceived interpersonal rejection. Difficulties in measuring this subtype have led to questions of its validity and prevalence.

• Melancholic depression is characterized by a loss of pleasure (anhedonia) in most or all activities, a failure of reactivity to pleasurable stimuli, a quality of depressed mood more pronounced than that of grief or loss, a worsening of symptoms in the morning hours, early-morning waking, psychomotor retardation, excessive weight loss (not to be confused with anorexia nervosa), or excessive guilt.

• Psychotic major depression (PMD), or simply psychotic depression, is the term for a major depressive episode, in particular of melancholic nature, wherein the patient experiences psychotic symptoms such as delusions or, less commonly, hallucinations. These are most commonly mood-congruent (content coincident with depressive themes).

• Catatonic depression is a rare and severe form of major depression involving disturbances of motor behavior and other symptoms. Here, the person is mute and almost stuporous, and either is immobile or exhibits purposeless or even bizarre movements. Catatonic symptoms can also occur in schizophrenia or a manic episode, or can be due to neuroleptic malignant syndrome.

• Postpartum depression (PPD) is listed as a course specifier in DSM-IV-TR; it refers to the intense, sustained and sometimes disabling depression experienced by women after giving birth. Postpartum depression, which affects 10–15% of women, typically sets in within three months of labor, and lasts as long as three months. It is quite common for women to experience a short-term feeling of tiredness and sadness in the first few weeks after giving birth; however, postpartum depression is different because it can cause significant hardship and impaired functioning at home, work, or school as well as, possibly, difficulty in relationships with family members, spouses, or friends, or even problems bonding with the newborn. In the treatment of postpartum major depressive disorders and other unipolar depressions in women who are breastfeeding, nortriptyline, paroxetine (Paxil), and sertraline (Zoloft) are in general considered to be the preferred medications. Women with personal or family histories of mood disorders are at particularly high risk of developing postpartum depression.

• Premenstrual dysphoric disorder (PMDD) is a severe and disabling form of premenstrual syndrome affecting 3–8% of menstruating women. The disorder consists of a "cluster of affective, behavioral and somatic symptoms" that recur monthly during the luteal phase of the menstrual cycle. PMDD was added to the list of depressive disorders in the Diagnostic and Statistical Manual of Mental Disorders in 2013. The exact pathogenesis of the disorder is still unclear and is an active research topic. Treatment of PMDD relies largely on antidepressants that modulate serotonin levels in the brain via serotonin reuptake inhibitors as well as ovulation suppression using contraception.

• Seasonal affective disorder (SAD), also known as "winter depression" or "winter blues", is a specifier. Some people have a seasonal pattern, with depressive episodes coming on in the autumn or winter, and resolving in spring. The diagnosis is made if at least two episodes have occurred in colder months with none at other times over a two-year period or longer. It is commonly hypothesised that people who live at higher latitudes tend to have less sunlight exposure in the winter and therefore experience higher rates of SAD, but the epidemiological support for this proposition is not strong (and latitude is not the only determinant of the amount of sunlight reaching the eyes in winter). It is said that this disorder can be treated by light therapy. SAD is also more prevalent in people who are younger and typically affects more females than males.

• Dysthymia is a condition related to unipolar depression, where the same physical and cognitive problems are evident, but they are not as severe and tend to last longer (usually at least 2 years). The treatment of dysthymia is largely the same as for major depression, including antidepressant medications and psychotherapy.

• Double depression can be defined as a fairly depressed mood (dysthymia) that lasts for at least two years and is punctuated by periods of major depression.

• Unspecified Depressive Disorder is designated by the code 311 for depressive disorders. In the DSM-5, Unspecified Depressive Disorder encompasses symptoms that are characteristic of depressive disorders and cause significant impairment in functioning, but do not meet the criteria for the diagnosis of any specified depressive disorders. In the DSM-IV, this was called Depressive Disorder Not Otherwise Specified.

• Depressive personality disorder (DPD) is a controversial psychiatric diagnosis that denotes a personality disorder with depressive features. Originally included in the DSM-II, depressive personality disorder was removed from the DSM-III and DSM-III-R. Recently, it has been reconsidered for reinstatement as a diagnosis. Depressive personality disorder is currently described in Appendix B in the DSM-IV-TR as worthy of further study.

• Recurrent brief depression (RBD), distinguished from major depressive disorder primarily by differences in duration. People with RBD have depressive episodes about once per month, with individual episodes lasting less than two weeks and typically less than 2–3 days. Diagnosis of RBD requires that the episodes occur over the span of at least one year and, in female patients, independently of the menstrual cycle. People with clinical depression can develop RBD, and vice versa and both illnesses have similar risks.

• Minor depressive disorder, or simply minor depression, which refers to a depression that does not meet full criteria for major depression but in which at least two symptoms are present for two weeks.

Bipolar disorders

• Bipolar disorder (BD) (also called "manic depression" or "manic-depressive disorder"), an unstable emotional condition characterized by cycles of abnormal, persistent high mood (mania) and low mood (depression), which was formerly known as "manic depression" (and in some cases rapid cycling, mixed states, and psychotic symptoms). Subtypes include:

• Bipolar I is distinguished by the presence or history of one or more manic episodes or mixed episodes with or without major depressive episodes. A depressive episode is not required for the diagnosis of Bipolar I Disorder, but depressive episodes are usually part of the course of the illness.
• Bipolar II consisting of recurrent intermittent hypomanic and depressive episodes or mixed episodes.
• Cyclothymia is a form of bipolar disorder, consisting of recurrent hypomanic and dysthymic episodes, but no full manic episodes or full major depressive episodes.
• Bipolar disorder not otherwise specified (BD-NOS), sometimes called "sub-threshold" bipolar, indicates that the patient has some symptoms in the bipolar spectrum (e.g., manic and depressive symptoms) but does not fully qualify for any of the three formal bipolar DSM-IV diagnoses mentioned above.

It is estimated that roughly 1% of the adult population has bipolar I, a further 1% has bipolar II or cyclothymia, and somewhere between 2% and 5% percent have "sub-threshold" forms of bipolar disorder. Furthermore, the possibility of getting bipolar disorder when one parent is diagnosed with it is 15–30%. Risk, when both parents have it, is 50–75%. Also, while with bipolar siblings the risk is 15–25%, with identical twins it is about 70%.

Substance-induced

A mood disorder can be classified as substance-induced if its etiology can be traced to the direct physiologic effects of a psychoactive drug or other chemical substance, or if the development of the mood disorder occurred contemporaneously with substance intoxication or withdrawal. Also, an individual may have a mood disorder coexisting with a substance abuse disorder. Substance-induced mood disorders can have features of a manic, hypomanic, mixed, or depressive episode. Most substances can induce a variety of mood disorders. For example, stimulants such as amphetamine, methamphetamine, and cocaine can cause manic, hypomanic, mixed, and depressive episodes.

Alcohol-induced

High rates of major depressive disorder occur in heavy drinkers and those with alcoholism. Controversy has previously surrounded whether those who abused alcohol and developed depression were self-medicating their pre-existing depression. Recent research has concluded that, while this may be true in some cases, alcohol misuse directly causes the development of depression in a significant number of heavy drinkers. Participants studied were also assessed during stressful events in their lives and measured on a Feeling Bad Scale. Likewise, they were also assessed on their affiliation with deviant peers, unemployment, and their partner's substance use and criminal offending. High rates of suicide also occur in those who have alcohol-related problems. It is usually possible to differentiate between alcohol-related depression and depression that is not related to alcohol intake by taking a careful history of the patient. Depression and other mental health problems associated with alcohol misuse may be due to distortion of brain chemistry, as they tend to improve on their own after a period of abstinence.

Benzodiazepine-induced

Benzodiazepines, such as alprazolam, clonazepam, lorazepam and diazepam, can cause both depression and mania.

Benzodiazepines are a class of medication commonly used to treat anxiety, panic attacks and insomnia, and are also commonly misused and abused. Those with anxiety, panic and sleep problems commonly have negative emotions and thoughts, depression, suicidal ideations, and often have comorbid depressive disorders. While the anxiolytic and hypnotic effects of benzodiazepines may disappear as tolerance develops, depression and impulsivity with high suicidal risk commonly persist. These symptoms are "often interpreted as an exacerbation or as a natural evolution of previous disorders and the chronic use of sedatives is overlooked". Benzodiazepines do not prevent the development of depression, can exacerbate preexisting depression, can cause depression in those with no history of it, and can lead to suicide attempts. Risk factors for suicide and suicide attempts while using benzodiazepines include high dose prescriptions (even in those not misusing the medications), benzodiazepine intoxication, and underlying depression.

The long-term use of benzodiazepines may have a similar effect on the brain as alcohol, and are also implicated in depression. As with alcohol, the effects of benzodiazepine on neurochemistry, such as decreased levels of serotonin and norepinephrine, are believed to be responsible for the increased depression. Additionally, benzodiazepines can indirectly worsen mood by worsening sleep (i.e., benzodiazepine-induced sleep disorder). Like alcohol, benzodiazepines can put people to sleep but, while asleep, they disrupt sleep architecture: decreasing sleep time, delaying time to REM sleep, and decreasing deep sleep (the most restorative part of sleep for both energy and mood). Just as some antidepressants can cause or worsen anxiety in some patients due to being activating, benzodiazepines can cause or worsen depression due to being a central nervous system depressant—worsening thinking, concentration and problem solving (i.e., benzodiazepine-induced neurocognitive disorder). However, unlike antidepressants, in which the activating effects usually improve with continued treatment, benzodiazepine-induced depression is unlikely to improve until after stopping the medication.

In a long-term follow-up study of patients dependent on benzodiazepines, it was found that 10 people (20%) had taken drug overdoses while on chronic benzodiazepine medication despite only two people ever having had any pre-existing depressive disorder. A year after a gradual withdrawal program, no patients had taken any further overdoses.

Just as with intoxication and chronic use, benzodiazepine withdrawal can also cause depression. While benzodiazepine-induced depressive disorder may be exacerbated immediately after discontinuation of benzodiazepines, evidence suggests that mood significantly improves after the acute withdrawal period to levels better than during use. Depression resulting from withdrawal from benzodiazepines usually subsides after a few months but in some cases may persist for 6–12 months.

Due to another medical condition

"Mood disorder due to a general medical condition" is used to describe manic or depressive episodes which occur secondary to a medical condition. There are many medical conditions that can trigger mood episodes, including neurological disorders (e.g. dementias), hearing loss and associated disorders (e.g. tinnitus or hyperacusis), metabolic disorders (e.g. electrolyte disturbances), gastrointestinal diseases (e.g. cirrhosis), endocrine disease (e.g. thyroid abnormalities), cardiovascular disease (e.g. heart attack), pulmonary disease (e.g. chronic obstructive pulmonary disease), cancer, and autoimmune diseases (e.g. multiple sclerosis). Pregnancy

Not otherwise specified

See also: DSM-IV codes

Mood disorder not otherwise specified (MD-NOS) is a mood disorder that is impairing but does not fit in with any of the other officially specified diagnoses. In the DSM-IV MD-NOS is described as "any mood disorder that does not meet the criteria for a specific disorder." MD-NOS is not used as a clinical description but as a statistical concept for filing purposes. The diagnosis of MD-NOS does not exist in the DSM-5, however the diagnoses of unspecified depressive disorder and unspecified bipolar disorder are in the DSM-5.

Most cases of MD-NOS represent hybrids between mood and anxiety disorders, such as mixed anxiety-depressive disorder or atypical depression. An example of an instance of MD-NOS is being in minor depression frequently during various intervals, such as once every month or once in three days. There is a risk for MD-NOS not to get noticed, and for that reason not to get treated.

Causes

Meta-analyses show that high scores on the personality domain neuroticism are a strong predictor for the development of mood disorders. A number of authors have also suggested that mood disorders are an evolutionary adaptation (see also evolutionary psychiatry). A low or depressed mood can increase an individual's ability to cope with situations in which the effort to pursue a major goal could result in danger, loss, or wasted effort. In such situations, low motivation may give an advantage by inhibiting certain actions. This theory helps to explain why negative life incidents precede depression in around 80 percent of cases, and why they so often strike people during their peak reproductive years. These characteristics would be difficult to understand if depression were a dysfunction.

A depressed mood is a predictable response to certain types of life occurrences, such as loss of status, divorce, or death of a child or spouse. These are events that signal a loss of reproductive ability or potential, or that did so in humans' ancestral environment. A depressed mood can be seen as an adaptive response, in the sense that it causes an individual to turn away from the earlier (and reproductively unsuccessful) modes of behavior.

A depressed mood is common during illnesses, such as influenza. It has been argued that this is an evolved mechanism that assists the individual in recovering by limiting their physical activity. The occurrence of low-level depression during the winter months, or seasonal affective disorder, may have been adaptive in the past, by limiting physical activity at times when food was scarce. It is argued that humans have retained the instinct to experience low mood during the winter months, even if the availability of food is no longer determined by the weather.

Much of what is known about the genetic influence of clinical depression is based upon research that has been done with identical twins. Identical twins have exactly the same genetic code. It has been found that when one identical twin becomes depressed the other will also develop clinical depression approximately 76% of the time. When identical twins are raised apart from each other, they will both become depressed about 67% of the time. Because both twins become depressed at such a high rate, the implication is that there is a strong genetic influence. If it happened that when one twin becomes clinically depressed the other always develops depression, then clinical depression would likely be entirely genetic.

Bipolar disorder is also considered a mood disorder and it is hypothesized that it might be caused by mitochondrial dysfunction.

Sex differences

Mood disorders, specifically stress-related mood disorders such as anxiety and depression, have been shown to have differing rates of diagnosis based on sex. In the United States, women are two times more likely than men to be diagnosed with a stress-related mood disorder. Underlying these sex differences, studies have shown a dysregulation of stress-responsive neuroendocrine function causing an increase in the likelihood of developing these affective disorders. Overactivation of the hypothalamic-pituitary-adrenal (HPA) axis could provide potential insight into how these sex differences arise. Neuropeptide corticotropin-releasing factor (CRF) is released from the paraventricular nucleus (PVN) of the hypothalamus, stimulating adrenocorticotropic hormone (ACTH) release into the blood stream. From here ACTH triggers the release of glucocorticoids such as cortisol from the adrenal cortex. Cortisol, known as the main stress hormone, creates a negative feedback loop back to the hypothalamus to deactivate the stress response. When a constant stressor is present, the HPA axis remains overactivated and cortisol is constantly produced. This chronic stress is associated with sustained CRF release, resulting in the increased production of anxiety- and depressive-like behaviors and serving as a potential mechanism for differences in prevalence between men and women.

Diagnosis

DSM-5

The DSM-5, released in May 2013, separates the mood disorder chapter from the DSM-TR-IV into two sections: Depressive and related disorders and bipolar and related disorders. Bipolar disorders fall in between depressive disorders and schizophrenia spectrum and related disorders "in recognition of their place as a bridge between the two diagnostic classes in terms of symptomatology, family history and genetics" (Ref. 1, p 123). Bipolar disorders underwent a few changes in the DSM-5, most notably the addition of more specific symptomology related to hypomanic and mixed manic states. Depressive disorders underwent the most changes, the addition of three new disorders: disruptive mood dysregulation disorder, persistent depressive disorder (previously dysthymia), and premenstrual dysphoric disorder (previously in appendix B, the section for disorders needing further research). Disruptive mood dysregulation disorder is meant as a diagnosis for children and adolescents who would normally be diagnosed with bipolar disorder as a way to limit the bipolar diagnosis in this age cohort. Major depressive disorder (MDD) also underwent a notable change, in that the bereavement clause has been removed. Those previously exempt from a diagnosis of MDD due to bereavement are now candidates for the MDD diagnosis.

Treatment

There are different types of treatments available for mood disorders, such as therapy and medications. Behaviour therapy, cognitive behaviour therapy and interpersonal therapy have all shown to be potentially beneficial in depression. Major depressive disorder medications usually include antidepressants; a combination of antidepressants and cognitive behavioral therapy has shown to be more effective than one treatment alone. Bipolar disorder medications can consist of antipsychotics, mood stabilizers, anticonvulsants and/or lithium. Lithium specifically has been proven to reduce suicide and all causes of mortality in people with mood disorders. If mitochondrial dysfunction or mitochondrial diseases are the cause of mood disorders like bipolar disorder, then it has been hypothesized that N-acetyl-cysteine (NAC), acetyl-L-carnitine (ALCAR), S-adenosylmethionine (SAMe), coenzyme Q10 (CoQ10), alpha-lipoic acid (ALA), creatine monohydrate (CM), and melatonin could be potential treatment options. In determining treatment, there are many types of depression scales that are used. One of the depression scales is a self-report scale called Beck Depression Inventory (BDI). Another scale is the Hamilton Depression Rating Scale (HAMD). HAMD is a clinical rating scale in which the patient is rated based on clinician observation. The Center for Epidemiologic Studies Depression Scale (CES-D) is a scale for depression symptoms that applies to the general population. This scale is typically used in research and not for self-reports. The PHQ-9 which stands for Patient-Health Questionnaire-9 questions, is a self-report as well. Finally, the Mood Disorder Questionnaire (MDQ) evaluates bipolar disorder.

Epidemiology

According to a substantial number of epidemiology studies conducted, women are twice as likely to develop certain mood disorders, such as major depression. Although there is an equal number of men and women diagnosed with bipolar II disorder, women have a slightly higher frequency of the disorder.

In 2011, mood disorders were the most common reason for hospitalization among children aged 1–17 years in the United States, with approximately 112,000 stays. Mood disorders were top principal diagnosis for Medicaid super-utilizers in the United States in 2012. Further, a study of 18 states found that mood disorders accounted for the highest number of hospital readmissions among Medicaid patients and the uninsured, with 41,600 Medicaid patients and 12,200 uninsured patients being readmitted within 30 days of their index stay—a readmission rate of 19.8 per 100 admissions and 12.7 per 100 admissions, respectively. In 2012, mood and other behavioral health disorders were the most common diagnoses for Medicaid-covered and uninsured hospital stays in the United States (6.1% of Medicaid stays and 5.2% of uninsured stays).

A study conducted in 1988 to 1994 amongst young American adults involved a selection of demographic and health characteristics. A population-based sample of 8,602 men and women ages 17–39 years participated. Lifetime prevalence were estimated based on six mood measures:

• major depressive episode (MDE) 8.6%,
• major depressive disorder with severity (MDE-s) 7.7%,
• dysthymia 6.2%,
• MDE-s with dysthymia 3.4%,
• any bipolar disorder 1.6%, and
• any mood disorder 11.5%.

Research

Kay Redfield Jamison and others have explored the possible links between mood disorders – especially bipolar disorder – and creativity. It has been proposed that a "ruminating personality type may contribute to both [mood disorders] and art."

Jane Collingwood notes an Oregon State University study that:

looked at the occupational status of a large group of typical patients and found that 'those with bipolar illness appear to be disproportionately concentrated in the most creative occupational category.' They also found that the likelihood of 'engaging in creative activities on the job' is significantly higher for bipolar than nonbipolar workers.

In Liz Paterek's article "Bipolar Disorder and the Creative Mind" she wrote:

Memory and creativity are related to mania. Clinical studies have shown that those in a manic state will rhyme, find synonyms, and use alliteration more than controls. This mental fluidity could contribute to an increase in creativity. Moreover, mania creates increases in productivity and energy. Those in a manic state are more emotionally sensitive and show less inhibition about attitudes, which could create greater expression. Studies performed at Harvard looked into the amount of original thinking in solving creative tasks. Bipolar individuals, whose disorder was not severe, tended to show greater degrees of creativity.

The relationship between depression and creativity appears to be especially strong among poets.