Amygdala

From Wikipedia, the free encyclopedia

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

 

Amygdala
Location of amygdalae in the human brain (view from below, anterior is at top)
Subdivisions of the amygdala

Human brain in the coronal orientation. Amygdalae are shown in dark red.

The amygdala (/əˈmɪɡdələ/; pl.: amygdalae /əˈmɪɡdəli, -laɪ/ or amygdalas; also corpus amygdaloideum) is a paired nuclear complex present in the cerebral hemispheres of vertebrates. It is considered part of the limbic system. In primates, it is located medially within the temporal lobes. It consists of many nuclei, each made up of further subnuclei. The subdivision most commonly made is into the basolateral, central, cortical, and medial nuclei together with the intercalated cell clusters. The amygdala has a primary role in the processing of memory, decision-making, and emotional responses (including fear, anxiety, and aggression). The amygdala was first identified and named by Karl Friedrich Burdach in 1822.

Structure

Subdivisions of the mouse amygdala

T1 MRI images of amygdala in human (highlighted in green)

Coronal

Sagittal

Transversal

Thirteen nuclei have been identified, each with its own subdivisions and distinct connections to the rest of the brain. The chief nuclei are the basolateral complex, the central nucleus, the cortical nucleus, the medial nucleus, and the intercalated cell clusters. The cortical and medial nuclei connect with the olfactory system and hypothalamus. The central nucleus has extensive projections to the brainstem.

The basolateral complex can be further subdivided into the lateral, the basal, and the accessory basal nuclei. It has extensive connections with higher-order cortical areas in the prefrontal, temporal, insular cortices, and the hippocampus. The basolateral complex is surrounded by the intercalated cell net that is inhibitory and projects to a broad variety of areas in the basal forebrain, hypothalamus, and the amygdala.

The primate amygdala contains about 32 different types of neuron.

Hemispheric specializations

The right and left portions of the amygdala have independent memory systems, but work together to store, encode, and interpret emotion.

The right hemisphere of the amygdala is associated with negative emotion. It plays a role in the expression of fear and in the processing of fear-inducing stimuli. Fear conditioning, which occurs when a neutral stimulus acquires aversive properties, occurs within the right hemisphere. When an individual is presented with a conditioned, aversive stimulus, it is processed within the right amygdala, producing an unpleasant or fearful response. This emotional response conditions the individual to avoid fear-inducing stimuli and more importantly, to assess threats in the environment.

The right hemisphere is also linked to declarative memory, which consists of facts and information from previously experienced events and must be consciously recalled. It also plays a significant role in the retention of episodic memory. Episodic memory consists of the autobiographical aspects of memory, permitting recall of emotional and sensory experience of an event. This type of memory does not require conscious recall. The right amygdala plays a role in the association of time and places with emotional properties.

In one study, electrical stimulations of the right amygdala induced negative emotions, especially fear and sadness. In contrast, stimulation of the left amygdala was able to induce either pleasant (happiness) or unpleasant (fear, anxiety, sadness) emotions. Other evidence suggests that the left amygdala plays a role in the brain's reward system.

Development and sex distinction

See also: Neuroscience of sex differences

When controlling for total brain volume or intracranial volume, there is no significant difference in the average size of the amygdala between men and women. Raw amygdala volumes are, on average, 10.6% larger in men, but men also have larger bodies and brains on average.

There is considerable growth within the first few years of structural development in both male and female amygdalae. Within this early period, female limbic structures grow at a more rapid pace than the male ones. Amongst female subjects, the amygdala reaches its full growth potential approximately 1.5 years before the peak of male development. The structural development of the male amygdala occurs over a longer period than in women.

There are observable developmental differences between the right and left amygdala. The left amygdala reaches its developmental peak approximately 1.5–2 years prior to the right amygdala. Despite the early growth of the left amygdala, the right increases in volume for a longer period of time. The right amygdala is associated with response to fearful stimuli as well as face recognition. For the left amygdala, it is inferred that the early development of it functions to provide infants the ability to detect danger due to its reported responds predominantly to fearful events and faces.In childhood, the amygdala is found to react differently to same-sex versus opposite-sex individuals. This reactivity decreases until a person enters adolescence, where it increases dramatically at puberty.

Functional and structural differences have been discovered between male and female amygdalae. The results of PET scans showed a different lateralization of the amygdala in men and women after watching an emotional film. Enhanced memory for the film was related to enhanced activity of the left, but not the right, amygdala in women, whereas it was related to enhanced activity of the right, but not the left, amygdala in men. Studies involving patients with amygdala damage came to a similar conclusion. In patients with unilateral amygdala damage, men with right (but not left) amygdala damage were more likely to be impaired in decision-making ability, while women with left (but not right) amygdala damage were more likely to be impaired in decision-making ability. One study found evidence that, on average, women tend to retain stronger memories for emotional events than men.

Function

Connections

Variability in amygdala connectivity has been related to a variety of behaviors and outcomes such as fear recognition and social network size. A simple view of the information processing through the amygdala follows as: the amygdala sends projections to the hypothalamus, septal nuclei and BNST (via the amygdalofugal tract), the dorsomedial thalamus (via the amygdalothalamic tract), the nuclei of the trigeminal nerve and the facial nerve, the ventral tegmental area, the locus coeruleus, and the laterodorsal tegmental nucleus.

The basolateral amygdala projects to the nucleus accumbens, including the medial shell. Glutamatergic neurons in the basolateral amygdala send projections to the nucleus accumbens shell and core. Activation of these projections drive motivational salience. The ability of these projections to drive incentive salience is dependent upon dopamine receptor D1. The endocannabinoid system that produces lipoid neuromodulators has its specific receptors (CB1) found in amygdalae.

Coronal section of brain through intermediate mass of third ventricle. Amygdala is shown in purple.

The medial nucleus is involved in the sense of smell and pheromone-processing. It receives input from the olfactory bulb and olfactory cortex. The lateral amygdalae, which send impulses to the rest of the basolateral complexes and to the centromedial nuclei, receive input from the sensory systems. The centromedial nuclei are the main outputs for the basolateral complexes, and are involved in emotional arousal in rats and cats.

Emotional learning

Main article: Emotion and memory

In complex vertebrates, including humans, the amygdalae perform primary roles in the formation and storage of memories associated with emotional events. Research indicates that, during fear conditioning, sensory stimuli reach the basolateral complexes of the amygdalae, particularly the lateral nuclei, where they form associations with memories of the stimuli. The association between stimuli and the aversive events they predict may be mediated by long-term potentiation, a sustained enhancement of signaling between affected neurons. There have been studies that show that damage to the amygdala can interfere with memory that is strengthened by emotion. One study examined a patient with bilateral degeneration of the amygdala. He was told a violent story accompanied by matching pictures and was observed based on how much he could recall from the story. The patient had less recollection of the story than patients with functional amygdala, showing that the amygdala has a strong connection with emotional learning.

Emotional memories are thought to be stored in synapses throughout the brain. Fear memories, for example, are considered to be stored in the neuronal connections from the lateral nuclei to the central nucleus of the amygdalae and the bed nuclei of the stria terminalis (part of the extended amygdala). These connections are not the sole site of fear memories given that the nuclei of the amygdala receive and send information to other brain regions that are important for memory such as the hippocampus. Some sensory neurons project their axon terminals to the central nucleus. The central nuclei are involved in the genesis of many fear responses such as defensive behavior (freezing or escape responses), autonomic nervous system responses (changes in blood pressure and heart rate/tachycardia), neuroendocrine responses (stress-hormone release), etc. Damage to the amygdalae impairs both the acquisition and expression of Pavlovian fear conditioning, a form of classical conditioning of emotional responses. Accumulating evidence has suggested that multiple neuromodulators acting in the amygdala regulates the formation of emotional memories.

The amygdalae are also involved in appetitive (positive) conditioning. It seems that distinct neurons respond to positive and negative stimuli, but there is no clustering of these distinct neurons into clear anatomical nuclei. However, lesions of the central nucleus in the amygdala have been shown to reduce appetitive learning in rats. Lesions of the basolateral regions do not exhibit the same effect. Research like this indicates that different nuclei within the amygdala have different functions in appetitive conditioning. Nevertheless, researchers found an example of appetitive emotional learning showing an important role for the basolateral amygdala: The naïve female mice are innately attracted to non-volatile pheromones contained in male-soiled bedding, but not by the male-derived volatiles, become attractive if associated with non-volatile attractive pheromones, which act as unconditioned stimulus in a case of Pavlovian associative learning. In the vomeronasal, olfactory, and emotional systems, Fos (gene family) proteins show that non-volatile pheromones stimulate the vomeronasal system, whereas air-borne volatiles activate only the olfactory system. Thus, the acquired preference for male-derived volatiles reveals an olfactory-vomeronasal associative learning. Moreover, the reward system is differentially activated by the primary pheromones and secondarily attractive odorants. Exploring the primary attractive pheromone activates the basolateral amygdala and the shell of nucleus accumbens but neither the ventral tegmental area nor the orbitofrontal cortex. In contrast, exploring the secondarily attractive male-derived odorants involves activation of a circuit that includes the basolateral amygdala, prefrontal cortex, and ventral tegmental area. Therefore, the basolateral amygdala stands out as the key center for vomeronasal-olfactory associative learning.

Memory modulation

The amygdala is also involved in the modulation of memory consolidation. Following any learning event, the long-term memory for the event is not formed instantaneously. Rather, information regarding the event is slowly assimilated into long-term (potentially lifelong) storage over time, possibly via long-term potentiation. Recent studies suggest that the amygdala regulates memory consolidation in other brain regions. Also, fear conditioning, a type of memory that is impaired following amygdala damage, is mediated in part by long-term potentiation. During the consolidation period, the memory can be modulated. In particular, it appears that emotional arousal following the learning event influences the strength of the subsequent memory for that event. Greater emotional arousal following a learning event enhances a person's retention of that event. Experiments have shown that administration of stress hormones to mice immediately after they learn something enhances their retention when they are tested two days later.

The amygdala, especially the basolateral nuclei, are involved in mediating the effects of emotional arousal on the strength of the memory for the event, as shown by many laboratories including that of James McGaugh. These laboratories have trained animals on a variety of learning tasks and found that drugs injected into the amygdala after training affect the animals' subsequent retention of the task. These tasks include basic classical conditioning tasks such as inhibitory avoidance, where a rat learns to associate a mild footshock with a particular compartment of an apparatus, and more complex tasks such as spatial or cued water maze, where a rat learns to swim to a platform to escape the water. If a drug that activates the amygdalae is injected into the amygdalae, the animals had better memory for the training in the task.

Amygdala activity at the time of encoding information correlates with retention for that information. However, this correlation depends on the relative "emotionalness" of the information. More emotionally arousing information increases amygdalar activity, and that activity correlates with retention. Amygdala neurons show various types of oscillation during emotional arousal, such as theta activity and gamma activity. These synchronized neuronal events could promote synaptic plasticity (which is involved in memory retention) by increasing interactions between neocortical storage sites and temporal lobe structures involved in declarative memory.

In rats, DNA damage was found to increase in the amygdala immediately after exposure to stress. Stress was induced by 30 minutes of restraint or by forced swimming. By seven days after exposure to these stresses, increased DNA damage was no longer detectable in the amygdala, probably because of DNA repair.

Buddhist monks who do compassion meditation have been shown to modulate their amygdala, along with their temporoparietal junction and insula, during their practice. In an fMRI study, more intensive insula activity was found in expert meditators than in novices.

Rorschach test blot 03

Research using Rorschach test blot 03 finds that the number of unique responses to this random figure links to larger sized amygdalae. The researchers note, "Since previous reports have indicated that unique responses were observed at higher frequency in the artistic population than in the nonartistic normal population, this positive correlation suggests that amygdalar enlargement in the normal population might be related to creative mental activity."

Neuropsychological correlates of amygdala activity

Early research on primates provided explanations as to the functions of the amygdala, as well as a basis for further research. As early as 1888, rhesus monkeys with a lesioned temporal cortex (including the amygdala) were observed to have significant social and emotional deficits. Heinrich Klüver and Paul Bucy later expanded upon this same observation by showing that large lesions to the anterior temporal lobe produced noticeable changes, including overreaction to all objects, hypoemotionality, loss of fear, hypersexuality, and hyperorality, a condition in which inappropriate objects are placed in the mouth. Some monkeys also displayed an inability to recognize familiar objects and would approach animate and inanimate objects indiscriminately, exhibiting a loss of fear towards the experimenters. This behavioral disorder was later named Klüver–Bucy syndrome accordingly, and later research proved it was specifically due to amygdala lesions. Monkey mothers who had amygdala damage showed a reduction in maternal behaviors towards their infants, often physically abusing or neglecting them. In 1981, researchers found that selective radio frequency lesions of the whole amygdala caused Klüver–Bucy syndrome.

Social function

The amygdala has a role in social function. Amygdala volume is associated with the size and complexity of social networks. Amygdala volume correlates positively with both the size (the number of contacts) and the complexity (the number of different groups) of social networks.

The amygdala is involved in facial recognition and emotional expressions. Its role in analysis of social situations stems specifically from its ability to identify and process changes in facial features, although it does not process the direction of a gaze toward a person.

The amygdala processes reactions to violations concerning personal space.

Alcoholism

The amygdala appears to play a role in binge drinking, being damaged by repeated episodes of intoxication and withdrawal. Protein kinase C-epsilon in the amygdala is important for regulating behavioral responses to morphine and ethanol and controlling anxiety-like behavior. The protein is involved in controlling the function of other proteins and plays a role in the development of the ability to consume a large amount of ethanol. The duration of chronic alcohol consumption and abstinence may affect dynamic brain network adaptations. When excessive drinking occurs, the amygdala is affected through behavioral changes and reduces the brain's plasticity. Often, when binge drinking or alcoholism occurs, the amygdala is affected and leads to behavior damage. These behavioral damages can be lack of control, inability to conduct oneself in a mature manner, irritability and aggressive behavior, anxiety, depression, personality disorders, excessive drug intake, bipolar disorder, confusion, higher tolerance levels, and inappropriate sexual behaviors with others and self.

Anxiety

Feelings of anxiety start with an environmental stimulus that provokes stress. This can include various smells, sights, and internal sensations that result in anxiety. The amygdala reacts to this stimuli by preparing to either stand and fight or to turn and run. The amygdala sends signals to the paraventricular nucleus of the hypothalamus for the initiation of the HPA axis response. Consequently, blood sugar rises, becoming immediately available to the muscles for quick energy. Shaking may occur in an attempt to return blood to the rest of the body. Long-term changes in amygdala neurons may also increase anxiety after long-term or traumatic stress, led by the action of stress-related hormones within the amygdala. On the flip side, blocking the action of stress hormones in the amygdala reduces anxiety. There may also be a link between the amygdala and anxiety.

The central nucleus of the amygdala has direct correlations to the hypothalamus and brainstem—areas directly related to fear and anxiety. This connection is evident from studies of animals that have undergone amygdalae removal.

The clusters of the amygdala are activated when an individual expresses feelings of fear or aggression. This occurs because the amygdala is the primary structure of the brain responsible for fight-or-flight response. Anxiety and panic attacks can occur when the amygdala senses environmental stressors that stimulate fight-or-flight response. The amygdala is involved in the expression of conditioned fear. Conditioned fear is the framework used to explain the behavior produced when an originally neutral stimulus is consistently paired with a stimulus that evokes fear. Fear is measured by changes in autonomic activity including increased heart rate, increased blood pressure, as well as in simple reflexes such as flinching or blinking. Studies in 2004 and 2006 showed that normal subjects exposed to images of frightened faces or faces of people from another race will show increased activity of the amygdala, even if that exposure is subliminal. However, the amygdala is not necessary for the processing of fear-related stimuli, since persons in whom it is bilaterally damaged show rapid reactions to fearful faces, even in the absence of a functional amygdala.

Patient S.M., sometimes referred to as SM-046, is an American woman with exclusive and complete bilateral amygdala destruction since late childhood as a consequence of Urbach–Wiethe disease, and has a physiologically greatly reduced ability to feel fear as a result. First described by scientists in 1994, S.M. has been studied extensively in scientific research; she has helped researchers elucidate the function of the amygdala.

Psychological disorders

With advances in neuroimaging technology such as MRI, neuroscientists have made significant findings concerning the amygdala in the human brain. A variety of data shows the amygdala has a substantial role in mental states, and is related to many psychological disorders. Some studies have shown children with anxiety disorders tend to have a smaller left amygdala. In the majority of the cases, there was an association between an increase in the size of the left amygdala with the use of SSRIs (antidepressant medication) or psychotherapy. The left amygdala has been linked to social anxiety disorder, obsessive and compulsive disorders, and post-traumatic stress disorder (PTSD), as well as more broadly to separation and generalized anxiety disorder.^[89] Multiple studies have found that the amygdalae may be responsible for the emotional reactions of PTSD patients. One study in particular found that when PTSD patients are shown pictures of faces with fearful expressions, their amygdalae tended to have a higher activation than someone without PTSD.

In 2006, researchers observed hyperactivity in the amygdala when patients were shown threatening faces or confronted with frightening situations. Patients with severe social phobia showed a correlation with increased response in the amygdala. Individuals with psychopathy show reduced autonomic responses to instructed fear cues than otherwise healthy individuals. Similarly, depressed patients showed exaggerated left amygdala activity when interpreting emotions for all faces, and especially for fearful faces. This hyperactivity was normalized when patients were administered antidepressant medication.

In a 2003 study, subjects with borderline personality disorder showed significantly greater left amygdala activity than normal control subjects. Some borderline patients even had difficulties classifying neutral faces or saw them as threatening. The amygdala has been observed to respond differently in people with bipolar disorder. Amygdala dysfunction during face emotion processing is well-documented in bipolar disorder. Individuals with bipolar disorder showed greater amygdala activity (especially the amygdala/medial-prefrontal-cortex circuit). For people with manic bipolar I disorder, a decreased negative functional connectivity between the orbitofrontal cortex and the amygdala was also observed. A 2003 study found that adult and adolescent bipolar patients tended to have considerably smaller amygdala volumes and somewhat smaller hippocampal volumes. Many studies have also focused on the connections between the amygdala and autism.

Market failure

From Wikipedia, the free encyclopedia

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

While factories and refineries provide jobs and wages, they are also an example of a market failure, as they impose negative externalities on the surrounding region via their airborne pollutants.

In neoclassical economics, market failure is a situation in which the allocation of goods and services by a free market is not Pareto efficient, often leading to a net loss of economic value. The first known use of the term by economists was in 1958, but the concept has been traced back to the Victorian writers John Stuart Mill and Henry Sidgwick. Market failures are often associated with public goods, time-inconsistent preferences, information asymmetries, failures of competition, principal–agent problems, externalities, unequal bargaining power, behavioral irrationality (in behavioral economics), and macro-economic failures (such as unemployment and inflation).

The neoclassical school attributes market failures to the interference of self-regulatory organizations, governments or supra-national institutions in a particular market, although this view is criticized by heterodox economists. Economists, especially microeconomists, are often concerned with the causes of market failure and possible means of correction. Such analysis plays an important role in many types of public policy decisions and studies.

However, government policy interventions, such as taxes, subsidies, wage and price controls, and regulations, may also lead to an inefficient allocation of resources, sometimes called government failure. Most mainstream economists believe that there are circumstances (like building codes, fire safety regulations or endangered species laws) in which it is possible for government or other organizations to improve the inefficient market outcome. Several heterodox schools of thought disagree with this as a matter of ideology.

An ecological market failure exists when human activity in a market economy is exhausting critical non-renewable resources, disrupting fragile ecosystems, or overloading biospheric waste absorption capacities. In none of these cases does the criterion of Pareto efficiency obtain.

Categories

Different economists have different views about what events are the sources of market failure. Mainstream economic analysis widely accepts that there are several causes of market failures. These include if the market is "monopolised" or a small group of businesses hold significant market power resulting in a "failure of competition"; if production of the good or service results in an externality (external costs or benefits); if the good or service is a "public good"; if there is a "failure of information" or information asymmetry; if there is unequal bargaining power; if there is bounded rationality or irrationality; and if there are macro-economic failures such as unemployment or inflation.

Failure of competition

Main articles: Market structure and market power

Agents in a market can gain market power, allowing them to block other mutually beneficial gains from trade from occurring. This can lead to inefficiency due to imperfect competition, which can take many different forms, such as monopolies, monopsonies, or monopolistic competition, if the agent does not implement perfect price discrimination.

In small countries like New Zealand, electricity transmission is a natural monopoly. Due to enormous fixed costs and small market size, one seller can serve the entire market at the downward-sloping section of its average cost curve, meaning that it will have lower average costs than any potential entrant.

It is then a further question about what circumstances allow a monopoly to arise. In some cases, monopolies can maintain themselves where there are "barriers to entry" that prevent other companies from effectively entering and competing in an industry or market. Or there could exist significant first-mover advantages in the market that make it difficult for other firms to compete. Moreover, monopoly can be a result of geographical conditions created by huge distances or isolated locations. This leads to a situation where there are only few communities scattered across a vast territory with only one supplier. Australia is an example that meets this description. A natural monopoly is a firm whose per-unit cost decreases as it increases output; in this situation it is most efficient (from a cost perspective) to have only a single producer of a good. Natural monopolies display so-called increasing returns to scale. It means that at all possible outputs marginal cost needs to be below average cost if average cost is declining. One of the reasons is the existence of fixed costs, which must be paid without considering the amount of output, what results in a state where costs are evenly divided over more units leading to the reduction of cost per unit.

Public goods

Some markets can fail due to the nature of the goods being exchanged. For instance, some goods can display the attributes of public goods or common goods, wherein sellers are unable to exclude non-buyers from using a product, as in the development of inventions that may spread freely once revealed, such as developing a new method of harvesting. This can cause underinvestment because developers cannot capture enough of the benefits from success to make the development effort worthwhile. This can also lead to resource depletion in the case of common-pool resources, whereby the use of the resource is rival but non-excludable, there is no incentive for users to conserve the resource. An example of this is a lake with a natural supply of fish: if people catch the fish faster than the fish can reproduce, then the fish population will dwindle until there are no fish left for future generations.

Externalities

A good or service could also have significant externalities, where gains or losses associated with the product, production or consumption of a product, differ from the private cost. These gains or losses are imposed on a third-party that did not take part in the original market transaction. These externalities can be innate to the methods of production or other conditions important to the market.

"The Problem of Social Cost" illuminates a different path towards social optimum showing the Pigouvian tax is not the only way towards solving externalities. It is hard to say who discovered externalities first since many classical economists saw the importance of education or a lighthouse, but it was Alfred Marshall who wanted to explore this more. He wondered why long-run supply curve under perfect competition could be decreasing so he founded "external economies". Externalities can be positive or negative depending on how a good/service is produced or what the good/service provides to the public. Positive externalities tend to be goods like vaccines, schools, or advancement of technology. They usually provide the public with a positive gain. Negative externalities would be like noise or air pollution. Coase shows this with his example of the case Sturges v. Bridgman involving a confectioner and doctor. The confectioner had lived there many years and soon the doctor several years into residency decides to build a consulting room; it is right by the confectioner's kitchen which releases vibrations from his grinding of pestle and mortar. The doctor wins the case by a claim of nuisance so the confectioner would have to cease from using his machine. Coase argues there could have been bargains instead the confectioner could have paid the doctor to continue the source of income from using the machine hopefully it is more than what the Doctor is losing. Vice versa the doctor could have paid the confectioner to cease production since he is prohibiting a source of income from the confectioner. Coase used a few more examples similar in scope dealing with social cost of an externality and the possible resolutions.

Congested Times Square in Midtown Manhattan, New York City, which leads the world in urban automobile traffic congestion, but which has implemented congestion pricing in January 2025 to address the problem

Traffic congestion is an example of market failure that incorporates both non-excludability and externality. Public roads are common resources that are available for the entire population's use (non-excludable), and act as a complement to cars (the more roads there are, the more useful cars become). Because there is very low cost but high benefit to individual drivers in using the roads, the roads become congested, decreasing their usefulness to society. Furthermore, driving can impose hidden costs on society through pollution (externality). Solutions for this include public transportation, congestion pricing, tolls, and other ways of making the driver include the social cost in the decision to drive.

Perhaps the best example of the inefficiency associated with common/public goods and externalities is the environmental harm caused by pollution and overexploitation of natural resources.

Coase theorem

The Coase theorem, developed by Ronald Coase and labeled as such by George Stigler, states that private transactions are efficient as long as property rights exist, only a small number of parties are involved, and transactions costs are low. Additionally, this efficiency will take place regardless of who owns the property rights. This theory comes from a section of Coase's Nobel prize-winning work The Problem of Social Cost. While the assumptions of low transactions costs and a small number of parties involved may not always be applicable in real-world markets, Coase's work changed the long-held belief that the owner of property rights was a major determining factor in whether or not a market would fail. The Coase theorem points out when one would expect the market to function properly even when there are externalities.

A market is an institution in which individuals or firms exchange not just commodities, but the rights to use them in particular ways for particular amounts of time. [...] Markets are institutions which organize the exchange of control of commodities, where the nature of the control is defined by the property rights attached to the commodities.

As a result, agents' control over the uses of their goods and services can be imperfect, because the system of rights which defines that control is incomplete. Typically, this falls into two generalized rights – excludability and transferability. Excludability deals with the ability of agents to control who uses their commodity, and for how long – and the related costs associated with doing so. Transferability reflects the right of agents to transfer the rights of use from one agent to another, for instance by selling or leasing a commodity, and the costs associated with doing so. If a given system of rights does not fully guarantee these at minimal (or no) cost, then the resulting distribution can be inefficient. Considerations such as these form an important part of the work of institutional economics. Nonetheless, views still differ on whether something displaying these attributes is meaningful without the information provided by the market price system.

Information failures

Information asymmetry is considered a leading type of market failure. This is where there is an imbalance of information between two or more parties to a transaction. One example is incomplete markets, for example where second hand car buyers know there is a risk a car may break down, and systematically under-pay to discount this risk: this leads to fewer cars being sold overall; or where insurers know that some policyholders will withhold information, and systematically refuse to insure certain groups because of this risk. This may result in economic inefficiency, but also have a possibility of improving efficiency through market, legal, and regulatory remedies. From contract theory, decisions in transactions where one party has more or better information than the other is considered "asymmetry". This creates an imbalance of power in transactions which can sometimes cause the transactions to go awry. Examples of this problem are adverse selection and moral hazard. Most commonly, information asymmetries are studied in the context of principal–agent problems. George Akerlof, Michael Spence, and Joseph E. Stiglitz developed the idea and shared the 2001 Nobel Prize in Economics.

Unequal bargaining power

Main article: Inequality of bargaining power

In The Wealth of Nations Adam Smith explored how an employer had the ability to "hold out" longer in a dispute over pay with workers because workers were more likely to go hungry more quickly, given that the employer has more property, and have fewer obstacles in organising. Unequal bargaining power has been used as a concept justifying economic regulation, particularly for employment, consumer, and tenancy rights since the early 20th century. Thomas Piketty in Capital in the Twenty-First Century explains how unequal bargaining power undermines "conditions of "pure and perfect" competition" and leads to a persistently lower share of income for labor, and leads to growing inequality. While it was argued by Ronald Coase that bargaining power merely affects distribution of income, but not productive efficiency, the modern behavioural evidence establishes that distribution or fairness of exchange does affect motivation to work, and therefore unequal bargaining power is a market failure. Notably, the price of labour was excluded from the scope of the original charts on supply and demand by their inventor, Fleeming Jenkin, who considered that the wages of labour could not be equated with ordinary markets for commodities such as corn, because of labour's unequal bargaining power.

Bounded rationality

Main articles: Bounded rationality and Behavioral economics

In Models of Man, Herbert A. Simon points out that most people are only partly rational, and are emotional/irrational in the remaining part of their actions. In another work, he states "boundedly rational agents experience limits in formulating and solving complex problems and in processing (receiving, storing, retrieving, transmitting) information" (Williamson, p. 553, citing Simon). Simon describes a number of dimensions along which "classical" models of rationality can be made somewhat more realistic, while sticking within the vein of fairly rigorous formalization. These include:

• limiting what sorts of utility functions there might be.
• recognizing the costs of gathering and processing information.
• the possibility of having a "vector" or "multi-valued" utility function.

Simon suggests that economic agents employ the use of heuristics to make decisions rather than a strict rigid rule of optimization. They do this because of the complexity of the situation, and their inability to process and compute the expected utility of every alternative action. Deliberation costs might be high and there are often other, concurrent economic activities also requiring decisions.

The concept of bounded rationality was significantly expanded through behavioral economics research, suggesting that people are systematically irrational in day-to-day decisions. Daniel Kahneman in Thinking, Fast and Slow explored how human beings operate as if they have two systems of thinking: a fast "system 1" mode of thought for snap, everyday decisions which applies rules of thumb but is frequently mistaken; and a slow "system 2" mode of thought that is careful and deliberative, but not as often used in making ordinary decisions to buy and sell or do business.

Macro-economic failures

Main articles: Unemployment, Inflation, and Macroeconomics

"Unemployment, inflation and "disequilibrium" are considered a category of market failure at a "macro economic" or "whole economy" level. These symptoms (of high job loss, or fast rising prices or both) can result from a financial crash, a recession or depression, and the market failure is evident in the sustained underproduction of an economy, or a tendency not to recover immediately. Macroeconomic business cycles are a part of the market. They are characterized by constant downswings and upswings which influence economic activity. Therefore, this situation requires some kind of government intervention.

Persistent labor shortages

Main article: Shortage § Labour shortage

Widespread and persistent domestic labour shortages in various countries are examples of market failure, whereby excessively low salaries (relative to the domestic cost of living) and adverse working conditions (excessive workload and working hours) in low-wage industries (hospitality and leisure, education, health care, rail transportation, warehousing, aviation, retail, manufacturing, food, construction, elderly care), collectively lead to occupational burnout and attrition of existing workers, insufficient incentives to attract the inflow supply of domestic workers, short-staffing and regular shift work at workplaces and further exacerbation (positive feedback) of staff shortages. Poor job quality and artificial shortages perpetuated by salary-paying employers, deter workers from entering or remaining in these roles.

Labour shortages occur broadly across multiple industries within a rapidly expanding economy, whilst labour shortages often occur within specific industries (which generally offer low salaries) even during economic periods of high unemployment. In response to domestic labour shortages, business associations such as chambers of commerce, trade associations or employers' organizations would generally lobby to governments for an increase of the inward immigration of foreign workers from countries which are less developed and have lower salaries. In addition, business associations have campaigned for greater state provision of child care, which would enable more women to re-enter the labour workforce at a lower wage rate to achieve economic equilibrium. However, as labour shortages in the relevant low-wage industries are often widespread globally throughout many countries in the world, immigration would only partially address the chronic labour shortages in the relevant low-wage industries in developed countries (whilst simultaneously discouraging local labour from entering the relevant industries) and in turn cause greater labour shortages in developing countries.

Interpretations and policy examples

The above causes represent the mainstream view of what market failures mean and of their importance in the economy. This analysis follows the lead of the neoclassical school, and relies on the notion of Pareto efficiency, which can be in the "public interest", as well as in interests of stakeholders with equity. This form of analysis has also been adopted by the Keynesian or new Keynesian schools in modern macroeconomics, applying it to Walrasian models of general equilibrium in order to deal with failures to attain full employment, or the non-adjustment of prices and wages.

Policies to prevent market failure are already commonly implemented in the economy. For example, to prevent information asymmetry, members of the New York Stock Exchange agree to abide by its rules in order to promote a fair and orderly market in the trading of listed securities. The members of the NYSE presumably believe that each member is individually better off if every member adheres to its rules – even if they have to forego money-making opportunities that would violate those rules.

A simple example of policies to address market power is government antitrust policies. As an additional example of externalities, municipal governments enforce building codes and license tradesmen to mitigate the incentive to use cheaper (but more dangerous) construction practices, ensuring that the total cost of new construction includes the (otherwise external) cost of preventing future tragedies. The voters who elect municipal officials presumably feel that they are individually better off if everyone complies with the local codes, even if those codes may increase the cost of construction in their communities.

CITES is an international treaty to protect the world's common interest in preserving endangered species – a classic "public good" – against the private interests of poachers, developers and other market participants who might otherwise reap monetary benefits without bearing the known and unknown costs that extinction could create. Even without knowing the true cost of extinction, the signatory countries believe that the societal costs far outweigh the possible private gains that they have agreed to forego.

Some remedies for market failure can resemble other market failures. For example, the issue of systematic underinvestment in research is addressed by the patent system that creates artificial monopolies for successful inventions.

Objections

See also: Government failure

Public choice

Economists such as Milton Friedman from the Chicago school and others from the Public Choice school, argue that market failure does not necessarily imply that the government should attempt to solve market failures, because the costs of government failure might be worse than those of the market failure it attempts to fix. This failure of government is seen as the result of the inherent problems of democracy and other forms of government perceived by this school and also of the power of special-interest groups (rent seekers) both in the private sector and in the government bureaucracy. Conditions that many would regard as negative are often seen as an effect of subversion of the free market by coercive government intervention. Beyond philosophical objections, a further issue is the practical difficulty that any single decision maker may face in trying to understand (and perhaps predict) the numerous interactions that occur between producers and consumers in any market.

Austrian

Some advocates of laissez-faire capitalism, including many economists of the Austrian School, argue that there is no such phenomenon as "market failure". Israel Kirzner states that, "Efficiency for a social system means the efficiency with which it permits its individual members to achieve their individual goals." Inefficiency only arises when means are chosen by individuals that are inconsistent with their desired goals. This definition of efficiency differs from that of Pareto efficiency, and forms the basis of the theoretical argument against the existence of market failures. However, providing that the conditions of the first welfare theorem are met, these two definitions agree, and give identical results. Austrians argue that the market tends to eliminate its inefficiencies through the process of entrepreneurship driven by the profit motive; something the government has great difficulty detecting, or correcting.

Marxian

Objections also exist on more fundamental bases, such as Marxian analysis. Colloquial uses of the term "market failure" reflect the notion of a market "failing" to provide some desired attribute different from efficiency – for instance, high levels of inequality can be considered a "market failure", yet are not Pareto inefficient, and so would not be considered a market failure by mainstream economics. In addition, many Marxian economists would argue that the system of private property rights is a fundamental problem in itself, and that resources should be allocated in another way entirely. This is different from concepts of "market failure" which focuses on specific situations – typically seen as "abnormal" – where markets have inefficient outcomes. Marxists, in contrast, would say that markets have inefficient and democratically unwanted outcomes – viewing market failure as an inherent feature of any capitalist economy – and typically omit it from discussion, preferring to ration finite goods not exclusively through a price mechanism, but based upon need as determined by society expressed through the community.

Ecological

Humanity's economic system viewed as a subsystem of the global environment

See also: Ecological economics § Not 'externalities', but cost shifting; Nicholas Georgescu-Roegen § Criticising neoclassical economics (weak versus strong sustainability); Tragedy of the commons; and Uneconomic growth

In ecological economics, the concept of externalities is considered a misnomer, since market agents are viewed as making their incomes and profits by systematically 'shifting' the social and ecological costs of their activities onto other agents, including future generations. Hence, externalities is a modus operandi of the market, not a failure: The market cannot exist without constantly 'failing'.

The fair and even allocation of non-renewable resources over time is a market failure issue of concern to ecological economics. This issue is also known as 'intergenerational fairness'. It is argued that the market mechanism fails when it comes to allocating the Earth's finite mineral stock fairly and evenly among present and future generations, as future generations are not, and cannot be, present on today's market. In effect, today's market prices do not, and cannot, reflect the preferences of the yet unborn. This is an instance of a market failure passed unrecognized by most mainstream economists, as the concept of Pareto efficiency is entirely static (timeless). Imposing government restrictions on the general level of activity in the economy may be the only way of bringing about a more fair and even intergenerational allocation of the mineral stock. Hence, Nicholas Georgescu-Roegen and Herman Daly, the two leading theorists in the field, have both called for the imposition of such restrictions: Georgescu-Roegen has proposed a minimal bioeconomic program, and Daly has proposed a comprehensive steady-state economy. However, Georgescu-Roegen, Daly, and other economists in the field agree that on a finite Earth, geologic limits will inevitably strain most fairness in the longer run, regardless of any present government restrictions: Any rate of extraction and use of the finite stock of non-renewable mineral resources will diminish the remaining stock left over for future generations to use.

Another ecological market failure is presented by the overutilisation of an otherwise renewable resource at a point in time, or within a short period of time. Such overutilisation usually occurs when the resource in question has poorly defined (or non-existing) property rights attached to it while too many market agents engage in activity simultaneously for the resource to be able to sustain it all. Examples range from over-fishing of fisheries and over-grazing of pastures to over-crowding of recreational areas in congested cities. This type of ecological market failure is generally known as the 'tragedy of the commons'. In this type of market failure, the principle of Pareto efficiency is violated the utmost, as all agents in the market are left worse off, while nobody are benefitting. It has been argued that the best way to remedy a 'tragedy of the commons'-type of ecological market failure is to establish enforceable property rights politically – only, this may be easier said than done.

The issue of climate change presents an overwhelming example of a 'tragedy of the commons'-type of ecological market failure: The Earth's atmosphere may be regarded as a 'global common' exhibiting poorly defined (non-existing) property rights, and the waste absorption capacity of the atmosphere with regard to carbon dioxide is presently being heavily overloaded by a large volume of emissions from the world economy. Historically, the fossil fuel dependence of the Industrial Revolution has unintentionally thrown mankind out of ecological equilibrium with the rest of the Earth's biosphere (including the atmosphere), and the market has failed to correct the situation ever since. Quite the opposite: The unrestricted market has been exacerbating this global state of ecological dis-equilibrium, and is expected to continue doing so well into the foreseeable future. This particular market failure may be remedied to some extent at the political level by the establishment of an international (or regional) cap and trade property rights system, where carbon dioxide emission permits are bought and sold among market agents.

The term 'uneconomic growth' describes a pervasive ecological market failure: The ecological costs of further economic growth in a so-called 'full-world economy' like the present world economy may exceed the immediate social benefits derived from this growth.

Zerbe and McCurdy

Zerbe and McCurdy connected criticism of market failure paradigm to transaction costs. Market failure paradigm is defined as follows:

"A fundamental problem with the concept of market failure, as economists occasionally recognize, is that it describes a situation that exists everywhere."

Transaction costs are part of each market exchange, although the price of transaction costs is not usually determined. They occur everywhere and are unpriced. Consequently, market failures and externalities can arise in the economy every time transaction costs arise. There is no place for government intervention. Instead, government should focus on the elimination of both transaction costs and costs of provision.

Emotion and memory

From Wikipedia, the free encyclopedia

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

Emotion can have a powerful effect on humans and animals. Numerous studies have shown that the most vivid autobiographical memories tend to be of emotional events, which are likely to be recalled more often and with more clarity and detail than neutral events.

The activity of emotionally enhanced memory retention can be linked to human evolution; during early development, responsive behavior to environmental events would have progressed as a process of trial and error. Survival depended on behavioral patterns that were repeated or reinforced through life and death situations. Through evolution, this process of learning became genetically embedded in humans and all animal species in what is known as flight or fight instinct.

Artificially inducing this instinct through traumatic physical or emotional stimuli essentially creates the same physiological condition that heightens memory retention by exciting neuro-chemical activity affecting areas of the brain responsible for encoding and recalling memory. This memory-enhancing effect of emotion has been demonstrated in many laboratory studies, using stimuli ranging from words to pictures to narrated slide shows, as well as autobiographical memory studies. However, as described below, emotion does not always enhance memory.

Arousal and valence in memory

One of the most common frameworks in the emotions field proposes that affective experiences are best characterized by two main dimensions: arousal and valence. The dimension of valence ranges from highly positive to highly negative, whereas the dimension of arousal ranges from calming or soothing to exciting or agitating.

The majority of studies to date have focused on the arousal dimension of emotion as the critical factor contributing to the emotional enhancement effect on memory. Different explanations have been offered for this effect, according to the different stages of memory formation and reconstruction. Memory has been shown to be better with arousal linked with emotion than without emotion. The use of a PET scan has allowed scientists to see that pictures with an "emotional-stimulus" have significantly larger amount of activity in the amygdala. In a study using fluoro-2-deoxyglucose (FDG-PET) to examine the brain during recall of films that were both neutral and aversive, there was a positive correlation between the brain glucose and metabolic rate in the amygdala. The activity in the amygdala is part of the episodic memory that was being created due to the adverse stimuli. Most recently, an intracranial EEG study found that the amygdala triggered more pronounced hippocampal sharp-wave ripples after the encoding of more arousing experiences, which are believed to play a critical role in memory consolidation.

However, a growing body of research is dedicated to the emotional valence dimension and its effects on memory. It has been claimed that this is an essential step towards a more complete understanding of emotion effects on memory. The studies that did investigate this dimension have found that emotional valence alone can enhance memory; that is, nonarousing items with positive or negative valence can be better remembered than neutral items.

Emotion and encoding

From an information processing perspective, encoding refers to the process of interpreting incoming stimuli and combining the processed information. At the encoding level the following mechanisms have been suggested as mediators of emotion effects on memory:

Selectivity of attention

Easterbrook's (1959) cue utilization theory predicted that high levels of arousal will lead to attention narrowing, defined as a decrease in the range of cues from the stimulus and its environment to which the organism is sensitive. According to this hypothesis, attention will be focused primarily on the arousing details (cues) of the stimulus, so that information central to the source of the emotional arousal will be encoded while peripheral details will not.

Accordingly, several studies have demonstrated that the presentation of emotionally-arousing stimuli (compared to neutral stimuli) results in enhanced memory for central details (details central to the appearance or meaning of the emotional stimuli) and impaired memory for peripheral details. Also consistent with this hypothesis are findings of weapon focus effect, in which witnesses to a crime remember the gun or knife in great detail but not other details such as the perpetrator's clothing or vehicle. In laboratory replications it was found that participants spend a disproportionate amount of time looking at a weapon in a scene, and this looking time is inversely related to the likelihood that individuals will subsequently identify the perpetrator of the crime. Other researchers have suggested arousal may also increase the duration of attentional focusing on the arousing stimuli, thus delaying the disengagement of attention from it. Ochsner (2000) summarized the different findings and suggested that by influencing attention selectivity and dwell time, arousing stimuli are more distinctively encoded, resulting in more accurate memory of those stimuli.

While these previous studies focused on how emotion affects memory for emotionally arousing stimuli, in their arousal-biased competition theory, Mather and Sutherland (2011) argue that how arousal influences memory for non-emotional stimuli depends on the priority of those stimuli at the time of the arousal. Arousal enhances perception and memory of high priority stimuli but impairs perception and memory of low priority stimuli. Priority can be determined by bottom-up salience or by top-down goals.

Prioritized processing

Emotional items also appear more likely to be processed when attention is limited, suggesting a facilitated or prioritized processing of emotional information. This effect was demonstrated using the attentional blink paradigm in which 2 target items are presented in close temporal proximity within a stream of rapidly presented stimuli.

The typical finding is that participants often miss the second target item, as if there were a "blink" of attention following the first target's presentation, reducing the likelihood that the second target stimulus is attended. However, when the second target stimulus elicits emotional arousal (a "taboo" word), participants are less likely to miss the target's presentation, which suggests that under conditions of limited attention, arousing items are more likely to be processed than neutral items.

Additional support for the prioritized processing hypothesis was provided by studies investigating the visual extinction deficit. People suffering from this deficit can perceive a single stimulus in either side visual field if it is presented alone but are unaware of the same stimulus in the visual field opposed to the lesional side, if another stimulus is presented simultaneously on the lesional side.

Emotion has been found to modulate the magnitude of the visual extinction deficit, so that items that signal emotional relevance (e.g., spiders) are more likely to be processed in the presence of competing distractors than nonemotional items (e.g., flowers).

Emotion and storage

In addition to its effects during the encoding phase, emotional arousal appears to increase the likelihood of memory consolidation during the retention (storage) stage of memory (the process of creating a permanent record of the encoded information). A number of studies show that over time, memories for neutral stimuli decrease but memories for arousing stimuli remain the same or improve.

Others have discovered that memory enhancements for emotional information tend to be greater after longer delays than after relatively short ones. This delayed effect is consistent with the proposal that emotionally-arousing memories are more likely to be converted into a relatively permanent trace, whereas memories for nonarousing events are more vulnerable to disruption.

A few studies have even found that emotionally arousing stimuli enhance memory only after a delay. The most famous of these was a study by Kleinsmith and Kaplan (1963) that found an advantage for numbers paired with arousing words over those paired with neutral words only at delayed test, but not at immediate test. As outlined by Mather (2007), the Kleinsmith and Kaplan effects were most likely due to a methodological confound. However, Sharot and Phelps (2004) found better recognition of arousing words over neutral words at a delayed test but not at an immediate test, supporting the notion that there is enhanced memory consolidation for arousing stimuli. According to these theories, different physiological systems, including those involved in the discharge of hormones believed to affect memory consolidation, become active during, and closely following, the occurrence of arousing events.

Another possible explanation for the findings of the emotional arousal delayed effect is post-event processing regarding the cause of the arousal. According to the post stimulus elaboration (PSE) hypothesis, an arousing emotional experience may cause more effort to be invested in elaboration of the experience, which would subsequently be processed at a deeper level than a neutral experience. Elaboration refers to the process of establishing links between newly-encountered information and previously-stored information.

It has long been known that when individuals process items in an elaborative fashion, such that meaning is extracted from items and inter-item associations are formed, memory is enhanced. Thus, if a person gives more thought to central details in an arousing event, memory for such information is likely to be enhanced. However, these processes could also disrupt consolidation of memories for peripheral details. Christianson (1992) suggested that the combined action of perceptual, attentional, and elaborative processing, triggered by an emotionally arousing experience, produces memory enhancements of details related to the emotion laden stimulus, at the cost of less elaboration and consolidation of memory for the peripheral details.

Emotion and elaboration

The processes involved in this enhancement may be distinct from those mediating the enhanced memory for arousing items. It has been suggested that in contrast to the relatively automatic attentional modulation of memory for arousing information, memory for non-arousing positive or negative stimuli may benefit instead from conscious encoding strategies, such as elaboration. This elaborative processing can be autobiographical or semantic.

Autobiographical elaboration is known to benefit memory by creating links between the processed stimuli, and the self, for example, deciding whether a word would describe the personal self. Memory formed through autobiographical elaboration is enhanced as compared to items processed for meaning, but not in relation to the self.

Since words such as "sorrow" or "comfort" may be more likely to be associated with autobiographical experiences or self-introspection than neutral words such as "shadow", autobiographical elaboration may explain the memory enhancement of non-arousing positive or negative items. Studies have shown that dividing attention at encoding decreases an individual's ability to utilize controlled encoding processes, such as autobiographical or semantic elaboration.

Thus, findings that participants' memory for negative non-arousing words suffers with divided attention, and that the memory advantage for negative, non-arousing words can be eliminated when participants encode items while simultaneously performing a secondary task, has supported the elaborative processing hypothesis as the mechanism responsible for memory enhancement for negative non-arousing words.

Emotion and retrieval

Retrieval is a process of reconstructing past experiences; this phenomenon of reconstruction is influenced by a number of different variables described below.

Trade-off between details

Kensinger argues there are two trade-offs: central/peripheral trade-off of details and a specific/general trade-off. Emotional memories may include increased emotional details often with the trade-off of excluding background information. Research has shown that this trade-off effect cannot be explained exclusively by overt attention (measured by eye-tracking directed to emotional items during encoding) (Steinmetz & Kensinger, 2013).

Contextual effects of emotion on memory

Contextual effects occur as a result of the degree of similarity between the encoding context and the retrieval context of an emotional dimension. The main findings are that the current mood we are in affects what is attended, encoded and ultimately retrieved, as reflected in two similar but subtly different effects: the mood congruence effect and mood-state dependent retrieval. Positive encoding contexts have been connected to activity in the right fusiform gyrus. Negative encoding contexts have been correlated to activity in the right amygdala (Lewis & Critchley, 2003). However, Lewis and Critchley (2003) claim that it is not clear whether involvement of the emotional system in encoding memory differs for positive or negative emotions, or whether moods at recall lead to activity in the corresponding positive or negative neural networks.

Mood congruence effect

The mood congruence effect refers to the tendency of individuals to retrieve information more easily when it has the same emotional content as their current emotional state. For instance, being in a depressed mood increases the tendency to remember negative events (Drace, 2013).

This effect has been demonstrated for explicit retrieval as well as implicit retrieval.

Mood-state dependent retrieval

Another documented phenomenon is the mood-state dependent retrieval, a type of context-dependent memory. The retrieval of information is more effective when the emotional state at the time of retrieval is similar to the emotional state at the time of encoding.

Thus, the probability of remembering an event can be enhanced by evoking the emotional state experienced during its initial processing. These two phenomena, the mood congruity effect, and mood-state dependent retrieval, are similar to the context effects which have been traditionally observed in memory research. It may also relate to the phenomena of state-dependent memory in neuropsychopharmacology.

When recalling a memory, if someone is recalling an event by themselves or within a group of people, the emotions that they remember may change as well recall of specific details. Individuals recall events with stronger negative emotions than when a group is recalling the same event. Collaborative recall, as it can be referred to, causes strong emotions to fade. Emotional tone changes as well, with a difference of individual or collaborative recall so much that an individual will keep the tone of what was previously felt, but the group will have a more neutral tone. For example, if someone is recalling the negative experience of taking a difficult exam, then they will talk in a negative tone. However, when the group is recalling taking the exam, they will most likely recount it in a positive tone as the negative emotions and tones fade. Detail recount is also something that changed based on the emotion state a person is in when they are remembering an event. If an event is being collaboratively recalled the specific detail count is higher than if an individual is doing it. Detail recall is also more accurate when someone is experiencing negative emotion; Xie and Zhang (2016) conducted a study in which participants saw a screen with five colors on it and when presented with the next screen were asked which color was missing. Those who were experiencing negative emotions were more precise than those in the positive and neutral conditions. Aside from emotional state, mental illness like depression relates to people's ability to recall specific details. Those who are depressed tend to overgeneralize their memories and are not able to remember as many specific details of any events as compared to those without depression.

Thematic vs. sudden appearance of emotional stimuli

A somewhat different contextual effect stemmed from the recently made distinction between thematical and sudden appearance of an emotionally arousing event, suggesting that the occurrence of memory impairments depends on the way the emotional stimuli are induced. Laney et al. (2003) argued that when arousal is induced thematically (i.e., not through the sudden appearance of a discrete shocking stimulus such as a weapon but rather through involvement in an unfolding event plot and empathy with the victim as his or her plight becomes increasingly apparent), memory enhancements of details central to the emotional stimulus need not come at the expense of memory impairment of peripheral details.

Laney et al. (2004) demonstrated this by using an audio narrative to give the presented slides either neutral or emotional meaning, instead of presenting shockingly salient visual stimuli. In one of the experiments, participants in both the neutral and emotional conditions viewed slides of a date scenario of a woman and man at a dinner date. The couple engaged in conversation, then, at the end of the evening, embraced. The event concluded with the man leaving and the woman phoning a friend.

The accompanying audio recording informed participants in the neutral condition that the date went reasonably well, while participants in the emotional condition heard that, as the evening wore on, the man displayed some increasingly unpleasant traits of a type that was derogatory to women, and the embrace at the end of the evening was described as an attempt to sexually assault the woman.

As expected, the results revealed that details central to the event were remembered more accurately when that event was emotional than when neutral, However, this was not at the expense of memory for peripheral (in this case, spatially peripheral or plot-irrelevant) details, which were also remembered more accurately when the event was emotional. Based on these findings it has been suggested that the dual enhancing and impairing effects on memory are not an inevitable consequence of emotional arousal.

Neurobiological mechanisms of emotional memory enhancement

The neural mechanism underlying emotional memory enhancement involves the interaction between the amygdala and the hippocampus, as well as several other factors that prioritize the encoding of emotional experiences. When an emotional experience occurs, the amygdala becomes highly active, signaling the hippocampus to strengthen the encoding and consolidation of these memories. This process is facilitated by the release of stress hormones and neurotransmitters, which modulate synaptic plasticity and enhance neural connectivity. Multiple mechanisms have been proposed to explain this prioritized encoding, including the neuromodulatory effects on plasticity and the dynamic interplay between the amygdala and the hippocampus. Intracranial EEG studies have shown that the amygdala triggers pronounced hippocampal sharp-wave ripples after encoding emotional experiences, further reinforcing the consolidation of these memories during both awake and sleep. This coordinated activity between the amygdala and hippocampus ensures that emotionally significant events are prioritized in long-term memory storage, leveraging both immediate neurochemical changes and enduring structural adaptations in neural circuits.

Memory of felt emotion

Many researchers use self-report measures of felt emotion as a manipulation check. This raises an interesting question and a possible methodological weakness: are people always accurate when they recall how they felt in the past? Several findings suggest this is not the case. For instance, in a study of memory for emotions in supporters of former U.S. presidential candidate Ross Perot, supporters were asked to describe their initial emotional reactions after Perot's unexpected withdrawal in July 1992 and again after the presidential election that November.

Between the two assessment periods, the views of many supporters changed dramatically as Perot re-entered the race in October and received nearly a fifth of the popular vote. The results showed that supporters recalled their past emotions as having been more consistent with their current appraisals of Perot than they actually were.

Another study found that people's memories for how distressed they felt when they learned of the 9/11 terrorist attacks changed over time and moreover, were predicted by their current appraisals of the impact of the attacks (Levine et al., 2004). It appears that memories of past emotional responses are not always accurate, and can even be partially reconstructed based on their current appraisal of events.

Studies have shown that as episodic memory becomes less accessible over time, the reliance on semantic memory to remember past emotions increases. In one study Levine et al. (2009) primes of the cultural belief of women being more emotional than men had a greater effect on responses for older memories compared to new memories. The long-term recall of emotions was more in line with the primed opinions, showing that long-term recall of emotions was heavily influenced by current opinions.

Emotion regulation effects on memory

An interesting issue in the study of the emotion-memory relationship is whether our emotions are influenced by our behavioral reaction to them, and whether this reaction—in the form of expression or suppression of the emotion—might affect what we remember about an event. Researchers have begun to examine whether concealing feelings influences our ability to perform common cognitive tasks, such as forming memories, and found that the emotion regulation efforts do have cognitive consequences. In the seminal work on negative affect arousal and white noise, Seidner found support for the existence of a negative affect arousal mechanism through observations regarding the devaluation of speakers from other ethnic origins."

In a study of Richards and Gross (1999) and Tiwari (2013), participants viewed slides of injured men that produced increases in negative emotions, while information concerning each man was presented orally with his slide. The participants were assigned to either an expressive suppression group (where they were asked to refrain from showing emotion while watching the slides) or to a control group (where they were not given regulatory instructions at all). As predicted by the researchers, suppressors showed significantly worse performance on a memory test for the orally presented information.

In another study, it was investigated whether expressive suppression (i.e., keeping one's emotions subdued) comes with a cognitive price. They measured expressive suppression when it spontaneously occurred while watching a movie of surgeries. After the movie, memory was tested and was found to be worse with a higher usage of suppression. In a second study, another movie was shown of people arguing. Memory of the conversation was then measured. When gauging the magnitude of cognitive cost, expressive suppression was compared with self-distraction, which was described as simply not trying to think about something. It was concluded that experimentally-induced suppression was associated with worse memory.

There is evidence that emotion enhances memory but is more specific towards arousal and valence factors. To test this theory, arousal and valence were assessed for over 2,820 words. Both negative and positive stimuli were remembered higher than neutral stimuli. Arousal also did not predict recognition memory. In this study, the importance of stimulus controls and experimental designs in research memory was highlighted. Arousal-related activities when affiliated with heightened heart rate (HR) stimulate prediction of memory enhancement. It was hypothesized that tonic elevations in HR (meaning revitalization in HR) and phasic HR (meaning quick reaction) declaration to help the memory. Fifty-three men's heart rates were measured while looking at unpleasant, neutral, and pleasant pictures and their memory tested two days later. It was concluded that tonic elevations created more accurate memory recall.

Several related studies have reached similar results. It was demonstrated that the effects of expressive suppression on memory generalize to emotionally positive experiences and to socially relevant contexts.

One possible answer to the question "why does emotion suppression impair memory?" might lay in the self monitoring efforts invested in order to suppress emotion (thinking about the behavior one is trying to control). A recent study found heightened self- monitoring efforts among suppressors relative to control participants.

That is, suppressors were more likely to report thinking about their behavior and the need to control it during a conversation. Increases in self-monitoring predicted decreases in memory for what was said, that is, people who reported thinking a lot about controlling their behavior had particularly impoverished memories. However, additional research is needed to confirm whether self-monitoring actually exerts a causal effect on memory

Emotion-induced forgetting

Further information: Motivated forgetting

Emotionally arousing stimuli can lead to retrograde amnesia for preceding events and anterograde amnesia for subsequent events. This has been demonstrated in lab studies with lists of words or pictures, in which people show impaired memory for stimuli appearing before or after arousing stimuli.

Depression and memory

Memory recall tends to be congruent with one's current mood, with depressed people more likely to recall negative events from the past. In addition, depression is often associated with poor memory in general, as outlined here.

Dementia and emotional memory

Several studies have demonstrated emotional memory enhancement in Alzheimer's patients suggesting that emotional memory enhancement might be used in the daily management of Alzheimer's patients. One study found that objects are recalled significantly better in Alzheimer's patients if they were presented as birthday presents to AD patients.

Aging and emotional memory

The enhancing effects of emotional arousal on later memory recall tend to be maintained among older adults and the amygdala shows relatively less decline than many other brain regions. However, older adults also show somewhat of a shift towards favoring positive over negative information in memory, leading to a positivity effect.

Emotional memory and sleep

Emotional memory and sleep has been a well-researched association. Emotional memories are consolidated greater during sleep, rather than neutral memories. Studies have investigated high valence and arousing words, in comparison to neutral words. Sleep enhances the consolidation of the high valence and arousing words and therefore these are remembered more post-sleep. This concept has been demonstrated in many studies using a variety of media such as pictures, film clips, and words.

Memories of 'future relevance' are also consolidated greater during sleep. In a study by Wilhelm et al., 2011, memories of items that participants knew were needed for the future (for the testing session) were remembered more after sleep. Sleep consolidated these memories of future relevance to a greater extent. Memories that are emotionally significant and relevant for the future are therefore preferentially consolidated during sleep. This can translate to mean that memories that are more meaningful or valuable to a person are consolidated more.

The concept of emotional memory and sleep can be applied to real-life situations e.g. by developing more effective learning strategies. One could integrate the memorization of information that possesses high emotional significance (highly salient) with information that holds little emotional significance (low salience), prior to a period of sleep.