Extinction (psychology)
Encyclopedia
Extinction is the conditioning
phenomenon in which a previously learned response to a cue is reduced when the cue is presented in the absence of the previously paired aversive or appetitive stimulus.
The simplest explanation of extinction is that as the CS is presented without the aversive US, the animal gradually "unlearns" the CS–US association which is known as the associative loss theory. However, this explanation is complicated by observations where there is some fear restoration, such as reinstatement (restoration of CR in the context where extinction training occurred but not a different context after aversive US is presented again), renewal (restoration of CR in context A but not in B when learning occurred in context A and extinction in context B), and spontaneous recovery
(restoration of CR when the retention test occurs after a long but not a short delay after extinction training) and alternative explanations have been offered.
Research on fear extinction in animal models (typically rats) has clinical implications such as exposure-based therapies
for the treatment of phobias and anxiety conditions.
Given the competing views and difficult observations for the various accounts researchers have turned to investigations at the cellular level (most often in rodents) to tease apart the specific brain mechanisms of extinction, in particular the role of the brain structures (amygdala, hippocampus, the prefontal cortex), and specific neurotransmitter systems (e.g., GABA
, NMDA
). A recent study in rodents by Amano, Unal and Paré published in Nature Neuroscience found that extinction is correlated with synaptic inhibition
in the fear
output neuron
s of the central amygdala
that project to the periaqueductal gray
that controls freezing behavior
. They infer that inhibition derives from the prefrontal cortex
and suggest promising targets at the cellular level for new treatments of anxiety.
paradigm, extinction refers to the decline of an operant response when it is no longer reinforced in the presence of its discriminative stimulus. Extinction is observed after withholding of reinforcement
for a previously reinforced behavior which decreases the future probability of that behavior. For example, a child who climbs under his desk, a response which has been reinforced by attention
, is subsequently ignored until the attention-seeking behavior no longer occurs. In his autobiography, B.F. Skinner noted how he accidentally discovered the extinction of an operant response due to the malfunction of his laboratory equipment:
When the extinction of a response has occurred, the discriminative stimulus is then known as an extinction stimulus (SΔ or S-delta). When an S-delta is present, the reinforcing consequence which characteristically follows a behavior does not occur. This is the opposite of a discriminative stimulus which is a signal that reinforcement will occur. For instance, in an operant chamber, if food pellets are only delivered when a response is emitted in the presence of a green light, the green light is a discriminative stimulus. If when a red light is present food will not be delivered, then the red light is an extinction stimulus (food here is used as an example of a reinforcer).
.
Take, as an example, a pigeon that has been reinforced to peck an electronic button. During its training history, every time the pigeon pecked the button, it will have received a small amount of bird seed as a reinforcer. So, whenever the bird is hungry, it will peck the button to receive food. However, if the button were to be turned off, the hungry pigeon will first try pecking the button just as it has in the past. When no food is forthcoming, the bird will likely try again ... and again, and again. After a period of frantic activity, in which their pecking behavior yields no result, the pigeon's pecking will decrease in frequency.
Although not explained by reinforcement theory, the extinction burst can be understood using control theory. In perceptual control theory, the degree of output involved in any action is proportional to the discrepancy between the reference value (desired rate of reward in the operant paradigm) and the current input. Thus, when reward is removed, the discrepancy increases, and the output is increased. In the long term, 'reorganisation', the learning algorithm of control theory, would adapt the control system such that output is reduced.
The evolutionary advantage of this extinction burst is clear. In a natural environment, an animal that persists in a learned behavior, despite not resulting in immediate reinforcement, might still have a chance of producing reinforcing consequences if they try again. This animal would be at an advantage over another animal that gives up too easily.
Despite the name, however, not every explosive reaction to adverse stimuli subsides to extinction. Indeed a small minority of individuals persist in their reaction indefinitely.
(DCS) is being trialed as an adjuvant
to conventional exposure-based treatments for anxiety disorders. The psychotropic responses are related to D-Cycloserine's action as a partial agonist
of the neuronal NMDA receptor
for glutamate and have been examined in implications with sensory-related fear extinction in the amygdala
.
Classical conditioning
Classical conditioning is a form of conditioning that was first demonstrated by Ivan Pavlov...
phenomenon in which a previously learned response to a cue is reduced when the cue is presented in the absence of the previously paired aversive or appetitive stimulus.
Fear conditioning
Extinction is typically studied within the Pavlovian fear conditioning framework in which extinction refers to the reduction in a conditioned response (CR; e.g., fear response/freezing) when a conditioned stimulus (CS; e.g., neutral stimulus/light or tone) is repeatedly presented in the absence of the unconditioned stimulus (US; e.g., foot shock/loud noise) with which it has been previously paired.The simplest explanation of extinction is that as the CS is presented without the aversive US, the animal gradually "unlearns" the CS–US association which is known as the associative loss theory. However, this explanation is complicated by observations where there is some fear restoration, such as reinstatement (restoration of CR in the context where extinction training occurred but not a different context after aversive US is presented again), renewal (restoration of CR in context A but not in B when learning occurred in context A and extinction in context B), and spontaneous recovery
Spontaneous recovery
Spontaneous recovery is a phenomenon first seen in Pavlovian conditioning and then later discovered in memory functioning. The general pattern of spontaneous recovery found in Pavlovian conditioning in animals essentially encompasses two varying habits learned by the animal where there is an...
(restoration of CR when the retention test occurs after a long but not a short delay after extinction training) and alternative explanations have been offered.
Research on fear extinction in animal models (typically rats) has clinical implications such as exposure-based therapies
Exposure therapy
Exposure therapy is a technique in behavior therapy intended to treat anxiety disorders and involves the exposure to the feared object or context without any danger in order to overcome their anxiety. Procedurally it is similar to the fear extinction paradigm in rodent work...
for the treatment of phobias and anxiety conditions.
Theories
The dominant account of extinction involves associative models. However, there is debate over whether extinction involves simply "unlearning" the US–CS association (e.g., the Rescorla–Wagner account) or, alternatively, a "new learning" of an inhibitory association that masks the original excitatory association (e.g., Konorski, Pearce and Hall account). A third account concerns non-associative mechanisms such as habituation, modulation and response fatigue. Myers and Davis laboratory work with fear extinction in rodents has suggested that multiple mechanisms may be at work depending on the timing and circumstances in which the extinction occurs.Given the competing views and difficult observations for the various accounts researchers have turned to investigations at the cellular level (most often in rodents) to tease apart the specific brain mechanisms of extinction, in particular the role of the brain structures (amygdala, hippocampus, the prefontal cortex), and specific neurotransmitter systems (e.g., GABA
Gabâ
Gabâ or gabaa, for the people in many parts of the Philippines), is the concept of a non-human and non-divine, imminent retribution. A sort of negative karma, it is generally seen as an evil effect on a person because of their wrongdoings or transgressions...
, NMDA
NMDA
N-Methyl-D-aspartic acid or N-Methyl-D-aspartate is an amino acid derivative which acts as a specific agonist at the NMDA receptor mimicking the action of glutamate, the neurotransmitter which normally acts at that receptor...
). A recent study in rodents by Amano, Unal and Paré published in Nature Neuroscience found that extinction is correlated with synaptic inhibition
Inhibitory postsynaptic potential
An inhibitory postsynaptic potential is a synaptic potential that decreases the chance that a future action potential will occur in a postsynaptic neuron or α-motoneuron...
in the fear
Fear
Fear is a distressing negative sensation induced by a perceived threat. It is a basic survival mechanism occurring in response to a specific stimulus, such as pain or the threat of danger...
output neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s of the central amygdala
Amygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
that project to the periaqueductal gray
Periaqueductal gray
Periaqueductal gray is the gray matter located around the cerebral aqueduct within the tegmentum of the midbrain. It plays a role in the descending modulation of pain and in defensive behaviour...
that controls freezing behavior
Freezing behavior
Freezing behavior is the fearful reaction to specific stimuli, most commonly observed by animals. It is caused by the sympathetic nervous system to deal with threats. Studies typically assess a conditioned freezing behavior response to stimuli that typically or innately do not cause fear, such as a...
. They infer that inhibition derives from the prefrontal cortex
Prefrontal cortex
The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas.This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior...
and suggest promising targets at the cellular level for new treatments of anxiety.
Operant conditioning
In the operant conditioningOperant conditioning
Operant conditioning is a form of psychological learning during which an individual modifies the occurrence and form of its own behavior due to the association of the behavior with a stimulus...
paradigm, extinction refers to the decline of an operant response when it is no longer reinforced in the presence of its discriminative stimulus. Extinction is observed after withholding of reinforcement
Reinforcement
Reinforcement is a term in operant conditioning and behavior analysis for the process of increasing the rate or probability of a behavior in the form of a "response" by the delivery or emergence of a stimulus Reinforcement is a term in operant conditioning and behavior analysis for the process of...
for a previously reinforced behavior which decreases the future probability of that behavior. For example, a child who climbs under his desk, a response which has been reinforced by attention
Attention
Attention is the cognitive process of paying attention to one aspect of the environment while ignoring others. Attention is one of the most intensely studied topics within psychology and cognitive neuroscience....
, is subsequently ignored until the attention-seeking behavior no longer occurs. In his autobiography, B.F. Skinner noted how he accidentally discovered the extinction of an operant response due to the malfunction of his laboratory equipment:
When the extinction of a response has occurred, the discriminative stimulus is then known as an extinction stimulus (SΔ or S-delta). When an S-delta is present, the reinforcing consequence which characteristically follows a behavior does not occur. This is the opposite of a discriminative stimulus which is a signal that reinforcement will occur. For instance, in an operant chamber, if food pellets are only delivered when a response is emitted in the presence of a green light, the green light is a discriminative stimulus. If when a red light is present food will not be delivered, then the red light is an extinction stimulus (food here is used as an example of a reinforcer).
Successful extinction procedures
In order for extinction to work effectively, it must be done consistently. Extinction is considered successful when responding in the presence of an extinction stimulus (a red light or a teacher not giving a bad student attention, for instance) is zero. When a behavior reappears again after it has gone through extinction, it is called resurgenceSpontaneous recovery
Spontaneous recovery is a phenomenon first seen in Pavlovian conditioning and then later discovered in memory functioning. The general pattern of spontaneous recovery found in Pavlovian conditioning in animals essentially encompasses two varying habits learned by the animal where there is an...
.
Extinction burst
While extinction, when implemented consistently over time, results in the eventual decrease of the undesired behavior, in the short-term the subject might exhibit what is called an extinction burst. An extinction burst will often occur when the extinction procedure has just begun. This consists of a sudden and temporary increase in the response's frequency, followed by the eventual decline and extinction of the behavior targeted for elimination.Take, as an example, a pigeon that has been reinforced to peck an electronic button. During its training history, every time the pigeon pecked the button, it will have received a small amount of bird seed as a reinforcer. So, whenever the bird is hungry, it will peck the button to receive food. However, if the button were to be turned off, the hungry pigeon will first try pecking the button just as it has in the past. When no food is forthcoming, the bird will likely try again ... and again, and again. After a period of frantic activity, in which their pecking behavior yields no result, the pigeon's pecking will decrease in frequency.
Although not explained by reinforcement theory, the extinction burst can be understood using control theory. In perceptual control theory, the degree of output involved in any action is proportional to the discrepancy between the reference value (desired rate of reward in the operant paradigm) and the current input. Thus, when reward is removed, the discrepancy increases, and the output is increased. In the long term, 'reorganisation', the learning algorithm of control theory, would adapt the control system such that output is reduced.
The evolutionary advantage of this extinction burst is clear. In a natural environment, an animal that persists in a learned behavior, despite not resulting in immediate reinforcement, might still have a chance of producing reinforcing consequences if they try again. This animal would be at an advantage over another animal that gives up too easily.
Despite the name, however, not every explosive reaction to adverse stimuli subsides to extinction. Indeed a small minority of individuals persist in their reaction indefinitely.
Extinction-induced variability
Extinction-induced variability serves an adaptive role similar to the extinction burst. When extinction begins, subjects can exhibit variations in response topography (the movements involved in the response). Response topography is always somewhat variable due to differences in environment or idiosyncratic causes but normally a subject's history of reinforcement keeps slight variations stable by maintaining successful variations over less successful variations. Extinction can increase these variations significantly as the subject attempts to acquire the reinforcement that previous behaviors produced. If a person attempts to open a door by turning the knob, but is unsuccessful, they may next try jiggling the knob, pushing on the frame, knocking on the door or other behaviors to get the door to open. Extinction-induced variability can be used in shaping to reduce problematic behaviors by reinforcing desirable behaviors produced by extinction-induced variability.D-Cycloserine
D-CycloserineCycloserine
Cycloserine is an antibiotic effective against Mycobacterium tuberculosis. For the treatment of tuberculosis, it is classified as a second line drug, i.e...
(DCS) is being trialed as an adjuvant
Adjuvant
An adjuvant is a pharmacological or immunological agent that modifies the effect of other agents, such as a drug or vaccine, while having few if any direct effects when given by itself...
to conventional exposure-based treatments for anxiety disorders. The psychotropic responses are related to D-Cycloserine's action as a partial agonist
Agonist
An agonist is a chemical that binds to a receptor of a cell and triggers a response by that cell. Agonists often mimic the action of a naturally occurring substance...
of the neuronal NMDA receptor
NMDA receptor
The NMDA receptor , a glutamate receptor, is the predominant molecular device for controlling synaptic plasticity and memory function....
for glutamate and have been examined in implications with sensory-related fear extinction in the amygdala
Amygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
.