Reward system
Encyclopedia
In neuroscience
, the reward system is a collection of brain structures which attempts to regulate and control behavior
by inducing pleasurable effects
. The neurological reward system is part of what makes reinforcement
possible.
A psychological reward is a process that reinforces
behavior — something that, when offered, causes a behavior to increase in intensity. Reward is an operational concept for describing the positive value an individual ascribes to an object, behavioral act or an internal physical state. Natural rewards include those that are necessary for the survival of species, such as eating, mating, and fighting.
Secondary rewards derive their value from the primary reward, and include shelter, money
, pleasant touch, beauty, music
, etc. The functions of rewards are based directly on the modification of behavior and indirectly on the sensory properties of rewards. For instance, altruism
may induce a larger psychological reward, although it doesn't cause sensations. Rewards are generally considered more effective than punishment
in enforcing positive behavior.
Rewards induce learning
, approach behavior and feelings of positive emotions.
In a fundamental discovery made in 1954, researchers James Olds
and Peter Milner found that stimulation of certain regions of the brain of the rat acted as a reward in teaching the animals to run mazes and solve problems. The conclusion from such experiments is that low-voltage electrical stimulation in certain parts of the brain gives the animals pleasure. Animals were tested in Skinner boxes where they could stimulate themselves by pressing a lever, the rats would repeatedly press the lever — even up to 2000 times per hour. Research in the next two decades established that dopamine is one of the main chemicals aiding neural signaling in these regions, and dopamine
was suggested to be the brain’s “pleasure chemical.”
and mesocortical
pathway. Of these pathways, the mesolimbic pathway plays the major role, and goes from the ventral tegmental area via the medial forebrain bundle
to nucleus accumbens
, which is the primary release site for the neurotransmitter
dopamine
. Dopamine acts on D1 or D2 receptors to either stimulate (D1) or inhibit (D2) the production of cAMP.
, amphetamine
, ethanol
and cocaine
. After prolonged use, psychological drug tolerance and sensitization arises.
protein, causing a larger dose to be needed to reach the same effect.
is an increase in the user's sensitivity to the effects of the substance, counter to the effects of CREB. A transcription factor, known as delta FosB, is thought to be involved by activating genes that causes sensitization. The hypersensitivity that it causes is thought to be responsible for the intense cravings associated with drug addiction, and is often extended to even the peripheral cues of drug use, such as related behaviors or the sight of drug paraphernalia.
Neuroscience
Neuroscience is the scientific study of the nervous system. Traditionally, neuroscience has been seen as a branch of biology. However, it is currently an interdisciplinary science that collaborates with other fields such as chemistry, computer science, engineering, linguistics, mathematics,...
, the reward system is a collection of brain structures which attempts to regulate and control behavior
Behavior
Behavior or behaviour refers to the actions and mannerisms made by organisms, systems, or artificial entities in conjunction with its environment, which includes the other systems or organisms around as well as the physical environment...
by inducing pleasurable effects
Pleasure
Pleasure describes the broad class of mental states that humans and other animals experience as positive, enjoyable, or worth seeking. It includes more specific mental states such as happiness, entertainment, enjoyment, ecstasy, and euphoria...
. The neurological reward system is part of what makes 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...
possible.
Psychological reward
A psychological reward is a process that reinforces
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...
behavior — something that, when offered, causes a behavior to increase in intensity. Reward is an operational concept for describing the positive value an individual ascribes to an object, behavioral act or an internal physical state. Natural rewards include those that are necessary for the survival of species, such as eating, mating, and fighting.
Secondary rewards derive their value from the primary reward, and include shelter, money
Money
Money is any object or record that is generally accepted as payment for goods and services and repayment of debts in a given country or socio-economic context. The main functions of money are distinguished as: a medium of exchange; a unit of account; a store of value; and, occasionally in the past,...
, pleasant touch, beauty, music
Music
Music is an art form whose medium is sound and silence. Its common elements are pitch , rhythm , dynamics, and the sonic qualities of timbre and texture...
, etc. The functions of rewards are based directly on the modification of behavior and indirectly on the sensory properties of rewards. For instance, altruism
Altruism
Altruism is a concern for the welfare of others. It is a traditional virtue in many cultures, and a core aspect of various religious traditions, though the concept of 'others' toward whom concern should be directed can vary among cultures and religions. Altruism is the opposite of...
may induce a larger psychological reward, although it doesn't cause sensations. Rewards are generally considered more effective than punishment
Punishment
Punishment is the authoritative imposition of something negative or unpleasant on a person or animal in response to behavior deemed wrong by an individual or group....
in enforcing positive behavior.
Rewards induce learning
Learning
Learning is acquiring new or modifying existing knowledge, behaviors, skills, values, or preferences and may involve synthesizing different types of information. The ability to learn is possessed by humans, animals and some machines. Progress over time tends to follow learning curves.Human learning...
, approach behavior and feelings of positive emotions.
History of discovery
James Olds
James Olds was an American psychologist who co-discovered the reward center of the brain with Peter Milner while he was a postdoctoral fellow at McGill University in 1954...
and Peter Milner found that stimulation of certain regions of the brain of the rat acted as a reward in teaching the animals to run mazes and solve problems. The conclusion from such experiments is that low-voltage electrical stimulation in certain parts of the brain gives the animals pleasure. Animals were tested in Skinner boxes where they could stimulate themselves by pressing a lever, the rats would repeatedly press the lever — even up to 2000 times per hour. Research in the next two decades established that dopamine is one of the main chemicals aiding neural signaling in these regions, and dopamine
Dopamine
Dopamine is a catecholamine neurotransmitter present in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this substituted phenethylamine functions as a neurotransmitter, activating the five known types of dopamine receptors—D1, D2, D3, D4, and D5—and their...
was suggested to be the brain’s “pleasure chemical.”
Anatomy
The major neurochemical pathway of the reward system in the brain involves the mesolimbicMesolimbic pathway
The mesolimbic pathway is one of the dopaminergic pathways in the brain. The pathway begins in the ventral tegmental area of the midbrain and connects to the limbic system via the nucleus accumbens, the amygdala, and the hippocampus as well as to the medial prefrontal cortex...
and mesocortical
Mesocortical pathway
The mesocortical pathway is a neural pathway that connects the ventral tegmentum to the cerebral cortex, particularly the frontal lobes. It is one of the four major dopamine pathways in the brain...
pathway. Of these pathways, the mesolimbic pathway plays the major role, and goes from the ventral tegmental area via the medial forebrain bundle
Medial forebrain bundle
The Medial forebrain bundle , is a complex bundle of axons coming from the basal olfactory regions, the periamygdaloid region, and the septal nuclei.-Anatomy:...
to nucleus accumbens
Nucleus accumbens
The nucleus accumbens , also known as the accumbens nucleus or as the nucleus accumbens septi , is a collection of neurons and forms the main part of the ventral striatum...
, which is the primary release site for the neurotransmitter
Neurotransmitter
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...
dopamine
Dopamine
Dopamine is a catecholamine neurotransmitter present in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this substituted phenethylamine functions as a neurotransmitter, activating the five known types of dopamine receptors—D1, D2, D3, D4, and D5—and their...
. Dopamine acts on D1 or D2 receptors to either stimulate (D1) or inhibit (D2) the production of cAMP.
Modulation by drugs
Almost all drugs causing drug addiction increase the dopamine release in the mesolimbic pathway, e.g. opioids, nicotineNicotine
Nicotine is an alkaloid found in the nightshade family of plants that constitutes approximately 0.6–3.0% of the dry weight of tobacco, with biosynthesis taking place in the roots and accumulation occurring in the leaves...
, amphetamine
Amphetamine
Amphetamine or amfetamine is a psychostimulant drug of the phenethylamine class which produces increased wakefulness and focus in association with decreased fatigue and appetite.Brand names of medications that contain, or metabolize into, amphetamine include Adderall, Dexedrine, Dextrostat,...
, ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
and cocaine
Cocaine
Cocaine is a crystalline tropane alkaloid that is obtained from the leaves of the coca plant. The name comes from "coca" in addition to the alkaloid suffix -ine, forming cocaine. It is a stimulant of the central nervous system, an appetite suppressant, and a topical anesthetic...
. After prolonged use, psychological drug tolerance and sensitization arises.
Psychological drug tolerance
The reward system is partly responsible for the psychological part of drug tolerance. One explanation of this is a sustained activation of the CREBCREB
CREB is a cellular transcription factor. It binds to certain DNA sequences called cAMP response elements , thereby increasing or decreasing the transcription of the downstream genes....
protein, causing a larger dose to be needed to reach the same effect.
Sensitization
SensitizationSensitization
Sensitization is an example of non-associative learning in which the progressive amplification of a response follows repeated administrations of a stimulus. An everyday example of this mechanism is the repeated tonic stimulation of peripheral nerves that will occur if a person rubs his arm...
is an increase in the user's sensitivity to the effects of the substance, counter to the effects of CREB. A transcription factor, known as delta FosB, is thought to be involved by activating genes that causes sensitization. The hypersensitivity that it causes is thought to be responsible for the intense cravings associated with drug addiction, and is often extended to even the peripheral cues of drug use, such as related behaviors or the sight of drug paraphernalia.
See also
- Anterior cingulate cortex#Reward based learning theory
- Classical conditioningClassical conditioningClassical conditioning is a form of conditioning that was first demonstrated by Ivan Pavlov...
- Operant conditioningOperant conditioningOperant 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...
- Brain stimulation rewardBrain stimulation rewardBrain stimulation reward is a phenomenon in which direct stimulation of regions of the brain through either electrical or chemical means is rewarding and can serve as an operant reinforcer. The stimulation activates the reward system and establishes response habits similar to those established by...
- Drug addiction#Reward circuit
- Reinforcer
- Decision makingDecision makingDecision making can be regarded as the mental processes resulting in the selection of a course of action among several alternative scenarios. Every decision making process produces a final choice. The output can be an action or an opinion of choice.- Overview :Human performance in decision terms...
- MotivationMotivationMotivation is the driving force by which humans achieve their goals. Motivation is said to be intrinsic or extrinsic. The term is generally used for humans but it can also be used to describe the causes for animal behavior as well. This article refers to human motivation...
- Addiction
- Psychoactive drugPsychoactive drugA psychoactive drug, psychopharmaceutical, or psychotropic is a chemical substance that crosses the blood–brain barrier and acts primarily upon the central nervous system where it affects brain function, resulting in changes in perception, mood, consciousness, cognition, and behavior...
- Ventral tegmentum#Reward system
- Incentive salienceIncentive salienceIncentive salience is a motivational "wanting" attribute given by the brain to reward-predicting stimuli. This "wanting" is unlike "liking" in that liking is a pleasure immediately gained from consumption or other contact with stimuli, while the "wanting" of incentive salience is a motivational...
- Pleasure centerPleasure centerPleasure center is the general term used for the brain regions involved in pleasure. Discoveries made in the 1950s initially suggested that rodents could not stop electrically stimulating parts of their brain, mainly the nucleus accumbens, which was theorized to produce great pleasure...
- Learned industriousnessLearned industriousnessLearned industriousness is a behaviorally rooted theory developed by Robert Eisenberger to explain the differences in general work effort among people of equivalent ability. According to Eisenberger, individuals who are reinforced for exerting high effort on a task are also secondarily reinforced...