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Fear is an intensely unpleasant emotion in response to perceiving or recognizing a danger or threat. Fear causes physiological changes that may produce behavioral reactions such as mounting an aggressive response or fleeing the threat. Fear in human beings may occur in response to a certain stimulus occurring in the present, or in anticipation or expectation of a future threat perceived as a risk to oneself. The fear response arises from the perception of danger leading to confrontation with or escape from/avoiding the threat, which in extreme cases of fear can be a freeze response or paralysis.
A phobia is a type of anxiety disorder defined by a persistent and excessive fear of an object or situation. Phobias typically result in a rapid onset of fear and are present for more than six months. Those affected will go to great lengths to avoid the situation or object, to a degree greater than the actual danger posed. If the object or situation cannot be avoided, they experience significant distress. Other symptoms can include fainting, which may occur in blood or injury phobia, and panic attacks, which are often found in agoraphobia. Around 75% of those with phobias have multiple phobias.
Operant conditioning is a type of associative learning process through which the strength of a behavior is modified by reinforcement or punishment. It is also a procedure that is used to bring about such learning.
The amygdala is one of two almond-shaped clusters of nuclei located deep and medially within the temporal lobes of the brain's cerebrum in complex vertebrates, including humans. Shown to perform a primary role in the processing of memory, decision making, and emotional responses, the amygdalae are considered part of the limbic system. The term amygdala was first introduced by Karl Friedrich Burdach in 1822.
Classical conditioning is a behavioral procedure in which a biologically potent stimulus is paired with a previously neutral stimulus. It also refers to the learning process that results from this pairing, through which the neutral stimulus comes to elicit a response that is usually similar to the one elicited by the potent stimulus.
In behavioral psychology, reinforcement is a consequence applied that will strengthen an organism's future behavior whenever that behavior is preceded by a specific antecedent stimulus. This strengthening effect may be measured as a higher frequency of behavior, longer duration, greater magnitude, or shorter latency.
Pavlovian fear conditioning is a behavioral paradigm in which organisms learn to predict aversive events. It is a form of learning in which an aversive stimulus is associated with a particular neutral context or neutral stimulus, resulting in the expression of fear responses to the originally neutral stimulus or context. This can be done by pairing the neutral stimulus with an aversive stimulus. Eventually, the neutral stimulus alone can elicit the state of fear. In the vocabulary of classical conditioning, the neutral stimulus or context is the "conditional stimulus" (CS), the aversive stimulus is the "unconditional stimulus" (US), and the fear is the "conditional response" (CR).
Conditioned taste aversion occurs when an animal acquires an aversion to the taste of a certain food after it has been paired with aversive stimuli. The Garcia effect is that the aversion develops more strongly for stimuli that cause nausea than other stimuli. This is considered an adaptive trait or survival mechanism that enables the organism to avoid poisonous substances before they cause harm. The aversion reduces consuming the same substance in the future, thus avoiding poisoning.
Extinction is a behavioral phenomenon observed in both operantly conditioned and classically conditioned behavior, which manifests itself by fading of non-reinforced conditioned response over time. When operant behavior that has been previously reinforced no longer produces reinforcing consequences the behavior gradually stops occurring. In classical conditioning, when a conditioned stimulus is presented alone, so that it no longer predicts the coming of the unconditioned stimulus, conditioned responding gradually stops. For example, after Pavlov's dog was conditioned to salivate at the sound of a metronome, it eventually stopped salivating to the metronome after the metronome had been sounded repeatedly but no food came. Many anxiety disorders such as post traumatic stress disorder are believed to reflect, at least in part, a failure to extinguish conditioned fear.
An avoidance response is a response that prevents an aversive stimulus from occurring. It is a kind of negative reinforcement. An avoidance response is a behavior based on the concept that animals will avoid performing behaviors that result in an aversive outcome. This can involve learning through operant conditioning when it is used as a training technique. It is a reaction to undesirable sensations or feedback that leads to avoiding the behavior that is followed by this unpleasant or fear-inducing stimulus.
The basolateral amygdala, or basolateral complex, consists of the lateral, basal and accessory-basal nuclei of the amygdala. The lateral nuclei receives the majority of sensory information, which arrives directly from the temporal lobe structures, including the hippocampus and primary auditory cortex. The basolateral amygdala also receives dense neuromodulatory inputs from ventral tegmental area (VTA), locus coeruleus (LC), and basal forebrain, whose integrity are important for associative learning. The information is then processed by the basolateral complex and is sent as output to the central nucleus of the amygdala. This is how most emotional arousal is formed in mammals.
Conditioned place preference (CPP) is a form of Pavlovian conditioning used to measure the motivational effects of objects or experiences. By measuring the amount of time an animal spends in an area that has been associated with a stimulus, researchers can infer the animal's liking for the stimulus. This paradigm can also be used to measure conditioned place aversion with an identical procedure involving aversive stimuli instead. Both procedures usually involve mice or rats as subjects. This procedure can be used to measure extinction and reinstatement of the conditioned stimulus. Certain drugs are used in this paradigm to measure their reinforcing properties. Two different methods are used to choose the compartments to be conditioned, and these are biased vs. unbiased. The biased method allows the animal to explore the apparatus, and the compartment they least prefer is the one that the drug is administered in and the one they most prefer is the one where the vehicle is injected. This method allows the animal to choose the compartment they get the drug and vehicle in. In comparison, the unbiased method does not allow the animal to choose what compartment they get the drug and vehicle in and instead the researcher chooses the compartments.
Freezing behavior or the freeze response or to be petrified is a reaction to specific stimuli, most commonly observed in prey animals. When a prey animal has been caught and completely overcome by the predator, it may respond by "freezing up/petrification" or in other words by uncontrollably becoming rigid. Studies typically assess a conditioned freezing behavior response to stimuli that typically or innately do not cause fear, such as a tone or shock. Freezing behavior is most easily characterized by changes in blood pressure and lengths of time in crouching position, but it also is known to cause changes such as shortness of breath, increased heart rate, sweating, or choking sensation. However, since it is difficult to measure these sympathetic responses to fear stimuli, studies are typically confined to simple crouching times. A response to stimuli typically is said to be a "fight or flight", but is more completely described as "fight, flight, or freeze." In addition, freezing is observed to occur before or after a fight or flight response.
The term conditioned emotional response (CER) can refer to a specific learned behavior or a procedure commonly used in classical or Pavlovian conditioning research. It may also be called "conditioned suppression" or "conditioned fear response (CFR)." It is an "emotional response" that results from classical conditioning, usually from the association of a relatively neutral stimulus with a painful or fear-inducing unconditional stimulus. As a result, the formerly neutral stimulus elicits fear. For example, if seeing a dog is paired with the pain of being bitten by the dog, seeing a dog may become a conditioned stimulus that elicits fear.
Many experiments have been done to find out how the brain interprets stimuli and how animals develop fear responses. The emotion, fear, has been hard-wired into almost every individual, due to its vital role in the survival of the individual. Researchers have found that fear is established unconsciously and that the amygdala is involved with fear conditioning.
Animals have many different tactics for defending themselves, depending on the severity of the threat they are encountering. Stages of threat vary along a spectrum referred to as the "predatory imminence continuum", spanning from low-risk (pre-encounter) to high-risk (interaction) threats. The main assumption of the predatory imminence continuum is that as threat levels increase, defensive response strategies change. During the pre-encounter period, an animal may engage in activities like exploration or foraging. But if the animal senses that a predator is nearby, the animal may begin to express species specific defense reactions such as freezing in an attempt to avoid detection by the predator. However, in situations where a threat is imminent, once the animal is detected by its predator, freezing may no longer be the optimal behaviour for survival. At this point, the animal enters the circa-strike phase, where its behaviour will transition from passive freezing to active flight, or even attack if escape is not possible.
Daniela Schiller is a neuroscientist who leads the Affective Neuroscience Lab at the Mount Sinai School of Medicine. She is best known for her work on memory reconsolidation, and on modification of emotional learning and memory.
Stephen Andrew Maren is an American behavioral neuroscientist investigating the brain mechanisms of emotional memory, particularly the role context plays in the behavioral expression of fear. He has discovered brain circuits regulating context-dependent memory, including mapping functional connections between the hippocampus, prefrontal cortex, and amygdala that are involved in the expression and extinction of learned fear responses.
Pavlovian-instrumental transfer (PIT) is a psychological phenomenon that occurs when a conditioned stimulus that has been associated with rewarding or aversive stimuli via classical conditioning alters motivational salience and operant behavior. Two distinct forms of Pavlovian-instrumental transfer have been identified in humans and other animals – specific PIT and general PIT – with unique neural substrates mediating each type. In relation to rewarding stimuli, specific PIT occurs when a CS is associated with a specific rewarding stimulus through classical conditioning and subsequent exposure to the CS enhances an operant response that is directed toward the same reward with which it was paired. General PIT occurs when a CS is paired with one reward and it enhances an operant response that is directed toward a different rewarding stimulus.
Catherine Hartley is an American psychologist and an Associate Professor of Psychology within the Department of Psychology and Center for Neural Science at New York University in New York City. Hartley's research explores how brain development impacts the evaluation of negative experiences, decision-making, and motivated behavior. Her work has helped to elucidate how uncontrollable aversive events affect fear learning and how learning to control aversive stimuli can improve emotional resilience.
References
- 1 2 LeDoux, J. E.; Moscarello, J.; Sears, R.; Campese, V. (January 2017). "The birth, death and resurrection of avoidance: a reconceptualization of a troubled paradigm". Molecular Psychiatry. 22 (1): 24–36. doi:10.1038/mp.2016.166. ISSN 1476-5578. PMC 5173426 . PMID 27752080.
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- 1 2 Lázaro-Muñoz, Gabriel; LeDoux, Joseph E.; Cain, Christopher K. (2010-06-15). "Sidman Instrumental Avoidance Initially Depends on Lateral and Basal Amygdala and is Constrained by Central Amygdala-mediated Pavlovian Processes". Biological Psychiatry. 67 (12): 1120–1127. doi:10.1016/j.biopsych.2009.12.002. ISSN 0006-3223. PMC 3085029 . PMID 20110085.
- 1 2 Campese, Vincent D.; Soroeta, Jose M.; Vazey, Elena M.; Aston-Jones, Gary; LeDoux, Joseph E.; Sears, Robert M. (2017-10-24). "Noradrenergic Regulation of Central Amygdala in Aversive Pavlovian-to-Instrumental Transfer". eNeuro. 4 (5): ENEURO.0224–17.2017. doi:10.1523/ENEURO.0224-17.2017. ISSN 2373-2822. PMC 5654237 . PMID 29071299.
- ↑ Campese, Vincent; McCue, Margaret; Lázaro-Muñoz, Gabriel; Ledoux, Joseph E.; Cain, Christopher K. (2013). "Development of an aversive Pavlovian-to-instrumental transfer task in rat". Frontiers in Behavioral Neuroscience. 7: 176. doi: 10.3389/fnbeh.2013.00176 . ISSN 1662-5153. PMC 3840425 . PMID 24324417.
- ↑ LeDoux, JE; Iwata, J; Cicchetti, P; Reis, DJ (1988-07-01). "Different projections of the central amygdaloid nucleus mediate autonomic and behavioral correlates of conditioned fear". The Journal of Neuroscience. 8 (7): 2517–2529. doi:10.1523/JNEUROSCI.08-07-02517.1988. ISSN 0270-6474. PMC 6569498 . PMID 2854842.
- ↑ Bukalo, Olena; Pinard, Courtney R.; Silverstein, Shana; Brehm, Christina; Hartley, Nolan D.; Whittle, Nigel; Colacicco, Giovanni; Busch, Erica; Patel, Sachin; Singewald, Nicolas; Holmes, Andrew (2015-07-01). "Prefrontal inputs to the amygdala instruct fear extinction memory formation". Science Advances. 1 (6): e1500251. Bibcode:2015SciA....1E0251B. doi:10.1126/sciadv.1500251. ISSN 2375-2548. PMC 4618669 . PMID 26504902.