Extinction (psychology)

Extinction (psychology)
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Name	Extinction
Field	Behavioral psychology, Learning theory
Related	Classical conditioning, Operant conditioning, Fear conditioning, Exposure therapy

Extinction (psychology). In behavioral psychology, extinction is the gradual weakening and eventual disappearance of a conditioned response. This occurs when a previously reinforced behavior is no longer followed by a reinforcing consequence, or when a conditioned stimulus is repeatedly presented without its associated unconditioned stimulus. The process is a fundamental component of learning theory and is central to therapeutic interventions for disorders like phobias and post-traumatic stress disorder.

Definition and theoretical basis

Extinction is formally defined as the reduction in the strength or frequency of a learned behavior when the reinforcement maintaining that behavior is discontinued. The concept originated from the work of Ivan Pavlov, who observed that dogs stopped salivating to a tone when it was no longer paired with food. This principle was later expanded within B.F. Skinner's framework of operant conditioning, where behaviors diminish when expected rewards or punishments are withheld. Theoretical accounts include the "memory interference" model, which posits that extinction involves new learning that competes with the original association, rather than erasing it. This view is supported by phenomena like spontaneous recovery, where the extinguished response reappears after a delay. The theoretical basis is further elaborated in the work of researchers like R. A. Rescorla and Allan R. Wagner, whose Rescorla-Wagner model provides a mathematical account of associative learning and extinction.

Procedures and paradigms

Experimental procedures for studying extinction vary by conditioning type. In fear conditioning paradigms, common in studies with Sprague Dawley rats, a tone (conditioned stimulus) paired with a footshock (unconditioned stimulus) elicits a freezing response; extinction involves repeated tone presentations alone. In operant conditioning, paradigms like the Skinner box are used, where a lever press (operant response) that previously delivered a food pellet (reinforcer) is no longer reinforced. Other key paradigms include appetitive conditioning, where a cue predicting a reward is presented without the reward, and instrumental learning tasks. The partial reinforcement extinction effect (PREE) is a well-studied phenomenon where behaviors reinforced on an intermittent schedule are more resistant to extinction than those reinforced continuously. Research at institutions like the University of California, Los Angeles and Yale University has utilized these procedures to delineate extinction processes.

Factors influencing extinction

Multiple factors modulate the rate and persistence of extinction. The strength of the original conditioning, influenced by parameters like US intensity and number of training trials, affects resistance to extinction. The context in which extinction occurs is critical, as explained by contextual renewal theories; a response extinguished in one environment may return if the subject is tested in the original conditioning context or a novel one. Individual differences, such as genetic predispositions studied in strains like C57BL/6 mice, or trait anxiety levels, also play a role. Pharmacological agents, particularly NMDA receptor agonists like D-cycloserine, have been shown to facilitate extinction learning when administered in conjunction with extinction training. The history of reinforcement, encapsulated in the PREE, and the passage of time, leading to spontaneous recovery, are other key modulating factors.

Neural mechanisms

The neural circuitry of extinction has been extensively mapped, primarily through studies of fear extinction in rodents. The ventromedial prefrontal cortex (vmPFC) and its rodent homolog, the infralimbic cortex, are crucial for the consolidation and retrieval of extinction memory. These regions inhibit output from the amygdala, a central structure for fear expression. The hippocampus is involved in contextual modulation of extinction, mediating renewal effects. Neurotransmitter systems are deeply implicated; glutamate activity at NMDA receptors in the amygdala and vmPFC is necessary for extinction learning, a finding leveraged by D-cycloserine research. Other key structures include the dorsal anterior cingulate cortex and the nucleus accumbens. Pioneering work by scientists like Joseph E. LeDoux and Michael Davis has been instrumental in elucidating this circuitry, with implications for understanding disorders treated at clinics like the Anxiety Disorders Center at the Institute of Living.

Clinical applications

Extinction principles form the bedrock of several evidence-based psychotherapies. Exposure therapy, a core component of treatments for anxiety disorders, specific phobias, obsessive-compulsive disorder, and post-traumatic stress disorder, is a direct clinical application of extinction. Therapies like Prolonged Exposure developed by Edna B. Foa, and Cognitive Behavioral Therapy (CBT), systematically expose patients to feared stimuli in a safe context without the feared outcome, promoting new inhibitory learning. The adjunctive use of D-cycloserine to enhance extinction learning has been investigated in clinical trials at centers like the Emory University School of Medicine. Furthermore, interventions for substance use disorders, such as cue exposure therapy, aim to extinguish conditioned responses to drug-associated cues. These applications are guided by translational research bridging laboratory findings with clinical practice at institutions like the National Institute of Mental Health.

Related phenomena and distinctions

Extinction is distinct from several related concepts. Forgetting is a passive decay of memory over time, whereas extinction is an active learning process. Habituation is a reduction in response to a repeated, non-threatening stimulus, not involving the breaking of a learned association. Key phenomena related to extinction include spontaneous recovery (the return of an extinguished response after a delay), renewal (the return of a response when the context changes), reinstatement (the return after an unsignaled presentation of the unconditioned stimulus), and rapid reacquisition (the quick relearning of a conditioned response after extinction). These phenomena, studied by researchers like Mark Bouton, demonstrate that the original association remains intact and can be expressed under certain conditions, highlighting that extinction creates a competing memory trace rather than erasure.

Category:Behavioral concepts Category:Learning