User:Mmartins3/sandbox

Note: Empty subsections are meant to have the same text as the original page; I just reorganized them. The text shown here is what I added/edited.

= Extinction (Psychology) = Extinction is a form of inhibitory learning that is manifest as a decrease in a previously conditioned response. The conditioned response can be to an appetitive (i.e., reinforcing) or aversive (i.e., unpleasant) event. This form of learning enables animals to readily adapt to changing environments. That is, animals learn whether expressing a conditioned response is appropriate or not based on environmental cues. A failure to extinguish a conditioned response can lead to maladaptive behaviors that are expressed inappropriately. For instance, fear and drug seeking are conditioned responses that if not properly extinguished can manifest as anxiety disorders and addiction, respectively.

Learning Paradigms
Extinction can be observed in both classically- and operantly-conditioned responses.

Classical Conditioning
Classical conditioning is a form of learning in which a neutral stimulus is paired with an unconditioned stimulus that naturally elicits a response in animals. After repeated pairings, the neutral stimulus becomes a conditioned stimulus such that it now triggers a conditioned response on its own. For example, in a fear conditioning paradigm, a tone that is consistently paired with a mild footshock can become a conditioned stimulus that elicits a fear response, even when presented on its own.

Extinction occurs when the animal is repeatedly re-exposed to the conditioned stimulus in the absence of the unconditioned stimulus. As the animal learns that the conditioned stimulus no longer predicts the coming of the unconditioned stimulus, conditioned responding gradually decreases, or extinguishes. Following from the previous example, after multiple presentations of the tone without a footshock, animals will no longer elicit a fear response when presented with the tone on its own.

Infralimbic Cortex
The infralimbic cortex (IL) plays a central role in extinction such that activity in this region has been found to suppress the return of classically- or operantly-conditioned responses after extinction in both the appetitive and aversive domains. The IL is important for the extinction of reward- and fear-associated responses in part through its neuronal projections to the nucleus accumbens shell (NAcS) and basolateral amygdala (BLA), respectively.

The IL contains glutamatergic neurons that innervate the NAcS. When activated after extinction training, this neural circuit has been found to suppress the return of appetitive responses. When inactivated following extinction, it was found that an increase in appetitive responding occurs. These findings suggest that the IL-to-NAcS neural circuit is important for the retrieval of extinction learning.