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, 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 neurons 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.
Read more about this topic: Extinction (psychology)
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