fearconditioned

Fear conditioning, sometimes described as fear-conditioned learning, is a form of associative learning in which a previously neutral stimulus (the conditioned stimulus, CS) is paired with an aversive unconditioned stimulus (US), such as a mild electric shock or loud noise. After repeated pairings, the CS elicits a conditioned fear response (CR) similar to the response originally produced by the US.

Acquisition involves CS+ paired with US, CS− presented without the US; CR increases to CS+ and is minimal to CS−. During extinction, the CS+ is presented without the US, and the CR diminishes over repeated exposures. Common dependent measures include autonomic responses (skin conductance, heart rate), startle reflex modulation, and neural activity observed via imaging or electrophysiology.

Neural circuits central to fear conditioning include the amygdala, especially the lateral and basolateral nuclei, which assign emotional significance to CS; the central nucleus orchestrates fear responses; the hippocampus encodes contextual information; the prefrontal cortex, particularly the infralimbic and prelimbic areas, regulates expression and extinction; other regions such as the bed nucleus of the stria terminalis (BNST) contribute to sustained or contextual fear.

Fear conditioning is a widely used model in neuroscience and psychology to study the mechanisms of fear, anxiety disorders, PTSD, and phobias, and to test pharmacological and behavioral interventions aimed at reducing pathological fear. It also informs understanding of fear generalization, safety learning, and extinction-based therapies.

Limitations include species differences, variability in protocols, and ethical constraints in human studies. While extinction does not erase the original memory, it creates new learning that inhibits fear expression, which can be context- or cue-dependent and subject to relapse.