Fear conditioning

Fear conditioning is the method by which organisms learn to fear new stimuli. It is a form of learning in which fear is associated with a particular neutral context (e.g., a room) or neutral stimulus (e.g., a tone). This can be done by pairing the neutral stimulus with an aversive stimulus (e.g., a shock, loud noise, or unpleasant odor). Eventually, the neutral stimulus alone can elicit the state of fear. In the vocabulary of classical conditioning, the neutral stimulus or context is the "conditioned stimulus" (CS), the aversive stimulus is the "unconditioned stimulus" (US), and the fear is the "conditioned response" (CR).

Fear conditioning has been studied in numerous species, from snails to humans. In humans, conditioned fear is often measured with verbal report and galvanic skin response. In other animals, conditioned fear is often measured with freezing (a period of watchful immobility) or fear potentiated startle (the augmetation of the startle reflex by a fearful stimulus). Changes in heart rate, breathing, and muscle responses via electromyography can also be used to measure conditioned fear.

Fear conditioning is thought to depend upon an area of the brain called the amygdala. Ablation or deactivating of the amygdala can prevent both the learning and expression of fear. Some types of fear conditioning (e.g. contextual and trace) also involve the hippocampus, an area of the brain believed to receive affective impulses from the amygdala and to integrate those impulses with previously existing information to make it meaningful. Some theoretical accounts of traumatic experiences suggest that amygdala-based fear bypasses the hippocampus during intense stress and can be stored somatically or as images that can return as physical symptoms or flashbacks without cognitive meaning (Bromberg 2003). Fear conditioning is used to study the formation of fear memory and to investigate the processes that may lead to pathological conditions such as dissociation, phobias and post-traumatic stress disorder.

Joseph Ledoux and his research on Fear Conditioning
He finds two amygdala pathways in the brain of laboratory mice, by the use of fear conditioning and lesion study. He names them the "high road" and "low road". The low road is a pathway which is able to transmit a signal from a stimuli to the thalamus, to the amygdala, which then activates a fear-response in the body. This sequence works without a conscious experience of what the stimuli consists of, and it is the fast way to a bodily response. The highroad is activated simultaneously, this is a slower road which also includes the cortical parts of the brain, thus creating a conscious impression of what the stimuli is. The low road only involves the sub-cortical part of the brain. It is therefore regarded as a more primitive mechanism of defense, only existing in its separate form in lesser developed animals who have not developed the more complex part of the brain. In more developed animals the high road and the low road works simultaneously to provide both fear-response and perceptual feedback.(Ledoux, 199)

See also:
 * classical conditioning
 * eyeblink conditioning