39 Studying Fear

Scientists have long realized there are at least two distinct types of fear:

  • Innate fear in which subjects avoid certain stimuli such as snakes or spiders even though they may never have seen them before
  • Learned fear in which a stimulus or situation causes arousal or anxiety because it has been associated with a painful or negative experience in the past

There are two important protocols used to examine learned fear: fear conditioning and conditioned defeat.

Fear Conditioning

One of the best studied laboratory models of fear comes from the work of John LeDoux who studied the brain circuit that mediates learned or conditioned fear in laboratory rats. In these studies, LeDoux used a classical conditioning procedure to induce what he called “conditioned fear”. In classical conditioning (think Pavlov’s dogs), a neutral stimulus that normally would not cause any physiological response (called a conditioned stimulus, e.g., a ringing bell) is paired with a meaningful stimulus (called an unconditioned stimulus, e.g., the presence of food) that elicits a behavioral response (unconditioned response, e.g., drooling). Eventually, the behavior (drooling) occurs in response to the conditioned stimulus (bell) alone.

Instead of pairing the conditioned stimulus with a positive unconditioned stimulus like food, LeDoux paired the conditioned stimulus with an electrical shock. After pairing the shock to the stimulus multiple times, the animals responded to the conditioned stimulus alone (no shock) in the same way they did to the electrical shock alone. This is referred to as the conditioned emotional response.

Illustration of the fear conditioning paradigm. Details in text and caption.
Figure 39.1 Fear conditioning. Left panel: Prior to conditioning, the conditioned stimulus (an auditory tone) has no effect on behavior. The unconditioned stimulus (shock) leads to startle-like behaviors that researchers refer to as “freezing”. Middle panel: During fear conditioning, the tone is paired with the shock and freezing behavior is seen. Right panel: After successful fear conditioning, the tone alone can elicit freezing behavior. ‘Fear Conditioning’ by Casey Henley is licensed under a Creative Commons Attribution Non-Commercial Share-Alike (CC BY-NC-SA) 4.0 International License.

Conditioned Defeat

In this model the experimental subject (the animal whose behavior is being examined) is placed in the home cage of a larger, resident animal. This typically results in aggressive behaviors displayed by the resident animal toward the experimental subject. The resident animal will usually win the encounter because it is larger and in its own territory. The experimental animals will show submissive and defensive posturing and does not attack or threaten its opponent.

Experiencing this defeat has major long-lasting effects on the experimental subject. Following defeat, the animal rarely shows aggression even to non-aggressive hamsters placed in the subject’s home cage (an intruder would typically cause aggression). Because this paradigm has parallels with the earlier fear conditioning studies that paired an acoustical tone with electrical shock to the feet, it is often referred to as “conditioned defeat;” the experimental subject has been conditioned to respond to all other hamsters with submissive defensive postures.

Illustration of the conditioned defeat paradigm. Details in text and caption.
Figure 39.2. Conditioned defeat. Left panel: Prior to defeat, the experimental subject and resident animal are kept separate, and behavior is normal. Middle panel: During the conditioned defeat trial, the experimental animal is placed into the home cage of the larger, resident animal. The resident will defend its territory, acting aggressively toward the smaller, experimental animal. The experimental animal will show submissive and defensive behaviors. Right panel: After defeat, the experimental animal will show submissive behaviors even toward non-aggressive animals placed into the experimental animal’s home cage. ‘Conditioned Defeat’ by Casey Henley is licensed under a Creative Commons Attribution Non-Commercial Share-Alike (CC BY-NC-SA) 4.0 International License.

Key Takeaways

  • Learned fear can be studied using either fear conditioning or conditioned defeat tests
  • Fear conditioning pairs a neutral stimulus, like a light or a tone, to a harmful stimulus, like a shock
  • Conditioned defeat submits an experimental animal to aggressive behaviors from another animal, after which the experimental animal will continuously show submissive behaviors to others



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Foundations of Neuroscience Copyright © 2021 by Casey Henley is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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