Chapter 12 endnote 47, from Lisa Feldman Barrett.
Some context is:
When you put them into a small box with tones and shocks arriving together at unpredictable times, rats indeed freeze, but in a larger enclosure, rats run away, unless they’re cornered, in which case they attack.
When a rat is faced with another member of its species (called a "conspecific"), and that conspecific is aggressive, the rat will attack. Rats will also attack a threat (like a predator) from which it can't escape. Rats perform defensive treading" which means pushing or throwing dirt forcefully in the direction of the threat. In the wild, rats will defensively tread when faced with a known threat (e.g., a rattlesnake) from which they can't escape. In the lab, rats defensively tread when faced with a shock prod (they kick up their bedding in the direction of the threat.
When faced with an ambiguous threat, animals sometimes freeze, but they can also be vigilant and explore their surroundings (i.e., careful scanning of environment from a crouched position (vigilance) and attempts to approach the threatening stimulus by stretching the body, digging, or rearing up). Exploration is observed even when an animal is expected to freeze. It seems like animals freeze when faced with ambiguous threats that are not moving (e.g., a foot shock), but they explore when the threat is ambiguous and moving (e.g., a predator).
Whether an animal freezes or explores depends which part of the central nucleus is active in the amygdala. The central nucleus is responsible for regulating systems in the body. A lesion to the amygdala does not disrupt defensive treading.
It is tempting to assume that there are different fear circuits for different types of fear, but a less essentialist hypothesis is that an animal has a number of different actions (i.e., a population) it can perform when faced with a threat, and different actions are optimal in different contexts.
Notes on the Notes
- Fanselow, Michael S. 1994. "Neural organization of the defensive behavior system responsible for fear." Psychonomic Bulletin & Review 1 (4): 429-438.
- Fanselow & Lester, 1998.
- Reynolds, Sheila M., and Kent C. Berridge. 2002. "Positive and negative motivation in nucleus accumbens shell: bivalent rostrocaudal gradients for GABA-elicited eating, taste “liking”/“disliking” reactions, place preference/avoidance, and fear." Journal of Neuroscience 22 (16): 7308-7320.
- Reynolds, Sheila M., and Kent C. Berridge. 2003. "Glutamate motivational ensembles in nucleus accumbens: rostrocaudal shell gradients of fear and feeding." European Journal of Neuroscience 17 (10): 2187-2200.
- Reynolds, Sheila M., and Kent C. Berridge. 2008. "Emotional environments retune the valence of appetitive versus fearful functions in nucleus accumbens." Nature neuroscience 11 (4): 423-425.
- Gozzi, Alessandro, Apar Jain, Aldo Giovanelli, Cristina Bertollini, Valerio Crestan, Adam J. Schwarz, Theodoros Tsetsenis, Davide Ragozzino, Cornelius T. Gross, and Angelo Bifone. 2010. "A neural switch for active and passive fear." Neuron 67 (4): 656-666.
- Gross, Cornelius T., and Newton Sabino Canteras. 2012. "The many paths to fear." Nature Reviews Neuroscience 13 (9): p. 653.
- Kopchia, Karen L., Harvey J. Altman, and Randall L. Commissaris. 1992. "Effects of lesions of the central nucleus of the amygdala on anxiety-like behaviors in the rat." Pharmacology Biochemistry and Behavior 43 (2): 453-461.