Fear or freezing?
Chapter 12 endnote 47, from Lisa Feldman Barrett.
Some context is:
When you put [rats] into a small box with tones and shocks arriving together at unpredictable times, rats indeed freeze, but in a larger enclosure, rats run away....
Lesions to a part of the amygdala that is thought to be crucial for "fear learning" (the basolateral nucleus) do make it difficult for a rat to freeze (even in spontaneous movements). These lesions do not impair other indications of "fear learning" however. For example even with basolateral amygdala lesions, rats still learn to avoid the location of a testing chamber where they were shocked. A testing chamber has a trough-shaped alley between two compartments separated by a partition that retracts into the floor. A rat is shocked in one chamber. Then later, the rat placed in the "safe" part of the chamber, and the door retracts to expose the place where the rat was shocked. Researchers measure how long it takes for the rat to reenter the place where it was shocked. the rat with basolateral lesions avoids that chamber but does not freeze. In other studies, lesioned rats similarly don't freeze but do show place avoidance.
So the bottom line is, nonhuman animals with lesions in basolateral amygdala retain "fear" learning when assessed by measures other than freezing, and they have difficulty freezing in contexts that are unrelated to fear.
Notes on the Notes
- Ambrogi Lorenzini, Carlo, Elisabetta Baldi, Corrado Bucherelli, Aldo Giachetti, and Giovanna Tassoni. 1991. "Effects of nucleus basolateralis amygdalae neurotoxic lesions on some spontaneous activities in the rat." Physiology & Behavior 50(6): 1215-1219.
- Berlau, Daniel J., and James L. McGaugh. 2003. "Basolateral amygdala lesions do not prevent memory of context-footshock training." Learning & Memory 10 (6): 495-502.
- Vazdarjanova, Almira, and James L. McGaugh. 1998. "Basolateral amygdala is not critical for cognitive memory of contextual fear conditioning." Proceedings of the National Academy of Sciences 95 (25): 15003-15007
- Selden, N. R. W., B. J. Everitt, L. E. Jarrard, and T. W. Robbins. 1991. "Complementary roles for the amygdala and hippocampus in aversive conditioning to explicit and contextual cues." Neuroscience 42 (2): 335-350.
- Killcross, Simon, Trevor W. Robbins, and Barry J. Everitt. 1997. "Different types of fear-conditioned behaviour mediated by separate nuclei within amygdala." Nature 388 (6640): 377-380.