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Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001.

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Neuroscience. 2nd edition.

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Box DFear and the Human Amygdala: A Case Study

Studies of fear conditioning in rodents show that the amygdala plays a critical role in the association of an innocuous auditory tone with an aversive mechanical sensation. Does this finding imply that the human amygdala is similarly involved in the experience of fear and the expression of fearful behavior? Recent reports of one extraordinary patient support the idea that the amygdala is indeed a key brain center for the experience of fear.

The patient (S.M.) suffers from a rare, autosomal recessive condition called Urbach-Wiethe disease. The disorder caused the bilateral calcification and atrophy of the anterior-medial temporal lobes. As a result, the amygdala in each of S.M.'s hemispheres is extensively damaged, with little or no detectable injury to the hippocampal formation or nearby temporal neocortex. She has no motor or sensory impairment, and no notable deficits in intelligence, memory, or language function. However, when asked to rate the intensity of emotion in a series of photographs of facial expressions, she cannot recognize the emotion of fear (figure A). Indeed, S.M.'s ratings of emotional content in fearful facial expressions were five standard deviations below the ratings of control patients who had suffered damage outside of the anterior-medial temporal lobe.

The investigators next asked S.M. (and the brain-damaged control subjects) to draw facial expressions of the same set of emotions from memory. Although the subjects obviously differed in artistic abilities and the detail of their renderings, S.M. (who has a background in art) produced skillful pictures of each emotion, except for fear (figure B). At first, she could not produce a sketch of a fearful expression and, when prodded to do so, explained that “she did not know what an afraid face would look like.” After several failed attempts, she produced the sketch of a cowering figure with hair standing on end, evidently because she knew these clichés about the expression of fear. In short, S.M. has a severely limited concept of fear and, consequently, fails to recognize the emotion of fear in facial expressions. Studies of other individuals with bilateral destruction of the amygdala are consistent with this account. As might be expected, S.M.'s disability also limits her ability to experience fear in situations where this emotion is appropriate.

Despite the adage “have no fear,” to truly live without fear is to be deprived of a crucial neural mechanism that facilitates and promotes appropriate social behavior, making advantageous decisions in critical circumstances, and, ultimately, survival.

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(A) Patients with brain damage outside of the anterior-medial temporal lobe and patient S.M. rated the emotional content of a series of facial expressions. Each colored line represents the intensity of the emotions judged in facial expressions. S.M. recognized happiness, surprise, anger, disgust, sadness and neutral qualities in facial expressions compared to controls. However, she failed to recognize the appropriate amount of fear (orange lines). (B) Sketches made by S.M. when asked to draw facial expressions of emotion.

References

  1. Adolphs R. , Tranel D. , Damasio H. , Damasio A. R. Fear and the human amygdala. J. Neurosci. (1995);15:5879–5891. [PMC free article: PMC6577662] [PubMed: 7666173]
  2. Bechara A. , Damasio H. , Damasio A. R. , Lee G. P. Differential contributions of the human amygdala and ventromedial prefrontal cortex to decision-making. J. Neurosci. (1999);19:5473–5481. [PMC free article: PMC6782338] [PubMed: 10377356]

From: The Importance of the Amygdala

Copyright © 2001, Sinauer Associates, Inc.

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