Monozygotic twins with amygdala damage (AM and BG)

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Chapter 1 endnote 34, from How Emotions are Made: The Secret Life of the Brain by Lisa Feldman Barrett.
Some context is:

One twin, BG, is much like SM: she has similar fear-related deficits yet experiences fear when breathing carbon dioxide–loaded air. The other twin, AM, has basically normal responses during fear: other brain networks are compensating for her missing amygdalae.

Patient AM can explicitly identify the wide-eyed faces used in the basic emotion method as fear, whereas Patient BG cannot. BG also makes more errors than control subjects in "recognizing" other posed faces as emotional; e.g., she has difficulty identifying posed scowling faces as angry, pouting faces as sad, and wrinkled-nose faces as disgusted (only the former reached conventional levels of statistical significance).[1] AM also has higher skin conductance responses during “fear learning” (as do normal control test subjects with intact amygdalae).[1] Both women can pose a wide-eyed fearful face which is a stereotyped expression for fear.[2] AM maintains her ability to perceive and experience fear via an alternative set of brain pathways involving premotor cortex.[1][2]

Recent evidence indicates that both AM and BG have other deficits, however. For example, both women have reduced ability to find a scowling face in a crowd (particularly a large crowd), but BG is significantly more impaired that AM.[3] Both women report panic and fear to CO2 challenge (like Patient SM) but they don’t show an anticipatory skin conductance response, meaning that they have not learned to anticipate what is going to happen based on prior experience.[4] Consistent with this hypothesis of impaired learning, both women also show some memory deficits.[5] Both also have reduced arousal ratings to evocative images.[6]

AM also shows other evidence of normal "fear" processing.  There is a scientific experiment where a loud tone is presented, and subjects startle.  If you present a negative image beforehand, the startle is even larger.  This is called  "fear potentiated" startle).  AM shows a normal startle response when she is presented with a loud tone, and this response is enhanced when an aversive image is presented before the tone (called "fear potentiated startle"; the startle response itself does not depend on the amygdala, but the modulation of the response by the negative images is supposed to be amygdala dependent).  BG does not have a normal potentiated startle.[1]

Notes on the Notes

  1. 1.0 1.1 1.2 1.3 Becker, Benjamin, Yoan Mihov, Dirk Scheele, Keith M. Kendrick, Justin S. Feinstein, Andreas Matusch, Merve Aydin et al. 2012. "Fear processing and social networking in the absence of a functional amygdala." Biological Psychiatry 72 (1): 70–77.
  2. 2.0 2.1 Mihov, Yoan, Keith M. Kendrick, Benjamin Becker, Jacob Zschernack, Harald Reich, Wolfgang Maier, Christian Keysers, and René Hurlemann. 2013. "Mirroring fear in the absence of a functional amygdala." Biological Psychiatry 73 (7): e9–e11.
  3. Bach, Dominik R., Rene Hurlemann, and Raymond J. Dolan. 2015. "Impaired threat prioritisation after selective bilateral amygdala lesions." Cortex 63: 206-213.
  4. Feinstein, Justin S., Colin Buzza, Rene Hurlemann, Robin L. Follmer, Nader S. Dahdaleh, William H. Coryell, Michael J. Welsh, Daniel Tranel, and John A. Wemmie. 2013. "Fear and panic in humans with bilateral amygdala damage." Nature Neuroscience 16 (3): 270–272.
  5. Hurlemann, René, Michael Wagner, Barbara Hawellek, Harald Reich, Peter Pieperhoff, Katrin Amunts, Ana-Maria Oros-Peusquens, Nadim J. Shah, Wolfgang Maier, and Raymond J. Dolan. 2007. "Amygdala control of emotion-induced forgetting and remembering: evidence from Urbach-Wiethe disease." Neuropsychologia 45 (5): 877–884.
  6. Scheele, Dirk, Yoan Mihov, Keith M. Kendrick, Justin S. Feinstein, Harald Reich, Wolfgang Maier, and René Hurlemann. 2012. "Amygdala lesions profoundly alters altruistic punishment." Biological Psychiatry 72 (3): e5-e7.