Regions of Interest — The Amygdala

By Darren Schreiber

I’m testing out a potential new feature for the neuropolitics listserv entitled “Regions of Interest.” I’ll be giving a brief overview of a portion of the brain that is relevant to neuropolitics. I’ll include a few brain images that will help orient readers as to its location, a description, and a discussion of its relevance to the social cognition. I will then provide a set of citations to recent articles that discuss the region, with particular emphasis on interesting experiments, meta-analyses, and reviews.

I’m starting off with the amygdala. This region has become almost a household word in the past decade. The typical way it is discussed is in its role in the experience and processing of fear. However, the story is far more nuanced than that. This almond sized region is located in the limbic system, deep within the brain, as can be seen in the axial, coronal, and sagittal images shown above.

I would particularly draw your attention to the meta-analyes listed below (7 & 9) as a way of getting a broader sense of the amygdala’s role. While it is active during fear and other negative emotions, it is also active during positive emotions and a variety of forms of social cognition (2 & 4). A particularly interesting line of work demonstrates that while this region is susceptible to automatic or subliminal activation, it is also down regulated by conscious mental processes (7). Its role in the processing of race has gotten a lot of attention (3, 5, 13) as people appear to have higher amygdala activations when viewing African Americans. However, darker skin tones in general seem to trigger the amygdala (13). It has also been implicated in risk and reward processing during decision making (6 & 12). My colleagues and I have some preliminary work suggesting that Republicans can be identified by their stronger activity in this area during a risk task. Finally, I would draw your attention to the review by Joseph LeDoux (11). He and Ralph Adolphs have been leading researchers in the amygdala’s role in the brain, particularly its function in social cognition.

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  1. Tsuchiya et al. Intact rapid detection of fearful faces in the absence of the amygdala. Nat Neurosci (2009) vol. 12 (10) pp. 1224-5The amygdala is thought to process fear-related stimuli rapidly and nonconsciously. We found that an individual with complete bilateral amygdala lesions, who cannot recognize fear from faces, nonetheless showed normal rapid detection and nonconscious processing of those same fearful faces. We conclude that the amygdala is not essential for early stages of fear processing but, instead, modulates recognition and social judgment.
  2. Kennedy et al. Personal space regulation by the human amygdala. Nat Neurosci (2009) vol. 12 (10) pp. 1226-7The amygdala plays key roles in emotion and social cognition, but how this translates to face-to-face interactions involving real people remains unknown. We found that an individual with complete amygdala lesions lacked any sense of personal space. Furthermore, healthy individuals showed amygdala activation upon close personal proximity. The amygdala may be required to trigger the strong emotional reactions normally following personal space violations, thus regulating interpersonal distance in humans.
  3. Platek and Krill. Self-face resemblance attenuates other-race face effect in the amygdala. Brain Res (2009) vol. 1284 pp. 156-60People respond favorably toward self-resembling faces. We investigated the pattern of responding in the amygdala of Caucasian participants to self-face resemblance expressed in same and other-race (African descent) faces. The amygdala response was 1) non-linear to faces as a function of self-facial resemblance and 2) attenuated to other-race self-resembling faces when regressed with implicit racial attitudes. These findings demonstrate that interactions of important facial social judgements are processed combinatorially in the amygdala.
  4. Said et al. Nonlinear amygdala response to face trustworthiness: contributions of high and low spatial frequency information. J Cognitive Neurosci (2009) vol. 21 (3) pp. 519-28Previous neuroimaging research has shown amygdala sensitivity to the perceived trustworthiness of neutral faces, with greater responses to untrustworthy compared with trustworthy faces. This observation is consistent with the common view that the amygdala encodes fear and is preferentially responsive to negative stimuli. However, some studies have shown greater amygdala activation to positive compared with neutral stimuli. The first goal of this study was to more fully characterize the amygdala response to face trustworthiness by modeling its activation with both linear and nonlinear predictors. Using fMRI, we report a nonmonotonic response profile, such that the amygdala responds strongest to highly trustworthy and highly untrustworthy faces. This finding complicates future attempts to make inferences about mental states based on activation in the amygdala. The second goal of the study was to test for modulatory effects of image spatial frequency filtering on the amygdala response. We predicted greater amygdala sensitivity to face trustworthiness for low spatial frequency images compared with high spatial frequency images. Instead, we found that both frequency ranges provided sufficient information for the amygdala to differentiate faces on trustworthiness. This finding is consistent with behavioral results and suggests that trustworthiness information may reach the amygdala through pathways carrying both coarse and fine resolution visual signals.
  5. Derntl et al. Amygdala activation during recognition of emotions in a foreign ethnic group is associated with duration of stay. Social neuroscience (2009) vol. 4 (4) pp. 294-307Cultural differences in emotion recognition performance have frequently been reported, whereby duration of stay in a foreign culture seems to be a crucial factor. Furthermore, cultural aspects influence the neural correlates of face and emotion processing thereby also affecting the response of the amygdala. Here, the exposure to a foreign culture and its influence on the cerebral correlates of facial emotion recognition were examined in 24 Asian and 24 age-matched European males. Subjects performed an explicit emotion recognition task and were imaged with a 3 T MR-scanner. Results demonstrate a significant cultural influence on the specific recognition of disgust and anger, with higher accuracy among the Europeans, while the functional data indicate generally elevated amygdala activation in Asians compared to Europeans. Moreover, a significant inverse correlation between duration of stay and amygdala response emerged, with stronger activation in those subjects with shorter duration of stay in Europe. The observed amygdala hyperactivation in Asians may reflect novelty aspects but might also be associated with greater effort and motivation in immigrants, thus it possibly reflects one neural correlate of the “alien-effect”. We conclude that exposure to a foreign culture and duration of stay affect the behavioral and neural response to facial expressions of emotions.
  6. Seymour and Dolan. Emotion, decision making, and the amygdala. Neuron (2008) vol. 58 (5) pp. 662-71Emotion plays a critical role in many contemporary accounts of decision making, but exactly what underlies its influence and how this is mediated in the brain remain far from clear. Here, we review behavioral studies that suggest that Pavlovian processes can exert an important influence over choice and may account for many effects that have traditionally been attributed to emotion. We illustrate how recent experiments cast light on the underlying structure of Pavlovian control and argue that generally this influence makes good computational sense. Corresponding neuroscientific data from both animals and humans implicate a central role for the amygdala through interactions with other brain areas. This yields a neurobiological account of emotion in which it may operate, often covertly, to optimize rather than corrupt economic choice.
  7. Costafreda et al. Predictors of amygdala activation during the processing of emotional stimuli: a meta-analysis of 385 PET and fMRI studies. Brain research reviews (2008) vol. 58 (1) pp. 57-70Although amygdala activity has been purported to be modulated by affective and non-affective factors, considerable controversy remains on its precise functional nature. We conducted a meta-analysis of 385 functional neuroimaging studies of emotional processing, examining the effects of experimental characteristics on the probability of detecting amygdala activity. All emotional stimuli were associated with higher probability of amygdala activity than neutral stimuli. Comparable effects were observed for most negative and positive emotions, however there was a higher probability of activation for fear and disgust relative to happiness. The level of attentional processing affected amygdala activity, as passive processing was associated with a higher probability of activation than active task instructions. Gustatory-olfactory and visual stimulus modalities increased the probability of activation relative to internal stimuli. Aversive learning increased the probability of amygdala activation as well. There was some evidence of hemispheric specialization with a relative left-lateralization for stimuli containing language and a relative right-lateralization for masked stimuli. Methodological variables, such as type of analysis and magnet strength, were also independent predictors of amygdala activation.
  8. Adolphs. Fear, faces, and the human amygdala. Curr Opin Neurobiol (2008) vol. 18 (2) pp. 166-72The amygdala’s historical role in processing stimuli related to threat and fear is being modified to suggest a role that is broader and more abstract. Amygdala lesions impair the ability to seek out and make use of the eye region of faces, resulting in impaired fear perception. Other studies in rats and humans revive earlier proposals that the amygdala is important not only for fear perception as such, but also for detecting saliency and biological relevance. Debates about some features of this processing now suggest that while the amygdala can process fearful facial expressions in the absence of conscious perception, and while there is some degree of preattentive processing, this depends on the context and is not necessarily more rapid than cortical processing routes. A large current research effort extends the amygdala’s putative role to a number of psychiatric illnesses.
  9. Sergerie et al. The role of the amygdala in emotional processing: a quantitative meta-analysis of functional neuroimaging studies. Neuroscience and biobehavioral reviews (2008) vol. 32 (4) pp. 811-30Functional neuroimaging studies have provided strong support for a critical role of the amygdala in emotional processing. However, several controversies remain in terms of whether different factors-such as sex, valence and stimulus type-have an effect on the magnitude and lateralization of amygdala responses. To address these issues, we conducted a meta-analysis of functional neuroimaging studies of visual emotional perception that reported amygdala activation. Critically, unlike previous neuroimaging meta-analyses, we took into account the magnitude (effect size) and reliability (variance) associated with each of the activations. Our results confirm that the amygdala responds to both positive and negative stimuli, with a preference for faces depicting emotional expressions. We did not find evidence for amygdala lateralization as a function of sex or valence. Instead, our findings provide strong support for a functional dissociation between left and right amygdala in terms of temporal dynamics. Taken together, results from this meta-analysis shed new light on several of the models proposed in the literature regarding the neural basis of emotional processing.
  10. Murray. The amygdala, reward and emotion. Trends Cogn Sci (Regul Ed) (2007) vol. 11 (11) pp. 489-97Recent research provides new insights into amygdala contributions to positive emotion and reward. Studies of neuronal activity in the monkey amygdala and of autonomic responses mediated by the monkey amygdala show that, contrary to a widely held view, the amygdala is just as important for processing positive reward and reinforcement as it is for negative. In addition, neuropsychological studies reveal that the amygdala is essential for only a fraction of what might be considered ‘stimulus-reward processing’, and that the neural substrates for emotion and reward are partially nonoverlapping. Finally, evidence suggests that two systems within the amygdala, operating in parallel, enable reward-predicting cues to influence behavior; one mediates a general, arousing effect of reward and the other links the sensory properties of reward to emotion.
  11. LeDoux. Primer: The amygdala. Curr Biol (2007) vol. 17 (20) pp. R868-74The amygdala is a complex structure involved in a wide range of normal behavioral functions and psychiatric conditions. Not so long ago it was an obscure region of the brain that attracted relatively little scientific interest. Today it is one of the most heavily studied brain areas, and practically a household word. Art critics are explaining the impact of a painting by its direct impact on the amygdala; essential oils are said to alter mood by affecting the amygdala; and there is a website where you can unleash your creativity by clicking your amygdala, and thereby popping your frontal cortex. In this Primer, I will focus on the scientific implications of the research, discussing the anatomical structure, connectivity, cellular properties and behavioral functions of the amygdala.
  12. Hampton et al. Contributions of the amygdala to reward expectancy and choice signals in human prefrontal cortex. Neuron (2007) vol. 55 (4) pp. 545-55The prefrontal cortex (PFC) receives substantial anatomical input from the amygdala, and these two structures have long been implicated in reward-related learning and decision making. Yet little is known about how these regions interact, especially in humans. We investigated the contribution of the amygdala to reward-related signals in PFC by scanning two rare subjects with focal bilateral amygdala lesions using fMRI. The subjects performed a reversal learning task in which they first had to learn which of two choices was the more rewarding, and then flexibly switch their choices when contingencies changed. Compared with healthy controls, both amygdala lesion subjects showed a profound change in ventromedial prefrontal cortex (vmPFC) activity associated with reward expectation and behavioral choice. These findings support a critical role for the human amygdala in establishing expected reward representations in PFC, which in turn may be used to guide behavioral choice.
  13. Ronquillo et al. The effects of skin tone on race-related amygdala activity: an fMRI investigation. Soc Cogn Affect Neur (2007) vol. 2 (1) pp. 39-44Previous work has shown differential amygdala response to African-American faces by Caucasian individuals. Furthermore, behavioral studies have demonstrated the existence of skin tone bias, the tendency to prefer light skin to dark skin. In the present study, we used functional magnetic resonance imaging (fMRI) to investigate whether skin tone bias moderates differential race-related amygdala activity. Eleven White participants viewed photographs of unfamiliar Black and White faces with varied skin tone (light, dark). Replicating past research, greater amygdala activity was observed for Black faces than White faces. Furthermore, dark-skinned targets elicited more amygdala activity than light-skinned targets. However, these results were qualified by a significant interaction between race and skin tone, such that amygdala activity was observed at equivalent levels for light- and dark-skinned Black targets, but dark-skinned White targets elicited greater amygdala activity than light-skinned White targets.
  14. Schaefer and Gray. A role for the human amygdala in higher cognition. Reviews in the neurosciences (2007) vol. 18 (5) pp. 355-63Considerable evidence suggests that the human amygdala plays an important role in higher cognitive functions in addition to its well-known role in emotional processing. In this article we review representative evidence showing the involvement of the human amygdala in long-term memory, working memory and attention. Results are discussed in terms of their relevance to current theories of amygdala function that can integrate its cognitive and emotional functions in a comprehensive framework.
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