The amygdala in social behaviors: not just about fear

Summary

The amygdala is classically thought of as mediating fear and fear learning, specifically. But is the role of the amygdala in social information processing and social behaviors limited to fear and fear learning?  A new study by Vrticka (2013) indicates that the amygdala is activated robustly and to an equal extent when subjects viewed either positively-valenced (pleasurable, desirable) or negatively-valenced (threatening, fear-inducing) social pictures. This study suggests that the amygdala is very sensitive to social stimuli, regardless of whether the emotional valence of the stimuli is positive or negative.

More details

The classical view of amygdala function is that the brain region primarily mediates fear and fear learning, including fear in a social context (e.g. amygdala activation while viewing threatening or fearful faces).    In my last post about desire for interpersonal closeness, I mentioned the hypothesis the human brain has “opposing emotional neural circuits” (Vrticka 2012)—one of which mediates social approach/reward, and the other which mediates social avoidance/aversion, with the latter circuit including the amygdala (Vrticka 2012).  But is mediating fear / aversion really the main role of the amygdala in social information processing and social behaviors?  Recent studies indicate that the amygdala, composed of a heterogeneous set of nuclei (Swanson 2003), plays a broader role in processing emotional and motivational salience of environmental stimuli (including social stimuli), including not only negatively valenced (aversive, fear-inducing) stimuli, but also very positively valenced (rewarding, pleasurable, desired) stimuli (Cunningham and Brosch 2012; Adophs 2010).  Consistent with this emerging perspective, a new study by Vrticka (2013) demonstrates similar levels of activation of the human amygdala in response to either negatively- or positively-valenced social stimuli.  In this study, 19 female participants (mean age ~25 years) underwent brain functional magnetic resonance imaging (fMRI) while viewing positively-valenced social pictures, negatively-valenced social pictures, positively-valenced non-social pictures, negatively-valenced non-social pictures, neutral social pictures, and neutral non-social pictures.  The data indicate that, overall, the amygdala is more strongly activated for social vs. non-social stimuli (significant main effect of social content), and this effect occurred with stimuli of all valences (positive, negative, and neutral).  These data support the notion that the amygdala is particularly responsive to social information, regardless of the type of emotional valence of the information.  The amygdala was activated at a similar level by negatively- and positively-valenced social stimuli, though was some indication of greater amygdala activation in response to negatively-valenced non-social stimuli vs. positively valenced non-social stimuli. Perhaps the classical view of the amygdala as mediating fear specifically may have more to do with amygdala responses to non-social stimuli than its responses to social stimuli, although additional studies would be needed to confirm this.  Other brain regions that showed a pattern of activation similar to that of the bilateral amygdala in this study included the right fusiform gyrus, right anterior superior temporal gyrus, and the medial orbitofrontal cortex, which, together with the amygdala, may form a brain network involved in social and emotional information processing (Vrticka, 2013).  One implication of this study, not directly tested here, may be that alterations in amygdala development or function may alter the salience of social stimuli in general, and not just fear or anxiety responses.

 References

Adolps R (2010) What does the amygdala contribute to social cognition?  Annals of the New York Academy of Sciences 1191(Mar):42-61.

Cunningham WA and Brosch T (2012) Motivational salience:  amygdala tuning from trains, needs, values, and goals.  Current Directions in Psychological Science 21(1):54-59.

Swanson LW (2003) The amygdala and its place in the cerebral hemisphere.  Annals of the New York Academy of Sciences 985(Apr):174-184.

Vrticka P (2012) Interpersonal closeness and social reward processing.  The Journal of Neuroscience 32(37):12649-12650.

Vrticka P, Sander D, Vuilleumier P (2013) Lateralized interactive social content and valence processing within the human amygdala. Frontiers in Human Neuroscience 6:358.

©2011-2013 Edward S. Brodkin.  All Rights Reserved

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