Archive for the ‘Amygdala’ Category

The amygdala in social behaviors: not just about fear

February 11, 2013

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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Social networks, social brain

November 9, 2012

Summary

What circuits in the brain mediate our tendency to socially connect with others?    An article by Bickart et al 2012 finds that the functioning of particular brain circuits—including specific parts of the amygdala, an important hub of the “emotional”/limbic system of the brain—is related to the size and complexity of people’s social networks.

More details

What circuits in the brain mediate our tendency to socially connect with others?    Many studies have implicated brain circuits involving the amygdala and the frontal cortex in social behaviors.  Some of these studies (e.g. Bickart et al 2011) have found a positive correlation between size of social networks and size of the amygdala, an important hub of the “emotional”/limbic system of the brain.  Now a new study (Bickart et al 2012) provides more detailed information about the relationship between specific brain circuits involving subdivisions of the amygdala and size of social networks in healthy, young adult humans.  Bickart and co-workers (2012) measured size of individuals’ social networks using the Social Network Index (Cohen et al 1997).  They used fMRI to measure the size of the each person’s amygdala, and used a method called resting-state functional connectivity magnetic resonance imaging (fcMRI) to assess connectivity between amygdala sub-regions and various other brain regions.  Replicating their previous work (Bickart et al 2011), this 2012 study found a positive correlation between size of the amygdala and size of the social network.  In addition, they found that the strength of a circuit supporting social perception (ventrolateral amygdala connected to orbitofrontal cortex, fusiform gyrus, ventromedial temporal cortex, and superior temporal sulcus) and a circuit supporting social affiliation (medial amygdala connected to ventromedial prefrontal cortex, rostral anterior cingulate cortex, and nucleus accumbens, and ventromedial hypothalamus) predicted social network size.  However, social network size was not related to the strength of a circuit including the dorsal amygdala that supports social aversion.  Moreover, social network size and complexity was not related to connectivity within other networks important for social cognition that do not include the amygdala, specifically networks involved in mentalizing (dorsomedial prefrontal cotex connected to temporoparietal junction) or in mirror networks (ventral premotor cortex, posterior superior temporal sulcus, and intraparietal sulcus).  The authors note that “This dissociation underscores the value of studying the component processes that contribute to social connectedness since there are clearly important divisions of labor.  In this case, the size and complexity of a person’s social network depends more on corticolimbic circuitry that is important for affective processing (Barett and Bar, 2009), which in part evaluates the salience of signals from other people (Seeley et al., 2007), than on corticocortical networks that have more limited relevance for affective processing” (Bickart et al 2012). Importantly, the authors note that their findings do not indicate the extent to which the strength of these circuits related to social network size are “hard-wired” by genetics, or are modifiable by experience or other environmental factors.

References

Barrett LF, Bar M (2009) See it with feeling:  affective predictions during object perception.  Philos Tras R Soc Lond B Biol Sci 364:1325-1334.

Bickart KC, Hollenbeck MC, Barrett LF, Dickerson BC (2012) Intrinsic amygdala-cortical functional connectivity predicts social network size in humans.  Journal of Neuroscience 32:14729-14741.

Bickart KC, Wright CI, Dautoff RJ, Dickerson BC, Barrett LF (2011) Amygdala volume and social network size in humans.  Nature Neuroscience 14:163-164.

Cohen S, Doyle WJ, Skoner DP, Rabin BS, Gwaltney JM Jr (1997) Social ties and susceptibility to the common cold.  JAMA 277:1940-1944.

Seeley WW, Menon V, Schatzberg AF, Keller J, Gover GH, Kenna H, Reiss AL, Greicius MD (2007) Dissociable intrinsic connectivity networks for salience processing and executive control.  Journal of Neuroscience 27:2349-2356.

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


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