Consistent with prior reports (Manuck et al., 2010
), there was robust bilateral activation within our anatomically defined ventral and dorsal amygdala ROIs.
Social support was correlated with measures of trait anxiety (r = −.26 to −.48, p < .01), but not with measures of amygdala reactivity (r = −.09 to −.13, p > .15). In interaction analyses, social support predicted anxiety and moderated amygdala-related anxiety (). Moreover, these results were consistent across multiple measures of anxiety and highly specific to anxiety. In those reporting less than average levels of social support, amygdala reactivity was positively and significantly correlated with measures of anxiety. However, in those reporting average or above average levels of support there was no correlation or non-significant negative correlation between these variables. The results were in the same direction for dorsal and ventral regions of the amygdala but much stronger in the dorsal regions (interaction terms predicting latent anxiety: left dorsal β = −.265, p = .005; left ventral β = −.122, p = .18; right dorsal β = −.267, p = .005; right ventral β = −.078, p = .40).
Summary of regressions predicting outcomes with main effects and interaction terms for self-report measures of anxiety, affect and social support, and left dorsal amygdala reactivity while controlling for gender
While this general pattern of moderation was present across broad measures of negative affect and emotionality (i.e., neuroticism, negative affect), the interaction terms did not reach significance. However, there were strong and significant interactions when analyzing specific subscales within these and other measures that selectively assess anxiety (i.e., anxiety proneness, harm avoidance, anticipatory worry, and trait anxiety). Interestingly, the results were strongest when a latent construct of anxiety was derived from these subscales and used as an outcome (). Moreover, within the various measures of anxiety, results were particularly strong for the anticipatory worry scale of harm avoidance. Similar analyses with measures of positive emotion and affect (i.e., extraversion, positive affect) did not produce significant results ().
Figure 1 Left dorsal amygdala reactivity differentially predicts a latent construct of anxiety as a function of perceived social support. The significant interaction term (β=−.265, p<.01) and simple slopes indicate that amygdala reactivity (more ...)
When examining the interaction within the left dorsal amygdala predicting the latent anxiety construct using simple slope calculations, the pattern of results became more evident: amygdala reactivity has a significant and positive correlation with anxiety at below average levels of social support (at 1 SD below the mean of social support, the simple slope = 1.56, SE = .55, p = .005), but at average or above average (+1 SD) levels of social support this relationship is not statistically significant (+1 SD: simple slope = −.824, SE = .59, p = .17; Mean: simple slope = .368, SE = .39, p > .3).
By using interaction methods described above (Preacher et al., 2006
), we were able to determine at what values of social support the relationship between left dorsal amygdala reactivity and the latent construct of anxiety became significant. In this regression, there is a significant positive relationship between amygdala reactivity and anxiety for those at or below 0.38 standard deviations below the mean of social support. As 34 of the 103 participants had social support scores that fell below this mark, this positive relationship between amygdala reactivity and anxiety is quite salient, even in this community sample. A statistically significant negative relationship between amygdala reactivity and social support only theoretically emerges for those 1.66 standard deviations above the mean of social support, which is beyond the range of reported social support values (range 6 – 36, mean = 28.5; SD =6.5). Thus, while the line in depicting the relationship between anxiety and amygdala reactivity for those high on social support appears to have a negative slope, this slope is not statistically significant and would not be statistically significant within the present range of data (see Supplemental Figure 1
for a plot of all participants’ scores).
To determine if these interaction effects were specific to amygdala reactivity, we examined several regions of interest in an extended corticolimbic circuitry also engaged by our fMRI paradigm. These regions of interest included orbitofrontal cortex (OFC; BA11), as well as bilateral ventrolateral prefrontal cortex (vlPFC; BA47) and hippocampal formation, and right posterior fusiform gyrus (see Supplemental Methods). Using methods identical to those for amygdala reactivity, we examined if extracted BOLD values from each of these brain regions interacted with social support to predict the latent construct of trait anxiety. We found a significant interaction effect between social support and task-related activation in OFC and right vlPFC. No significant interaction effects were found for the other brain regions, although a trend emerged for left vlPFC (). For regions exhibiting a significant interaction effect (i.e., OFC and right vlPFC), the graphs of these interactions and simple slope analyses were nearly identical to those for the amygdala: at low levels of social support there is a significant positive relationship between activation and anxiety, but at mean or high levels of social support there is no significant relationship.
Table 2 Summary of additional corticolimbic regions of interest (ROI) tested for interaction effects with social support. Note that each regression included sex as a covariate, main effects of social support, main effects of the ROI, and the interaction between (more ...)