The omnibus ANOVA examining the effects of Emotion, Attention and Temperament on the 5-point subjective rating scores revealed no significant interactions involving Temperament, F’s < 2.12, p’s > 0.13 (). This includes the omnibus three-way interaction between Emotion, Attention, and Temperament, F(6,144) = 1.32, p = 0.27, ε= 0.60, f = 0.26.
Figure 1 Mean (a) rating scores and (b) reaction times in the face processing task: Fear ratings (“How Afraid are you”), Hostility ratings (“How Hostile is the face”), and ratings of the Nose-width (“How Wide is the Nose”) (more ...)
However, there were significant main effects for Emotion and Attention, F’s > 22.89, p’s < 0.001, indicating that ratings differed significantly as a function of the depicted emotions (fearful, angry, happy, neutral) and the topic being rated (subjective fear, stimulus hostility, nose width). These main effects were subsumed by a significant Emotion by Attention interaction, F(6,144) = 40.45, p < 0.001, ε= 0.60, f = 1.30. As expected, fear and hostility ratings were highest for the Fearful and Angry faces.
A parallel analysis for reaction time found no significant effects involving Temperament, F’s < 0.90, p’s > 0.48. The ANOVA again found significant main effects for Emotion and Attention, F’s > 18.45, p’s < 0.001, which were subsumed by an Emotion by Attention interaction, F(6,144) = 10.34, p < 0.001, ε= 0.73, f = 0.66.
These results suggest that subjects properly engaged in the task, as anticipated, with no evidence of behavioral group differences in task performance. Thus, any differences in brain activation cannot be attributed to differences in behavioral performance.
Peak BOLD signal change analyses
As noted above, the initial contrast focused on amygdala activation during the fear rating (directed attention) condition versus the passive viewing (non-directed attention) condition for the fearful faces. Consistent with our hypothesis, BI adolescents showed greater amygdala activation to the directed attention condition than the non-directed attention condition relative to BN adolescents (; Table 3).
Figure 2 Statistical maps of voxel-wise between-group comparisons of amygdala activation during the fear rating condition relative to the passive viewing condition during the presentation of (a) fearful and (b) happy faces. BI adolescents compared to BN adolescents (more ...)
Subsequent analyses using SPSS 13.0 were based on the individual amygdala peak activations extracted from the SPM dataset and originating from the MNI coordinates of peak activations localized on the initial contrast.
Similarly to the behavioral analysis, a full factorial ANOVA was first conducted to examine all possible main effects and interactions. The Attention by Temperament interaction was significant, F(3,75) = 2.98, p = 0.04, ε = 0.90, f = 0.35 ().
Figure 3 Between-group comparisons of event-elicited BOLD signal change for the amygdala during the four Attention conditions (How Afraid are you, How Hostile is the face, How Wide is the Nose, Passive Viewing). Behaviorally inhibited adolescents demonstrated (more ...)
This interaction reflected greater amygdala activation in the BI group, as contrasted with the BN group, during the internal fear rating, relative to other attention states, with particularly robust amygdala deactivation in the BI group during passive viewing. No group differences were found in the two other attention conditions (hostility rating or nose width ratings).
In contrast to previous findings in anxiety disorders (McClure et al., 2007
), Emotion did not modulate these findings (i.e., there were no significant interactions involving Temperament and Emotion), and responses were not specific to the negative-valence faces.
Although Emotion was not found to modulate the effects of Temperament, we conducted exploratory analyses of amygdala responses to each facial emotion, because of our strong a priori hypotheses regarding the emotion specificity of the amygdala response (Fox et al., 2005
, McClure et al., 2007
). Moreover, these analyses also provided insights on potential differences in activation patterns among clinically anxious and behaviorally inhibited adolescents. As expected, BI adolescents showed significant amygdala deactivation, relative to BN adolescents, when passively viewing fearful faces, t
(25)=− 2.69, p
Figure 4 Between group comparisons of amygdala activation for the (a) fear rating and (b) passive viewing conditions. These demonstrate a pattern of hyperactivation when rating internal fear states and deactivation when attention is left unconstrained for BI adolescents. (more ...)
The only other significant finding was that BI adolescents showed particularly high levels of amygdala activation to the happy faces when asked to report their subjective fear, t(25) = 2.61, p = 0.02, d = 1.04 (). Potential explanations for this finding are discussed below.
Analyses were conducted with the full sample and then repeated after excluding adolescents with any DSM-IV diagnosis. We found no changes in the results. In particular, the central Temperament by Attention interaction remained significant when observing only healthy adolescents, F(3,60) = 3.74, p = 0.02, ε = 0.88, f = 0.43.