The amygdala mediates the emotional modulation of threat-elicited skin conductance response

Abstract

The ability to respond adaptively to threats in a changing environment is an important emotional function. The amygdala is a critical component of the neural circuit that mediates many emotion-related processes, and thus likely plays an important role in modulating the peripheral emotional response to threat. However, prior research has largely focused on the amygdala's response to stimuli that signal impending threat, giving less attention to the amygdala's response to the threat itself. From a functional perspective, however, it is the response to the threat itself that is most biologically relevant. Thus, understanding the factors that influence the amygdala's response to threat is critical for a complete understanding of adaptive emotional processes. Therefore, we used functional MRI to investigate factors (i.e., valence and arousal of co-occurring visual stimuli) that influence the amygdala's response to threat (loud white noise). We also assessed whether changes in amygdala activity varied with the peripheral expression of emotion (indexed via skin conductance response; SCR). The results showed that threat-elicited amygdala activation varied with the arousal, not valence, of emotional images. More specifically, threat-elicited amygdala activation was larger to the threat when presented during high-arousal (i.e., negative and positive) versus low-arousal (i.e., neutral) images. Further, the threat-elicited amygdala response was positively correlated with threat-elicited SCR. These findings indicate the amygdala's response to threat is modified by the nature (e.g., arousal) of other stimuli in the environment. In turn, the amygdala appears to mediate important aspects of the peripheral emotional response to threat.

Figure 1

Threat-elicited skin conductance response (SCR). Larger SCRs were produced by the threat presented during negative compared to neutral valence IAPS images. Threat-elicited SCR during images of positive valence fell at an intermediate level and did not differ from negative or neutral stimuli. Asterisk reflects significant difference (p < 0.05). Error bars reflect SEM after adjusting for between-subject variance (Loftus & Masson, 1994).

Figure 2

Threat-elicited amygdala activity. The threat-elicited fMRI signal response observed within the amygdala was enhanced by images of high arousal content (i.e. both negative and positive images; top graphs). Error bars reflect SEM after adjusting for between-subject variance (Loftus & Masson, 1994), and the asterisk indicates significant difference. The threat-elicited response within the bilateral amygdala varied with the amplitude of the threat-elicited SCR such that as threat-elicited amygdala activity increased, the magnitude of the threat-elicited SCR increased (bottom graphs). Pearson correlations between amygdala activity and SCR were conducted across subjects on the combined (i.e. average of negative, neutral, and positive) threat response.