Amygdala activation to threat under attentional load in individuals with anxiety disorder

During functional magnetic resonance imaging, spider-phobicand healthy control subjects were presented with phobia-related and neutral stimuli while performing a distraction task with varying perceptual load (high vs low).Our data revealed a pattern of simultaneously increased amygdala and visual cortical activation to threat vs neutral pictures in phobic individuals, compared with controls, occurring regardless of attentional load.These results suggest that, in contrast to studies in healthy subjects, amygdala activation to clinically relevant threat stimuli is more resistant to attentional load.In accordance with theories suggesting a critical function of the amygdala in the processing of threat signals and the mediation of fear responses [1,2], several studies found increased amygdala activation to threatening vs neutral stimuli in individuals with anxiety disorders [3-8] and in healthy subjects [9-14]. Furthermore, there are strong theoretical accounts proposing an automatic response of the amygdala to threat signals even when target stimuli are presented during attentional distraction [1,2,14]. Whereas some studies indeed suggest an automaticity of amygdala activation to threat-related stimuli under conditions of attentional distraction [9,13,14], several recent studies in healthy subjects, however, indicated a complete inhibition of differential activation to threat vs neutral stimuli within the amygdala, given sufficiently strong perceptual load by a main task [15-18]. Thus, it seems that, at least in healthy subjects, automatic activation of the amygdala to emotional stimuli does not occur when demanding cognitive tasks exhaust the available processing resources.Bishop et al., for example, used a perceptual load task, while subjects were exposed to fearful and neutral faces. Perceptual load was induced by varying the number of task-relevant items [19,20] within a letter string presented along with the facial expression. When perceptual identification was eas