Brain structures activated by overt and covert emotional visual stimuli.

Research data suggest that the amygdala and some related brain structures modulate the processing of emotional visual stimuli even when they are not consciously perceived. In this study, we examined neural responses to investigate whether and how other brain areas anatomically connected to the amygdala might become activated during both overt and covert presentation of conditioned emotional visual stimuli. In the covert presentation, a conditioned angry face was shown for 15 ms followed by a neutral masking face (CSmask). In the overt condition, an angry face associated with a painful stimulus (CS+), a happy (H) and a neutral face (N) were presented for 75 ms. Based on results of functional magnetic resonance imaging (fMRI) in 10 healthy volunteers, we show evidence that a network of brain structures anatomically connected to the amygdala (including the anterior insula, the fusiform gyrus and the superior temporal sulcus) are involved in the subliminal processing of visual emotional stimuli. Of particular interest was the dissociation between the anterior and posterior insula: the anterior insula responded to both overt and covert presentation of the conditioned stimulus, whereas the posterior insula responded only to the overt presentation of the face associated with a painful electrical stimulation. This response pattern suggests that the anterior insula, the fusiform gyrus and the temporal sulcus cooperate with the amygdala in the unconscious processing of pain-conditioned stimuli.