It has already been demonstrated that the amygdala plays an important role in the processing of fear (Adolphs et al., 1994, 1995; Broks et al., 1998; Calder et al., 1996) and the insula, in the processing of disgust (Hennenlotter et al., 2004, Sprengelmeyer et al., 1998, Calder et al., 2000, Wicker et al., 2003).
There is some-temporally sluggish-evidence that the amygdala is involved in the processing of high-spatial frequency eye information (Whalen et al., 2005; Adolphs et al. 2005). However, little is known about what the insula might respond to in disgusted faces. Here, we used the Bubbles technique (Gosselin & Schyns, 2001) with intracranial electroencephalography (EEG) to shed new light on these issues.
Patient DA, who was undergoing intracranial clinical monitoring for epilepsy, was shown 21,600 stimuli that varied in their emotional content while EEG was being recorded from chronic depth electrodes (four contacts in the right amygdala and four in the right insula). On each trial, one of four faces (fearful and disgusted man and woman from Eckman & Friesen, 1976, set) was sampled by randomly located Gaussian apertures (Gosselin & Schyns, 2001). We performed multiple linear regression on the location of the information samples and wavelet coefficients of the electroencephalographic activity for every electrode contact and emotion category (Chauvin et al., 2005; Smith et al., 2006).
Fear classification images show the eyes region, especially the eye on the ipsilateral side of the image as early as 200 ms after stimulus onset in some of the amygdala contacts. Disgust classification images show the nose region, especially the nasolabial ferrows as early as 60 ms after stimulus onset in some of the insula contacts. This confirms the hypothesis that the amygdalas and the insula participate to the processing of the facial expression of fear and disgust (Smith et al., 2005).