Activation of the amygdala and anterior cingulate during nonconscious processing of sad versus happy faces.

Previous functional neuroimaging studies have demonstrated that the amygdala activates in response to fearful faces presented below the threshold of conscious visual perception. Using a backward masking procedure similar to that of previous studies, we used functional magnetic resonance imaging (fMRI) to study the amygdala and anterior cingulate gyrus during preattentive presentations of sad and happy facial affect. Twelve healthy adult females underwent blood oxygen level dependent (BOLD) fMRI while viewing sad and happy faces, each presented for 20 ms and "masked" immediately by a neutral face for 100 ms. Masked happy faces were associated with significant bilateral activation within the anterior cingulate gyrus and amygdala, whereas masked sadness yielded only limited activation within the left anterior cingulate gyrus. In a direct comparison, masked happy faces yielded significantly greater activation in the anterior cingulate and amygdala relative to identically masked sad faces. Conjunction analysis showed that masked affect perception, regardless of emotional valence, was associated with greater activation within the left amygdala and left anterior cingulate. Findings suggest that the amygdala and anterior cingulate are important components of a network involved in detecting and discriminating affective information presented below the normal threshold of conscious visual perception.