Neural mechanism of unconscious perception of surprised facial expression.

Previous functional neuroimaging studies have uncovered partly separable neural substrates for perceiving different facial expressions presented below the level of conscious awareness. However, as one of the six basic emotions, the neural mechanism of unconsciously perceiving surprised faces has not yet been investigated. Using a backward masking procedure, we studied the neural activities in response to surprised faces presented below the threshold of conscious visual perception by means of functional magnetic resonance imaging (fMRI). Eighteen healthy adults were scanned while viewing surprised faces, which presented for 33 ms and immediately "masked" by a neutral face for 467 ms. As a control, they viewed masked happy or neutral faces as well. In comparison to both control conditions, masked surprised faces yielded significantly greater activation in the parahippocampal gyrus and fusiform gyrus, which associated previously with novelty detection. In the present study, automatic activation of these areas to masked surprised faces was investigated as a function of individual differences in the ability of identifying and differentiating one's emotions, as assessed by the 20-item Toronto Alexithymia Scale (TAS-20). The correlation results showed that, the subscale, Difficulty Identifying Feelings, was negatively correlated with the neural response of these areas to masked surprised faces, which suggest that decreased activation magnitude in specific brain regions may reflect increased difficulties in recognizing one's emotions in everyday life. Additionally, we confirmed activation of the right amygdala and right thalamus to the masked surprised faces, which was previously proved to be involved in the unconscious emotional perception system.