Neural processing of emotional valence of facial expressions

Degree of emotional valence and arousal have been shown to covary with blood oxygen level dependent (BOLD) signal levels in several brain structures. Here we studied brain activity in 17 healthy subjects during perception of facial expressions varying in valence and arousal using functional magnetic resonance imaging (fMRI). Our results revealed correlations with the perceived valence in dorsolateral and ventrolateral prefrontal cortex, dorsomedial prefrontal cortex, and anterior insula. These findings corroborate results of our previous study where we used pictures of varying valence taken from the International Affective Picture System (IAPS). Together, the results of these two studies suggest existence of common brain areas processing valence of both emotional pictures and facial expressions. Additionally, BOLD signal exhibited distinctive dependency on perceived valence in intraparietal sulcus and supramarginal gyrus in the present study. BOLD activity correlated with negative and positive valence in separate cortical areas, and some areas demonstrated either a U-shaped or an inverted U-shaped relationship with valence (i.e., either minimal or maximal activation was observed to neutral expressions). This nonlinear dependency suggests that brain mechanisms underlying perception of negative and positive valence are at least to some extent independent. Perceived arousal correlated positively with the strength of the BOLD signal only in the left inferior frontal gyrus, which is an important node of the mirror neuron system.