Processing emotional ambiguity: When the prefrontal cortex jumps at a subtle smile

Introduction Reading other peopleʼs emotional facial expressions is a crucial aspect of social communication. What most people take for granted, is an insurmountable obstacle for patients suffering from an Autism-Spectrum-Disorder (ASD) or people affected with a condition called emotional blindness (Alexithymia). In the present study, we aimed to gain a deeper understanding of the underlying brain areas involved in such a complex task as the successful categorization of emotions. While most research on emotion categorization has been conducted with stereotypic emotions, real-life situations are more complex involving highly ambiguous emotional expressions. Hence, we set out to delineate the involvement of the prefrontal cortex (PFC) when subjects are confronted with pictures of ambiguous emotional faces.

Methods 30 healthy right-handed subjects were included in a functional magnetic resonance (fmri) study. Each subject perceived 480 morphed emotional face stimuli varying in their emotional content from prototypic emotions (happy, angry, sad, fearful) to complete ambiguity. For each emotional face stimulus, subjects indicated the predominant emotion in a two-alternative forced choice task.

Results When using the emotional intensity as a parametric modulator, we could show that the PFC together with the anterior insular gets increasingly activated while the emotional content is reduced to complete ambiguity. Task performance (steepness of the psychometric curve) was correlated with brain activity in the inferior frontal gyrus (IFG), indicating a central role of the IFG in top-down processing of ambiguous emotions.

Conclusion These preliminary results are an important groundwork to further investigate emotion categorization in patients with ASD and Alexithymia.