Human Amygdala Tracks a Feature-Based Valence Signal Embedded within the Facial Expression of Surprise

Area of Science:

• Neuroscience
• Cognitive Psychology
• Affective Science

Background:

• The human amygdala's role in processing emotional valence (positive vs. negative) is debated.
• Alternative theories suggest it processes general emotional arousal or specific emotion categories.
• Differentiating valence from arousal and emotion type is challenging due to natural covariation.

Purpose of the Study:

• To investigate if the human amygdala specifically tracks affective valence, independent of arousal or emotion category.
• To utilize surprised facial expressions, which have inherent valence ambiguity, to dissociate valence and arousal.
• To identify the visual features driving amygdala valence processing.

Main Methods:

• Measured valence and arousal dimensions within surprised facial expressions, demonstrating their natural uncorrelation.
• Acquired functional magnetic resonance imaging (fMRI) data from male and female participants.
• Employed a machine learning classifier to analyze visual features of facial expressions.

Main Results:

• Amygdala responses in participants tracked the consensus valence values of surprised facial expressions.
• These amygdala responses were unconfounded by emotional arousal levels.
• Specific visual features in the mouth region of surprised faces were identified as predictors of the amygdala's valence response.

Conclusions:

• The human amygdala is sensitive to the affective valence of emotional cues, beyond general arousal or specific emotion types.
• Surprised facial expressions serve as a valuable model for dissociating valence and arousal.
• Visual cues, particularly in the mouth region, play a crucial role in how the amygdala detects emotional valence.