Effects of Intensity of Facial Expressions on Amygdalar Activation Independently of Valence.

Huiyan Lin,Martin Mothes-Lasch,Thomas Straube,Wolfgang H R Miltner,Miriam Mueller-Bardorff,Leonie Brinkmann,Christine Buff

doi:10.3389/fnhum.2016.00646

Abstract

For several stimulus categories (e.g., pictures, odors, and words), the arousal of both negative and positive stimuli has been shown to modulate amygdalar activation. In contrast, previous studies did not observe similar amygdalar effects in response to negative and positive facial expressions with varying intensity of facial expressions. Reasons for this discrepancy may be related to analytical strategies, experimental design and stimuli. Therefore, the present study aimed at re-investigating whether the intensity of facial expressions modulates amygdalar activation by circumventing limitations of previous research. Event-related functional magnetic resonance imaging was used to assess brain activation while participants observed a static neutral expression and positive (happy) and negative (angry) expressions of either high or low intensity from an ecologically valid, novel stimulus set. The ratings of arousal and intensity were highly correlated. We found that amygdalar activation followed a u-shaped activation pattern with highest activation to high intense facial expressions as compared to low intensity facial expressions and to the neutral expression irrespective of valence, suggesting a critical role of the amygdala in valence-independent arousal processing of facial expressions. Additionally, consistent with previous studies, intensity effects were also found in visual areas and generally increased activation to angry versus happy faces were found in visual cortex and insula, indicating enhanced visual representations of high arousing facial expressions and increased visual and somatosensory representations of threat.

Highlights

From an evolutionary perspective, fast perception of emotional information is critical for human beings in forming rapid and appropriate behavioral responses to adapt to the environment
In the present study, we investigated whether the intensity of facial expressions is associated with increase of amygdalar activation independently of valence
We found increased activation in the amygdala to high intensity facial expressions as compared to low intensity and neutral facial expressions regardless of valence

Summary

Introduction

Fast perception of emotional information is critical for human beings in forming rapid and appropriate behavioral responses to adapt to the environment. According to the dimensional model of emotion (e.g., Barrett, 1995, 1998), emotional information is generally perceived from two dimensions: valence (positive to negative) and arousal (high to low). How these two dimensions of emotional information are processed in the brain has become an important topic of research in psychology and human neuroscience (e.g., Davis and Whalen, 2001; Sabatinelli et al, 2005; Kuppens et al, 2013; Lang and Bradley, 2013; Sieger et al, 2015; Styliadis et al, 2015). These findings suggest that the amygdalar activation is involved in the processing of arousal (Sabatinelli et al, 2005) and is associated with general emotional relevance of stimuli (Davis and Whalen, 2001; Sander et al, 2003; Phelps and LeDoux, 2005)

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Results

Conclusion