Abstract
Effective interpersonal communication depends on the ability to perceive and interpret nonverbal emotional expressions from multiple sensory modalities. Current theoretical models propose that visual and auditory emotion perception involves a network of brain regions including the primary sensory cortices, the superior temporal sulcus (STS), and orbitofrontal cortex (OFC). However, relatively little is known about how the dynamic interplay between these regions gives rise to the perception of emotions. In recent years, there has been increasing recognition of the importance of neural oscillations in mediating neural communication within and between functional neural networks. Here we review studies investigating changes in oscillatory activity during the perception of visual, auditory, and audiovisual emotional expressions, and aim to characterize the functional role of neural oscillations in nonverbal emotion perception. Findings from the reviewed literature suggest that theta band oscillations most consistently differentiate between emotional and neutral expressions. While early theta synchronization appears to reflect the initial encoding of emotionally salient sensory information, later fronto-central theta synchronization may reflect the further integration of sensory information with internal representations. Additionally, gamma synchronization reflects facilitated sensory binding of emotional expressions within regions such as the OFC, STS, and, potentially, the amygdala. However, the evidence is more ambiguous when it comes to the role of oscillations within the alpha and beta frequencies, which vary as a function of modality (or modalities), presence or absence of predictive information, and attentional or task demands. Thus, the synchronization of neural oscillations within specific frequency bands mediates the rapid detection, integration, and evaluation of emotional expressions. Moreover, the functional coupling of oscillatory activity across multiples frequency bands supports a predictive coding model of multisensory emotion perception in which emotional facial and body expressions facilitate the processing of emotional vocalizations.
Highlights
Effective communication is crucial for the formation and maintenance of social relationships in complex societies
Nonverbal emotion perception is driven by dynamic, contextdependent interactions within and between brain regions involved in the detection, integration, and evaluation of emotional expressions
It is clear that the perception of facial, body, and vocal expressions of emotion is mediated by oscillatory activity in multiple frequency bands
Summary
Effective communication is crucial for the formation and maintenance of social relationships in complex societies. Within the context of emotion perception, alpha oscillations may be involved in the selective attention to emotionally salient social cues through active inhibition of task-irrelevant regions and pathways It is notable, that many studies using static faces have found no difference in alpha synchronization between emotional and neutral expressions (Balconi and Lucchiari, 2006; Balconi and Pozzoli, 2007, 2008, 2009). Greater for supraliminally-presented facial expressions, gamma synchronization is observed in response to facial expressions processed subliminally (Balconi and Lucchiari, 2008; Luo et al, 2009), suggesting that gamma synchronization can be influenced by emotion even in the absence of visual awareness These findings are supported by intracranial studies showing localized gamma synchronization in brain regions implicated in emotion processing—most notably, the amygdala and OFC. Gamma synchronization in the OFC may reflect the attention-dependent binding of emotionally salient stimuli with internal representations of their motivational significance
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