Affective Cortical Asymmetry at the Early Developmental Emergence of Emotional Expression

Abstract

Emotions have an important survival function. Vast amounts of research have demonstrated how affect-related changes in physiology promote survival by effecting short and long-term changes in adaptive behavior. However, if emotions truly serve such an inherent function, they should be pervasive across species and be established early in life. Here, using electroencephalographic (EEG) brain activity we sought to characterize core neurophysiological features underlying affective function at the emergence of emotional expression, i.e., at the developmental age when human infants start to show reliable stimulus-elicited emotional states (4-6 months). Using an approach which eschews traditional EEG frequency band delineations (like theta, alpha), we demonstrate that negative emotional states induce a strong right hemispheric increase in the prominence of the resonant frequency (~5-6 Hz) in the infant frontal EEG. Increased rightward asymmetry was strongly correlated with increased heart rate responses to emotionally negative compared to neutral states. We conclude that functional frontal asymmetry is a key component of emotional processing and suggest that the rightward asymmetry in prominence of the resonant frequency during negative emotional states might reflect functional asymmetry in the central representation of anatomically-driven asymmetry in the autonomic nervous system. Our findings indicate that the specific mode hallmarking emotional processing in the frontal cortex is established in parallel with the emergence of stable emotional states very early during development, despite the well-known protracted maturation of frontal cortex. 3 Significance Statement Emotions provide an important survival function and are associated with unique brain states that should theoretically be present early in life. In this paper, we demonstrate in 4-6 month infants (i.e. when infants first reliably express emotions) that negative emotions are linked to increased prominence in the resonant EEG frequency of the right compared to left frontal cortex. The extent of this asymmetry was linked to heart rate reactivity. These results show that emotion induces asymmetric patterns in brain activity at the emergence of emotional expression, possibly laying the foundation for more complex functional asymmetries observed later in life.

A Review on the Role of Affective Stimuli in Event-Related Frontal Alpha Asymmetry

“…Three studies in our selection used real social interaction cues. In a study with 25 infant-parent dyades, Bolinger et al (2020) used positive (e.g., parent played peek-a-boo with the infant) and negative prompts (e.g., parent pretended that the infant has rash on his/her face) and found significantly increased right-sided frontal alpha asymmetry (reflecting avoidance or withdrawal) for the negative prompts. No effects were observed for positive and neutral stimuli.…”