What Does Physiology Have to Do With Emotional Development?

Why do we study anxiety as a multi-faceted construct? Does it matter to our phenomenology, how we experience this emotion, and how we behave? This begs the question: What matters most in the study of emotion? As we discussed in this blog over the last year, understanding the development of anxiety is complex and not as straightforward as we would think or hope. Even with our most robust predictors like fearful temperament, not all fearful children become anxious and not all individuals who are anxious were temperamentally fearful as children. It may seem more obvious why researchers are interested in the environment (such as parenting) relative to why we would care about physiological processes. However, we argue that these biological components are just as important to understand, and we are only beginning to identify the role they play in socio-emotional development.

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Source: Dr. William Doan

I have spent the better part of my career trying to understand the role of physiological processes in the development of emotions and anxiety. It was a question that was initially inspired by the foundational work of Dr. Megan Gunnar where we leveraged measurement of the hormone cortisol to understand the role of this stress marker on behavior and adjustment in infants and children. It can be tempting to hypothesize that there was a direct link between the physiological response and the behaviors we observe particularly in infancy (for example, pain equals crying). Although this is not this straightforward, we know from decades of work that physiological processes matter in understanding behavioral development.

Even though the biological systems that we study do not exist solely to support our emotions and psychology, predictable associations exist between the behaviors we study (fear and anxiety) and various physiological systems. Changes in the brain are also dynamic throughout development and with major transitions throughout childhood into early adulthood. The development of these systems is also fundamental to the development of the emotions and behaviors accompanying anxiety development.

Here, we have collected some of our favorite research findings that highlight the importance of including physiological measures to understand the development of anxiety and depression. These studies highlight that physiology can provide unique insight into the etiology and treatment of socio-emotional problems by addressing one or more of the following key goals of developmental psychophysiological research.

First, measuring physiology allows us to understand biology for biology’s sake; that is, how do nervous systems change in development, and how do those changes relate to behavioral, social, and emotional outcomes. For example, the neural circuitry underlying emotion regulation undergoes profound maturation and refinement throughout childhood and adolescence. One pattern of brain activity thought to reflect emotion regulation, delta-beta coupling, has been shown to predict children’s adaptive behavior during emotional challenges two years later (Myruski and colleagues, 2022).

Second, physiological measures, such as those associated with emotion regulation, can also predict risk and resilience. We have repeatedly shown that heart rate variability (HRV) in toddlerhood (a marker of emotion regulation) predicts which fearful children will become socially anxious and inhibited with peers (Buss and colleagues, 2018). Moreover, individual differences in HRV appear earlier in infancy and predict trajectories of social fearfulness and inhibition across early childhood (Brooker and colleagues, 2013). Neural markers of emotion regulation allow researchers to define objective targets for psychology interventions. For example, delta-beta coupling has been associated with better treatment response for depressed adolescents. (Venanzi and colleagues, 2024).

Third, examining physiology allows us to capture abilities that are not readily accessible via self-report due to developmental stage limitations (that is, language and introspection abilities). In particular, our work also demonstrates that children's abilities to reflect on and articulate how emotions are experienced and managed are somewhat limited; neurophysiology provides a window into how children regulate emotions which is less accessible via their own reports of how they regulate emotions (Babkirk and colleagues, 2015). A pattern of brain activity reflecting effortful down-regulation of unpleasant emotions, the late positive potential (LPP), has been shown to predict observed child emotion regulation (Babkirk and colleagues, 2015), and can be enhanced by parent support (Myruski and colleagues, 2019). Another strength of physiological approaches is the ability to measure implicit processes (that is, outside conscious awareness) or those not evident in behavior directly. Several studies report increased amplitudes of P1, N2, P3, and LPP in response to threatening faces among anxious children compared to controls. For example, neural differences are evident in response to the presentation of threatening stimuli for anxious compared to non-anxious children (Wauthia and colleagues, 2016).

In summary, leveraging physiology helps us understand child social-emotional development, identify those children at highest risk for anxiety and depression, and identify targets for intervention.