AUCD's network of Intellectual and Developmental Disability Research Centers (IDDRCs) consists of 16 Centers. Fifteen Centers currently receive funding from the Eunice Kennedy Shriver National Institute for Child Health and Human Development (NICHD). IDDRCs contribute to the development and implementation of evidence-based practices by evaluating the effectiveness of biological, biochemical, and behavioral interventions; developing assistive technologies; and advancing prenatal diagnosis and newborn screening.

How do babies learn to be social? Babies are born into the world with so much to learn, from basic body movements to complex communication and interaction skills. Philosopher John Locke believed that babies are born into the world as “blank slates” (tabula rasas)—everything to learn will be gained from their environment and experience¹. Indeed, environment and experience are critical for learning—studies on enriched environments highlight this^2,3. However, research continues to highlight the influence of inherent characteristics, underlying neurobiology and genetics on how and what we learn or know⁴. Researchers aim to understand what and how we learn by studying the dynamic interplay between inherent biological traits, physiological states, and the environment⁴.

Consider the complex environment an infant is exposed to at any moment, an environment that has constantly changing sensory stimuli—auditory, tactile, olfactory, proprioceptive, and visual. How does an infant determine what information is important? What information does an infant choose to learn from amongst that complex sensory environment? Psychologist B.F. Skinner proposed a formative model known as operant conditioning which proposes that we learn from our experience based on reward or punishment⁵. In short, if we like it, we learn to do it more; if we don’t like it, we learn to do it less. Many therapies that aim to promote skill development have foundations in Skinner’s operant conditioning model (e.g., applied behavior analysis). Whether a baby likes or feels rewarded, and then learns from the environment or activity, is related to a child’s sensory processing of and physiological response to, the activity or environment. Imagine, for example, an infant who upon seeing their mother’s face during peek-a-boo, experiences a pleasurable physiological response (or arousal); the infant is likely enjoying this and feels rewarded by the activity, is likely to engage more, and learn about this social interaction (reciprocal smiling, relationship between verbal and physical play interactions, etc). In short, our internal reward experience, including physiological arousal response, will influence what we engage with and learn from our environment.

The biology behind physiological arousal is complex. Many things happen when our body responds to stimuli in the environment. Relatively quick responses include dilation or constriction of the pupils. Other responses are changes in heart rate and breathing rate, quicker or slower depending on the saliency of the experience. Changes also occur at the neurobiological level when reacting to salient stimuli including changes in key neural chemicals (e.g., dopamine⁶) as well as activation of multiple, functionally connected brain regions (e.g., frontal cortex and subcortical structures such as the amygdala). While dissecting the neural circuitry of arousal in humans is complex and limited by technology, physiological markers of arousal can be ascertained relatively easily (e.g., pupillary, cardiac, and respiratory dynamics) and may be a homolog to underlying neural activity that can ultimately be tested in non-human models. There is evidence that physiological arousal has a key role in human psychology. For example, many therapies integrate autonomic nervous system regulation into treatment, mostly for anxiety and trauma-related disorders (e.g., biofeedback^7–9), and psychopharmacology utilizes the downstream release or reuptake of neurotransmitters associated with arousal to regulate feelings of anxiety or depression¹⁰. Despite the acknowledged importance of arousal regulation, the dynamic nature of various physiological arousal phenomena makes it very difficult to measure arousal in naturalistic situations, despite the potential relevance to learning and adaptation systems.

In addition to anxiety and mood disorders, other psychiatric conditions have increasing awareness of arousal dysregulation as a core feature. The 2013 changes to the diagnostic criteria for autism spectrum disorder (ASD) include sensory aversions, perhaps akin to over-arousal, to the second symptom domain. It is possible that the early biological and neurobiological differences of infants with or at likelihood for developing a neurodevelopmental disorder, like ASD, may be associated with dysregulation of the arousal system. This dysregulation may be present very early in life (potentially even prior to birth) and lead to downstream deficits in social motivation and ultimately symptoms of ASD such as social communication impairments. There is evidence to support this theory. Parents of infants as young as six months of age report significant sensory arousal differences in those infants who go on to develop ASD¹¹. These patterns of atypical arousal vary from over-reactivity, under-reactivity, or broad dysregulation across stimuli¹². Researchers have also hypothesized that some of the core features of an ASD diagnosis (e.g., repetitive motor movements) may exist and persist due to dysregulated arousal and a child’s attempts to regulate arousal¹³. Interestingly, early symptoms of atypical arousal have been linked to later severity of ASD symptoms¹², poorer social skills¹⁴, and lower communication abilities¹². This evidence points to the critical role arousal plays in ASD.

Despite this evidence and an increasing interest in sensory reactivity amongst the ASD research community, much of the literature is constrained by an ability to acquire meaningful, objective metrics of arousal. Eye tracking studies have shown that time spent looking at the eyes is a feature of ASD and may reflect deficits in social motivation^15–18 though the specificity and onset of these differences is less robust, and no study has linked these findings with arousal biometrics. Much of the literature on arousal to date has focused on parent or observational reports of infant or child behavior that is interpreted as over- or under-reactive to sensory stimuli, an inherently subjective method. Little research has examined physiological aspects of arousal such as temporal dynamics of pupillary changes, heart rate, and breathing rate. No research has integrated multiple metrics of arousal in infants nor those with or at high likelihood for ASD. Our research team combines the expertise of psychologists, neuroscientists, and engineers to design methods to fill these critical gaps in the field. We use existing methods to promote the field’s understanding of atypical arousal and its relationship with ASD diagnosis, functional outcomes, and patterns of learning. We are actively gathering arousal biometrics in infants at low and high likelihood for developing ASD (based on whether they have an older sibling with ASD).

In the context of ASD, many researchers and clinicians recognize that regulation of the arousal system is necessary to promote learning (e.g., Adapted Responsive Teaching^13,19). Teaching parents to recognize signs of dysregulation in their infant and methods to provide support to assist in regulation provides an opportunity to promote more, sustained regulated states, and ultimately increasing times during which an infant is in an optimal learning state. At this point, interventions that consider arousal regulation rely on infant behavioral cues to indicate possible dysregulation (e.g., increase of stimming behaviors). Our work will advance the understanding of arousal to promote the use of its underlying physiology to help parents and clinicians aid in regulating difficult behaviors.

The use of arousal biometrics also has the potential to catalyze therapeutic developments and new mechanistic discoveries. Though we are in the initial stages of our work, the theoretical and practical foundations robustly support further examination of arousal as an influential component underlying neurodevelopmental disorders. We are eager to continue this groundbreaking work and to improve the lives of those with ASD and other NDDs.

References

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