Research

EARLY LIFE CONDITIONS

Environmental conditions early in development are known to impact learning through organizational effects on the brain. In the extreme case, developmental challenges such malnutrition and exposure to pathogens or toxins can impair learning throughout life. On-going work in the Sewall lab is examining how environmental contaminants such as lead and mercury, postnatal nutrition, and early life infection may impair learning by interfering with postnatal brain development. Song learning in birds provides an excellent opportunity to pursue these questions because this form of learning occurs during a critical period early in life and is underpinned by neuronal growth within a specific neural circuit.

SOCIAL DYNAMICS

Sociality is argued to select for intelligence in animals, because navigating social relationships requires superior cognition and associated brain mechanisms. Although evolutionary change underlies some specialization for sociality, within species correlations between group size, cognition, and neuroplasticity suggest that these traits can also change during an animal’s lifetime. However, surprisingly few studies have examined how individuals’ cognitive performance and underlying neuroplasticity change as a function of social conditions. Understanding how animals respond to changing social conditions includes assessing such plasticity, which requires evaluating developmental plasticity (aka organizational effects), life-long flexibility, and the physiological mechanisms that modulate traits.

Historically, research on plasticity in cognition has been focused on negative consequences of social interactions. The potential for group membership to enhance individuals’ cognitive performance, communication, and neuroplasticity may be overlooked because as group size and social contact increase, so too does competition and social conflict. While social contact can improve cognitive performance and support neuroplasticity by providing learning opportunities and social enrichment, social conflict can be a chronic stressor that can impair cognitive performance, generating a trade-off between these social factors. Specifically, social conflict raises stress hormone (glucocorticoid) levels, and chronic elevated levels can impair cognition and brain function. However, the relationship between glucocorticoid levels and neural performance is not linear and levels that are too low can also impair cognitive performance by compromising motivation and attention to important stimuli. Social contact could play an important role in stabilizing and maintaining glucocorticoid levels in an optimal range, thereby enhancing cognitive performance and neuroplasticity, but this hypothesis has not been directly tested. The overarching goal of our research is to fill gaps in our knowledge of the plasticity and mechanisms regulating cognitive performance to deepen our understanding of the consequences of group living.

URBANIZATION

Human habitat disturbance is now recognized as impacting the phenotypes of wild animals and is a particular concern for wild birds. Though some species are threatened by human habitat disturbance, many animals adjust their behavior and physiology through phenotypic plasticity to cope with environmental change. Such plasticity is often sufficient to permit animals to adjust to changing environmental conditions and behavior can be the first means by which animals respond to ecological change in an effort to maintain homeostasis.

Endocrine mechanisms are a major link between organisms’ perceptions of environmental conditions and behavioral and physiological responses and, thus, play a central role in mediating phenotypic plasticity. There is an urgent need to understand the endocrine mechanisms that permit animals to cope with changing environments because understanding the proximate basis of phenotypic adjustments to habitat disturbance will shed light on why some species persist and others decline when faced with a changing environment. Reciprocally, determining how novel environmental conditions alter endocrine phenotypes provides insight into the function and evolution of these mechanisms.

Our lab studies song sparrows living along a rural-urban gradient around Blacksburg, VA. We have found that urban song sparrows are more aggressive than their rural counterparts and that stress hormones (glucocorticoids) and activation of the social behavior network in the brain, but not testosterone, may underpin this behavioral difference.