The vibrant, diverse neuroscience community at Illinois is working to find solutions to some of today’s most pressing societal health challenges in fields including aging; learning, memory and plasticity; nutrition and cognition; neuroengineering; neuro-and socio-genomics; bioinformatics; and more. More than 300 faculty and staff on the Urbana-Champaign campus identify as researchers in the neuroscience space—regardless of their home department affiliation. These researchers are using leading-edge imaging tools, pioneering studies that progress from the lab to clinical applications with the goal of improving the health and lives of people everywhere.
John Polk, PhD
Associate Professor of Anthropology
Dr. John Polk’s research focuses on human locomotor biomechanics, with particular interest in relating locomotor behavior to brain size and development and skeletal morphology in humans, nonhuman primates and other mammalian model organisms. His work contributes to a better understanding of the evolution and development of human locomotor function and the neurological, skeletal, physiological, and adaptive implications of evolutionarily important changes in locomotor behavior (i.e., bipedal walking, endurance running).
Explain your research in neuroscience, in a nutshell.
Humans are well known to have relatively large brains for their body size, in comparison to other primates and mammals. Extensive research has tried to explain why and how this change has taken place. Previous explanations in comparative biology and anthropology have inferred that brain size evolution resulted from selection acting directly on cognitive abilities related to social complexity or tool use, or they resulted from increased energetic resources from improved diets (food quality/cooking) or energetic trade-offs in the size of different organ systems, freeing resources for energetically-expensive brain growth and maintenance. Unfortunately, these inferences have been based largely on interspecific correlations, yet underlying physiological and developmental mechanisms are rarely defined.
Several years ago, a colleague and I proposed an alternative explanation: that the increase in human brain size resulted, as a byproduct, from selection acting on non-cognitive factors. Specifically, around the same time that early human brain size increased, humans also evolved amazing endurance running capabilities in a hot climatic region. This increased endurance capability had wide-ranging effects on many anatomical and physiological systems including increasing lower limb length, increasing our capacity for evaporative sweating, loss of body hair, improved aerobic capacity, and increase in energy-efficient slow-twitch muscle fiber composition (among many more things). We argued that selection for endurance running was causally connected to brain growth through upregulation of growth factors like IGF-B, VEGF, and especially Brain-Derived Neurotrophic Factor (BDNF) during development. All of these growth factors had been demonstrated to be important in underlying brain size growth and maintenance during our (and other animals’) lifetimes.
We put this information in an evolutionary context because we found that selection on non-cognitive factors can alter expression of these growth factors. For example, research by other scholars had demonstrated that upregulation in BDNF and increases in the size of specific brain regions in rodents occurred as a consequence of selection for voluntary wheel running, or selection for aerobic capacity. These results indicated that selection on locomotor behavior can have indirect effects on brain size evolution.
My current research seeks to expand knowledge of the factors that regulate BNDF, and to evaluate whether these factors are related to human endurance running capabilities.
How are you currently conducting your research?
We recently submitted a review of BDNF’s role in brain size evolution. We have found evidence that BDNF is expressed longer in humans than in other primates, allowing a prolonged period of brain development. We have also identified several genes that help to promote BDNF. Two genes (PPARGC1A and MEF2) are involved in mitochondrial regulation and slow twitch muscle fiber development, and are therefore related to energy budgets and endurance running. PPARGC1A is distinctly different from comparable genes in our closest relative, chimpanzees. A second set of molecules is involved in the body’s thermoregulatory response. Particularly, nitric oxide, produced in response to heat stress in the skin allows for maintenance of vasodilation in the skin, bringing warm blood near the body’s surface for cooling. Nitric oxide can also cross the blood-brain barrier and promote BDNF expression. There are likely many other genes and processes involved, and we’re just beginning to identify relevant pathways. My lab is also working to evaluate whether selection for endurance capabilities is associated with brain size evolution in other mammalian groups (e.g., canids), since discovering multiple independent instances of the same processes provides stronger support for adaptive evolutionary trends.
How does being part of the broader Illinois research community support and enhance your work?
Illinois has a long history of strong research on the ways that neuroscience are impacted by aerobic capacity. I was inspired to pursue this research by some of some of Art Kramer and Kirk Ericson’s work that identified how changes in brain size in elderly people could be stimulated by aerobic exercise, and by Chuck Hillman and the ‘Fit Kids’ study that sought similar patterns during growth in children.
Justin Rhodes’ research is also inspiring since he takes an evolutionary approach to understanding the mechanisms that underlie neurologic changes. I am constantly encountering researchers at Illinois whose work stimulates more discussion about the mechanisms that underlie human cognitive function and evolution.
In what ways to you envision your work improving society or reaching people?
Knowing that humans have evolved exceptional endurance capabilities can inspire people to achieve greater fitness goals than they may realize. In addition, aerobic exercise has so many benefits during our lifetime (cognitive, cardiovascular, stress relief, disease prevention, general well-being etc.), and this information is actively being applied to a broad range of health interventions and best practices. Targeting the genes and physiological pathways that underlie brain growth and maintenance may lead to novel therapies to limit cognitive declines in aging populations and promote cognitive growth in kids and adults. Finally, evolutionary approaches to understanding health and medicine allows us to better understand how our bodies and their systems function, and to identify interventions that best suit our evolved capabilities.
Do you have a personal story or path that led to your interest in this particular area of research?
When I initially started down an academic path, I intended to become a paleoanthropologist. However, since the fossil record can be incomplete and difficult to access (particularly as a student), I altered my focus toward experimental approaches to understanding the evolution of skeletal and locomotor systems in primates and other mammals. As a post-doc, I worked in a lab where the PI Dan Lieberman examined endurance running ability in human evolution. This background experience and training in evolutionary biology prepared me for putting Kramer’s and Hillman’s ideas about the influences of aerobic capacity on brain growth into an evolutionary context and application.