Chelsea M. Stillman

Mediators of Physical Activity on Neurocognitive Function: A Review at Multiple Levels of Analysis

Physical activity (PA) is known to maintain and improve neurocognitive health. However, there is still a poor understanding of the mechanisms by which PA exerts its effects on the brain and cognition in humans. Many of the most widely discussed mechanisms of PA are molecular and cellular and arise from animal models. While information about basic cellular and molecular mechanisms is an important foundation from which to build our understanding of how PA promotes cognitive health in humans, there are other pathways that could play a role in this relationship. For example, PA-induced changes to cellular and molecular pathways likely initiate changes to macroscopic properties of the brain and/or to behavior that in turn influence cognition. The present review uses a more macroscopic lens to identify potential brain and behavioral/socioemotional mediators of the association between PA and cognitive function. We first summarize what is known regarding cellular and molecular mechanisms, and then devote the remainder of the review to discussing evidence for brain systems and behavioral/socioemotional pathways by which PA influences cognition. It is our hope that discussing mechanisms at multiple levels of analysis will stimulate the field to examine both brain and behavioral mediators. Doing so is important, as it could lead to a more complete characterization of the processes by which PA influences neurocognitive function, as well as a greater variety of targets for modifying neurocognitive function in clinical contexts.

Body–Brain Connections: The Effects of Obesity and Behavioral Interventions on Neurocognitive Aging

Obesity is a growing public health problem in the United States, particularly in middle-aged and older adults. Although the key factors leading to a population increase in body weight are still under investigation, there is evidence that certain behavioral interventions can mitigate the negative cognitive and brain (“neurocognitive”) health consequences of obesity. The two primary behaviors most often targeted for weight loss are caloric intake and physical activity. These behaviors might have independent, as well as overlapping/synergistic effects on neurocognitive health. To date obesity is often described independently from behavioral interventions in regards to neurocognitive outcomes, yet there is conceptual and mechanistic overlap between these constructs. This review summarizes evidence linking obesity and modifiable behaviors, such as physical activity and diet, with brain morphology (e.g., gray and white matter volume and integrity), brain function (e.g., functional activation and connectivity), and cognitive function across the adult lifespan. In particular, we review evidence bearing on the following question: Are associations between obesity and brain health in aging adults modifiable by behavioral interventions?

Physical activity predicts reduced plasma β amyloid in the Cardiovascular Health Study

Higher levels of physical activity (PA) reduce the risk of cognitive impairment, but the underlying mechanisms are unclear. Using longitudinal data from the Cardiovascular Health Study, we examined whether PA predicted plasma Aβ levels and risk for cognitive decline 9–13 years later.

Physical activity is associated with reduced Implicit learning but enhanced relational memory and executive functioning in young adults

Accumulating evidence suggests that physical activity improves explicit memory and executive cognitive functioning at the extreme ends of the lifespan (i.e., in older adults and children). However, it is unknown whether these associations hold for younger adults who are considered to be in their cognitive prime, or for implicit cognitive functions that do not depend on motor sequencing. Here we report the results of a study in which we examine the relationship between objectively measured physical activity and (1) explicit relational memory, (2) executive control, and (3) implicit probabilistic sequence learning in a sample of healthy, college-aged adults. The main finding was that physical activity was positively associated with explicit relational memory and executive control (replicating previous research), but negatively associated with implicit learning, particularly in females. These results raise the intriguing possibility that physical activity upregulates some cognitive processes, but downregulates others. Possible implications of this pattern of results for physical health and health habits are discussed.

Task-related functional connectivity of the caudate mediates the association between trait mindfulness and implicit learning in older adults

Accumulating evidence shows a positive relationship between mindfulness and explicit cognitive functioning, i.e., that which occurs with conscious intent and awareness. However, recent evidence suggests that there may be a negative relationship between mindfulness and implicit types of learning, or those that occur without conscious awareness or intent. Here we examined the neural mechanisms underlying the recently reported negative relationship between dispositional mindfulness and implicit probabilistic sequence learning in both younger and older adults. We tested the hypothesis that the relationship is mediated by communication, or functional connectivity, of brain regions once traditionally considered to be central to dissociable learning systems: the caudate, medial temporal lobe (MTL), and prefrontal cortex (PFC). We first replicated the negative relationship between mindfulness and implicit learning in a sample of healthy older adults (60–90 years old) who completed three event-related runs of an implicit sequence learning task. Then, using a seed-based connectivity approach, we identified task-related connectivity associated with individual differences in both learning and mindfulness. The main finding was that caudate-MTL connectivity (bilaterally) was positively correlated with learning and negatively correlated with mindfulness. Further, the strength of task-related connectivity between these regions mediated the negative relationship between mindfulness and learning. This pattern of results was limited to the older adults. Thus, at least in healthy older adults, the functional communication between two interactive learning-relevant systems can account for the relationship between mindfulness and implicit probabilistic sequence learning.

Weight-Loss Outcomes from a Pilot Study of African Dance in Older African Americans: African Dance and Weight Loss

Obesity is a risk factor for both cognitive and physical impairment in late adulthood. Though the rates of obesity are high in many groups, older African Americans are disproportionately affected. A randomized pilot intervention of African Dance was conducted with 28 African American older adults with obesity (mean age = 68.4 ± 5.1 years; mean BMI = 33.4 ± 6.2). The goal of the study was to evaluate the physiological outcomes of a culturally sensitive exercise intervention and specifically changes in weight.

Cardiorespiratory fitness is associated with enhanced hippocampal functional connectivity in healthy young adults.

Consistent associations have been found between higher cardiorespiratory fitness (CRF) and indices of enhanced brain health and function, including behavioral measures of cognition as well as neuroimaging indicators such as regional brain volume. Several studies have reported that higher CRF levels are associated with a larger hippocampus, yet associations between volume and memory or functional connectivity metrics remain poorly understood. Using a multi‐modal framework, we hierarchically examine the association between CRF and hippocampal volume and resting state functional connectivity (rsFC) in younger adults, as well as their relationship between with memory function. We conducted theoretically‐driven analyses with seeds in the anterior and posterior hippocampus, as well as control seeds in the caudate nucleus. We tested whether (1) hippocampal connectivity with prefrontal cortical regions was associated with CRF in an adult sample much younger than traditionally tested, (2) associations between CRF and rsFC remain significant after adjusting for volume, and (3) volume and rsFC are related to memory. We found that higher CRF levels were associated with larger anterior hippocampal volume and more positive rsFC of the anterior hippocampus to several regions including the prefrontal cortex. rsFC also accounted for significant variance in CRF, above and beyond volume. CRF can thus be independently linked to increased anterior hippocampal volume, as well as stronger hippocampal rsFC in a population much younger than those typically tested, suggesitng it is critical to maintainig multiple aspects of brain health.

Physical activity as a model for health neuroscience

Health neuroscience is a new interdisciplinary field that combines theories and techniques from health psychology and cognitive and social–affective neuroscience in order to understand how the brain affects and is affected by health behaviors. Physical activity (PA) research can serve as a useful model for various ways in which the brain can be incorporated into health neuroscience studies to better understand variability in the adoption and maintenance of, as well as benefits gained from, health behaviors. Here, we summarize evidence linking PA to brain and cognitive performance from studies conceptualizing the brain as either an outcome or mediator of cognitive change. We then discuss an emerging body of studies using a brain as a predictor approach. We discuss how studies using this approach complement existing PA studies and provide insight into a major source of variability in the outcomes of PA interventions, above and beyond the variability accounted for by known biological and demographic moderators. A more complete understanding of the bidirectional relationships between brain and behaviors, such as PA, could provide valuable insight into how to tailor interventions to optimally affect individuals, identify key barriers, and inform the development of novel policies to promote public health.