Introduction

It is well known that exercise generally enhances cognitive function1,2,3,4,5,6,7,8,9,10. However, the environment in which exercise is performed may be just as important as the exercise itself11,12,13. A growing body of research highlights nature's positive impacts on improving cognition and mental health14,15,16. Thus, with considerable evidence to support the benefits of exercise and being in nature, it is logical to expect that combining these two factors would lead to an ever-greater overall increase in cognition. Indeed, evidence supports this supposition: exercising outdoors in natural environments produces more benefits to the brain than exercising indoors12,17,18,19,20,21,22,23. Yet the findings are unclear for acute exercise durations under 20 min. This raises the question: How does the environment influence cognitive function for a brief exercise period? Gaining a deeper understanding of these underlying influences on the brain is important to combat the world’s growing urbanization and the associated increase in the amount of time spent indoors24.

In terms of cognition, acute outdoor exercise has primarily been found to enhance executive functions dependent on the prefrontal cortex, such as attention, working memory, and inhibitory control1,3. For instance, Bailey and colleagues19 found that participants who walked in an outdoor natural environment performed significantly better on a cognitive task—the Stroop task—than those who walked inside. These findings are further supported by Berman et al.20, who had participants complete a different cognitive task (the backwards digit span task) before and after a 35-min walk in a forest or an urban environment. In a key manipulation, the researchers induced cognitive fatigue in participants by having them complete a rigorous memory task before walking. Berman and colleagues’ results showed that on the cognitive task performed after the walk, participants who walked in the forest performed better than those who had walked in an urban environment suggesting that nature played an essential role in restoring the cognitive resources that were depleted by the memory task20. Together, these results provide evidence that outdoor exercise enhances executive function to a greater extent than indoor exercise.

Neuroimaging has provided key insight into the impact of acute exercise on the brain. Research with functional magnetic resonance imaging and functional near-infrared spectroscopy (fNIRS) has demonstrated that acute exercise drives improvements in cognition via increased cerebral blood flow (CBF) to the prefrontal cortex25,26,27,28,29,30,31,32. For example, Yanagisawa and colleagues used fNIRS to examine brain regions activated through acute exercise-induced enhancements in cognitive performance27. The researchers found that acute moderate exercise improved performance on the Stroop task and elicited increased activation in the dorsolateral prefrontal cortex- a region explicitly associated with executive function27. In addition, a range of neurotransmitters have been implicated in acute exercise's signalling pathways that induce positive cognitive and mood effects1,3,28,29,30,31,32. Specifically, several studies have found increases in dopamine, epinephrine, and norepinephrine in the prefrontal cortex post-exercise; all indicated to be involved in neuromodulating behaviours such as attention, reward, learning, and memory29,30,31,32,33. Collectively, these findings highlight the impact of acute exercise on the prefrontal cortex and indicate several mechanisms by which acute exercise influences the neurophysiology of this process.

Here we used neuroimaging to investigate the interaction of brief exercise and environment on cognition. Specifically, we utilized mobile electroencephalography (mEEG) to measure indices of cognitive performance prior to and after brief 15-min indoor and outdoor walks. Before and after each walk, participants completed a standard visual oddball task while mEEG data was recorded. Based on the abundance of literature indicating that exercise enhances cognitive performance1,2,3,4,5,6,7,8,9,10, we hypothesized that we would see an increase in the amplitude of the P300—a component of the human event-related brain potential (ERP) associated with working memory and attention—following exercise. Additionally, given the well-documented positive effects of nature on the brain14,15,16, we further hypothesized that the increase in the amplitude of the P300 would be greater following exercise outside than the following exercise inside.

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