<p>Although physical activity or exercise has a beneficial effect on brain structure and function, physical activity levels are decreasing due to sedentary lifestyles in contemporary society. For this reason, there has been increasing attention paid to the practical application of mild intensity exercise, which might be more attractive to and applicable for both young and older adults with a sedentary lifestyle. Indeed, long-term mild exercise training in older adults has been shown to prevent atrophy of the prefrontal cortex as well as moderate-intensity exercise intervention. However, it is still unknown whether acute mild exercise has beneficial effects on brain function, particularly executive function, mediated by the prefrontal cortex, and underlying neural substrates. To address this question, we combined an executive-function task that has been confirmed in many neuroimaging studies to target specific neural substrates and fNIRS neuroimaging techniques that allow the monitoring of task-related cortical activation shortly after exercising. We recently demonstrated that even acute mild exercise can improve executive task performance, which was positively correlated with increased arousal level and also evoked task-related cortical activation on the left dorsolateral prefrontal cortex and left frontopolar area. Although the exact neuronal substrate is still intriguing, animal microdialysis studies have demonstrated that mild exercise increased several neurotransmitters such as acetylcholine and dopamine, which could play an important role in the mild-exercise-elicited higher cognitive function.</p>