Reduced gray matter in the prefrontal cortex and hippocampus: a potential neuroanatomical feature of insomnia comorbid with anxiety.

Running has an extremely long history as a means of locomotion for humans. Human beings can navigate long distances through bipedal running (). It is interesting to hypothesize that human upright bipedal running is also strongly tied to the evolutionary expansion of the Homo sapiens’ frontal lobes and higher cognitive functions (). Against this background, running may be viewed not simply as another exercise modality, but as a biologically foundational form of human movement with particular relevance to brain function. Running not only decreases the risk of cardiovascular diseases in general but also has positive effects on mental and brain health. There are numerous studies reporting the effects of acute exercise on cognitive function (), but major studies often focus on cycling, with which exercise intensity is easier to control. Accordingly, although acute exercise is known to benefit cognition, it remains unclear whether running produces comparable effects on executive function and prefrontal cortical activity, particularly at very light intensity. There is a limited number of studies that have focused on running with precisely defined intensities; among these, research exploring neural mechanisms has predominantly used event-related potentials derived from electroencephalographic data (; ; ; ; ; ). Consequently, few past studies have used neuroimaging techniques that allow region-specific analyses to examine the effects of acute running on cognitive function in subregions of the prefrontal cortex (PFC). Additionally, the few existing studies that used functional near-infrared spectroscopy (fNIRS) did not perform region-specific analyses within the PFC (; ). Thus, a key unresolved issue is whether a single bout of running facilitates executive function together with activation of anatomically defined prefrontal subregions. Of particular interest is the dorsolateral PFC (DLPFC), which has long been considered a brain region crucial for executive function (; ; ). One of our previous studies used multichannel fNIRS to show that moderate-intensity running exercise (50% o) activates the DLPFC and frontopolar areas (FPA) of both hemispheres and enhances executive function (), extending previous pedaling findings (; ; ; ). However, moderate-intensity exercise is the intensity at which the hypothalamic stress response occurs (). As such, vulnerable individuals, such as those with low fitness levels and older adults, may find it difficult to adhere to moderate-intensity running, which is relatively fast and imposes greater joint loading than pedaling exercise. It is, therefore, important to determine whether comparable effects can be elicited at a lower, stress-response-free intensity and at an extremely slow speed, close to normal walking speed (about 4–6 km/h). If so, the cognitive and neural benefits of running would not be limited to more demanding exercise intensities.