Researchers in Japan have identified a new and relatively easy way to ascertain if the link between higher aerobic fitness and more efficient executive functions is mediated by activity in the brain's dopamine system. This study (Kuwamizu et al., 2021) was recently published in the peer-reviewed journal Medicine & Science in Sports & Exercise.
For this study, a team of scientists from the University of Tsukuba led by first author Ryuta Kuwamizu and senior author Hideaki Soya used spontaneous eye blink rate (sEBR) measurements to investigate if higher levels of cardiorespiratory fitness, increased sEBR, and more efficient neural activity in the prefrontal cortex are interconnected.
Accumulating evidence suggests that spontaneous eye blink rate is a non-invasive marker of central dopamine function; higher sEBR predicts more robust dopamine function (Jongkees & Colzato, 2016). Previous research has also shown that moderate-to-vigorous physical activity (MVPA) and high-intensity interval training (HIIT) stimulate dopamine release in numerous brain regions.
Although multiple neural mechanisms (e.g., BDNF, neurogenesis, synaptic plasticity) and various neurotransmitters (e.g., endocannabinoids, serotonin) influence the brain-enhancing benefits of physical activity, it's well established that MVPA and HIIT workouts increase dopamine levels and that, when it comes to the neuromodulation of aerobic exercise, the dopaminergic system is of paramount importance (Heijnen et al., 2016).
For the recent University of Tsukuba study, Soya Lab's goal was to determine if sEBR is an effective marker for tracking exercise-induced changes in neural efficiency that previous studies link to the brain's dopamine system.
"The dopaminergic system is associated with both executive function and motivated behavior, including physical activity," Kuwamizu explains in a February 1 news release. "We used sEBR as a non-invasive measure of dopaminergic system function to test whether it could be the missing link between aerobic fitness and cognitive function."
To test this hypothesis, the researchers had a cohort of 35 healthy young men (18-24 years old) undergo an aerobic fitness evaluation in conjunction with sEBR assessments; they also performed a Stroop task to measure executive functions. During the color-word Stroop task, cortical activity in the prefrontal cortex (DLPFC) was monitored using functional near-infrared spectroscopy (fNIRS). Among other findings, correlation analyses showed that "higher sEBR was correlated with higher neural efficiency of the l-DLPFC."
"As expected, we found significant correlations between aerobic fitness, cognitive function, and sEBR," Soya noted. "When we examined these relationships further, we found that the connection between higher aerobic fitness and enhanced cognitive function was mediated in part by dopaminergic regulation."
"Although previous studies have indicated that aerobic fitness and cognitive function are correlated, this is the first to provide a neuromodulatory basis for this connection in humans," Kuwamizu added. "Our data indicate that dopamine has an essential role in linking aerobic fitness and cognition."
"These results indicate that the sEBR mediates the association between aerobic fitness and executive function through prefrontal neural efficiency, which clearly supports the hypothesis that brain dopaminergic function works to connect, at least in part, the missing link between aerobic fitness and executive function," the authors conclude.
Ryuta Kuwamizu, Kazuya Suwabe, Chorphaka Damrongthai, Takemune Fukuie, Genta Ochi, Kazuki Hyodo, Taichi Hiraga, Atsuko Nagano-Saito, Hideaki Soya. "Spontaneous Eye Blink Rate Connects Missing Link between Aerobic Fitness and Cognition." Medicine & Science in Sports & Exercise (Published online ahead of print: December 29, 2020) DOI: 10.1249/MSS.0000000000002590
Bryant J. Jongkees and Lorenza S. Colzato. "Spontaneous Eye Blink Rate as Predictor of Dopamine-Related Cognitive Function—A Review." Neuroscience & Biobehavioral Reviews (First published online: December 16, 2016) DOI: 10.1016/j.neubiorev.2016.08.020
Saskia Heijnen, Bernhard Hommel, Armin Kibele, and Lorenza S. Colzato. "Neuromodulation of Aerobic Exercise—A Review." Frontiers in Psychology (First published: January 07, 2016) DOI: 10.3389/fpsyg.2015.01890
Tzu-Wei Lin and Yu-Min Kuo. "Exercise Benefits Brain Function: The Monoamine Connection." Brain Sciences (First published online: January 13, 2013) DOI: 10.3390/brainsci3010039