Cortical hemodynamics as a function of handgrip strength and cognitive performance: a cross-sectional fNIRS study in younger adults

Abstract

Background There is growing evidence for a positive correlation between measures of muscular strength and cognitive abilities. However, the neurophysiological correlates of this relationship are not well understood so far. The aim of this study was to investigate cortical hemodynamics [i.e., changes in concentrations of oxygenated (oxyHb) and deoxygenated hemoglobin (deoxyHb)] as a possible link between measures of muscular strength and cognitive performance. Methods In a cohort of younger adults (n = 39, 18–30 years), we assessed (i) handgrip strength by a handhold dynamometer, (ii) short-term working memory performance by using error rates and reaction times in the Sternberg task, and (iii) cortical hemodynamics of the prefrontal cortex (PFC) via functional near-infrared spectroscopy (fNIRS). Results We observed low to moderate negative correlations (rp = ~ − 0.38 to − 0.51; p < 0.05) between reaction time and levels of oxyHb in specific parts of the PFC. Furthermore, we noticed low to moderate positive correlations (rp = ~ 0.34 to 0.45; p < 0.05) between reaction times and levels of deoxyHb in distinct parts of the PFC. Additionally, higher levels of oxyHb (rp (35) = 0.401; p = 0.014) and lower levels of deoxyHb (rp (34) = − 0.338; p = 0.043) in specific parts of the PFC were linked to higher percentage of correct answers. We also found low to moderate correlations (p < 0.05) between measures of handgrip strength and levels of oxyHb (rp = ~ 0.35; p < 0.05) and levels of deoxyHb (rp = ~ − 0.25 to − 0.49; p < 0.05) in specific parts of the PFC. However, there was neither a correlation between cognitive performance and handgrip strength nor did cortical hemodynamics in the PFC mediate the relationship between handgrip strength and cognitive performance (p > 0.05). Conclusion The present study provides evidence for a positive neurobehavioral relationship between cortical hemodynamics and cognitive performance. Our findings further imply that in younger adults higher levels of handgrip strength positively influence cortical hemodynamics although the latter did not necessarily culminate in better cognitive performance. Future research should examine whether the present findings can be generalized to other cohorts (e.g., older adults).

U-Shape by Quadratic Equation: A Best-fit for Modelling Hemodynamic Changes in the DCCS Task

“…The fNIRS technology allows us to monitor brain activation by measuring hemodynamic changes such as the concentration of oxy-hemoglobin (HbO) and deoxy-hemoglobin (HbR) in targeted brain areas. The HbO and HbR data are dynamic and changing over time; thus, careful and advanced statistical analyses are needed to examine this type of time-sensitive data [1][2][3]. However, no systematic and standardized approaches were established in the first decade of this millennium; thus, fNIRS scientists had the liberty to choose the statistical methods they believed to be appropriate and adequate.…”

“…Since then, employing GLM to estimate the hemodynamic changes has become the standard inference statistics in fNIRS studies. GLM empowers scientists to estimate the subject, channel, and task-specific evoked hemodynamic responses and robustly separate the evoked brain activity from systemic physiological interference using independent measures of nuisance regressors [1][2][3]. In addition, GLM can significantly enhance the contrast to noise ratio of the brain signal, improve feature separability, and ultimately lead to better classification accuracy.…”

“…In contrast, the Heavy-user pattern was 'not normal and needs further exploration'. However, the hemodynamic changes in each channel should be a kind of nonlinear relationship [1][2][3]; thus, polynomial regression via quadratic function might be more appropriate for estimating the HbO changes in targeted brain areas. Accordingly, in this study, we proposed a quadratic function for better modeling the hemodynamic changes:…”

“…The GLM results could only demonstrate a significant HbO increase for the Non-user group and a significant decrease for the Heavy-user group. However, HbO changes evoked by cognitive shifting are not a linear function of time; instead, there is a nonlinear relationship [1][2][3]. Therefore, first, a set of quadratic equation analyses was conducted to re-analyze Li et al [4] data.…”

“…The functional near-infrared spectroscopy (fNIRS) technology is a portable and comfortable way to measure the hemodynamic changes in targeted brain areas [1][2][3]. It can generate time-sensitive data that could be analyzed using general linear modeling (GLM) to estimate the oxygenated hemoglobin (HbO) changes between the task and baseline.…”