Gray matter volume moderates the effect of acute physical activity on cognitive load and relates to reading comprehension in adolescents: the Cogni-Action Project

Abstract

Acute physical activity reduces cognitive load (CL) and improves reading comprehension; however, the role of gray matter volume in these effects is unknown. This study examined how gray matter volume moderates the effects of physical activity on cognitive load, and explored its association with reading comprehension. A total of 13 male adolescents (aged 12–13 years), a neuroimaging subsample of a larger cohort, completed a randomized crossover trial that involved three energy-matched conditions: sedentary condition (SC), moderate-intensity continuous training (MICT), and cooperative high-intensity interval training (C-HIIT). We measured gray matter volume in the hippocampus, pars opercularis, and brainstem using MRI. The primary outcome cognitive load (pupil dilation) was analyzed using within-subject permutation with max- T correction and bootstrapping. Reading comprehension served as a secondary, exploratory outcome. Physical activity was a significant predictor of cognitive load ( p  < 0.001). Comprehension improved for the C-HIIT condition compared to SC; gray matter volume alone did not predict these results. Volume significantly moderated cognitive load in a region-specific pattern: hippocampal volume amplified the cognitive load increases associated with C-HIIT [ β  = 0.26, 95% CI (0.21, 0.30)], while pars opercularis and brainstem volumes reduced the cognitive load ( β  = −0.30 to −0.32, p  < 0.001); C-HIIT resulted in the lowest absolute cognitive load. Reading comprehension was higher under C-HIIT compared to SC ( g  = 0.87) and MICT ( g  = 0.50), with gains exploratorily associated with the pars opercularis volume (rho = 0.53–0.59). Gray matter volume influenced cognitive load through its interaction with physical activity modality, with C-HIIT producing the lowest cognitive load. Comprehension gains under C-HIIT were exploratorily associated with pars opercularis volume, suggesting that specific neuroanatomical characteristics may complement activity modality for cognitive benefits in school settings.