Active Bilingual Immersion may Lead to Active Brain Cleansing: Multimodal Evidence for L2 Engagement Optimizing Glymphatic Function

BackgroundThe brains glymphatic system plays a vital role in maintaining neural health. However, little is known about whether second language (L2) immersion can influence this clearance pathway. Methods50 high-proficiency L2 English speakers (mean age: 32.6 years; 78% female) were assessed for glymphatic function using three multimodal MRI markers: BOLD-CSF coupling strength (fMRI), choroid plexus ratio (structural MRI), and DTI-ALPS index (diffusion MRI). Analyses examined relationships between glymphatic markers and L2 immersion duration, age of acquisition (AOA), and active use environment, controlling for age, education, and sex. ResultsL2 immersion duration correlated significantly with better glymphatic function. Longer immersion related to better BOLD-CSF coupling strength (r = -0.315, p < 0.05) and decreased choroid plexus ratios (r = -0.39, p < 0.05), suggesting enhanced brain-CSF coordination and fewer pathological CSF production structures. Mediation analyses demonstrated that immersion influenced ALPS indirectly through effects on choroid plexus morphology and BOLD-CSF coupling. L2 AOA moderated the immersion-coupling relationship: individuals who began learning after age 9.53 showed stronger associations between immersion and BOLD-CSF coupling, though AOA did not moderate choroid plexus effects. As for L2 immersive active is associated with better glymphatic function, while L2 immersive passive and L2 non-immersive active are both unrelated. ConclusionsL2 immersion associates with better glymphatic system function through multiple pathways, including improved brain-CSF coordination, optimized choroid plexus structure, and increased perivascular flow. These findings provide novel neurobiological evidence that bilingual experience may confer neuroprotective benefits through brain waste clearance mechanisms.