Microstate Dynamics Alterations in Response To 40 Hz Rhythmic Light Intervention in Mild Cognitive Impairment

This study investigated the neuromodulatory effects of 40 Hz rhythmic light (RL) versus a rhythmic light control condition (RLCC) on microstate dynamics in individuals classified with mild cognitive impairment (MCI) and healthy controls. This study employed a two-session, within-subjects design in which each participant completed both 40 Hz and RLCC sessions. EEG was recorded immediately before (pre) and during each RL session, while cognitive assessments were conducted pre and post each session. Twenty-four participants classified with MCI and 27 healthy controls were exposed to both light conditions and underwent electroencephalography recordings, cognitive performance testing (2-back task), and subjective sleepiness questionnaires (Karolinska Sleepiness Scale). We used microstate analysis to examine alterations in microstate dynamics in responses to each light condition. Microstate analysis revealed a reduction in the duration of microstate B and the occurrence rate of microstate C following 40 Hz RL stimulation, suggesting enhanced neural processing efficiency. Both MCI and control participants exhibited stable microstate configurations (A–D) across light conditions, with balanced coverage (~ 20–30%) and subtle shifts—particularly between microstates A and B—indicating dynamic brain state reorganization under 40 Hz stimulation, especially in the MCI group. 40 Hz RL may support compensatory neural mechanisms in individuals with MCI while enhancing sensory and cognitive processing in healthy aging individuals. These findings highlight the potential use of 40 Hz RL as a non-invasive intervention to modulate brain networks and promote cognitive function. Future longitudinal studies are needed to explore the sustained effects of 40 Hz RL on cognitive function and neural integrity in aging populations.