1000 Section - Differential Effects of tNIRS Parameter Combinations on Middle-Aged and Elderly Adults:A Multi-Modal Evaluation Study

Objectives : Transcranial near-infrared light stimulation (tNIRS) shows promising prospects for cognitive enhancement and neuroprotection in middle-aged and elderly populations, but its dose-response relationship remains unclear due to age, anatomical variations, and diseases, leading to a lack of unified parameter standards. This study adopted a multimodal assessment approach to explore differential effects of tNIRS protocols with varying wavelengths, power densities, and irradiation durations on neurophysiology, behavior, and safety in this population.

Design: Thirty healthy participants aged 40–80 years were enrolled in a randomized within-subject crossover trial, with the left dorsolateral prefrontal cortex as the target. Eight parameter combinations (two wavelengths: 808 nm/1064 nm; two power densities: 10/22 mW/cm²; two durations: 10/20 min) were tested, using EEG-fNIRS monitoring, high-load behavioral tasks, and safety assessments.

Results: Results confirmed significant parameter dependence of tNIRS effects. The 808 nm (10 mW/cm², 20 min) protocol achieved optimal cortical regulation, elevating EEG α/β/γ band power and prefrontal signal complexity, and optimizing local cortical excitability via matching cytochrome c oxidase absorption peaks. Conversely, 1064 nm enhanced long-distance and deep-brain connectivity. This neurophysiological optimization correlated with improved visuospatial memory accuracy (p< 0.01) and information processing efficiency. All protocols exhibited good safety and regulated autonomic function by reducing systolic blood pressure and heart rate.

Conclusion: The multimodal assessment results of this study confirm that parameter optimization is a critical prerequisite for ensuring the intervention efficacy of tNIRS on the aging brain.The 808 nm wavelength can effectively enhance cortical metabolic function and memory performance, while the 1064 nm wavelength protocol has greater advantages in regulating deep neural networks.This study verifies that parameter optimization is critical for tNIRS efficacy in aging brains, providing evidence for standardized clinical protocols.