Modulating cerebrospinal fluid dynamics using pulsed photobiomodulation.

Area of Science:

• Neuroscience
• Biomedical Engineering

Background:

• Photobiomodulation (PBM) is explored for enhancing brain health, particularly glymphatic drainage and neurotoxic waste clearance.
• This therapeutic potential is significant for neurodegenerative diseases like Alzheimer's disease.

Purpose of the Study:

• To investigate if PBM can modulate cerebrospinal fluid (CSF) flow in healthy adults.
• To assess the effects of transcranial PBM (tPBM) and intranasal PBM (iPBM) on CSF dynamics.

Main Methods:

• 45 healthy young adults underwent forehead tPBM and intranasal iPBM.
• Cerebrospinal fluid (CSF) dynamics were measured using blood-oxygenation level-dependent (BOLD) functional MRI (fMRI).

Main Results:

• A 4-minute PBM session induced immediate increases in intracranial CSF volume and reduced CSF inflow.
• Skin melanin affected tPBM response, with lighter skin showing higher responses.
• Both iPBM and tPBM demonstrated a dose-dependent effect on CSF dynamics.
• iPBM achieved significant CSF modulation with lower irradiance compared to tPBM.
• PBM-induced vasodilation likely explains increased CSF outflow pressure and altered CSF volume.

Conclusions:

• PBM effectively modulates CSF flow in the healthy human brain in real time.
• iPBM may be more efficient due to olfactory system proximity and lack of melanin dependence.
• Further research is needed on melanin's influence on tPBM, iPBM feasibility, and dose dependence in various populations.