Researchers used transcranial electrical stimulation (tES) to enhance deep slow-wave sleep and measured how brain electrical impedance changed throughout the night. Lower impedance signals more open extracellular space, which is thought to allow cerebrospinal fluid to flush out toxic waste products like amyloid beta and tau — proteins linked to Alzheimer's disease. The study found that brain impedance naturally decreases during sleep, especially in REM, but the tES protocol produced additional significant decreases during the transition from light to deep sleep. This suggests that targeted brain stimulation during sleep may actively improve the glymphatic system's ability to clear metabolic waste, potentially offering a non-drug strategy to reduce neurodegeneration risk as we age.
