Building upon a significant 2016 study that established a link between flickering light and Alzheimer’s treatment, researchers at Georgia Tech have now tapped into the brain chemistry behind the light’s effectiveness.
The original study, authored by Annabelle Singer when she was a professor at MIT, discovered that light flickering at 40 Hz entices brain immune cells—called microglia—to purge amyloid beta plaque, which have long been linked to the onset of Alzheimer’s Disease. The 40 Hz frequency stems from the observation that brains of Alzheimer's patients suffer early on from a lack of gamma, moments of gentle, constant brain waves that activate neuron activity. Its most common frequency is around 40 Hz—making that number the perfect target. (It’s worth nothing that, in an unrelated 2016 study, research connected gamma to working memory, a function key to train of thought.)
In the current study, Singer and colleagues in her Georgia Tech lab exposed healthy mice to light pulsing at 40 Hz and saw a surge of cytokines, accompanied by phosphoproteins. According to the researchers, the surging cytokines hinted at a connection with microglial activity, and in particular, the cytokine Macrophage Colony-Stimulating Factor (M-CSF). Since the phosphoproteins showed up first—about 15 minutes into the flickering of the light—the researchers hypothesize the proteins actually triggered the release of the cytokines at about the 1-hour mark.
“The vast majority of cytokines went up, some anti-inflammatory and some inflammatory, and it was a transient response,” said Georgia Tech’s Levi Wood, who co-led the study. “Often, a transient inflammatory response can promote pathogen clearance; it can promote repair.”
Interestingly, while the study was conducted on mice, the results are directly related to an undergoing human clinical trial at Emory University.
"I'll be running samples from mice in the lab, and around the same time, a colleague will be doing a strikingly similar analysis on patient fluid samples," said Kristie Garza, graduate research assistant in the Singer Lab and the study's first author.
In future studies, the researchers plan to look for a causal connection between a surge of cytokines and microglia activation. Additionally, based on results from stimuli intended as controls, the researchers may examine additional light frequencies—especially 20 Hz.
“At 20 Hz, cytokine levels were way down. That could be useful, too. There may be circumstances where you want to suppress cytokines,” said Singer. “We're thinking different kinds of stimulation could potentially become a platform of tools in a variety of contexts like Parkinson's or schizophrenia. Many neurological disorders are associated with immune response.”