Exposure to light pulsing at 40 hertz — 40 beats per second — causes brains to release a surge of signaling chemicals that may help fight Alzheimer’s Disease, Georgia Tech researchers have discovered.

Though conducted on healthy mice, the study directly connects to human trials, in which researchers exposed Alzheimer’s patients to 40 Hz light and sound. Insights gained in mice are informing the human trials in collaboration with 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,”

says first author Kristie Garza, a graduate research assistant in the lab of Annabelle Singer at the Georgia Institute of Technology and also a member of Emory’s neuroscience program.

The Neuroimmune System

One of the surging signaling molecules in the study on mice is strongly associated with the activation of brain immune cells called microglia, which purge an Alzheimer’s hallmark — amyloid beta plaque, junk protein that accumulates between brain cells.

In 2016, researchers discovered that light flickering at 40 Hz mobilized microglia in mice afflicted with Alzheimer’s to clean up that junk. In the new study[1], researchers looked for brain chemistry that connects the flicker with microglial and other immune activation in mice and exposed a surge of 20 cytokines —small proteins secreted externally by cells and which signal to other cells.

Accompanying the cytokine release, internal cell chemistry — the activation of proteins by phosphate groups — left behind a strong calling card.

“The phosphoproteins showed up first. It looked as though they were leading, and our hypothesis is that they triggered the release of the cytokines,”

says Singer, an assistant professor in the biomedical engineering department at Georgia Tech and Emory.

“Beyond cytokines that may be signaling to microglia, a number of factors that we identified have the potential to support neural health,”

says Levi Wood, an assistant professor in Georgia Tech’s George W. Woodruff School of Mechanical Engineering who co-led the study with Singer.

Gamma Waves

Alzheimer’s strikes, with few exceptions, late in life. It destroys up to 30% of a brain’s mass, carving out ravines and depositing piles of amyloid plaque, which builds up outside of neurons. Inside neurons, phosphorylated tau protein forms similar junk known as neurofibrillary tangles suspected of destroying mental functions and neurons.

After many decades of failed Alzheimer’s drug trials costing billions, flickering light as a potentially successful Alzheimer’s therapy seems surreal even to the researchers.

“Sometimes it does feel like science fiction,”

Singer says.

Microglia Activation

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 acting like a dance beat for neuron activity. Its most common frequency is right around 40 Hz, and exposing mice to light flickering at that frequency restored gamma and also appears to have prevented heavy Alzheimer’s brain damage.

[caption id=“attachment_102525” align=“aligncenter” width=“700”]A flickering light strip A flickering light strip used to expose mice to 40 Hertz light stimuli in Annabelle Singer’s lab. The exposure triggered very strong releases of signaling chemicals in the brain.
Credit: Georgia Tech / Allison Carter[/caption]

Adding to the surrealness, gamma has also been associated with esoteric mind expansion practices, in which practitioners perform light and sound meditation. Then, in 2016, research connected gamma to working memory, a function key to train of thought.

In the current study, the surging cytokines hinted at a connection with microglial activity, and in particular, the cytokine Macrophage Colony-Stimulating Factor (M-CSF).

“M-CSF was the thing that yelled, ‘Microglia activation!'”

Singer says.

Cytokine Surge

The researchers will look for a causal connection to microglia activation in an upcoming study, but the overall surge of cytokines was a good sign in general, they says.

“The vast majority of cytokines went up, some anti-inflammatory and some inflammatory, and it was a transient response. Often, a transient inflammatory response can promote pathogen clearance; it can promote repair,”

Wood says.

“Generally, you think of an inflammatory response as being bad if it’s chronic, and this was rapid and then dropped off, so we think that was probably beneficial,”

Singer adds.

The 40 Hz stimulation did not need long to trigger the cytokine surge.

“We found an increase in cytokines after an hour of stimulation,” Garza says. “We saw phosphoprotein signals after about 15 minutes of flickering.”

Perhaps about 15 minutes was enough to start processes inside of cells and about 45 more minutes were needed for the cells to secrete cytokines. It is too early to know.

Not For DIYers

As controls, the researchers applied three additional light stimuli, and to their astonishment, all three had some effect on cytokines. But stimulating with 20 Hz stole the show.

“At 20 Hz, cytokine levels were way down. That could be useful, too. There may be circumstances where you want to suppress cytokines,” Singer says. “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.”

The research team warns against people improvising light therapies on their own, since more data is needed to thoroughly establish effects on humans, and getting frequencies wrong could possibly even do damage.

Funding for the research came from the National Institute of Neurological Disorders and Stroke at the National Institutes of Health, the Packard Foundation, the Friends and Alumni of Georgia Tech, and by the Lane family.

[1] Kristie M. Garza, Lu Zhang, Ben Borron, Levi B. Wood, Annabelle C. Singer. Gamma Visual Stimulation Induces a Neuroimmune Signaling Profile Distinct from Acute Neuroinflammation. Journal of Neuroscience 5 February 2020, 40 (6) 1211-1225; DOI: 10.1523/JNEUROSCI.1511-19.2019

Top Image: Allison Carter/Georgia Tech


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