Can Low-Power Light Improve Working Memory?


[Image: Getty Images]

Editor’s note: This news story describes experimental research on a possible light-based therapy. Readers should not interpret the story as medical advice or as an endorsement of the technique, which is still under study.

Photobiomodulation, also known as low-level laser therapy, administers light from low-power lasers or light-emitting diodes (LEDs) to the surface of the body as a form of medical treatment. The noninvasive approach has been tested for pain relief, hair regrowth, nerve injuries and wound healing.

Now, an international team of researchers has found that transcranial photobiomodulation applied to the brain may enhance working-memory capacity in humans (Sci. Adv., doi: 10.1126/sciadv.abq3211). More studies are needed to verify the results, as well as to fully understand the underlying mechanism and duration of the response.

A different kind of laser treatment

The first photobiomodulation experiment occurred on the heels of the invention of the first laser. In 1967, the Hungarian physician Endre Mester illuminated the shaved backs of mice with the newly discovered ruby laser. While he hoped to eradicate tumors implanted under their skin, the laser power was far too low to have such an impact. Instead, Mester noticed a faster rate of hair growth for the treated mice as compared with controls.

Today, photobiomodulation—while still not a standardized treatment for any condition—is recognized for having some anti-inflammatory and pain-relieving effects. It differs from other light-based medical treatments, which typically heat and cut the tissue. Photobiomodulation employs low power and does not cause a significant increase in temperature.

Dongwei Li at the Beijing Normal University, China, and his colleagues aimed to explore the technique as an intervention to improve cognitive function. In particular, they wanted to test its influence on working memory, the type of short-term memory used to store information temporarily during the completion of cognitive tasks.

“People with conditions like ADHD (attention deficit hyperactivity disorder) or other attention-related conditions could benefit from this type of treatment, which is safe, simple and non-invasive, with no side-effects,” said study author Li, who is also a visiting Ph.D. student at the University of Birmingham’s Centre for Human Brain Health, UK, in a press release accompanying the research.

Enhancement in working memory

Research setup

In their experiment, the researchers shined 1064-nm laser light at the right prefrontal cortex of test subjects for 12 minutes. [Image: C. Zhao et al., Sci. Adv., doi: 10.1126/sciadv.abq3211 (2022); CC BY 4.0]

The researchers employed a diode-pumped solid-state laser with a continuous power output of 2271 mW, or around one-fifth of the skin’s maximum permissible exposure. They positioned the handheld light source over the right prefrontal cortex of 90 young adults for 12 minutes, followed by tests of visual working-memory capacity. The participants were asked to memorize the orientation of lines as well as blocks of colors.

The results revealed that transcranial photobiomodulation at 1064 nm was linked to an improvement in test scores of about 25%. No effect was observed for transcranial photobiomodulation at 852 nm or with stimulation of the left prefrontal cortex. Electroencephalogram (EEG) data also correlated with test performance, although the mechanism behind the effect remains unclear.

“As a next step, we need to figure out how long the effect of the laser treatment lasts,” said study author Ole Jensen, co-director of the Centre for Human Brain Health. “We would also like to investigate how the stimulation can help participants with attention and working-memory problems.”

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