Transcranial Photobiomodulation Can Improve Working Memory in Young Adults

Transcranial photobiomodulation (tPBM), a laser light therapy, applied to the right prefrontal cortex (PFC) can improve working memory in young adults, according to study findings published in the journal Science Advances.

For the study, researchers sought to assess the effect of tPBM applied to different parts of the brain using different wavelengths. They compared the effect of 1064 nm tPBM applied to the right PFC over a 12-minute session vs 3 other double-blind, sham-controlled tPBM experiments that included: 1064 nm tPBM applied to the left PFC, the same intervention applied at a lower frequency, and a sham intervention. Participants comprised 90 college students who were neurotypical (mean age, 22 years); each participant only completed 1 of the 4 experiments.

Students took part in 2 different sessions of tPBM, which were separated by 1 week, with either sham or active tPBM applied on the PFC. They received 2 types of change-detection memory tasks: participants had to remember the orientation (experiment 1) or the color (experiment 2) of a series of items. The researchers conducted a series of follow-up experiments that compared the different wavelengths (1064 nm vs 852 nm; experiment 3) and different stimulation sites (right vs left PFC; experiment 4). Electroencephalography (EEG) recordings were done during the intervention and memory tasks. On the eighth day, researchers asked participants to report or guess which session involved active of sham tPBM.

Researchers found a significant main effect of tPBM stimulation (P <.001), but no significant interaction between tPBM stimulation and the task (P =.779). Specifically, compared with sham tPBM, K values increased after 1064-nm tPBM in both the orientation working memory task (experiment 1: P =.009, 2-tailed) and the color working memory task (experiment 2: P =.013, 2-tailed).

The mean tPBM effect (ie, active minus sham) on the K values for experiment 1 was 0.186±0.065; the mean tPBM effect on the K values for experiment 2 was 0.188±0.051. These results thus support the theory that 1064 nm tPBM on the right PFC is associated with enhancement of working memory capacity.

The contralateral delay activity (CDA) set-size effect during retention mediated the effect between 1064 nm tPBM and subsequent working memory capacity. For the orientation task: r=.446 and P <.04; for the color task r=.563 and P <.02. In fact, the behavioral benefits and corresponding changes in the CDA set-size effect were not present with tPBM at a wavelength of 852 nm or with stimulation of the left PFC.

“The results suggest that, for both color and orientation WM [working memory] tasks, the tPBM-associated changes in CDA set-size effects can predict tPBM-associated behavioral benefits,” the researchers noted.

Several limitations of the study warrant mention. There was a relatively short follow-up period. The reported literature demonstrates that when evaluating the behavioral benefits of tPBM, almost all studies applied stimulation to sites on the forehead. Due to the absorption of light by the hair, other areas such as the intraparietal sulcus may receive limited effects if being stimulated directly by tPBM.

“Further study should be conducted to explore the time course of the behavioral effects of the stimulation,” the researchers stated. They concluded that “Further work should break the barrier between hair and laser light to expand the applicability of tPBM to the whole brain.”

This article originally appeared on Neurology Advisor