The effect of transcranial photobiomodulation on cognitive function and attentional performance of older women with mild cognitive impairment: a randomized controlled trial

Introduction
Mild cognitive impairment (MCI) is a progressive age-related condition caused by physiological and structural changes in the brain, such as neurodegeneration and hypometabolism. Transcranial photobiomodulation (tPBM) is a neuromodulation technique that improves brain metabolism and oxygenation by irradiating red to near-infrared light on a specific area of the head. This study aimed to investigate the effect of multi-session tPBM on the cognitive capacities and attentional function of older women with MCI.

Material and methods
In this randomized controlled trial, 42 older women with MCI were randomly assigned to 2 equal groups: real and sham. The mini-mental state examination (MMSE) and the attentional Go/No-Go task were used to examine the patients. On the right frontal-pole of the cortex, 5 sessions of 850 nm tPBM were given. Re-examinations were conducted on the participants. For the Go/No-Go task, the reaction time to the target (RTT), the percentage of correct trials (PCT), and the efficiency score (ES) were measured.

Results
The findings revealed a significant interaction between group × time for MMSE (F (1, 40) = 20, p < 0.001, h2 = 0.33), and the post-hoc paired-samples t-tests revealed a substantial rise in the mean MMSE in the real group (t = 15.9; p = 0.001; d = 9.3). Additionally, for ES (F (1, 40) = 19, p < 0.001, h2 = 0.32), RTT (F (1, 40) = 17, p < 0.001, h2 = 0.38), and PCT (F (1, 40) = 13, p < 0.001, h2 = 0.31), a significant group  time interaction was discovered, and post-hoc paired-samples t-tests revealed a significant improvement in attention performance of the real group for increases in the mean of ES (F (1,40) = 20, p < 0.001, h2 = 0.33), (t = 5.3, p < 0.001,d = 0.034), decreases in the mean of RTT (t = 4.8; p = 0.001; d = –37.4), and increases in the mean of PCT (t = 2.67; p = 0.015; d = 6.3).

Conclusions
According to the findings of this study, tPBM had a positive effect on older people’s attention and cognitive abilities.