Zeng J. et al. - Transcranial Photobiomodulation and Cognitive Function Following Traumatic Brain Injury: A Systematic Review

This systematic review selected 6 studies from among 131 identified articles and reports cognitive improvements in patients with chronic traumatic brain injury following transcranial photobiomodulation. The authors highlight the lack of randomized controlled trials in this field and a level of heterogeneity so high that no optimal parameters can be defined.

What this study measured

The authors conducted a systematic review of the literature in accordance with the PRISMA guidelines. The databases PubMed, Web of Science, Scopus, EMBASE, and the Cochrane Library were searched through October 31, 2023. The objective was to compile the cognitive outcomes of clinical trials evaluating transcranial photobiomodulation in traumatic brain injury.

This is a systematic review, not a meta-analysis: no overall effect size, standardized mean difference, or confidence interval is calculated. The synthesis is qualitative, which means the level of evidence is lower than that of a quantitative synthesis.

Key Findings

This review provides very few figures.

• 131 articles were found in the initial search.
• 6 studies were ultimately included after applying the inclusion and exclusion criteria.
• Reported Cognitive Improvement in Patients with Chronic Traumatic Brain Injury Following Transcranial Photobiomodulation.
• No optimal treatment parameters can be identified due to significant heterogeneity among the protocols.
• The authors note the lack of randomized controlled trials in this field.

The journal does not provide effect sizes, the total number of participants, or the aggregate follow-up duration. Therefore, these data cannot be reported here.

How Transcranial Photobiomodulation Works

The authors propose several mechanisms, which remain hypothetical. Transcranial photobiomodulation is thought to increase the volume of total cortical gray matter, subcortical gray matter, and the thalamus. It is also thought to improve cerebral blood flow, functional connectivity, and cerebral oxygenation. Upstream, the absorption of red and near-infrared light by mitochondrial cytochrome c oxidase is thought to increase ATP production, an effect that is further enhanced by a modulation of oxidative stress. These mechanisms are proposed as explanations; they are not demonstrated in the review.

Limits You Should Know

Only six studies were included, which is very few. The authors explicitly state that there is a lack of randomized controlled trials in this area; therefore, the available data are based on designs that are susceptible to the placebo effect and expectation bias.

The diversity of applications is such that no optimal parameter—whether wavelength, dose, or number of sessions—can be recommended. The authors themselves describe their conclusion as encouraging but uncertain, and call for randomized trials to settle the matter.

Finally, the findings pertain to chronic traumatic brain injury. They do not apply to the acute phase or to other causes of cognitive impairment.

What This Means in Practice

Based on this review, transcranial photobiomodulation cannot be recommended for cognitive rehabilitation following traumatic brain injury. The review indicates that this issue warrants further investigation in randomized trials, which the authors explicitly call for. Individuals experiencing cognitive sequelae from a traumatic brain injury should receive neurological follow-up and rehabilitation under professional supervision.

Frequently Asked Questions

How many studies are there on photobiomodulation following a head injury?

This review, published in 2024, identified 131 articles but included only 6 after applying its criteria. This very small number reflects the recent and fragmented nature of the field. The authors also note that no randomized controlled trials were available.

Is there a recommended protocol?

No. The authors note that the heterogeneity of the applications prevents them from summarizing optimal parameters. Wavelength, power, duration, and number of sessions vary from one study to another. Therefore, no dosage recommendations can be derived from this review.

What effects on the brain do the authors describe?

They cite an increase in the volume of cortical and subcortical gray matter as well as the thalamus, and an improvement in cerebral blood flow, functional connectivity, and cerebral oxygenation. These observations are presented as possible mechanisms derived from the included studies. They have not been confirmed in a randomized trial.

Reference

Zeng J, Wang C, Chai Y, Lei D, Wang Q. Can transcranial photobiomodulation improve cognitive function in patients with traumatic brain injury? A systematic review. Frontiers in Psychology, 2024. PMID 38952831. DOI 10.3389/fpsyg.2024.1378570. https://pubmed.ncbi.nlm.nih.gov/38952831/

This summary is provided for informational purposes only and does not constitute medical advice. Photobiomodulation is not a substitute for prescribed treatment. Consult a healthcare professional.