Transcranial Photobiomodulation and Firefighter Health and Wellness: A Single-Arm,Open-Label Pilot Study

Abstract

Background:

First responders are often exposed to many physically and mentally stressful events throughout their careers, and common complaints include poor sleep quality, chronic pain, post-traumatic stress symptoms, mood dysregulation, and cognitive impairments.

Objective:

We performed an open protocol, active treatment-only study with a small sample of male firefighters (n = 16) to examine the effects of transcranial photobiomodulation (PBM) on self-reported symptom measures and objective measures of cognitive function.

Methods/Materials and Methods:

The treatment consisted of 810 nm near-infrared light to the head using four transcranial LEDs and one intranasal LED. Treatment duration was 20 min per session, 3–4 sessions per week for 8 weeks.

Results:

We found significant pre-/post-treatment improvements with moderate-to-large effect sizes in mood and post-traumatic stress symptoms, pain interference, and readiness for social reintegration, and across all measures of fluid cognition.

Conclusions:

This proof-of-concept study also demonstrated no significant side effects, good compliance, and feasibility of use in a first responder population. Though additional research is required, PBM may present a relatively cost-effective, well-tolerated, low-risk, and easy-to-use treatment to enhance both specific symptoms and general wellness.

Introduction

Firefighters encounter a myriad of formidable challenges in their line of work, which can significantly strain both their physical and mental well-being. The demanding nature of their job often involves long, irregular hours and unpredictable schedules that disrupt normal routines and rest periods. Beyond logistical difficulties, firefighters are also exposed to hazardous situations that can lead to personal injury and profound psychological stress. Each emergency call they respond to can potentially leave lasting effects, contributing to a range of physical and mental health issues, including orthopedic injuries, chronic pain,^1,2 post-traumatic stress disorder (PTSD), anxiety, and depression.³ This intricate interplay of factors not only elevates the risk of physical injuries but also increases the likelihood of enduring mental health problems. As a result, first responders, including firefighters, experience a higher rate of morbidity and mortality compared to other occupational groups.^4

–7 Consequently, there is an urgent need for lifestyle-based therapeutic interventions that can be easily integrated into their daily routines to enhance their overall functional, social, and physical resilience.

In recent years, photobiomodulation (PBM) has emerged as a promising alternative therapy for various health and wellness conditions, attracting considerable attention from researchers and practitioners.^8
–10 PBM is a safe, accessible, non-invasive therapy that leverages specific wavelengths of red and near-infrared (NIR) light to elicit biological responses at the cellular level. Clinical studies also demonstrate many positive benefits. For example, using stringent randomized clinical trial methods, researchers have shown the benefit of active PBM treatments over placebo controls. Langella, et al. (2018) showed significant reductions in pain scores and reductions in serum pro-inflammatory cytokines in the active treatment arm in patients who underwent total hip arthroplasty. Wells et al. (2024) found accelerated recovery from muscle contusions in athletes treated with PBM compared to placebo controls.¹¹ Further, Salehpour et al. (2019) conducted a systematic review and meta-analysis indicating that tPBM significantly improved cognitive performance, attention, and executive functioning among young, healthy adults, with moderate to large effect sizes across several cognitive domains.

There is growing evidence identifying the biological mechanisms underlying these functional improvements, including reductions in acute and chronic inflammation, enhanced circulation, and improved mitochondrial function.^12,13 These properties suggest that PBM could serve as an effective treatment for numerous acute and chronic health issues. Given these potential positive outcomes, limited risk profile, accessibility, and noninvasive nature, PBM presents a possible therapeutic avenue that could bolster both physical and mental health resilience among first responders when incorporated into their routine care.¹⁴

The primary aim of this study was to gather preliminary data on the effects of transcranial PBM (tPBM) among a small sample of active-duty firefighters. This proof-of-concept investigation assessed the feasibility and potential benefits of tPBM treatment within this unique population. The insights gleaned from this research could lay the groundwork for more rigorous clinical trials—characterized by randomization and placebo control—that would further explore the treatment’s effects on first responders. Specifically, this study evaluated changes in self-reported mood, sleep quality, pain severity, and pain interference alongside objective measures of cognitive function, utilizing a comprehensive set of standardized and validated assessment tools. After a dedicated eight-week regimen of active tPBM treatment, we hypothesized that participants would experience notable improvements in symptoms and cognitive function, contributing to a better understanding of how such interventions could enhance the well-being of firefighters, thereby providing a functional foundation for future investigations.

Methods

Participants

Participants in this study included 16 active-duty firefighters from the Clark County Fire Department in Las Vegas, Nevada. In this pilot sample, only male firefighters were selected for participation to limit any potential sex effects that might impact such a small sample. All participants were on active service and were between the ages of 24 and 48. Thirteen of the 16 participants completed all phases of this preliminary treatment trial, while three were unavailable for follow-up assessment due to work and family conflicts.

Trial design

This was a nonrandomized active treatment-only trial, and data were collected as a proof-of-concept (i.e., can an at-home device be deployed effectively in the first responder population without interfering with active service) data set for future reference. Each participant underwent a baseline assessment, including a mix of standardized symptom questionnaires and cognitive testing described below. After the baseline assessment, participants were shown how to use and care for the device and then instructed to use the tPBM device every other day for 20 min for eight weeks and track their treatment use. At the end of the 8th week, each participant underwent a post-treatment assessment using the same baseline assessment battery.

Symptom measures

Each participant was administered a standardized battery of symptom questionnaires at baseline and post-treatment (see Table 1 for a description), which included the after as primary outcome measures: mood was measured using the Center for Epidemiological Studies Depression Scale (CES-D) and PTSD Checklist, 5th edition (PCL-5), the Pittsburgh Sleep Quality Index (PSQI) was used to measure sleep quality, pain severity/pain interference was measured using the Patient-Reported Outcomes Measurement Information System (PROMIS) pain interference scale, and readiness for social re-integration was measured using the Mayo-Portaland Ability Index (MPAI). Additional questionnaires about alcohol use [Alcohol Use Disorders Identification Test (AUDIT)], brain injury exposure [Ohio State University Traumatic Brain Injury Identification Method (OSU-TBI-ID)], and headaches (Headache Impact Test, HIT-6) were also collected to characterize the sample further, but given the sample size, they were not included in the present analysis.

Table 1.

Descriptions of All Symptom Measures

Measure	Description	Scoring considerations
CES-D	20-item questionnaire with response options ranging from 0 to 3 for each item (0 = Rarely or None of the Time, 1 = Some or Little of the Time, 2 = Moderately or Much of the time, 3 = Most or Almost All the Time). Scores range from 0 to 60, with high scores indicating greater depressive symptoms.	Cut-off: ≥ 16 Reliable change: 10
PCL-5	20-item questionnaire with response options ranging from 0 to 4 (0 = Not at all, 1 = A little bit, 2 = Moderately, 3 = Quite a bit, 4 = Extremely). Total score is determined by summing all item scores and ranges from 0–80; higher scores indicate more severe PTSD symptoms.	Cut-off: ≥ 31 Clinically meaningful change: 10–20 Reliable change: 5–10
PSQI	A 19-item questionnaire that assesses sleep quality and patterns in adults over the past month. Components measured include sleep latency, sleep duration, sleep efficiency, sleep disturbances, use of medications, and daytime sleep dysfunction. Items include a combination of Likert-type and open-ended questions, which are later converted to standardized scores using provided guidelines. Scores for each question range from 0–3, with higher scores indicating more acute sleep disturbances.	Cut-off: ≥ 5
PROMIS-PI	An 8-item computer adaptive tests that asks questions about the severity of pain experienced daily and how much the pain interferes with regular daily activities. Each item is rated on a 5-point scale (0 = Not at all, 1 = A little bit, 2 = Somewhat, 3 = Quite a bit, 4 = Very much), and the total score across items is converted to a standardized T-score (M = 50 ± 10), where higher scores indicate more severe symptoms.	Cut-offs (T-scores): Mild = 55–59 Moderate = 60–69 Severe ≥70 Clinically meaningful change: 2–3
MPAI	This is 35-item measure of the physical, cognitive, emotional, behavioral, and social problems people might encounter. It has 3 indices (Ability, Adjustment, Participation) and a total score with lowers scores indicating greater integration. Each item is rated on a 5-point scale (0 = no functional disabilities, 1 = impairment is mild and, with appropriate assists, function is generally normal, 2 = impairment interferes with the activity less than 25% of the time, 3 = impairment interferes with the activity 25% to 50% of the time, 4 = impairment interferes most of the time.

CES-D, Center for Epidemiological Studies Depression Scale; MPAI, Mayo-Portland Ability Index; PCL-5, PTSD checklist, 5th edition; PROMIS-PI, Patient Reported Outcomes Measurement Information System-Pain Interference; PSQI, Pittsburgh Sleep Quality Index.

Cognitive measures

This study utilized two standardized, computer-administered neuropsychological measures (See Table 2 for description). First, the Conners Continuous Performance Test-3rd Edition (CPT-3) was used to measure sustained attention, impulsiveness, and vigilance. Second, the Cognitive Battery from the NIH Toolbox was used to briefly (25 to 30 min total) capture each participant’s premorbid ability, cognitive processing speed, basic executive function, and visual memory. Outcome measures from both measures included normative standardized scores adjusted for age and educational level.

Table 2.

Descriptions of All Cognitive Measures

Measure	Description	Standardized score references
CPT-3		T-score (50 ± 10)
Detectability (d’)	Average ability to differentiate targets from non-targets. A lower score indicates better performance.
Omission errors	Average rate of missed targets. A lower score indicates better performance.
HRT SD	Consistency in reaction time across time blocks. A lower score indicates better performance.
HRT ISI	Change in the response speed at longer interstimulus intervals. A lower score indicates better performance.
NIH Toolbox		Standard score (100 ± 15)
PVT	Measure of crystalized intelligence and an estimate of premorbid (pre-injury) intelligence. A higher score indicates better performance.
ORR	Measure of crystalized intelligence and educational attainment/exposure that is not expected to change after injury. A higher score indicates better performance.
DCCS	Measure of cognitive flexibility or executive function. A higher score indicates better performance.
FICA	Measure of attention and inhibitory control (executive function). A higher score indicates better performance.
PSM	Measure of visual memory and sequencing. A higher score indicates better performance.
LSWM	Measure of working memory. A higher score indicates better performance.
PCPS	Measure of cognitive processing speed. A higher score indicates better performance.
Cognitive Composite	Global score for the NIH Toolbox that summarizes the performance across all the measures. A higher score indicates better performance.

CPT-3, Conners Continuous Performance Test, 3rd edition; DCCS, dimensional change card sort; FICA, Flanker Inhibitory Control and Attention; HRT, hit reaction time; SD, standard deviation; ISI, inter-stimulus interval change; LSWM, List Sorting Working Memory; NIH, National Institute of Health; ORR, oral reading recognition; PCPS, Pattern Comparison Processing Speed; PSM, Picture Sequence Memory; PVT, Picture Vocabulary Test.

tPBM device

Participants used the VieLight Neuro Alpha PBM devices v1 (Toronto, Canada), which deliver 810 nm NIR light to the head using four transcranial LEDs. Three LEDs provide 100 mW/cm² irradiance and a fourth at 75 mW/cm². A fifth LED is also placed in the nostril, emitting 810 nm NIR light with an irradiance of 25 mW/cm². Participants underwent tPBM treatments of 20 min each, 3–4 times weekly for eight weeks, totaling approximately 24–32 sessions. LEDs were placed at standardized positions on the scalp targeting prefrontal and temporal cortices, critical regions implicated in mood regulation, stress response, and cognitive control. The fifth LED inserted intranasally enabled direct stimulation of deeper brain structures. Importantly, this protocol aligns with previous studies demonstrating effectiveness for mood and cognitive enhancement.^14
–16 The selected 810 nm wavelength is supported by previous findings demonstrating optimal skull penetration and neural effects with minimal side effects.¹² Additional details of device specifications, settings, and brain regions targeted are provided in Table 3.

Table 3.

Photobiomodulation Device Specifications and Settings

Specifications
Manufacturer	Vielight (montreal, Canada)
Model	Neuro alpha v1 (2020)
Number of emitters	5
Emitter type	Light Emitting Diode (LED)
Center wavelength	810 nm
Spectral bandwidth	Full Width Half Max: ± 20.2 nm
Operating mode	Pulsed
Frequency	40 Hz
Duty cycle	50%
Pulse on duration	25 ms
Aperture diameter	1 cm²
Beam shape	Circular
Beam divergence	0 degrees on contact
Exposure duration	1200 s * 0.5 (duty cycle) = 600 s
Total Intervention Exposure	Every other day (3–4 days/week) for 8 weeks (∼28 sessions)

Emitter distribution, irradiance, and energy delivered
Energy Source	Nasal Applicator	Headset
Energy Source	Nasal Applicator	Anterior	Lateral	Posterior
LEDs	1	1	2	1
Wavelength (nm)	810	810	810	810
Pulse rate (Hz, 50% duty-cycle)	40	40	40	40
Beam spot (cm²)	1	2.5	2.5	2.5
Power output density (mW/cm²)	25	75	100	100
Energy dose density (J/cm²)	15	45	60	60
Tissue penetrated	Mucosa	Scalp	Scalp	Scalp
Target(s)	Midline orbitofrontal cortex, bilateral entorhinal cortices, olfactory bulbs	Midline dorsomedial prefrontal cortex	Left and right lateral parietal lobes	Midline precuneus, posterior cingulate cortex

Total energy dose delivered to target surfaces
Per session	15J/cm² + (3 * 60 J/cm²) + 45 J/cm² = 240 J/cm²
Total intervention	240 J/cm² × 28 sessions = 6,720 J/cm²

Statistical analysis

Demographic variables were assessed for normality using Shapiro Wilk’s tests, and clinical variables were assessed for normality and homogeneity of variance using Shapiro Wilks and Levine’s tests, respectively. Multiple imputation with predictive mean matching (knn = 3) was used to impute missing data for the three participants who were unable to complete post-testing assessments. Paired t-tests or Wilcoxon Signed-Rank tests were used to assess change in clinical variables between the pre- and post-treatment visits for continuous variables that met or violated parametric assumptions, respectively. To control multiple comparisons, the Benjamini–Hochberg false discovery rate procedure¹⁷ was used for all 20 null hypothesis tests, and statistical significance was thresholded at α = 0.05. All p values are reported with 95% confidence intervals, and exact p values are reported for all non-parametric comparisons. All parametric results are reported along with Cohen’s d, for which |d| ≥ 0.20, 0.50, and 0.80 are interpreted as small, moderate, and large effects, respectively, and nonparametric comparisons are reported along with r as a measure of effect size, for which |r| ≥ 0.10, 0.30, and 0.50 are interpreted as small moderate, and large, respectively.¹⁸ All statistical procedures were performed using StataBE v18.0 (StataCorp, College Station, TX).

Results

Demographics

Basic demographic characteristics of this sample are provided in Table 4. Compliance with the use of the tPBM devices was quite high (median number of treatments = 27 [71.4% of the sample]; range = 23 to 29; expected was 28). It should be noted that one participant completed 23 treatments due to a faulty headset that required replacement.

Table 4.

Demographic Characteristics of the Present Sample (n = 16)

Characteristic	n	%
Sex/gender
Male	16	100.00
Marital status
Never married	3	18.75
Married	11	68.75
Divorced	1	6.25
Widowed	1	6.25
Race
White	9	56.25
Asian	4	25.00
American Indian	1	6.25
Native Hawaiian	2	12.50
Ethnicity
Not Hispanic	12	75.00
Hispanic	2	12.50
Unknown	1	6.25
Not reported	1	6.25

	M ± SD	Range
Age	38.78 ± 6.70	24–48
Years of education	14.38 ± 0.89	13–16

Symptom measures

Descriptive statistics at each time point and the results of statistical tests comparing performance over time on all symptoms and cognitive measures are reported in Table 5.

Table 5.

Change over Time on Symptom and Cognitive Measures

Measure	Baseline		Follow-up		Difference^a		95% CI^a		t(15) / z	p	d / r
Measure	M/Mdn	SD/IQR	M/Mdn	SD/IQR	M/Mdn	SD/SE	LL^a	UL^a	t(15) / z	p	d / r
Symptom
CES-D	16.63	11.49	10.24	9.68	−6.38	7.48	−10.37	−2.40	−3.41	.004	−0.85
PCL-5	23.63	14.32	13.93	8.88	−9.69	12.27	−16.23	−3.16	−3.16	.007	−0.79
PSQI	8.44	3.35	6.98	3.11	−1.46	3.07	−3.10	0.17	−1.91	.076	−0.48
PROMIS-PI	55.19	7.43	48.98	6.72	−6.21	7.84	−10.39	−2.03	−3.17	.006	−0.79
MPAI
Ability	7.88	5.64	4.11	3.77	−3.77	4.55	−6.19	−1.35	−3.31	.005	−0.83
Adjustment	10.25	6.26	5.56	4.32	−4.69	5.65	−7.70	−1.68	−3.32	.005	−0.83
Participation^b	3.50	1.00–6.50	1.00	0.00–2.00	−1.73	0.94	−3.57	0.11	−2.76	.005	−0.69
Total^b	15.50	10.50–31.00	8.00	4.50–15.50	−9.00	1.64	−12.22	−5.78	−3.21	.000	−0.80
Cognitive
CPT-3
Detectability (d’)	45.69	7.08	42.19	6.55	−3.50	7.76	−7.64	0.64	−1.80	.091	−0.45
Omission Errors^b	45.00	45.00–46.00	45.00	45.00–45.00	0.00	0.12	−0.23	0.23	−0.57	.688	−0.14
HRT SD	44.38	4.62	41.38	4.26	−3.00	3.10	−4.65	−1.35	−3.87	.002	−0.97
HRT ISI	49.88	4.72	49.25	7.00	−0.63	4.72	−3.14	1.89	−0.53	.604	−0.13
NIH Toolbox
PVT	106.81	8.10	107.06	8.74	0.25	4.97	−2.40	2.90	0.20	.843	0.05
ORR	105.69	11.02	108.94	8.78	3.25	8.92	−1.50	8.00	1.46	.166	0.36
DCCS	115.63	13.50	125.69	12.21	10.06	9.79	4.84	15.28	4.11	.001	1.03
FICA	100.31	14.02	108.69	12.02	8.38	10.36	2.85	13.90	3.23	.006	0.81
PSM^b	111.00	103.00–117.50	114.50	106.50–138.50	10.00	4.05	2.06	17.94	2.54	.009	0.63
LSWM	99.63	13.00	111.50	12.51	11.88	9.94	6.58	17.17	4.78	.000	1.19
PCPS^b	114.50	103.00–122.50	130.50	123.50–137.50	16.00	2.63	10.84	21.16	2.87	.002	0.72
Cognitive Composite	111.00	9.30	121.44	10.29	10.44	5.94	7.27	13.60	7.02	.000	1.76

N = 16. Bold text indicates a statistically significant difference that survived the multiple comparison correction (FDR > p < 0.05).

Bootstrapping with 1,000 repetitions was used to estimate standard error and confidence intervals for the median difference.

Wilcoxon signed-rank test was used for statistical comparison due to failure to meet parametric assumptions. For these measures, exact p values and effect sizes are reported as r coefficients.

CI, confidence interval; FDR, false discovery rate; M, mean; Mdn, Median; SD, standard deviation; IQR, interquartile range; SE, standard error; LL, lower limit; UL, upper limit.

CES-D

At baseline, depression severity for the group was in the clinical range (M = 16.63, SD = 11.49). After treatment, the average range was below the clinical cutoff (M = 10.24, SD = 9.68), and the reduction in symptom severity at the end of the 8 weeks of treatment was statistically significant (t = −3.41, p = 0.004). The average decrease of −6.38 points is considered a large effect (d = −0.85) and exceeds published reliable change indices.

PCL-5

At baseline, the average group total score was 23.63 (SD = 14.32). There was an average reduction in symptoms of −9.69 (follow-up M = 13.93, SD = 8.88) which was statistically significant (t = −3.16; p = 0.007), with a moderate effect size (d = 0.79) and exceeds what is considered a reliable change based on published norms (change >12 points¹⁹).

PSQI

At baseline, the average total score for the PSQI was 8.44 (SD = 3.35) which is below clinical cutoffs. There was an improvement of −1.46 in sleep quality; though this change was not significant statistically, the improvement occurred with a small effect size (d = −0.48).

PROMIS pain interference

The average T-score for pain interference was 55.19 (SD = 7.43), which is within the normal range of pain interference. There was a reduction in pain interference scores of −6.21 (follow-up M = 48.98, SD = 6.72), which was statistically significant (t = −3.17; p = 0.006) and considered a moderate effect size (d = −0.79).

MPAI

Changes in the total score and sub-scale scores were all found to be significantly improved after treatment (p < 0.05), all with large effect sizes (d ≥−0.80), except the Participation subscale, which had a moderate effect size (d = −0.69).

Cognitive measures

Table 5 also includes baseline, post-treatment, change scores, and statistical findings for cognitive measures.

CPT-3

No significant differences were noted for detectability, omissions, or the hit reaction time inter-stimulus interval, although a small effect size was demonstrated for improvement in detectability (d = −0.45). A significant improvement with a large effect size was observed in hit reaction time standard deviation (t = −3.87, p = 0.002, d = −0.97), with the post-treatment scores (M = 41.38, SD = 4.26) demonstrating a more consistent response speed when compared to pre-treatment (M = 44.38, SD = 4.62).

NIH Toolbox

As expected, the measures of crystallized intelligence (Picture Vocabulary and Oral Reading) did not show any significant changes between the time points (p = 0.843 and 0.166, respectively). All individual measures of fluid cognitive abilities demonstrated statistically significant improvement (ps <0.01) with moderate (Picture Sequence Memory d = 0.63; Pattern Comparison Processing Speed d = 0.72) to large effect sizes (dimensional change card sort d = 1.03; Flanker Inhibitory Control and Attention d = 0.81; List Sorting Working Memory d = 1.19). A significant improvement and large effect size were also demonstrated on the Total Cognitive Composite score, where standard scores increased by more than half a standard deviation (M = 10.44, SD = 5.94), t = 7.02, p = 0.000, d = 1.76.

Discussion

The results of this preliminary active treatment trial appear to demonstrate group improvements in mood, post-traumatic stress symptoms, sleep quality, pain interference, and cognitive functioning after eight weeks of active tPBM treatment. Qualitatively, the participants in the sample had no significant concerns with regard to compliance or side effects during the treatment, consistent with many other published studies.^15,20
–22 This positive preliminary finding requires additional validation using more rigorous randomized clinical trial methods and larger samples, but it adequately demonstrates the feasibility of executing such a study without significant interruption of daily activities in first responders.

First responders, such as those participating in this study, are at risk of developing several conditions for which PBM might be well suited to address. The risk of PTSD and subsequent mood issues is one of the main issues that one could expect in individuals responding to assaults, car accidents, individuals in physical health crises, fires, and other events. In fact, we did note elevations in PTSD symptom reporting in this group at baseline. However, improvements in symptom reporting severity were both statistically significant, with moderate to large effect sizes, and reliable for those in the sample. Our findings are consistent with other small sample studies and case reports, clinical trials, and meta-analyses that have reported PBM treatment-related changes in measures of PTSD-related symptoms, mood, and/or anxiety.^20,21,23,24

Given the shift-work nature of the job requirements for firefighters, sleep quality might also be expected to be affected as constant interruptions during the night are expected during work shifts. This was, in fact, the case for this sample, with many significant and frequent interruptions of sleep each shift reported by our participants. Importantly, most participants remarked that they were not necessarily concerned about a call out but noted significant difficulty when trying to return to sleep, because they were often wondering when the next call out would happen. This prevented them from sleeping consistently while on shift. Though improvements noted after PBM treatment were not statistically significant, a meaningful effect size was observed (d = −0.48), and many spontaneously discussed that there was an increased ability to return to sleep more efficiently, even after a call out. They further remarked that they were able to relax more quickly as they noted fewer ruminating thoughts and worries. These effects are consistent with other studies that have examined the impact of PBM on sleep quality.^25
–27

Although pain interference was within the average range for this firefighter sample at both baseline and post-treatment, a statistically significant reduction was observed. This finding is somewhat difficult to interpret, as it suggests that while there was a measurable decrease in pain interference, it may not have been a substantial issue for these individuals to begin with, or they are individuals who frequently work through pain to accomplish work-related responsibilities. Possible explanations include the high sensitivity of the measurement tool detecting small but statistically significant changes, regression to the mean where transient factors at baseline resolved over time, or psychological factors such as influencing expectation effects influencing responses. Additionally, the intervention may have provided benefits that were not fully captured by baseline scores, such as improving resilience to minor discomfort or reducing the perceived burden of pain in daily activities. To determine the practical significance of this change, further analyses could examine whether reduced pain interference is linked to meaningful improvements in work performance, mobility, or quality of life.

MPAI is frequently used to assess function after brain injury; however, the subscales measure important daily activities that cover a range of physical, cognitive, emotional, behavioral, and social problems that can affect individuals without a history of TBI. Importantly, after tPBM treatment, there were significant improvements across each of the MPAI subscales, indicating that substantial improvements occurred across daily functional states. Qualitatively, participants remarked in unsolicited ways about improvements in relationships with family and significant others, they described work-related benefits, and increased energy. The moderate-to-large effect sizes observed should be a focus of future research in firefighters and other similar populations, as these measures would suggest that there is an improvement in quality of life.

Cognitive function was also found to be significantly improved across fluid cognitive domains, while measures of “crystallized” cognitive function (e.g., word reading and picture vocabulary) remained relatively stable. The absence of change on these crystallized measures, in addition to the magnitude of the effect sizes for fluid aspects of cognitive function, supports the likelihood that the post-treatment differences are real improvements rather than solely practice effects on these measures. Our results are generally consistent with other studies that have reported improved memory, attention, processing speed, and/or executive functioning in populations of healthy individuals;^14,28

–31 individuals with mild cognitive impairment, dementia or other memory complaints;^22,32
–34 and in those with conditions commonly encountered in populations of first responders, including PTSD and other mood disorders.^16,35

It should be noted that there are several neuromodulation techniques, including transcranial direct current stimulation (tDCS), repetitive transcranial magnetic stimulation (r^TMS), and transcranial focused ultrasound, that have demonstrated therapeutic potential for pain, mood, and cognitive disorders.^36,37 However, these methods often require trained medical personnel, expensive equipment, and specialized settings, restricting their widespread adoption. In contrast, tPBM presents distinct advantages due to its non-invasive nature, safety profile, simplicity, cost-effectiveness, portability, and the feasibility of home-based administration. Further, unlike other neuromodulation devices, PBM’s unique mechanisms of cellular modulation likely offer broader therapeutic applications.^12,14

Strengths, limitations, and remaining gaps

Additional research is required before conclusions about the effectiveness of tPBM in first responders can be made. We acknowledge that there are important limitations of this study, including a small sample size, a male-only sample, and active treatment-only (open protocol) assignment. Additionally, the single post-treatment assessment study design could not address longer-term symptom reduction and cognitive improvement maintenance. Placebo effects and effects related to participation in a study are also possible and will require additional study design elements to reduce their impact. Future studies utilizing more rigorous methods (e.g., blinding, randomization, sham-control, etc.), larger sample sizes, and additional longitudinal follow-up assessments are currently underway. Additionally, while we report several improvements our participants commonly verbalized regarding their quality of life, future qualitative research studies would benefit our understanding of the impact on quality of life.

Finally, we acknowledge general gaps in understanding of optimal treatment dosing and pulsation parameters, the mechanism of delivery, positioning of devices, treatment duration, and specific sex- and age-related effects that exist in the field of PBM. This is evident in this study as not all participants showed improvement across all the measures. Though no declines were noted in the data, some individual participants did not show any improvement. As such, there are key protocol questions that future studies must address, including identifying ideal wavelengths (e.g., comparing 810 nm vs. 1064 nm), determining optimal treatment durations (e.g., 10 vs. 20 vs. 30 min), and defining session frequencies (daily vs. every-other-day treatments) beyond the suggested treatment protocol provided by the manufacturer. Future studies would also benefit from exploring individualized parameters, such as adjustments for anatomical factors, including skull thickness, hair density, hair color, and individual variability in baseline cognitive or mood symptoms. Additionally, research could be used to clarify the best stimulation locations for distinct clinical outcomes, such as prefrontal cortex stimulation for mood and executive function, or temporal cortex for PTSD and emotional regulation.^15,16 Rigorous randomized controlled trials with sham control groups, larger sample sizes, and long-term follow-up are essential next steps to establish the efficacy, durability, and clinical utility of tPBM.

Conclusions

The present findings support a growing body of literature indicating the potential therapeutic effects of PBM therapy. Though additional research is warranted, non-invasive neuromodulatory treatments such as this may present a relatively cost-effective, well-tolerated, low-risk, and easy-to-use treatment to enhance both specific symptoms and general wellness in individuals at risk for developing mood disorders, chronic pain, and cognitive decline. Nevertheless, this initial study demonstrated both feasibility and efficacy, including the calculation of effect sizes to guide sample size requirements in future studies. Together, these findings demonstrate that this type of treatment could easily be scaled in first responder populations, as these types of at-home treatment devices make delivery of treatment easy (high compliance rates) and allow first responders to engage in treatment at their leisure or in between call-outs. In addition to its indications as a disease-modifying treatment in a host of conditions, PBM may potentially play a role in optimizing wellness in individuals where mood stability, decreased anxiety, improved sleep quality, enhanced physical fitness, attention, executive functioning, and processing speed are critical to job performance and safety.

Footnotes

Acknowledgments

The authors are incredibly grateful to the Clark County Firefighters Union for their generous endorsement and support of this research study. The authors also acknowledge Vielight, Inc., which contributed headset devices used in this study.

Authors’ Contributions

D.F.T. participated in the design, implementation, recruitment of participants, data collection, data analyses, and article preparation and revisions. H.M.L. contributed to the data analysis, interpretation of outcomes, and article preparation and revisions. E.A.W. participated in the design, data collection, data analyses, and article edits and revisions.

Ethical Approval

The University of Utah School of Medicine institutional review board approved and monitored all participant interactions and informed consent. As such, all research was conducted according to strict ethical guidelines protecting data collection and participant management.

Disclaimer

All views expressed in this article are those of the authors and do not represent the United States Veterans Administration or otherwise constitute an official viewpoint of the United States Government.

Data and Materials

All the data are available upon request after the request specifics are reviewed and legally binding data use agreements are established, which include appropriate protection of participant confidentiality.

Author Disclosure Statement

No conflicts of interest are noted by either author.

Funding Information

This study was partially funded by generous private donations to the Larry and Laurie Carr PBM Research Fund. Vielight, Inc. provided the photobiomodulation (PBM) equipment used in this study and paid the open access fee for this publication. Otherwise, Vielight did not have any input into the design or execution of the studies, nor were they involved in the analysis or reporting of the results.

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