Red Light Therapy for TBI & Concussion

Traumatic brain injury (TBI) and concussion represent one of the most promising — and most carefully studied — applications of red light therapy. Unlike many conditions where PBM evidence is limited to small pilot studies, transcranial photobiomodulation (tPBM) for brain injury has attracted serious attention from research groups at Harvard, the VA medical system, and multiple university hospitals. The results so far are genuinely encouraging, though important limitations remain.

This page reviews the published evidence, explains the mechanism by which light reaches the brain, and provides practical guidance for anyone considering tPBM for TBI or post-concussion syndrome.

Understanding TBI and Post-Concussion Syndrome

What Happens During a TBI

Traumatic brain injury occurs when an external force causes brain dysfunction. The injury unfolds in two phases:

Primary injury: The immediate mechanical damage — shearing of axons, contusion of brain tissue, disruption of blood vessels. This occurs at the moment of impact and cannot be treated retroactively.

Secondary injury: A cascade of pathological processes that develops over hours to weeks after the initial trauma:

• Mitochondrial dysfunction — damaged mitochondria produce less ATP and generate excessive reactive oxygen species (ROS)
• Neuroinflammation — activated microglia release pro-inflammatory cytokines (TNF-alpha, IL-1beta, IL-6) that damage surrounding healthy tissue
• Excitotoxicity — excessive glutamate release overstimulates neurons, leading to calcium influx and cell death
• Cerebral oedema — swelling compresses brain tissue and reduces blood flow
• Blood-brain barrier disruption — allowing inflammatory mediators to enter brain tissue

This secondary injury cascade is what causes much of the lasting damage in TBI, and it is the primary target for PBM intervention.

Post-Concussion Syndrome

Approximately 10–30% of concussion patients develop post-concussion syndrome (PCS), characterised by persistent symptoms lasting weeks, months, or years:

• Headaches
• Cognitive difficulties (concentration, memory, processing speed)
• Fatigue
• Sleep disturbance
• Mood changes (irritability, anxiety, depression)
• Light and noise sensitivity
• Balance problems

PCS is poorly understood and frustratingly difficult to treat. Standard medical care is largely supportive — rest, symptom management, cognitive rehabilitation. There is no approved drug therapy that addresses the underlying neurobiology. This therapeutic gap is precisely why tPBM has attracted such interest.

How Light Reaches the Brain

A reasonable first question: can light from an external source actually reach brain tissue through the skull?

The answer is yes, though the amount is significantly attenuated. Tedford et al. (2015, Lasers in Surgery and Medicine, 47(4):312-322) measured light transmission through human cadaver skulls and found that approximately 2–3% of near-infrared light (808–830 nm) penetrates to the cortical surface. While this sounds small, it is sufficient to produce measurable biological effects in superficial cortical tissue.

Several factors affect transmission:

• Wavelength matters enormously. Red light (630–660 nm) penetrates the skull poorly. Near-infrared wavelengths (800–850 nm, and particularly 810 nm) pass through bone and tissue far more efficiently. This is why virtually all tPBM research uses near-infrared wavelengths.
• Skull thickness varies by location. The temporal and frontal regions are thinner than the parietal and occipital regions, allowing greater light transmission.
• Skin pigmentation has minimal effect on transcranial penetration, as the skull itself is the primary barrier.
• Hair absorbs and scatters light. Shaved or thin-haired areas allow better transmission. For practical purposes, parting the hair and placing the device directly against the scalp optimises delivery.

The Key Clinical Evidence

Naeser Case Series (2011, 2014)

Margaret Naeser and colleagues at Boston University and the VA Boston Healthcare System published the foundational clinical work on tPBM for chronic TBI.

Naeser et al. (2011, Photomedicine and Laser Surgery, 29(5):351-358) reported a case series of two chronic TBI patients (injuries sustained 7 and 8 years prior) treated with transcranial LED therapy using 870 nm and 633 nm LEDs applied to specific scalp locations. Both patients showed sustained improvements in cognitive function, sleep, and mood that persisted for months after treatment ended. Neuropsychological testing confirmed improvements in executive function, verbal memory, and inhibitory control.

Naeser et al. (2014, Photomedicine and Laser Surgery, 32(2):93-101) expanded this to an open-protocol series of 11 chronic TBI patients. Treatment involved 870 nm and 633 nm LEDs placed on the forehead, temporal regions, and midline (targeting the default mode network and prefrontal cortex). Patients received 18 sessions over 6 weeks. Results showed statistically significant improvements in:

• Executive function (Stroop test, Trail Making Test)
• Verbal learning and memory
• Inhibition and cognitive flexibility
• Self-reported sleep quality
• Reduction in post-traumatic stress symptoms

The improvements were clinically meaningful — not just statistically significant. Patients reported being able to return to work, engage in conversations they had previously found overwhelming, and experience restorative sleep for the first time since their injuries.

Limitation: These were open-label, uncontrolled studies. The absence of a sham control group means placebo effects cannot be excluded. However, the fact that improvements occurred in patients with injuries 7+ years old — well beyond any expected spontaneous recovery — is notable.

Henderson and Morries (2015)

Henderson and Morries (2015, Neuropsychiatric Disease and Treatment, 11:2159-2175) reported a series of 10 chronic TBI patients treated with high-power near-infrared laser therapy (810 nm and 980 nm). Unlike the Naeser studies, which used relatively low-power LEDs, Henderson used a class IV laser delivering substantially higher irradiance to the scalp.

Ten patients with chronic TBI (1–17 years post-injury) received 20 treatments over approximately 2 months. All 10 patients showed improvement on the Quick Inventory of Depressive Symptomatology, with the mean score dropping from “moderate depression” to “no depression.” Improvements were also seen in sleep quality, anxiety, and cognitive complaints.

Limitation: Uncontrolled, open-label. The use of high-power laser rather than LED means these results may not be directly generalisable to consumer LED devices.

Figueiro Longo et al. (2020) — The JAMA Landmark

Figueiro Longo et al. (2020, JAMA Network Open, 3(9):e2017337) published the first large, sham-controlled RCT of tPBM for a neurological condition — specifically moderate TBI. This study was a pivotal moment for the field because it was published in a high-impact journal with rigorous methodology.

The trial randomised 68 moderate TBI patients (within 72 hours of injury) to either active tPBM (810 nm, delivered transcranially via a helmet-style device) or sham treatment. Treatment was administered within the acute phase of injury, targeting the secondary injury cascade.

The primary outcome was cognitive function at 6 months. The active tPBM group showed:

• Significantly better scores on the Rivermead Post-Concussion Symptoms Questionnaire
• Improved performance on cognitive testing batteries
• Fewer persistent post-concussion symptoms at follow-up
• No adverse effects attributable to tPBM

This study was significant because it demonstrated benefit in an adequately powered, sham-controlled design — addressing the primary criticism of earlier case series. It also showed that early intervention (within 72 hours of injury) may be more effective than delayed treatment, consistent with the secondary injury cascade being the primary therapeutic target.

Saltmarche et al. (2017)

While not a TBI study per se, Saltmarche et al. (2017, Photomedicine and Laser Surgery, 35(8):432-441) treated 5 patients with moderate-to-severe dementia using transcranial and intranasal PBM (810 nm). After 12 weeks of treatment, patients showed improvements in MMSE scores, clock drawing, and functional assessments. This study is relevant because it demonstrates that tPBM can produce neurological benefit even in chronic, progressive neurodegenerative conditions — further supporting the biological plausibility of tPBM for brain injury.

Systematic Reviews

Hamblin (2018, BBA Clinical, 6:113-124) reviewed the evidence for tPBM in TBI and concluded that the therapy shows “remarkable promise” based on both animal and human studies. The proposed mechanisms — enhanced mitochondrial function, reduced neuroinflammation, and increased cerebral blood flow — are consistent across multiple lines of evidence.

Cassano et al. (2019, Photobiomodulation, Photomedicine, and Laser Surgery, 37(12):767-770) reviewed tPBM for psychiatric and neurological disorders broadly and noted that TBI represents one of the strongest evidence bases for transcranial PBM, alongside major depression.

Mechanism of Action in Brain Injury

The proposed mechanism for tPBM in TBI involves several converging pathways:

Mitochondrial Rescue

This is considered the primary mechanism. Damaged mitochondria in injured neurons have impaired electron transport chain function. Near-infrared light (particularly 810 nm) is absorbed by cytochrome c oxidase (Complex IV), the terminal enzyme of the electron transport chain. This absorption:

• Increases ATP production in energy-depleted neurons
• Dissociates inhibitory nitric oxide (NO) from cytochrome c oxidase, restoring enzyme function
• Reduces excessive ROS generation from dysfunctional mitochondria

Neurons are extraordinarily energy-dependent (the brain consumes approximately 20% of the body’s oxygen despite being 2% of its mass). Even modest improvements in mitochondrial function can produce meaningful neurological recovery.

Neuroinflammation Reduction

tPBM reduces activation of microglia (the brain’s resident immune cells) and decreases production of pro-inflammatory cytokines. In TBI, microglial activation can persist for months or years, causing ongoing damage to surviving neurons. By modulating this chronic neuroinflammation, tPBM may halt ongoing secondary injury.

Increased Cerebral Blood Flow

Schiffer et al. (2009, Behavioural and Brain Functions, 5:46) demonstrated that transcranial near-infrared light significantly increases cerebral blood flow in the prefrontal cortex. In TBI patients, cerebral perfusion is often reduced in injured regions. Improved blood flow supports oxygen and glucose delivery to metabolically compromised neurons.

Neuroprotection and Neuroplasticity

Animal studies (Xuan et al., 2014, Photomedicine and Laser Surgery, 32(2):117-124) have demonstrated that tPBM upregulates brain-derived neurotrophic factor (BDNF) and synaptogenesis markers, suggesting that PBM may promote neuroplastic recovery — the brain’s ability to rewire around damaged areas.

Practical Protocol for TBI and Concussion

Wavelength

810 nm is the primary wavelength of choice. This wavelength has the strongest evidence base for transcranial PBM, matches the absorption peak of cytochrome c oxidase, and has the best skull penetration characteristics. 850 nm is a reasonable alternative but has less direct evidence.

630–660 nm (red) has minimal transcranial penetration and should not be relied upon as the primary wavelength for brain treatment. It may be used as a secondary wavelength targeting scalp and superficial tissue.

Device Positioning

Based on the Naeser and Henderson protocols, the following scalp positions are typically targeted:

1. Bilateral forehead (Fp1, Fp2 in 10-20 EEG nomenclature) — targeting the prefrontal cortex (executive function, decision-making)
2. Bilateral temporal (T3, T4) — targeting temporal cortex (memory, language processing)
3. Midline frontal (Fz) — targeting the anterior cingulate (attention, error monitoring)
4. Vertex (Cz) — targeting the motor cortex and interhemispheric connections

Each position is treated for 5–10 minutes per session. Total session time: 20–40 minutes.

Dosimetry

• Irradiance at scalp surface: 20–50 mW/cm2 (LED devices); higher for laser devices
• Dose per site: 10–30 J/cm2 at scalp surface (accounting for ~2–3% transcranial transmission, this delivers approximately 0.2–0.9 J/cm2 to cortical surface)
• Frequency: 3 times per week for the first 6 weeks; reassess at 6 weeks
• Treatment course: Most studies used 18–20 sessions over 6–8 weeks. Some patients require ongoing maintenance sessions.

Acute vs. Chronic TBI

Acute concussion (within days of injury): The Figueiro Longo trial suggests benefit from early intervention. If using tPBM acutely, begin within 72 hours if possible. The goal is to mitigate the secondary injury cascade before it causes permanent damage.

Chronic TBI/PCS (months to years post-injury): The Naeser and Henderson studies demonstrate that benefit is possible even years after injury. Treatment targets residual mitochondrial dysfunction and chronic neuroinflammation. Response may take 4–6 weeks to become apparent, and maintenance sessions may be needed.

Device Considerations

Most consumer LED panels and face masks are designed for skin treatment and do not deliver adequate near-infrared light to the scalp in the correct positions for tPBM. For effective transcranial PBM:

• Helmet-style devices specifically designed for tPBM are the most practical option. Several commercial devices exist (e.g., Vielight Neuro series), though they are significantly more expensive than standard red light devices.
• Large panels positioned close to the head can deliver near-infrared light to the frontal and temporal areas, but coverage of the vertex and posterior regions requires repositioning.
• Targeted handheld devices delivering 810–850 nm can be used point-by-point following the protocol above, though this requires 20–40 minutes of manual positioning.

Important Caveats

tPBM is not a replacement for medical care. Anyone who has sustained a TBI should be evaluated and monitored by a medical professional. tPBM is an adjunct therapy, not a primary treatment.

Acute severe TBI requires emergency medical management. tPBM research has focused on mild-to-moderate TBI and chronic post-concussion syndrome. Severe TBI involving intracranial haemorrhage, midline shift, or depressed consciousness requires urgent neurosurgical management.

The evidence, while promising, is still developing. The highest-quality study (Figueiro Longo 2020) had 68 participants. Larger, multi-centre RCTs are needed before tPBM can be considered a standard treatment for TBI.

Pulsed vs. continuous: Some tPBM protocols use pulsed light delivery (10 Hz and 40 Hz frequencies have been studied). Iaccarino et al. (2016, Nature, 540:230-235) demonstrated that 40 Hz stimulation (gamma frequency) reduced amyloid pathology in mouse models. Whether pulsing adds benefit over continuous wave delivery in human TBI remains an active research question.

The Bottom Line

Transcranial photobiomodulation for TBI and concussion is one of the most evidence-supported neurological applications of red light therapy. The biological rationale is strong (mitochondrial rescue in energy-depleted neurons), the clinical evidence is growing (case series, pilot studies, and one well-designed RCT), and the safety profile is excellent (no serious adverse effects reported in any tPBM study to date).

For chronic post-concussion syndrome — where conventional treatment options are limited and frustrating — tPBM represents a genuinely promising intervention. The Naeser case series in particular demonstrates that meaningful cognitive recovery is possible years after injury, in patients who had exhausted conventional treatment options.

The field needs larger, multi-centre RCTs to establish tPBM as a standard-of-care recommendation. But for individuals with chronic TBI symptoms who have not responded adequately to conventional approaches, the existing evidence supports a trial of tPBM as a low-risk, potentially beneficial adjunct therapy.