Understanding Infrared Light as a Therapeutic Modality

Henderson and Morries used a 10 Watt beam of 810 nm infrared light and demonstrated the immense barrier which human hair represents. These data argue that very little, if any, infrared light from a 0.5 Watt LED could penetrate to the brain. If 98% of the energy from a 0.5 W LED is absorbed by hair, 80-90% is absorbed by 2 mm of skin, and 96% of incident energy is attenuated by skull, then the claims of neurophysiological benefits of LED-based devices become highly questionable.
Another misconception propagated by companies selling LED-based devices is that multiple LEDs somehow increase light penetration. Adding multiple LEDs – even hundreds of them – would not change the situation as each LED is projecting light on its own path through the hair, tissue and skull. A hundred 0.5 Watt LEDs do not generate 50 Watts on the brain. They generate 0.5 Watt on 100 spots (Henderson & Morries, Photobiomodulation and the Brain: Low-level Laser (Light) Therapy in Neurology and Neuroscience. Academic Press, London, 2019). The argument proposed by some that light scattering in the brain provides the cumulative value of multiple LEDs falls apart if nothing can get through the overlying tissues.

Given that only a very small percentage (less than 1%) of the incident infrared light gets through human scalp and skull, we must question the results of human trials using LEDs. Indeed, whether we examine the human studies of traumatic brain injury (TBI) or depression, there is a recurring pattern in the LED-based studies. First, all of the studies demonstrated very small, almost insignificant, positive effects (see below). Second, the benefits are generally transient and fade after the infrared light treatment is stopped (Morries LD & Henderson TA. Photobiomodulation and the Brain: Low-level Laser (Light) Therapy in Neurology and Neuroscience. Academic Press, London, 2019). In contrast, our multi-Watt infrared light protocol yields persistent and robust clinical changes in patients with TBI, PTSD, and depression.

LED Photobiomodulation in Comparison
Naeser and colleagues (Naeser et al, Photomed Laser Surg 29:351, 2011) described two cases with TBI treated with LED instruments. The patients were treated daily for approximately one hour by applying three separate LED cluster heads – two applied to the head and one applied to the foot. The first patient was seven years post-TBI and had significant post-concussive symptoms. The patient received weekly treatments of 8J/cm2 to 20 J/cm2 over seven months and then switched to daily treatments at home. The patient continued home treatments for over six years. Notably, the patient has only transient benefit from this protocol. If the patient stopped treatment, then symptoms returned within two weeks (Naeser et al, Photomed Laser Surg 29:351, 2011). The second patient received daily treatments with a similar device. Within four months, the patient had improvement of most symptoms (decreased memory, poor sleep, emotional dysregulation, irritability) and returned to work. This patient also noted that symptoms returned if treatments were stopped for more than one week.

Naeser and colleagues (Naeser et al, J Neurotrauma 31:1008, 2014) later reported on an open-label series of eleven patients with TBI who had persistent cognitive dysfunction and were treated with a similar low-power LED protocol. Patients were treated for 18 sessions over six weeks with each session lasting 20 minutes. At the follow-up neuropsychological testing, a significant effect on attention, inhibition and inhibition switching in the Stroop task; similarly improved verbal learning and memory, as well as enhanced long-delay free recall on the California Verbal Learning Test were reported. Eight subjects were identified as having mild, moderate or severe depression. The LED treatment led to mild improvement in three cases, but no change in depression symptoms in the remaining five cases(Naeser et al, J Neurotrauma 31:1008, 2014). The group did not report on the persistence of the symptom relief.

Hipskind and colleagues (Hipskind et al, Photobiomod Photomed Laser Surg 37:77, 2019) reported a series of twelve patients treated with an LED device with 220 LEDs, each with a power of 0.5 watt. Patients were treated for 18 sessions over six weeks with each session lasting 20 minutes. While the group reports a significant improvement in psychological testing results (p= 0.45), they did not correct for multiple comparisons, but instead used parallel paired t-tests – a flawed statistical protocol which exaggerates findings. They did not report on the persistence of symptom improvement.

PTSD has received considerably less attention. A scattered sampling of patients with PTSD are described in open-label cohorts in several studies (e.g., Schiffer and colleagues, Behav Brain Funct 8:46, 2009). Reportedly, a clinical trial by Naeser and colleagues began in 2015; however, they are still recruiting subjects five years later and have not released any results (Clinical Trials.gov).

A small number of studies have exampled depression. Cassano and colleagues described the treatment of four patients with depression using a somewhat higher power (5 W) laser (Cassano et al Psychiatry J 2015). A double-blind, sham-controlled extension of these initial findings was recently published (Cassano et al. Photomed Laser Surg 36:634, 2018). Subjects in the actively treated group received 16 treatments over eight weeks with each treatment lasting 30 minutes. In a sample of 13 completers, Hamilton-D-17 scores separated in the active treatment from sham controls (-15.7 + 4.41 vs -6.1 + 7.86, p = 0.031). In contrast, in an open-label trial of a 13 watt laser (Henderson & Morries, Front Psych 8:187, 2017), Henderson and colleagues showed that the Hamilton-D-17 decreased from a baseline of 21.48 + 5.24 to 6.0 + 5.12 (p = 6.45 X 10-13). The comparison of the results from LED and low-power infrared light studies compared to our multi-Watt infrared light studies in summarized in the Table.