CDMRP 2012 Investigator Vignette

Low-Level Light Therapy for Traumatic Brain Injury

Michael Hamblin, PhD; Massachusetts General Hospital

Traumatic brain injury is a real big problem in society as a whole. Not only is it a problem with the soldiers in the military, it's also a huge problem in civilian life-a lot of athletes, a lot of football players, and people in car crashes, but by and large there's not really any good single treatment for traumatic brain injury.

A lot of pharmaceutical companies have studied this, a lot of drugs have been tested, pretty much all of which have failed. And then there's a bunch of physical therapies. The research that my lab has been doing is one of these physical therapies.

It's here at the Wellman Center for Photomedicine, we study how light impacts all aspects of medical research. A lot of people use light for diagnosing disease for in vivo imaging with various high-tech things.

But not only do we image disease with light, we treat disease with light. So we treat with light. You can treat with ultraviolet light. You can treat with high-powered lasers. Sometimes we have a photosensitizing drug and use that for killing things like killing cancers, killing infections, but when you use the light alone without the photosensitizing drug, it interestingly enough has a completely opposite effect. It actually stimulates healing, it stimulates regeneration. It relieves pain and inflammation and causes tissue to repair itself.

You can use what we call low-level light therapy or photo-biome modulation. This is use of visible near infrared light to cause healing and stimulation.

Near infrared light can go quite deep in the body, so if you shine onto your head it goes through your scalp, through your skull, and quite a lot of it actually gets into your brain.

So once you realize that, you think, OK, all these diseases of the brain that need regeneration and healing you can maybe treat with light. Most of my research is in small animal models, mice and rats basically, so we give the mice and rats a traumatic brain injury and shine near infrared light on the head and it has remarkable effects.

One of the studies we published was on what exactly is the best wavelength. So we tried four different wavelengths and we found that 810 was by far the best. And that really is quite interesting because it gives added information to the so-called action spectrum and other words what is the biological chromo-form that's absorbing these photons.

Another study we did was to look at the effective pulsing so you can either have this light CW, sort of photons coming all in a nice smooth stream or you can pulse the light. And the frequency can be anything from let us say 10 times a second or 100 times a second, up to tens of thousands of times a second. You call this "hertz," cycles per second.

So we compared 10 hertz, 100 hertz, and CW and we found that if you use CW or 100 hertz, it worked just fine; but if you used 10 hertz it actually worked even better.

Now this is quite interesting because you have to think what could be going on in the body or the brain which means that 10 hertz gave you added benefit. And we have a couple of possible hypotheses. One of the things, the light maybe opens ion channels in the neurons or the mitochondria of the neurons. But an alternative explanation was that we were affecting the theta-rhythms of the brain, so the theta-rhythm is 10 hertz and it's also situated in the hippocampus. We've discovered that the hippocampus is a very important part of the brain for the response to light therapy. It's one of the seats of neurogenesis which is why neural-progenitor cells are formed, and they can migrate and differentiate into new cortical neurons.

A third very interesting finding we got from the DRMRP funding was that the treatment repetition was important. So we treated these mice once 4 hours after their brain injury and that worked fine, so it was pretty logical to say well, what happens if we treat them once a day for 3 days. So that worked even better. Okay, treat them once a day for 7 days. Well that works even better still. When you treat them once a day for 14 days, all the benefit is gone. It's like you didn't do any treatment at all. That's kind of intriguing and we're looking on a molecular level to see exactly what's going on in the brain.

There's a neurotrophic factor called BDNF, a brain-derived neurotrophic factor that's of great importance in neuro-science. And we believe that BDNF levels are modulated by laser therapy so that if you get the laser therapy right you can increase the BDNF in the brain and that may be responsible for a lot of the beneficial effects that we see.

We got into this really with the traumatic brain injury although it has huge implications of much wider treatment of brain diseases, psychiatric diseases, and degenerative diseases. And you know if there's transcranial laser therapy can really encourage neural-progenitor cells and brain repair, well that could be a real big deal. I think it'll still require quite a lot of convincing people before they accept it as-as a valid approach. But once the number of published papers reaches like a critical mass then people can't ignore it anymore.