For years now, scientists have shown that daily exposure to bright light therapy, which simulates the intensity of outdoor light, can be beneficial for people with insomnia and other sleep disorders, Seasonal Affective Disorder or other forms of depression. But what if bright light therapy can help people recover from concussions or other traumatic brain injuries? And what if it can also lower the risk of neurodegenerative diseases like Parkinson’s or Alzheimer’s, which people with TBIs are at higher risk for?
Scientists at Oregon Health & Science University were recently awarded a $4 million grant from the U.S. Department of Defense to explore these questions and possibly unlock more secrets about sleep and its effect on health. The OHSU researchers will recruit nearly 120 military veterans who have suffered a TBI. The participants will be given a light box to use at home for one hour each morning for four weeks. Blood samples will be drawn from participants to look for changes in markers that signal inflammation in the brain and changes in oxygen uptake in brain cells.
MRI scans of participants’ brains will also help reveal if the bright light therapy has improved activity of the glymphatic system - a relatively recent discovery about the role of sleep in reducing toxins that can lead to neurodegenerative diseases like Alzheimer’s.
Joining us for more details of the study and to share new insights about sleep science is Jonathan Elliott, assistant professor of neurology and co-director of the Sleep & Health Applied Research Program at OHSU.
Note: The following transcript was transcribed digitally and validated for accuracy, readability and formatting by an OPB volunteer.
Dave Miller: From the Gert Boyle Studio at OPB, this is Think Out Loud. I’m Dave Miller. For years now, scientists have shown that daily exposure to bright light therapy, which simulates the intensity of outdoor light, can be beneficial for people with sleep disorders, Seasonal Affective Disorder, and other forms of depression. But what if bright light therapy can also help people recovering from concussions or other traumatic brain injuries, and what if it can also lower the risk of neurodegenerative diseases like Parkinson’s or Alzheimer’s?
Scientists at Oregon Health and Science University were recently awarded a $4 million grant from the U.S. Department of Defense to explore these questions. Jonathan Elliott is the principal investigator. He is an assistant professor of neurology and co-director of the Sleep & Health Applied Research Program at OHSU. And he joins us now. It’s great to have you on Think Out Loud.
Jonathan Elliott: Thanks so much for having me.
Miller: So you’re looking at the effects of bright light therapy on brain health. I just wanna start with a basic definition of terms. Are we talking essentially about the same therapy that people would use now for Seasonal Affective Disorder?
Elliott: Really, it’s exactly the same. It’s a lightbox that you use in the morning, after waking up, and it’s really the same intensity, the same duration, kind of the same general specs as you see there.
Miller: How much is currently known about the effects that this kind of light therapy might have on brain health? What’s the status of our current knowledge?
Elliott: There’s been lots of work over the years, over the decades really, showing that light therapy does help improve sleep, especially in people with concussion and traumatic brain injury. The translation to whether the improvements in sleep or just the light therapy in general also confer improvements in brain health is a little bit less clear, really, because less has been done.
So there’ve been a few studies in the past that have shown changes on MRI markers of things like gray matter volume and white matter volume, but nothing specific to some of the outcomes that we’re looking at in this grant.
Miller: What’s the connection between sleep and traumatic brain injuries or the ability to actually have a brain heal? This gets to the purpose of sleep, I suppose. But how are they connected?
Elliott: Yeah, how much time do we have, right?
Miller: Thirteen minutes. But this is an important question. So you can linger on this one.
Elliott: Sleep, we know, is impacted substantially by traumatic brain injuries. And an important point also is that it doesn’t need to be a severe injury that you’re hospitalized for. It can be a really mild injury. Even benign, in the sense that you’re playing high school football and you get your bell “rung,” or you see stars for a minute or even lose consciousness for a split second. I mean that is, arguably, a mild traumatic brain injury and really superficial. But those types of events do have lasting effects. They don’t always recover, they can persist chronically and sleep impairments are one of the most common. So with sleep impairments come problems with mood, anxiety, concentration and cognitive function, just a whole multitude of sequelae there.
Miller: Can you explain something that I’d never heard of, before I started prepping for this conversation, known as the glymphatic function? What is this? And this is like an lymphatic with a G in front of it. What does it mean?
Elliott: This is getting to the “how does sleep help brain health” question. The glymphatic function is, conceptually, the same thing as the lymphatic system of every other organ in the body, the difference being that it’s fundamentally mechanistically different. There aren’t the same vessels. So what this is doing is providing a means to move water and solutes really efficiently through the brain. It’s a solid structure. It’s hard to move fluid through the brain without the system in place.
Before the description of the glymphatic system, it was really unknown how we were able to move, via just diffusion, all this stuff through the brain as it is. But it’s a mechanism in place to clear the brain of all these metabolic byproducts that are produced normally, naturally.
And it turns out that it’s most active during sleep. So one train of thought is that if sleep is impaired following traumatic brain injury, and we know that the risk for long-term poor outcomes for brain health is increased with traumatic brain injury, maybe the glymphatic system is one of these things that’s linking that connection.
Miller: So is this a fair way to put it or is this reading too much into it, that ideally, when we sleep, our brains are clearing out these sort of waste products from thought, from brain function. The brain sort of shuttles them out more when we’re sleeping than we’re when we’re awake. And one of the big functions of sleep is to help us literally clean our brains?
Elliott: Yeah, I mean that was said perfectly. Then really, the description of the glymphatic system in 2012 was, in part, really exciting and novel in the scientific world because it gave sleep a kind of validation of purpose. Before that, there were theories and there were ideas, and there’s still good data to say that it’s important for memory consolidation, cognitive function and a lot of other things.
But fundamentally, if we’re sleeping for eight hours a day, evolutionarily speaking, that meets to serve a very important purpose. We can survive longer without food than we can without sleep. So there’s something very important about sleep. It remains a mystery, but the glymphatic system is clearly a really important point and maybe even an essential role of sleep.
Miller: Is the idea, in terms of connecting all of these dots, that if our sleep is disturbed, or it’s not as deep, or we don’t have as many good quality cycles, then the flushing mechanism is less effective and we’re less likely to be getting rid of some of those byproducts that we don’t want there all the time?
Elliott: Yeah, I think that’s very logical, kind of like putting the pieces together. I don’t think enough’s been done to really say for sure, but there’s certainly ideas out there. A lot of this is currently actively being done in terms of maybe there’s modifiable levers or certain drugs we might be able to take to enhance glymphatic function, or recognizing that maybe certain sleep aids, pharmacologic sleep aids impair glymphatic function. If they suppress slow wave sleep or a deep sleep, that might not be beneficial, even though you’re actually falling asleep. There’s a cost to that.
Miller: Oh, it’s not the best kind of sleep for glymphatic function, perhaps. But you’re saying these are huge questions that are still open and because we’ve only really known about the mechanism of glymphatic function for about a dozen years?
Elliott: Yeah, and most of that time has been spent answering these really fundamental mechanistic-based questions and basic science designs. We’re just now translating to humans, and just now, discovering ways to non-invasively measure in humans glymphatic function.
Miller: So let’s turn to this new study which the Department of Defense … wait, is it still called the Department of Defense? No. Department of War?
Elliott: I think technically the Department of War.
Miller: So the Department of War is giving you $4 million for four years. Can you describe, first, just the setup of this experiment?
Elliott: This is a clinical trial format. It’s got two different groups: an active arm and a sham arm. One of the arms is a bright light therapy arm. They both have the same design, in terms of being a two-week baseline period where we record their sleep and get a sense of how they’re sleeping before the intervention. We then intervene. We give them a device. We give them a lightbox or this sham control device and record their sleep over four weeks. And then [we] stop the intervention, wait four more weeks, collect more data at the end of this follow-up period and test the effect of the intervention.
Miller: What are you hoping to learn from this?
Elliott: Well, we expect to see a change in sleep. The point of the study is to confirm that. But we expect to see a change in sleep, and through that, we hope to show that markers of systemic inflammation, likely reflecting central inflammation in the brain, are improving. We hope to show that mitochondrial function – these key organelles in the cells of our body that produce energy – are improving, their function’s improving. And we hope to show that the glymphatic system is improving. The glymphatic transport of fluid is improving.
Miller: After this conversation, we’re gonna be talking with somebody who has become an advocate for thinking differently about Alzheimer’s and dementia. I mentioned it briefly in my intro. What’s the connection between brain injuries, as best as we understand it now, and degenerative diseases like Alzheimer’s?
Elliott: It’s a good question. It’s a little bit controversial in the literature. My take personally is that there is a strong connection. And a lot of this comes down to nuances, and study design, and how long-term you’re looking, and the type of brain injury, and all these variables. But generally speaking, I think there’s a strong case to be made that there is a strong association between brain injury, whether it be mild or severe, and long-term evolution of Alzheimer’s disease, Parkinson’s disease and the like.
Miller: Is it your hope that better sleep hygiene, more healthful sleep for people with traumatic brain injuries, could have some kind of preventative effect, that would make it less likely that people would develop dementia?
Elliott: The short answer is yes. Knowing how poor sleep is in this group of people, especially military service members who, like I say, have comorbid traumatic experiences and post-traumatic stress, or PTSD, depression, anxiety, all these other factors, chronic pain that influence and contribute to poor sleep … They’re likely [to have] even further increased rates of these long-term, poor neurologic outcomes.
So, yes, if we can intervene and improve sleep, this is a population that would stand to benefit greatly.
Miller: We’re talking now in the days that are the closest to the solstice, closest to the least light of the year in the Northwest. And it’s a pretty rainy atmospheric river time. So even in the middle of the day – we’re talking at 12:30 – there’s not much light out there. For people who don’t feel like they suffer or deal with Seasonal Affective Disorder or feel like they sleep all right, is there science to say that they, too, should be using bright light therapy? I mean, is this something that is generally recommended? Or should it be reserved for people who say, “I feel like I’m suffering. I need some help”?
Elliott: There are very few contraindications to bright light therapy. And I’m not a clinician, so this is not clinical advice, but things like bipolar disorder might be one that you would want to steer away from this. But otherwise, there’s virtually nothing that says you shouldn’t be exposed to bright light. There’s no reason to believe that it wouldn’t help. But if you’re doing all right and you don’t perceive problems, that’s meaningful. But also remember that self-reported sleep is different than objectively-measured sleep. And oftentimes people say they sleep well, but on objective measuring, it’s not so great.
Miller: That happens often?
Elliott: Oh yeah, very often.
Miller: What’s more common, that someone says, “I think I sleep great,” but the research says no, you don’t, or “I have some sleep problems,” but then you put them in a sleep lab and then it turns out, “no, I actually think you’re getting a good REM” or whatever?
Elliott: I actually don’t know how this pans out in the population at large. But I typically see people who would say they sleep poorly come in for a consult, and then I see them, as a research participant, but in fact they sleep well objectively. They fall asleep quickly. They sleep well.
Miller: What does it mean to sleep well objectively?
Elliott: Well that gets to the question of what is sleep “quality?” And it depends on how you define it. We would typically say longer duration, up to a point. So if you’re sleeping too short, say six hours of night sleep, then seven or eight would be an improvement. Nine or 10 is not great. There’s a U-shaped curve here where too little and too much is not good. There’s a sweet spot in terms of total sleep time. But then there’s metrics like how much you wake up during the night, and how restless you are, and whether you can’t maintain sleep or you wake up too early. These are all factors of sleep quality.
Miller: What do you think is a misconception about sleep that more people should be aware of?
Elliott: A few years ago, I’d say it should just be more recognized how important it is. But now, I think it’s getting so much more press and it’s so much more of a thing to optimize.
Miller: In the course of your career studying it, you’ve noticed it? Just in a couple of years, you’ve noticed it?
Elliott: A hundred percent, yeah. Especially more, maybe in the past five or plus years.
Miller: But in optimization sort of podcast-dude world. OK, so this is a part of optimizing your life, like one more piece of your life that should be optimized. But in this case, I’m speaking derogatorily, I suppose, because of my allergy to some of that talk. But you’re saying this is actually true and it’s helpful?
Elliott: Yeah, and I’m sure you could take it too far. But yes, it’s a fundamental piece of our biology. It would be worth optimizing in my opinion.
Miller: Jonathan Elliott, thank you so much.
Elliott: Thanks for having me.
Miller: Jonathan Elliott is an assistant professor of neurology and the co-director of the Sleep & Health Applied Research Program at OHSU. He is also the principal investigator of this new study that’s going to be looking at the use of bright light therapy for people recovering from traumatic brain injuries.
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