IRA FLATOW: This is Science Friday. I’m Ira Flatow. As we approach the shortest day of the year, for some, the winter is an especially challenging season. About 5% of adults experience Seasonal Affective Disorder, also known as S-A-D.

My next guest is researching why some people are more susceptible to seasonal depression and the most effective treatments. Dr. Kathryn Roecklein is an associate professor of psychology at the University of Pittsburgh based in Pittsburgh, Pennsylvania. Welcome to Science Friday.

KATHRYN ROECKLEIN: Thank you. Thanks for having me.

IRA FLATOW: Oh, it’s nice to have you. Can you give us a definition of what seasonal affective disorder is?

KATHRYN ROECKLEIN: It actually has all of the same symptoms as non-seasonal depression, but it occurs during particular seasons. So we usually see onset in the fall or winter and remission in the spring and summer.

IRA FLATOW: And can you give us a reason why this happens seasonally?

KATHRYN ROECKLEIN: Well, so what we’re researching in my lab is whether or not some people are more or less sensitive to the light in our environment. When it comes to weather and climate, the factor that seems to be most important in triggering SAD is the length of the day– so the number of minutes from dawn to dusk.

But in Pittsburgh, as well as many other places, we all undergo the same shortening of days, and darker skies more rain, more cloud cover, but only a fraction of individuals develop depression. So the theory is that some individuals are just more sensitive to those lower light levels.

And in summer, when light levels are high enough, it may not be an issue, and days are nice and long. But when the light levels in the days drop below a certain threshold, then individuals may be more vulnerable to developing depression.

IRA FLATOW: Hmm. Does it have something to do with how responsive your eye is to light?

KATHRYN ROECKLEIN: Well, that’s what we’re wondering. It could be how responsive your eye is to light, or it could be how responsive your brain is to that information from the eye. So I decided we should just start with the eye because it’s step one in that neural pathway.

And when I started graduate school, Iggy Provencio and Mark Rollag had just discovered a class of cells in the retina that nobody knew had existed before. This was 2001, and they discovered a class of cells that are sensitive to light that are not the rods and cones. We used to think it was just rods and cones. But they discovered that there are these retinal ganglion cells that are sensitive to light.

IRA FLATOW: Oh, really? Wow.

KATHRYN ROECKLEIN: And they send their axons to the circadian clock in the brain. So immediately everybody studying circadian rhythms and sleep and mood disorders got really interested. And I’ve been trying to find out if there’s anything about these cells that differs between individuals and could explain why some of us develop SAD and some don’t.

IRA FLATOW: So the cells, they wind up in an emotional part in the brain. What part of the brain?

KATHRYN ROECKLEIN: Well, there are many different parts of the brain that these cells seem to project to. One is the circadian clock. And the circadian clock then has impacts on mood centers of the brain. But these cells do seem to project to parts of the habenula, which is directly involved in mood, as, well as the amygdala.

IRA FLATOW: Wow. Is seasonal depression, then, different from depression during, let’s say, other times in the year?

KATHRYN ROECKLEIN: Yeah, that’s a really good question, and it’s really hard to answer. I would say that people are vulnerable to different triggers. So in SAD, the main trigger is falling light levels. In other kinds of depression or other forms, people might be vulnerable to things we call negative life events, like losing a job or losing a family member.

And the thing is, though, that you don’t have to have just one of those vulnerabilities. Some people have multiple vulnerabilities. So we think that the difference might be more in what starts off the episode.

IRA FLATOW: And how might your research into SAD help scientists better understand other types of depression?

KATHRYN ROECKLEIN: So the reason why studying SAD might be helpful for all kinds of depression is that we can predict when it will begin and when it will remit. So I can do a research study where I look at individuals who are depressed and then I can do similar measurements of all kinds of biomarkers and psychological factors when they’re in a remitted state. So that allows me to determine what preexisting risk factors are as opposed to things that are just correlated with having depressive episode. It’s a lot harder to predict when other types of depression will occur and when they’ll remit.

IRA FLATOW: I’m just thinking maybe if you’re bipolar and that might be a trigger for you, that sort of stuff.

KATHRYN ROECKLEIN: Yeah. So bipolar is interesting. What we’ve been talking so far about is unipolar depression where people just experience depressive episodes and then a return to a neutral mood. And bipolar disorder, that’s actually very seasonal. Almost half of people with bipolar disorder have depressive episodes that follow a seasonal pattern occurring in fall or winter, as well as those episodes of mania in the spring and summer. So bipolar disorder might actually be more seasonal than unipolar depression.

IRA FLATOW: OK, so what are the most effective treatments for SAD then?

KATHRYN ROECKLEIN: Well, one of the most beneficial things is that there are up to three treatments that have a good evidence base in SAD. The one that’s been studied the longest is light therapy, and that involves sitting in front of a bright light. Or what they have now, which are visors that you wear that have little light diodes that point the light directly at your eyes. So this is helpful.

And they even have some that go on the visor of your car so that you can be getting light therapy while you commute, or while you are running around the house in the morning, or if you have some other kind of morning routine that prevents you from sitting still in front of a light box for 30 to 45 minutes in the morning.

IRA FLATOW: Yeah, that’s probably hard to do for most people who want to get out of the house.

KATHRYN ROECKLEIN: Absolutely. So light therapy is effective for about half of people with SAD, which is actually a better response rate than antidepressant medications. And then the third type of treatment is cognitive behavioral therapy for SAD or CBT SAD. And that’s similar to Cognitive Behavioral Therapy for depression, for non-seasonal depression, except it adds a few different aspects that are specific to coping with the seasons.

IRA FLATOW: And how effective is that talk therapy compared to the light box therapy?

KATHRYN ROECKLEIN: It’s better. And what the most interesting thing is that it has what we think are protective effects in subsequent years. So if you do light therapy and it’s effective in year one, like this winter, then you would just start it up again next winter. And you’d have to use it every winter to get the effects. But with CBT SAD, it looks like if you were to do 12 sessions of CBT SAD this winter and then did absolutely nothing next winter, your risk of a SAD episode is lower.

IRA FLATOW: Dr. Roecklein, you’re looking at the genetic components of seasonal depression. What is the research question you’re currently trying to answer? I mean, does it run in families?

KATHRYN ROECKLEIN: Yeah, some portion of SAD is genetic. It’s about 33%. And I am looking at the gene for the light sensitive molecules in those cells in the eyes we were talking about earlier. So I’m wondering if maybe the protein there that’s sensitive to light, it changes shape when it absorbs a photon of light. Maybe the gene– that gene for melanopsin has a different sequence in people with SAD and it causes it to function a little bit differently.

IRA FLATOW: Wow.

KATHRYN ROECKLEIN: So that’s the study we’re hoping to do this January.

IRA FLATOW: Well, good luck, and please let us know what you find out.

KATHRYN ROECKLEIN: I will.

IRA FLATOW: Dr. Kathryn Roecklein, thank you for taking time to be with us today.

KATHRYN ROECKLEIN: Thank you for having me.

IRA FLATOW: Dr. Roecklein is an associate professor of psychology at the University of Pittsburgh. Of course, that’s in Pittsburgh, Pennsylvania.

Copyright © 2023 Science Friday Initiative. All rights reserved. Science Friday transcripts are produced on a tight deadline by 3Play Media. Fidelity to the original aired/published audio or video file might vary, and text might be updated or amended in the future. For the authoritative record of Science Friday’s programming, please visit the original aired/published recording. For terms of use and more information, visit our policies pages at http://www.sciencefriday.com/about/policies/