Suffering From Intense Winter Blues? Blame It On The Brain Circuit

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Winter can cause severe depression in some people (Credit: KRiemer/Pixabay/CCO)

Many of us experience mood shifts during the colder, shorter, and gloomier winter days. However, for those diagnosed with seasonal affective disorder (SAD), winter blues take on a whole new meaning. While mental health professionals have attributed the symptoms of SAD, which include depression and a feeling of hopelessness, to the lack of sunlight, no one was sure how the brain made the connection. Now, some researchers have found the culprit – a brain circuit which connects special light-sensing cells in the retina with the areas of the brain that impact our moods.

The research that eventually led to this groundbreaking discovery began in the early 2000s when Samer Hattar, chief of the section on light and circadian rhythms at the US National Institute of Mental Health, and David Berson, a neuroscience professor at Brown University, were studying retinal cells. Back then, most scientists were under the impression that there were only two kinds of photoreceptor cells in the retina – rods and cones. However, Hattar and Berson were confident that there were more. "People used to laugh at us if we say there are other photoreceptors distinct from rods and cones in the retina," says Hatter.

RGC’s have a direct pathway to the brain’s area responsible for regulating
moods (Credit: Jamie Simon, Salk Institute for Biological Studies)

But the skeptics turned into believers when the team found the retinal ganglion cells (RGCs) in 2002. However, the photoreceptor cells, which contained a light-sensitive substance called melanopsin not found in rods and cones, were not part of the ocular system.

Instead, they played a crucial role in helping keep the brain's internal clock in sync with changes in the amount of light received. The finding led many scientists to assume that this circadian function also explained seasonal depression.

But Hattar and Berson were not satisfied. They were confident there was a better explanation for the disorder. Sure enough, in 2018 while exploring the function of these new cells in a study involving mice, Hattar’s team found a pathway linking RGCs to the area of the brain responsible for regulating moods. When these cells were present, an artificially-shortened cycle of light and dark caused a version of depression in the mouse. But when the team removed the cells with gene-editing tools, the mouse did not become depressed. The researchers, who published their findings in the online journal Cell on August 30, 2018, concluded that the direct connection between melanopsin and moods might be a key factor for the seasonal disorder, which impacts over 10 million Americans.

Intrigued by Hattar and Berson's findings, Jerome Sanes, also a neuroscientist at Brown University, decided to investigate whether the results apply to human brains as well. His team put young adults in an MRI machine and measured their brain activity as they were exposed to different levels of light. This enabled them to identify brain areas that were receiving signals from the photoreceptors. Sure enough, they observed that the regions of the brain which responded to the variations in light intensity were the same ones that are responsible for depression and other affective disorders. "It's very likely that things like seasonal affective disorder involve this pathway," says Sanes.

RGCs have a direct connection to the brain areas that affect moods (Credit: Hatter Et al./Cell.com)

While Sanes’ findings need to be confirmed, the researchers involved in the two studies are quite confident that this newly-found circuit is the link between light exposure and mood. The researchers are not sure why the lack of light impacts some people more severely than others. Hattar is also curious about another thing. "You will understand why you would need light to see," he says, "but why do you need light to make you happy?" Whether we are able to solve these mysteries remains to be seen. Meanwhile, the scientists recommend getting as much daylight as possible to keep those winter blues at bay!

Resources: NPR.org, cell.com.

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265 Comments
  • Amora Flores Friday, September 20, 2019 at 8:06 pm
    Wow 😮 that’s amazing I love it ❤️
    • animelover_11
      animelover_11Tuesday, May 28, 2019 at 7:08 am
      That has never happened to me before...but, i am very interested in disorders. Like Schizophrenia ( mah real disorder) and Bi-polar disorder...basically all of them. So, this is very enlightening to learn about this disorder I never knew about. Thanks!
      • lillianThursday, April 25, 2019 at 7:28 am
        love it sooooooooo much
        • lillianWednesday, April 24, 2019 at 10:31 am
          I love this
          • AvaMonday, April 8, 2019 at 6:45 am
            I was never sad.But its Apirl now and im happy. I bilt a sand castle with my brothr.
            • sayeemaThursday, April 4, 2019 at 5:33 pm
              i love this the best
              • MissyFriday, March 22, 2019 at 11:51 am
                I have deppreshion
                • dre22
                  dre22Thursday, March 21, 2019 at 11:27 am
                  this is the best one
                  • meTuesday, March 12, 2019 at 11:29 am
                    to awsone
                    • johTuesday, March 12, 2019 at 11:27 am
                      cool and good