What’s New in Psychology?

Why Does Light Therapy Improve Mood?  

Jim Windell

            If the cloudy days of fall and winter sap your energy and increase your moodiness, you may be experiencing seasonal affective disorder (SAD). This may be especially the case if your mood is upbeat and your energy grows by leaps and bounds on bright, sunny days.

           SAD is a type of depression that's related to changes in seasons. Recommended treatment for SAD usually includes medications, psychotherapy -- and phototherapy.

           Phototherapy, or light therapy, has been found helpful and can improve the mood of people with seasonal affective disorder – particularly during those short winter days. But how exactly does light therapy work?

           Scientists have not been able to pinpoint exactly why phototherapy works.

           However, a new study sheds some light on this. The new study by Urs Albrecht at the University of Fribourg, published recently in the journal PLOS Genetics, finds that light therapy's beneficial effects come from activating the circadian clock gene Period1 in a part of the brain involved in mood and sleep-wake cycles.

           Recognizing that nighttime light has strong effects on the physiology and behavior of mammals, including resetting an animal's circadian rhythms, Albrecht and his colleagues, investigated how nighttime light impacts mood using mice as a model.

           In their research, the scientists exposed mice to a pulse of light at different points during the night and then tested them for depressive behavior.

           They discovered that light exposure at the end of the dark period -- two hours before daytime – had an antidepressant effect on the animals. The pulse of light activated the Period1 gene in a brain region called the lateral habenula, which plays a role in mood. However, light at other times had no effect. When they deleted the Period1 gene, the mice no longer experienced the light's beneficial effects.

           These results seems to provide evidence that turning on Period1 in the lateral habenula is the key to light's mood-boosting powers. The discovery that mice appeared to be less depressed when exposed to light at the end of the dark period, as opposed to the beginning, is similar to findings in humans. It’s been found in other studies that light therapy is more efficient in the early morning than in the evening for people with SAD.

           The researchers caution against making too many direct comparisons to humans since mice are nocturnal animals. However, the researchers point out that "Light perceived in the late part of the night induces expression of the clock gene Period1, which is related to improvement of depression like behavior in mice."

           To read the original article, find it with this reference:

Iwona Olejniczak, Jürgen A. Ripperger, Federica Sandrelli, Anna Schnell, Laureen Mansencal-Strittmatter, Katrin Wendrich, Ka Yi Hui, Andrea Brenna, Naila Ben Fredj, Urs Albrecht. Light affects behavioral despair involving the clock gene Period 1. PLOS Genetics, 2021; 17 (7): e1009625 DOI: 10.1371/journal.pgen.1009625