Depression Linked to Nighttime Brightness, Even with Normal Sleep Patterns
New research has found that depression can be caused by nighttime brightness, even in individuals with normal sleep patterns and a functioning internal clock. Artificial light at night not only affects mood, but also learning ability. American scientists conducted experiments on mice, which showed that an artificial disruption of the light-dark cycle caused depression. The cause of this is the activation of special light-sensing cells in the eye, which are normally only active during the day but are also activated by nighttime lighting. The researchers warn that too much light at night can cause depression in humans, leading to mood swings, disinterest, and weakened cognitive brain function.
Samer Hattar of Johns Hopkins University in Baltimore recommends using less lighting or dimming lights at night to avoid activating the specific ganglion cells in the retina. The study found that light-sensing cells not involved in the visual process emit signals that negatively affect mood and performance. Cells containing the light-absorbing pigment melanopsin are present in both mice and humans, leading Hattar to believe that the results of the mouse experiments can be applied to humans.
The mice were kept in a room that was lit for 3.5 hours at night, which did not affect their sleep patterns or daily activity rhythms. However, mice exposed to nighttime light had significantly higher levels of the stress hormone corticosterone, were less active, showed little interest in new objects, and had slower reactions to offered sugar treats. They also performed poorly in various memory and learning tests. Treatment with the antidepressants fluoxetine or desipramine neutralized the depressive behavior and the decreased learning ability. The researchers believe that nighttime light triggers depression, which then impairs the cognitive abilities of the mice.
In conclusion, the study warns that too much light at night can cause depression, even in individuals with normal sleep patterns. The activation of specific light-sensing cells in the eye can negatively affect mood and cognitive function. The researchers recommend using less lighting or dimming lights at night to avoid activating these cells.
