Many people may leave the TV on at night or some sort of dim light thinking it is harmless. A new study
on hamsters is saying that it is possible that this kind of exposure to a dim light at night could create changes in the brain that lead to mental health concerns such as depression.
“People might want to try to avoid falling asleep with their TVs on all night,” said Tracy Bedrosian, a doctoral student in neuroscience at Ohio State University. “They might want to try to minimize light exposure during the night,”
Bedrosian and colleagues placed hamsters in two different settings that involved light. In one setting hamsters were exposed to 16 hours of daylight and eight hours of complete darkness each day. In the other, the animals experienced 16 hours of daylight, but at nighttime, a dim light was kept on, about the intensity of a TV screen lighting up a dark room.
What the researchers discovered was that after eight weeks the researchers would evaluated behaviors that would suggest they were depressed. For example, they looked to see whether the hamsters still engaged in activities they normally enjoy, such as drinking sugar water.
Hamsters in both groups were given a choice between drinking tap water or sugar water. The hamsters exposed to light at night drank similar amounts of tap and sugar water — they’d lost their preference for the sweet treat.
“That suggests to us that they are not getting the same pleasurable and rewarding feeling from drinking their sugar water, and that it may be interpreted as a depression-like response,” Bedrosian said.
The hamsters exposed to night light had a reduced number of so-called dendritic spines on the surface of cells in this region. Dendritic spines are hair-like protrusions that brain cells use to communicate with one another.
The findings agree with studies on humans that have found the hippocampus to be involved in depression. A patient with major depression has a smaller hippocampus, Bedrosian said.
The brain changes in the hamsters might arise from fluctuations in the production of the hormone melatonin, Bedrosian said. Melatonin signals to the body that it’s nighttime, but a light at night dampens its production. The hormone has been shown to have some antidepressant effects, and so a decrease in melatonin might spur depression symptoms, Bedrosian said.
This study adds to previous findings connecting exposure to light during sleep and depressive behavior. One study found that mice exposed to bright lights at night tend to become depressed and to gain weight.