Children who watch television late at night could be 'more likely to develop depression', The Daily Telegraph has claimed. The research behind this report has been covered by several other newspapers, which say that streetlights could also be responsible.
This research housed mice for several weeks in a room that was lit 24 hours a day, testing measures thought to indicate depression and distress. These mice showed more depressive symptoms than similar mice exposed to a normal cycle of light and dark. The researchers believe that the findings could apply to humans, as they used the same methods that pharmaceutical companies do in preliminary testing of anti-depressive and anti-anxiety medication.
This was animal research, so applying its findings to humans should be treated with caution due to the numerous major differences between species. Furthermore, the extreme lighting regime tested on mice does not mirror real life in humans.
This study did not test the effects of streetlights or television on human mood, so any conclusions about their effects should be considered as speculation.
Where did the story come from?
This research was carried out by Dr Laura Fonken and colleagues from the Departments of Psychology and Neuroscience at Ohio State University. The study was supported by grants from the National Science Foundation and published in the peer-reviewed journal Behavioural Brain Research.
What kind of scientific study was this?
In this animal study the researchers wanted to test whether constant light conditions produce affective responses (changes in mood). They also wanted to see whether these behaviour changes would be the result of differences in concentrations of glucocorticoid, a steroid hormone released by stress.
The researchers took 24 eight-week-old mice and allowed them to drink and feed freely. After a week of getting used to their cages, they were randomly assigned to either the control group or experimental treatment group. The 12 mice assigned to the control group were maintained under a cycle of 16 hours of light followed by eight hours of dark, while the experimental group was maintained in constant light for the remainder of the study.
After three weeks under the different lighting conditions the mice underwent several behavioural tests to measure responses believed by the researchers to be similar to human anxiety and depression. These tests included:
- An open field test, in which total movement was tracked for 30 minutes and analysed for the percentage of specific movements, such as rearing up and the tendency to remain in the centre of the test chamber. Both of these are thought to represent low anxiety responses.
- An elevated maze test in which mice navigated a maze one metre above the floor. The time spent before exploring an open arm of the maze is linked to anxiety.
- Monitoring sucrose consumption, as it is a measure of a mouse s contentment level.
- In the Porsolt forced swim test, the length of time a mouse spent floating stationary was measured. This length of time is thought to represent a depressive-like response.
Following the testing, the mice were killed humanely and their adrenal glands, spleens, testes and fat pads were collected and weighed.
