Thursday, November 15, 2012

Is your laptop making you depressed? Bright screens at night could trigger the condition

  • Mice exposed to light more regularly than they would on a natural cycle exhibited depressive behaviour
  • Scientists say mice and humans share the same brain pathways that activate in response to light
  • Experts conclude 'we should switch on fewer lamps and stick to less-intense light bulbs' in the evenings
By Daily Mail Reporter
Mice exposed to bright lights more regularly than they would naturally exhibited depressive behaviour
Warning: Mice exposed to bright lights more regularly than they would be naturally exhibited depressive behaviour 

Using your laptop or tablet in the evenings could put you at risk from depression, according to a new study.

Researchers have found exposure to bright light at night elevates levels of a stress hormone in the body which triggers the condition and reduces the ability to learn.

Study leader Samer Hattar, from Johns Hopkins University in the U.S, said: 'Basically, what we found is that chronic exposure to bright light - even the kind of light you experience in your own living room at home or in the workplace at night if you are a shift worker - elevates levels of a certain stress hormone in the body, which results in depression and lowers cognitive function.'

Up until the invention of electricity, humans rose with the sun and slept when it set. However, since then people can now work, play or party into the early hours.

The new study on mice found this typical 21st Century scenario may come at a serious cost.

It demonstrates how special cells in the eye - called intrinsically photosensitive retinal ganglion cells, or ipRGCs - are activated by bright light, affecting the brain’s centre for mood, memory and learning.

Prof Hattar added: 'Mice and humans are actually very much alike in many ways, and one is that they have these ipRGCs in their eyes, which affect them the same way.

'In addition, in this study, we make reference to previous studies on humans, which show that light does, indeed, impact the human brain’s limbic system. And the same pathways are in place in mice.'

The scientists knew that shorter days in the winter cause some people to develop a form of depression known as 'seasonal affective disorder' - or SAD - and that some patients with the mood disorder benefit from 'light therapy' which is simple, regular exposure to bright light.
Prof Hattar’s team believed that mice would react the same way, and tested their theory by exposing laboratory rodents to a cycle consisting of 3.5 hours of light and then 3.5 hours of darkness.

Prof Hattar said: 'Of course, you can’t ask mice how they feel, but we did see an increase in depression-like behaviours, including a lack of interest in sugar or pleasure seeking, and the study mice moved around far less during some of the tests we did.

'They also clearly did not learn as quickly or remember tasks as well. They were not as interested in novel objects as were mice on a regular light-darkness cycle schedule.'
He said the animals also had increased levels of cortisol, a stress hormone that has been linked in numerous previous studies with learning issues. 

Treatment with Prozac, a commonly prescribed anti-depressant, mitigated the symptoms, restoring the mice to their previous healthy moods and levels of learning, and bolstering the evidence that their learning issues were caused by depression.

Prof Hattar said the results indicate that humans should be wary of the kind of prolonged, regular exposure to bright light at night that is routine in our lives, because it may be having a negative effect on our mood and ability to learn.

He added: 'I’m not saying we have to sit in complete darkness at night, but I do recommend that we should switch on fewer lamps, and stick to less-intense light bulb.
'Basically, only use what you need to see. That won’t likely be enough to activate those ipRGCs that affect mood.'
The findings were published in the journal Nature.

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