Night light changes brain

A little more than 100 years ago our ancestors of the Victorian era were sleeping an average of ten hours per night. It wasn’t that they were waiting for blue ray to be invented, but without the convenient and powerful lighting afforded by electricity, staying up late was less of an option. In some ways electricity has freed us but in others it may have made us slaves.

When the Victorians slept, they mostly slept in total darkness. In the modern developed world, particularly in towns and cities, complete darkness rarely occurs. Street lights infiltrate through the slits around your curtains and then there are digital alarm clock displays, televisions, and even the little warning lights that many appliances carry. True darkness is difficult to come by and that may be having an impact on our psyches.

Depression is often described as one of the plagues of our age and new research suggests that constant exposure to low levels of light at night may be changing our brains in ways that contribute to depression.

To study the effect of light at night on the brain researchers exposed some Siberian hamsters to differing light conditions. Half of the hamsters experienced sixteen hours per day of daylight (at an intensity of 150 lux) and then eight hours of darkness. The other hamsters experienced eight hours of daylight but then at night eight hours of dim light (at about five lux). This level of lighting is roughly equivalent to what would be given by a television screen.

They were then tested for depressive behaviours using the same tests that are used to test antidepressant drugs when they are in development. For instance, hamsters like sugar water but will not drink as much when they are “depressed”.

The hamsters that lived with the dim light at night showed more signs of being depressed than the ones that experienced full night time darkness. When the researchers looked at images of the brains of the hamsters there were even more significant findings.

Those hamsters exposed to dim night light had a different hippocampus (a part of the brain) to the other hamsters. The dim light hamsters had a reduction in dendritic spines in the hippocampus. These dendritic spines are hair like growths on neurons. Since the hippocampus plays a key role in depression finding changes there is significant.

The other interesting thing is that the dim light hamsters did not show raised levels of cortisol, a stress hormone. Cortisol has been shown to cause changes in the hippocampus, but it is not the culprit this time. The researchers believe that it might be the light sensitive hormone melatonin that is the issue here.

Light at night time suppresses secretion of melatonin which is involved in letting your body know that it is night-time. Low levels of melatonin may be the cause of the low rate of formation of dendritic spines in the hippocampus.

Aside from inspiring a phrase like “the dim light hamsters” which surely must be the name soon adopted by a pop group, this study shines light on a possible cause of a dreadful modern epidemic.

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