A new study conducted by US scientists at the Vanderbilt University suggests that the permanently turned on neon light in neonatal intensive care units may affect premature babies' biological clocks and can cause emotional and mood disorders in infants, such as depression.

Researchers sustain that premature babies in hospitals fail to get used to the day/light cycle, as they are permanently living on "daylight" cause by the neons in ICU. The team suggests that hospitals should consider resorting to the natural day/night cycle instead of using the 24 h artificial light.

Prof. Douglas McMahon of Vanderbilt University in Tennessee and leader of the research explained: "We are interested in the effects of light on biological clocks because they regulate our physiology extensively and also have an important effect on our mood."

The master biological clock is located in all mammals in the area of the brain known as SCN. The master biological clock influences the activity of many organs, such as the brain, lungs, liver etc. Therefore, it is very important to keep the biological master clock fully functioning.

In order to see if continuous exposure to light affects the SCN and the brain, researchers used genetically modified mice babies who had clock neurons (neurons in the SCN brain's region) which produced a bright glow when active. When exposed to normal, natural cycle of day/night light, the mice's neurons were found to easily synchronize. On the contrary, when the baby mice were exposed to constant light, their clock neurons cloud did not maintain coherent rhythms of functioning.

When mice babies were exposed to permanent artificial light for a short period of time and then again to natural light cycle, their neurons in the SCN region rehabilitated and became synchronized again. But when the mice were exposed for a much longer period of time to continuous neon light, clock neurons in 2/3 of them could not find their path again and function properly when exposed again to day/night cycle.

Previous studies have shown that also adult mammals' master biological clocks are affected when exposed to constant artificial light. Also, previous study showed that babies in neonatal intensive care units with natural, cycling light, tend to sleep earlier at night and to gain weight faster.

"This study suggests that cycling the lights in neonatal intensive care units may be better than constant lighting for premature babies, from the perspective of developing their internal clocks. All this is speculative at this point. But, certainly the data would indicate that human infants benefit from the synchronizing effect of a normal light cycle," concluded Prof. Douglas McMahon.