Professor of Biological Sciences Douglas McMahon, and team say their experiment provides the first proof of seasonal imprinting of biological clocks in mammals. In this case, the imprinting effect in baby mice may help us understand better why humans born during the winter months are more likely later on in life to develop some neurological disorders.
"Our biological clocks measure the day length and change our behavior according to the seasons. We were curious to see if light signals could shape the development of the biological clock."
The mice which had been born in the winter environment demonstrated a consistent slowing of their daily activity period compared to the summer-born mice, no matter what subsequent cycle they were in after weaning.
They used a gene which makes the clock cells glow green when they are active so they could examine their master biological clocks. Here they also found a slowing in the winter-born mice's gene clocks compared to those born in the summer environment.
Team member, Chris Ciarleglio, said:
"What is particularly striking about our results is the fact that the imprinting affects both the animal's behavior and the cycling of the neurons in the master biological clock in their brains."
"The mice raised in the winter cycle show an exaggerated response to a change in season that is strikingly similar to that of human patients suffering from seasonal affective disorder."
This study makes one wonder what impact seasonal light/darkness cycles very early in life might have in the development of our personalities.
"We know that the biological clock regulates mood in humans. If an imprinting mechanism similar to the one that we found in mice operates in humans, then it could not only have an effect on a number of behavioral disorders but also have a more general effect on personality. It's important to emphasize that, even though this sounds a bit like astrology, it is not: it's seasonal biology!"
"We know from previous studies that light can affect the development of other parts of the brain, for example the visual system. Our work shows that this is also true for the biological clock."
The master biological clock is located in the suprachiasmatic nucleus (SCN) - an area in the middle brain behind the eyes.
"Perinatal photoperiod imprints the circadian clock"
Christopher M Ciarleglio, John C Axley, Benjamin R Strauss, Karen L Gamble & Douglas G McMahon
Nature Neuroscience. Year published: (2010) DOI: doi:10.1038/nn.2699