Night shifts could affect learning and alter behaviour, finds report

New Delhi : The loss of darkness might hurt the brain”s capacity to learn, say Delhi University scientists who conducted an 18-month long experiments on song birds called zebra finches that were exposed to perpetual daylight conditions for over 18 months.

They recorded the melodies of zebra finches, challenged them with reward games, measured their exploratory behaviour and documented the “negative effects” of the loss of exposure to the day-night cycle on three generations of the birds.

Their studies suggest that the elimination of the 24-hour day-night cycle, to which the lives of zebra finches appear as attuned as those of humans, can impair the birds” capacity to learn and perform tasks and alter their behaviour.

The findings, published in the journal Animal Behaviour, provide insights into how the disruption of biological clocks – whether through widespread, overly lit urban habitats for birds or through night shifts for people – might affect learning and behaviour.

“Singing is a learned behaviour in zebra finches. Young male zebra finches learn songs just as human babies learn speech – stage by stage, babbling first, then picking up parts of words, then uttering full words,” said Neelu Anand Jha, a research scholar in zoology.

Scientists have known for decades that banishment from day-night cycles de-synchronises the circadian or biological clocks found in all organisms, from bacteria and birds to animals and people.

In humans, misaligned biological clocks – through night shifts, for instance – have already been shown to affect sleep, alertness and performance. Josephine Arendt, an authority on biological clocks at the University of Surrey in Britain, had suggested in 2010 that the observations of increased heart disease risk and cancer associated with shift work might be linked to de-synchronised clocks.

Jha and her supervisor Vinod Kumar, professor of zoology, designed experiments to track learning and behaviour patterns among zebra finches across generations for whom the normal day-night cycle was replaced with perpetual daytime.

They tracked 16 pairs of zebra finches and two generations of their offspring maintained in a 12-hour day and 12-hour night cycle, and another set of 16 pairs of zebra finches and their two generations maintained in a 24-hour day cycle with no night, using artificial lights to simulate daytime.

The birds exposed to perpetual light sang less than those exposed to light and darkness. The songs sung by them raised in perpetual light were shorter and appeared incomplete compared with the songs of those exposed to light and darkness.

“The deterioration in the complexity of songs suggests poor learning and memory,” said Kumar, who leads a project supported by India”s department of biotechnology to study the disruption of biological clocks in songbirds.

In other experiments, the scientists challenged zebra finches with colour-picking and position-picking tasks, with rewards for correct picks, and observed that those exposed to light and darkness learnt faster than those exposed to perpetual light. Also, the birds exposed to perpetual light appeared less curious to explore novel objects placed in their cages.

“We”re doing studies that cannot be replicated in humans,” Kumar said. “But the findings may have implications not just for birds exposed to bright city lights but also for people exposed to night shifts or those whose biological clocks are disrupted for other reasons.”