If your teenaged son or daughter is regularly waking up till late in the night, he or she is likely to have poor sleep, which may increase their risk of developing mood disorders, especially depression, researchers have warned.The study, led by Peter Franzen from the University of Pittsburgh in the US, showed that teenagers with sleep deprivation may indulge more in risk-taking behaviour and addictions.This is because chronic sleep deprivation reduces the proper functioning of putamen -- an area of the brain that plays a role in goal-based movements and learning from rewards. Lack of proper sleep also leads to less activity in the brain's reward system.For the research, presented in the 56th Annual Meeting of American college of Neuropsychopharmacology in California, the team studied the sleeping behaviour of participants aged between 11 to 15 years.The team divided the total participants in two groups and allowed one group to sleep for four hours while the rest completed 10 hours of sleep. While noting the MRI scans of the participants each time the team repeated the same sleeping patterns and interchanged it in between the groups.The participants were also made to answer questions while playing a game that involved receiving monetary rewards of $10 and $1, which measured their emotional functioning and depression symptoms.The results showed that when the participants were sleep-deprived and played the reward game for longer hours, the putamen was less responsive. While in the rest condition, the brain region did not show any difference between high and low-reward conditions.After a night of restricted sleep, the participants who experienced less activation in the putamen also reported more symptoms of depression.