Lack of sleep can give us headaches, make us grouchy and can even leave us feeling drunk. What many don't know is that lack of sleep can also cause a sense of euphoria that can cloud our judgment and reasoning ability. According to researchers at the University of California, Berkeley, this euphoria and lack of sound mind can also make some more susceptible to addictive behavior. Researchers at UC Berkeley and Harvard Medical School used MRI scans to study the brains of 27 healthy, young adults - half of whom received a good night's rest while the other half received no sleep at all. What researchers discovered was that sleep-deprivation led to stimulation of the pleasure pathways in the brain. Interestingly, those same pleasure pathways responsible for generating feelings of euphoria, reward, and motivation, are also big motivating factors in risk-seeking behavior. Lead researcher, Matthew Walker, states that sleep deprivation leaves the brain operating a little like a pendulum, swinging between mood extremes. After a proper night's rest, the brain is able to equalize the mood spectrum, allowing for better decision-making skills. Conversely, a lack of sleep tends to make one focus on positive rewards while discounting the potential negative outcome. Both groups of participants were shown cards with pictures and were asked to rate them as positive or neutral. Those who had no sleep were more likely to assign a positive rating, while those well-rested individuals tended to be more neutral in their responses. Additionally, MRI scans of those lacking sleep showed increased activity in the mesolimbic pathway of the brain. This is the part of the brain controlled by dopamine, which is responsible for feelings of positivity, drive, sexual desire, addiction, hunger and reasoning ability. The UC Berkeley study is consistent with other findings on the same topic. In fact, a recent study conducted by researchers at Duke University shows that gambling after little sleep leaves people hoping for a big win instead of trying to minimize their loss. Just as alcohol provides liquid courage, it appears that lack of sleep encourages gamblers to place bets that they might not have otherwise wagered because they became overly optimistic. The Duke study examined 29 individuals in good health who took to the casino after staying up all night with no sleep. Researchers sought to understand the effect that sleep deprivation had on their decision making skills, and participants were also analyzed via MRI scans. Examinations of the brain scans showed a change in the part of the brain called the vetromedial prefrontal cortex, which helps the gambler weigh and access risk. This part of the brain was noticeably more active than normal causing the gambler to have skewed views of his odds of winning and losing. Researchers say that the results of both studies pave the way for future research into the effects of sleep deprivation on job performance. Professor Huettel of Duke University Medical Centre says that, similar to the participants in the study who had to weigh gambling risk with little sleep, doctors and other health professionals must daily access risk of implementing procedures amidst grueling schedules and little rest. These individuals may focus more on the positive outcome of the procedure and less on its potential risk. In professions with little margin for error, one small error could mean the difference between life and death.