LOS ANGELES — Sleep deprivation just isn’t a good idea for most people. Besides the increase in accidents and poor work and school performance due to the fatigue, a new study shows sleep loss can also lead to skewed thinking and bad decisions.

This must be why students who pull an all-nighter studying for an exam often believe they did great on the test — that is, until the grade comes in. Researchers found that a night of sleep deprivation boosts production of brain regions that assess positive outcomes and minimizes the parts of the brain that analyzes negative outcomes. What this means is that tired people may make riskier choices in decisions that involve avoiding loss and pursuing gain.

The study involved 29 healthy, young adults who underwent MRI brain scans after a night of restful sleep and after a night of sleep deprivation. On the following days, they were asked to perform a task that involved risky decision-making. The scans showed sleep deprivation caused an increase in activity in ventromedial prefrontal region of the brain and decreases in the region called the anterior insula. The participants’ behavior showed a tendency to be more insensitive to losses.

“Sleep-deprived persons narrow down their choices towards those that seem to promise bigger gains, and likely ignore better choices that improve one’s overall probability of winning at least something,” said Michael Chee, the lead author of the study from the Duke-NUS Neurobehavioral Disorders Program in Singapore.

The authors suggest that changes in the brain chemical dopamine after sleep deprivation lead to altered decision-making behavior. The findings also raise questions about the effectiveness, overall, of stimulant medications to treat sleep deprivation. Those medications may improve vigilance, the authors note, but it’s not clear what effect they have on other aspects of cognition, such as decision-making.