After a long day of thinking and working hard, it’s easy to make poor decisions, such as eating unhealthy foods. A new study published in the journal Current Biology shows that the brain fatigue that results from thinking and making decisions all day at work influences the neurotransmitters in our brains that affect our ability to control our impulses. In the study, researchers at the Paris Brain Institute gave 40 participants either an easy or hard version of a mental task for over six hours. The researchers questioned each subject on their level of fatigue and measured their neurotransmitters throughout the day. They then offered each participant the choice of a small, immediately gratifying reward or a delayed reward that had a greater value. The participants who had to think harder for the six-hour task were more likely to take the smaller, immediate reward. The researchers believe that after people spend long periods of time thinking hard, certain neurotransmitters accumulate and make it more difficult for us to make strategic decisions, and we end up making impulsive decisions that aren’t in our best-long-term interests.