One of the smallest parts of the human brain may be one of the most important, playing a crucial role in decision-making, Canadian scientists say. The function of the lateral habenula, a region of the brain linked to depression and avoidance behaviors, has been largely misunderstood and may be integral in cost-benefit decisions people make all the time, scientists at the University of British Columbia reported in the journal Nature Neuroscience. "These findings clarify the brain processes involved in the important decisions that we make on a daily basis, from choosing between job offers to deciding which house or car to buy," said Stan Floresco of the university's Brian Researcher Center. "It also suggests that the scientific community has misunderstood the true functioning of this mysterious, but important, region of the brain." In their study, the researchers trained lab rats to choose between a consistent small reward (one food pellet) or a potentially larger reward (four food pellets) that appeared sporadically. The tended to choose larger rewards when costs -- in this case, the amount of time they had to wait before receiving food -- were low, but preferred smaller rewards when such risks were higher. When the lateral habenula region of the rats' brains were inactivated, they researchers found, the rats selected either option at random, no longer able to choose the best option for them. The study may have important implications for depression treatment, the researchers said. "Deep brain stimulation -- which is thought to inactivate the lateral habenula -- has been reported to improve depressive symptoms in humans," Floresco said. "But our findings suggest these improvements may not be because patients feel happier; they may simply no longer care as much about what is making them feel depressed." A greater understanding of decision-making processes is crucial, the researchers said, because many psychiatric disorders such as schizophrenia, stimulant abuse and depression are associated with impairments in these processes.