Researchers from the University of British Columbia found the lateral habenula, a region of the brain linked to depression and avoidance behaviours, has been largely misunderstood and may be integral in cost-benefit decisions.
"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 Professor Stan Floresco of UBC's Dept of Psychology and Brain Research Centre (BRC).
"It also suggests that the scientific community has misunderstood the true functioning of this mysterious, but important, region of the brain," Floresco said.
In the study, scientists trained lab rats to choose between a consistent small reward (one food pellet) or a potentially larger reward (four food pellets) that appeared sporadically.
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Like humans, the rats tended to choose larger rewards when costs - in this case, the amount of time they had to wait before receiving food - were low and preferred smaller rewards when such risks were higher.
Previous studies suggest that turning off the lateral habenula would cause rats to choose the larger, riskier reward more often, but that was not the case.
The findings have important implications for depression treatment.
"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," Floresco added.
The study is published in the journal Nature Neuroscience.