Researchers have found that a very small portion of your brain plays a key role in decision making. A University of British Columbia study published in Nature Neuroscience says that we need to rethink what we know about the lateral habenula, a region of the brain previously linked to depression and avoidance behaviours; they claim that it is critically involved in cost-benefit decisions.

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“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,” says Prof. 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.”

Neurons in the lateral habenula are ‘reward-negative’ – they are activated by stimulus associated with unpleasant events, the absence of the reward or punishment – especially when this is unpredictable. But researchers suspected there was more to this region than initially thought. In this purpose, they trained lab rats to choose between a consistent small reward (one food pellet) or a potentially larger but less likely reward (four food pellets, every once in a while). Just like humans, rats tended to choose risks were low, and preferred smaller rewards when risks were high.

However, when the lateral habenula was turned off, instead of going for more riskier options as was presumed, the rats simply chose randomly – no longer showing the ability of distinguishing what’s better for them.

“Deep brain stimulation — which is thought to inactivate the lateral habenula — has been reported to improve depressive symptoms in humans,” Floresco says. “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.”

The findings are very interesting, especially considering that evolution wise, the lateral habenula is one of the oldest regions of the brain. However, since this is actually the first study to study the connection between the area and decision making, so any implications regarding its role in human evolution are at the moment pure speculation.