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The Grand Mystery of How Your Brain Makes a Really Simple Choice

New research points to how humans and other animals understand "good" and "bad."
Image via fiverlocker/Flickr

Most likely, you take decision making somewhat for granted. Maybe not big, life-changing decision making, the sort where you make columns of pros and cons and sit down with friends and family for deep meaningful conversations, but decisions like, Do I want to listen to a tape of some band or do I want to listen to NPR on this drive to the grocery store, or, Wait, do I need to go to the grocery store at all or maybe just Rite Aid, or maybe Walgreens is a little closer. It might be easier to just take the highway to Walmart but fuck Walmart. You probably don’t spend 20 percent of your day stumped over little things that don’t actually matter in the grand scheme—you just do them.

Making decisions—choosing—is one of the most crucial tasks your brain is responsible for, and certainly one of its most easily taken for granted. Inability to make decisions or having an extremely difficult time making them is a symptom of some mental illnesses—depression and schizophrenia, especially—that doesn’t get due credit for its debilitating effects. You need to be able to choose. Otherwise, life is a neverending series of roadblocks always compounding and always feeding back into the initial illness. Limbo is the inability to choose, and it traces back to a small and ill-understood part of the brain called the lateral habenula, the decision-making role of which is described in a paper out yesterday in Nature Neuroscience.

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The University of British Columbia's Stan Floresco, the lead author of the paper, explained your brain's decision-making process in an interview on Sunday. "Although we still have a lot to figure out about the neural circuits underlying different types of decision making," he said, "one way you can look at it is that there are numerous brain regions, many of them in the frontal lobes, that use different types of information—your memories, your individual personality and preference, your current motivations etc—to help make value judgments about different courses of action.

"Different brain regions may be nudging you to go in one direction or another," Floresco said. "I like to use the analogy that there are battles going on in your brain pushing you one way or another. What our results suggest is that this nucleus, the lateral habenula, helps this circuitry reach a definitive decision and/or helps you implement it once there is an apparent 'winner' in this battle."

via Hidenori Aizawa, RIKEN Brain Science Institute

The lateral habenula doesn’t give us good decision making ability; it gives us the ability to make decisions at all. This revelation comes from rats set up in an elaborate cost-reward scheme. Basically, they were offered choices between consistent small rewards and sporadic larger rewards: some food all of the time or more food just sometimes. With their lateral habenulas turned on, the rats tended to choose the less risky option, making the smart or good decision. Earlier studies have suggested that, with this brain region turned off, the rats would make crappy, riskier decisions. That wasn't the case in the new study.

"The general impression that was emerging in the field was that this part of the brain was a sort of aversion or 'anti-reward' center," Floresco said. "It would signal when bad things happened or were about to happen.  While this is partially true, our results suggests that its function is a bit broader than that. Rather than just signaling what is bad in your environment, it also helps you figure out what is good, especially when comparing between two different types of rewards. So, rather than being an 'anti-reward' center, our findings suggest it’s more of a comparator or preference center, that evaluates good and bad things in your environment and helps you choose a course of action that you may think is better for you."

The rats with inactive lateral habenulas just didn’t decide at all—or, rather, they didn’t demonstrate any decision-making ability. In rat-food-scheme terms, they chose both options equally. This finding has potential implications for treating mental illness.

"Although this is still very speculative, what may be going on [in depression] is that when the habenula is inactivated, it pushes patients towards a more ambivalent emotional state (not bad, but not good either).  So if a patient feels very bad in a depressed state, moving to 'neutral' state would actually present as a clinical improvement in symptoms."

The research raises the question of whether the lateral habenulas might represent a link between schizophrenia and depression. The short answer is not yet. Some literature points to the disorders sharing some of the same brain circuitry, but the problems with that circuitry may be different between the two. For now, the lateral habenulas may represent a potential target for deep brain stimulation therapy for depression. In the meantime: just flip a coin already.

@everydayelk