DEPRESSION
December 2, 2013

The Brain's Decider

Decisions, motivation and depression all seem to come from the same area of the brain. No wonder pie is hard to resist.

We all have trouble trying to make important decisions. Our brains constantly weigh the pros and cons of dozens of decisions every day. Bigger decisions, such as what type of car to buy, may inspire us to gather lots of information and require taking many factors into account. Others, such as whether to splurge on dessert, may be less well considered.

Regardless of the magnitude of the decision, however, new research suggests that the part of our brain making these cost-benefit analyses may lie in a region called the lateral habenula.

The lateral habenula is especially interesting because other research has linked it to depression and motivation. Previous studies have found that when this brain region is stimulated, animals are less motivated. The connection may help explain why our willpower can falter when we are in the process of grappling with difficult decisions.

Scientists now believe deep-brain stimulation deactivates the lateral habenula and causes people to no longer care about what’s been making them depressed.

In the current study, University of British Columbia (UBC) researchers trained rats to choose between a consistent small reward (one food pellet) and a sporadic large reward (four food pellets). The rats developed a preference — choosing the larger reward when the time between rewards (costs) was short. When the costs were higher — they had to wait a long time for the four pellets to arrive — they preferred the smaller, but more frequent, reward.

The scientists then infused GABA, an inhibitory brain chemical, directly into the rats' brains to switch off the lateral habenula. To their surprise, the scientists saw that the rats no longer cared about the costs, and chose either reward at random.

The results suggest that the lateral habenula is a critical player in cost-benefit motivation, and that without it, you may not really care as much about the impact of your decisions.

The findings have important implications for people suffering from major depressive disorder. Deep-brain stimulation, a promising treatment for depression, has been shown to inactivate the lateral habenula.

Earlier research found that deep-brain stimulation increased the levels of neurotransmitters, such as serotonin, which make people feel happier. Based on the current study, however, Dr. Stan Floresco and Ph.D. candidate Colin Stopper believe deep-brain stimulation deactivates the lateral habenula and causes people to forget about the costs of their decisions — so they no longer care about what’s been making them depressed.

“These findings clarify the brain processes involved in the important decisions that we make…[and] also suggest that the scientific community has misunderstood the true functioning of this mysterious, but important, region of the brain,” Floresco, a professor in the Department of Psychology and UBC's Brain Research Centre, said.

The lateral habenula may be involved in other psychiatric disorders marked by impaired decision-making processes, such as substance abuse and schizophrenia.

The study was published in the journal, Nature Neuroscience.

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