Ancient decision-making brain region misunderstood: UBC study
Though it's deep in the human brain and rarely studied, scientists believed the lateral habenula, one of the oldest regions of the brain evolution-wise, was linked to reward-avoidance and to depression.
In a 2007 study, Japanese scientists discovered that lateral habenula neurons in rhesus monkeys were excited when pursuing a task not linked to a reward. In a 2010 study, German researchers examined the habenular complex in 44 post-mortem patients and discovered that it had significantly less volume in those who had suffered from depression in life than those who hadn't or those who had schizophrenia. Deep-brain stimulation, which has helped some depressed patients who did not respond to treatment, is thought to inactivate the lateral habenula.
But a new Nature Neuroscience study of rat behaviour from the University of British Columbia has shown that our understanding of the region and its link to decision-making might be all wrong.
Professor Stan Floresco and PhD student Colin Stopper trained 16 rats to choose between a low-risk, low-reward option (a single food pellet dispensed at regular intervals) or a high-risk, high-reward option (four food pellets dispensed over longer intervals.) After nearly a month of training, the rats behaved as one might expect: they were more likely to choose the bigger reward when the risk was lower, i.e. when it was dispensed more often.
Then the researchers surgically disabled the lateral habenula. When they started subjecting the rats to the tests again a week later, they expected the rats to choose the bigger, riskier reward more often, since the region was thought to control reward-seeking.
That wasn't the case. When they averaged the rats decisions, the animals were now just as likely to choose the riskier reward as the safe reward.
The paper's title is "What's better for me?" The rats appeared to lack the ability to answer that question, simply choosing between the risks and rewards at random.
Floresco noted in a statement that deep brain stimulation in humans has been reported to improve symptoms of depression. “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 researchers would like to continue their investigation into this region, since understanding cost-benefit analysis can help us understand not just depression but disorders like drug abuse and schizophrenia.
Kate Allen is the Star's science and technology reporter. Find her on Twitter at @katecallen.