Insights into decision-making processes that may lead to improved treatment for depression

News Editor: Tina Pentland

Our capacity for decision-making is influenced by a little-known and poorly understood region of the brain called the lateral habenula (LHb)—one of the oldest regions of the brain, evolution-wise. According to the study, “What’s better for me? Fundamental role for lateral habenula in promoting subjective decision biases”, published this month in Nature Neuroscience, the LHb may in fact be integral to decision-making that relies specifically on subjective assessments of cost-benefit—that is, our ability to assess the “cost” of any choice we make relative to the “reward”. The significance of this study may be that the LHb is also linked to depression and other avoidance behaviours, hence this research could have wider implications in the treatment of psychiatric illnesses, such as schizophrenia, stimulant abuse and depression, which are associated with impaired decision-making.

The study, which was carried out by Professor Stan Floresco and Colin Stopper at the University of British Columbia’s Department of Psychology and Brain Research Centre, measured the decision-making habits of rats when the LHb was turned off, compared to a control group. The rats were trained to choose between a small or large reward (1 or 4 food pellets), where the cost was measured as the length of time they had to wait to get the reward. Under control conditions all rats made choices fairly consistently, based on their assessment of cost versus reward—just like humans, perhaps, they tended to choose the large reward if the cost was low, and the small reward if the cost was high. In contrast, LHb inactivation caused the rats to behave haphazardly—meaning that choice behaviour of the group was no better than chance. Thus, contra the initial hypothesis—that when the LHb was turned off the rats would opt for the larger, more risky reward, more often—this was not the case. Instead, the rats made their choices randomly. In other words, LHb inactivation caused the rats to be indifferent when choosing between rewards associated with different subjective costs or risks, but not larger or smaller rewards of equal cost. Thus the LHb appears to have a role in expressing subjective preferences in decision-making—that is, assessing cost-benefit.

This result has important implications for the treatment of depression and other psychiatric disorders. For example, it had been thought previously that deep brain stimulation (used to treat depression) inactivated the LHb, and that this contributed to a lessening of depressive symptoms. In contrast, the findings of this study (that inactivation of the LHb produces random behaviour) suggest rather strongly, as Floresco points out, that any improvement may not be because patients feel happier but, rather, that they “no longer care as much about what is making them feel depressed”.

Clearly, more research into the brain functions involved in cost-benefit decision processes and related behaviours is needed, Floresco suggests. In particular, a better understanding of   decision-making processes is crucial in order to improve treatment of the psychiatric disorders that are specifically associated with an inability to make decisions.

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