Scientists have identified a brain region that can generate negative moods which lead to irrational decision-making, a study has found.
Stimulating the caudate nucleus region causes animals to give far more weight to the anticipated drawback of a situation than its potential benefit, according to the study published in the journal Neuron.
Many patients with neuropsychiatric disorders such as anxiety or depression experience negative moods that lead them to focus on the possible downside of a given situation more than the potential benefit.
Now, neuroscientists at Massachusetts Institute of Technology (MIT) in the US have pinpointed the brain region that can generate this type of pessimistic mood.
In tests in animals, they showed that stimulating this region, known as the caudate nucleus, induced animals to make more negative decisions.
They gave far more weight to the anticipated drawback of a situation than its benefit, compared to when the region was not stimulated.
This pessimistic decision-making could continue through the day after the original stimulation, researchers said.
The findings could help scientists better understand how some of the crippling effects of depression and anxiety arise, and guide them in developing new treatments.
"We feel we were seeing a proxy for anxiety, or depression, or some mix of the two," said Ann Graybiel, a professor at MIT.
"These psychiatric problems are still so very difficult to treat for many individuals suffering from them," said Graybiel.
Researchers have previously identified a neural circuit that underlies a specific kind of decision-making known as approach-avoidance conflict.
These types of decisions, which require weighing options with both positive and negative elements, tend to provoke a great deal of anxiety.
Her lab has also shown that chronic stress dramatically affects this kind of decision-making: More stress usually leads animals to choose high-risk, high-payoff options.
In the new study, the researchers wanted to see if they could reproduce an effect that is often seen in people with depression, anxiety, or obsessive-compulsive disorder.
These patients tend to engage in ritualistic behaviours designed to combat negative thoughts, and to place more weight on the potential negative outcome of a given situation.
This kind of negative thinking, the researchers suspected, could influence approach-avoidance decision-making.
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