Neuroscientists may have found a region of the brain that plays a role in having a pessimistic outlook. In an animal model, researchers found that stimulating the caudate nucleus can induce a negative assessment of a situation. The researchers believe that the effects of the stimulation can persist through to the day after the original stimulus.
“We feel we were seeing a proxy for anxiety, or depression, or some mix of the two,” senior author Ann Graybiel, an MIT Institute professor and member of MIT’s McGovern Institute for Brain Research, said in a statement. “These psychiatric problems are still so very difficult to treat for many individuals suffering from them.”
The findings, reported in the journal Neuron, shine further light on the role of the basal ganglia (where the caudate nucleus is located) in decision-making. While neuroscientists already knew that the frontal lobe and basal ganglia both contribute to the decision-making process, they didn’t know the relative contributions of the latter.
To learn more, the team constructed a way to test decision-making by exploiting the so-called “approach-avoidance conflict”. The animals were given juice as a reward but this was paired with a puff of air to the face, which was the negative stimulus they would like to avoid. In each trial, the ratio of juice to puff of air was varied, and the animals could choose to accept it or not.
This is a scenario that requires cost-benefit analysis. Is the juice worth it? The researchers discovered that once the caudate nucleus was stimulated, the cost-benefit analysis became distorted, and the animals rejected combinations that before they had accepted. This suggests they began to focus more on the cost of the situation than prior to the stimulation.
“There must be many circuits involved,” Professor Graybiel explained. “But apparently we are so delicately balanced that just throwing the system off a little bit can rapidly change behavior.”
The team also discovered that brainwave activity in the caudate nucleus was altered when the decision-making patterns changed. This could be used as a potential biomarker to monitor negative and pessimistic states. It could also be useful to test the effectiveness of drugs designed to reduce anxiety and depression.
The caudate nucleus is within the limbic system, the region that regulates mood, and it has connections to the motor areas of the brain and where the organ produces dopamine, the hormone linked to reward-motivated behavior.
The team hopes to use these findings to better understand the often-crippling effects of depression, anxiety, and obsessive-compulsive disorder. While this won’t have immediate applications, it can help work out the effectiveness of current solutions.