Disorders like anxiety and depression have been linked to experiencing a pessimistic mood. This causes the affected person to focus on the possible drawback in a situation instead of the possible benefit.
Now, the region of the brain responsible for generating this pessimistic mood may have been identified by a team of scientists at the Massachusetts Institute of Technology (MIT).
The study titled “Striatal Microstimulation Induces Persistent and Repetitive Negative Decision-Making Predicted by Striatal Beta-Band Oscillation” was published in the journal Neuron on Aug. 9.
“We feel we were seeing a proxy for anxiety, or depression, or some mix of the two,” said senior author Ann Graybiel, an MIT Institute Professor and a member of the McGovern Institute for Brain Research.
The latest figures have indicated a rise in anxiety and depression diagnoses in the United States, especially among young adults and adolescents.
“These psychiatric problems are still so very difficult to treat for many individuals suffering from them,” Graybiel added.
The research team examined the brain region known as the caudate nucleus, which is linked to emotional decision-making. By using a small electrical current, they stimulated this region in the brains of animals.
The team conducted a series of trials where the animals were offered a reward (juice) which would be provided along with an unpleasant stimulus (a puff of air to the face).
“In each trial, the ratio of reward to aversive stimuli was different, and the animals could choose whether to accept or not,” stated the press release. “If the reward is high enough to balance out the puff of air, the animals will choose to accept it, but when that ratio is too low, they reject it.”
Upon stimulation of the caudate nucleus, the animals started to avoid combinations they would have accepted previously. This effect continues past the end of the stimulation as it was observed even during the next day before gradually disappearing.
The value of the reward perceived by the animals, thus, diminished. It suggested they focused more on the cost of the aversive stimulus which resulted in their choice to reject.
“This state we’ve mimicked has an overestimation of cost relative to benefit,” Graybiel said.
Noting the abnormal activity observed in the caudate nucleus during the study, the researchers also suggested it may somehow play a role in the disruption of dopamine activity.
“There must be many circuits involved,” Graybiel stated. “But apparently we are so delicately balanced that just throwing the system off a little bit can rapidly change behavior.”
In light of the new findings, she is currently working with psychiatrists at McLean Hospital in Massachusetts to study the brain activity of patients who are diagnosed with depression and anxiety.