A team of neuroscientists led by researcher Ann Graybiel, from the Massachusetts Institute of Technology in Cambridge (USA) has discovered what is the area of the brain responsible for pessimism. New research suggests that both anxiety and depression are caused by overstimulation of the caudate nucleus.
The work, which has been published in the journal Neuron , has examined the neurological underpinnings of pessimism in mice and has also found clues to anxiety and depression in humans.
The experts focused on a type of decision-making process known as approach-avoidance conflict (an object of desire that is both desired and rejected).
This approach describes situations in which people (or mammals) have to decide between two options by weighing the positives and negatives of each alternative.
Previous research had already identified the brain circuits responsible for this type of decision-making. Then they found that having to decide in this scenario can induce significant stress, and that chronic stress causes rodents to choose the riskiest option that has the highest potential payoff.
The caudate nucleus and decision making
In the new study, to recreate the scenario in which rodents have to choose and weigh positives and negatives, the scientists offered the mice a squirt of juice as a reward, but combined it with an aversive stimulus: a puff of air into the mouth. expensive.
In several trials, the researchers varied the relationship between the reward and the unpleasant stimuli and gave the rodents a choice whether to accept the reward with the aversive stimulus or not.
As the researchers explain, this model requires rodents to perform a cost-benefit analysis. If the reward is high enough to compensate for the unpleasant puff of air, the animals will choose to accept it, but when the ratio is deemed too low, they will reject it.
They also applied a small electric shock to the rodents’ caudate nucleus to see how it affected their decision-making. When this area was stimulated, the rodents did not make the same decisions as before receiving a stimulus.
Specifically, the rodents focused much more on the cost of the unpleasant stimulus than the value of the reward. This result suggests that the animals began to devalue the reward they wanted , and focused more on the cost of the negative stimulus. “This state that we have imitated has an overestimation of the cost in relation to the benefit,” explains Graybiel.
In addition, the scientists found that stimulation of the caudate nucleus led to a change in the brain wave activity of the rodents.
Anxiety, depression and a “delicate balance”
The researchers say these findings could help clinicians better understand the magnitude of depression and anxiety symptoms and point to new treatments.
“ We felt like we were looking at an indicator of anxiety, depression, or some combination of both, ” explains Graybiel. “These psychiatric problems are still very difficult to treat for many people who suffer from them.”
Next, the team is looking to examine whether people living with depression and anxiety show similar hyperactivity in the caudate nucleus of the brain. Researchers suspect that stimulation of this area of the brain causes a disruption in dopamine , the ‘happiness hormone’.
Reference: Striatal Microstimulation Induces Persistent and Repetitive Negative Decision-Making Predicted by Striatal Beta-Band Oscillation. Neuron, DOI: 10.1016 / j.neuron.2018.07.022
