Which Area of the Brain is Responsible for Pessimism?

February 6, 2020
Experts have identified the region of the brain that might be responsible for pessimism. The cause appears to be overstimulation of the caudate nucleus.

Most of us, at one point or another, have felt or shown a pessimistic attitude. But what’s pessimism exactly? Is there an area of the brain responsible for pessimism? Pessimism is a mental attitude in which you anticipate an undesirable result stemming from a specific situation. Pessimists tend to focus on the negative aspects of particular situations. Sometimes, this extends to a negative perspective on life itself.

Many patients with psychological disorders such as anxiety or depression have such a mindset. They often commonly experience moods that lead them to focus on the possible roadblocks in a given situation more than the possible beneficial points of it.

A team of neuroscientists has identified a region of the brain that might be involved in this. They believe that this pessimistic mood stems from this area of the brain. The research studies suggest that overstimulation of the caudate nucleus may cause anxiety and depression.

Ann Graybiel is a professor at the MIT McGovern Institute in Cambridge, Massachusetts. She directed a study that was published in the journal Neuron. This study examines the neurological foundations of pessimism in mice. She also found clues regarding anxiety and depression in humans.

A drawing of a brain displaying pessimism with a frown.

Her findings might help scientists better understand how these disorders arise. In other words, they might discover some of the reasons behind some of the paralyzing effects of depression and anxiety. That could then lead them toward the development of new treatments.

The area of the brain responsible for pessimism

The researchers have shown that stimulating the caudate nucleus can create negative mood states. These can lead a person to make irrational decisions. According to the results of this study, stimulation of the caudate nucleus makes animals act differently. The animals place much more reasoning weight on the anticipated disadvantages of a situation. They do this while ignoring the potential benefits of the situation.

For this study, Graybiel and her colleagues focused on a specific type of decision-making process. This was the process known as the avoidance-avoidance conflict. The avoidance-avoidance conflict arises in situations where people (or any mammal) has to choose between two options. In order to do so, they weigh the negative and positive aspects of each alternative.

Experts believe that the overstimulation of the caudate nucleus, an area of the brain, is responsible for pessimism.

Chronic stress study

One study that the same group conducted previously had already identified an important structure for this. It identified a neural circuit that underlies a specific type of decision-making known as the approach-avoidance conflict. These types of decisions, which require reflecting on both positive and negative elements, tend to cause a lot of anxiety.

Also, they showed that chronic stress dramatically affects this type of decision-making. More stress generally makes animals opt for options with a high level of risk and reward.

In this new study, the researchers wanted to see if they could reproduce a common effect. Experts commonly see this effect in people with depression, anxiety, or obsessive-compulsive disorder. These patients tend to become absorbed in ritual behaviors designed to fight negative thoughts and give more weight to possible negative outcomes of given situations. The researchers suspected that these types of negative thoughts influence decision-making.

A man with a frown face on a whiteboard in front of his face.

In order to recreate this scenario for the rodents, they offered them a little bit of juice as a reward. However, they combined this reward with an aversive stimulus. This stimulus was a blast of air to the face.

Emotional decisions

In order to test this hypothesis, the researchers stimulated the caudate nucleus. This is a region of the brain linked to emotional decision making. Through various attempts, the researchers varied the relationship between reward and disagreeable stimuli. They also gave the rodents the ability to decide whether they would accept the reward with the aversive stimulus or not.

As the researchers explain, this model requires the rodents to undertake a cost-benefit analysis. If the reward is sufficiently high to balance out the blast of air, they’ll accept. However, if the proportion isn’t in their favor, they’ll reject it.

When the researchers stimulated the caudate nucleus of the animals, the direction of the cost-benefit analysis changed. This time, the animals began to avoid combinations that they would have previously accepted. This continued even after the researchers stopped stimulating their caudate nuclei. They even had the same disposition the next day. After that, however, it gradually began to disappear.

These results suggest that when the animals started to evaluate the reward, they focused more on the cost. In this case, the “cost” was the aversive stimulus. Graybiel explained that this state they created caused them to overvalue the costs in relation to the benefits.

Anxiety and depression, a delicate balance

The researchers also found that brainwave activity in the caudate nucleus changed as the decision-making pattern did. They found this change in the beta frequency. The researchers believed it could be a biomarker for controlling whether animals or patients would respond to pharmacological treatment.

Researchers are working on a study involving patients suffering from depression and anxiety. They want to see whether or not their brains show abnormal activity in the caudate nucleus and the nucleus of the neocortex. They want to check whether abnormal activity occurs during decision-making to avoid the approach. Magnetic resonance studies have shown abnormal activity in two regions of the medial prefrontal cortex. These are regions that are connected to the caudate nucleus.

Inside the caudate nucleus, there are regions connected to the limbic system. This system regulates a person’s mood. It also sends information to the motor regions of the brain, as well as the areas that produce dopamine. Researchers believe that the abnormal activity seen in the caudate nucleus in this study could somehow be changing dopamine activity.

  • Amemori, K., Amemori, S., Gibson, D., y Graybiel, A. (2018). Striatal Microstimulation Induces Persistent and Repetitive Negative Decision-Making Predicted by Striatal Beta-Band Oscillation. Neuron99(4), 829-841.e6. doi: 10.1016/j.neuron.2018.07.022