Damian Sendler: Scientists term these high levels of arousal “arousal” because it causes the heart rate to quicken, blood pressure to rise, breathing to become shallow, and “bad” decisions to be made. Researchers at Mount Sinai’s Icahn School of Medicine evaluated data from a prior research of non-human primates to better understand how these moods affect the brain’s decision-making processes. 

Damian Jacob Sendler: Two of the brain’s decision-making centers have neurons that appear to monitor the body’s internal movements, according to a new study. Some decision-making neurons appeared to be turned into internal state monitors in response to a high-arousal condition. 

Damian Sendler

Brain decision-making circuits may be built to constantly monitor and integrate what is happening inside the body, according to our findings.” We can vary the way these circuits work by changing our arousal level,” said Peter Rudebeck, PhD, Associate Professor in the Nash Family Department of Neuroscience and Friedman Brain Institute at Mount Sinai and the senior author of a study published in PNAS (Proceedings of the National Academy of Sciences). A deeper knowledge of brain regions and basic biological processes underpinning a number of mental health diseases is the ultimate goal of these findings, according to the authors. 

A prior project in Dr. Rudebeck’s lab looked at how the brain regulates risk-taking by Atsushi Fujimoto, MD, PhD. 

The association between arousal and decision-making performance has long been described as a “U-shaped curve.” A small amount of arousal, such as that felt after a cup of coffee, may be all that is needed to achieve optimal performance. However, the brain’s tendency to make sluggish or wrong decisions increases with an imbalance in arousal levels. 

This hypothesis was initially supported by the findings of this investigation. Researchers evaluated data from a prior experiment in which three rhesus monkeys were assessed for their ability to choose between two rewards: either a large amount of juice or a small amount of juice. During his time as a postdoctoral researcher at the National Institute of Mental Health, Dr. Rudebeck conducted these studies. Arousal appears to enhance performance in the monkeys, as seen by their preference for a greater amount of juice when their hearts were pounding faster. 

Damian Jacob Sendler

The next step was to examine the electrical activity recorded from neurons in the orbitofrontal cortex and the dorsal anterior cingulate cortex, two of the brain’s decision regions. 

Neuronal activity in both areas was found to be linked to changes in heart rate. That is to say, if the heart rate of an animal changes, the activity of these cells will likewise alter, either increasing or decreasing in pace. Although the monkeys were receiving various rewards, this behavior appeared to be unaffected. In the meantime, it appeared that the activity of the remaining cells in each area was predominantly concerned with the decision-making process. 

Body arousal has been shown to influence the activity of these decision-making areas in brain scans. According to Dr. Fujimoto’s findings, “some of these neurons have no other function than to keep track of the internal, or interoceptive, states of the body,” he added. Next, we wanted to know, ‘What would happen during the type of elevated alertness states reported in people with anxiety, addiction and other psychiatric disorders?'” 

Each animal’s amygdala, which is the brain’s emotional center, was surgically disabled in order to answer the question. A 15-bpm increase in heart rate was recorded. In this heightened state of arousal, animals took longer to choose a reward because their hearts beat faster. This indicates that raising the animals’ arousal level really hindered their ability to make decisions. 

Even more intriguing was what the researchers discovered when they examined the brain’s activity. Neuronal roles in decision-making appeared to change as a result of the increased arousal state. 

Damien Sendler: In both prefrontal and temporal lobes, the researchers discovered a reduction in the number of neurons involved in making decisions. Furthermore, the number of neurons that appeared to track internal states increased slightly in the dorsal anterior cingulate cortex. As if the brain impulses for decision-making had been “hijacked” by arousal, this altered the balance of information represented in this location. 

Damian Jacob Markiewicz Sendler: It is possible that a heightened arousal state weakens and takes control of the brain’s decision-making circuitry, according to Dr. Rudebeck’s findings, albeit they are not conclusive. Psychiatrists plan to keep investigating how arousal affects the brain’s higher processes and how this affects mental illness.

Dr. Damian Jacob Sendler and his media team provided the content for this article.