Anxiety, addiction, and other psychiatric problems are frequently marked by high levels of arousal: the heart beats faster, blood pressure rises, breathing shorten, and “poor” decisions are made. Scientists from Mount Sinai’s Icahn School of Medicine evaluated data from a prior research on non-human primates in order to better understand how these moods affect the brain’s decision-making processes. They discovered neurons in two of the brain’s decision-making areas that may only monitor the body’s internal dynamics. Furthermore, a high level of arousal appeared to rewire one of the centers, transforming some decision-making neurons into internal state monitors.
“Our findings imply that the brain’s decision-making circuits are set up to constantly monitor and integrate what’s going on within the body. As a result, changes in our degree of arousal can affect how these circuits function “Peter Rudebeck, PhD, an associate professor in Mount Sinai’s Nash Family Department of Neuroscience and the Friedman Brain Institute, and the study’s principal author, said (Proceedings of the National Academy of Sciences). “We believe that these findings will aid researchers in learning more about the brain areas and fundamental cellular processes that underpin a variety of psychiatric diseases.”
Atsushi Fujimoto, MD, PhD, an Instructor in Dr. Rudebeck’s lab who previously researched how the brain controls risk-taking, conducted the study.
The association between arousal and decision-making performance has been described as a “U-shaped curve” by experts for years. Basically, a small amount of arousal, such as that felt after a cup of coffee, can lead to peak performance. Arousal levels that are excessively high or too low, on the other hand, increase the likelihood of the brain making slow or wrong decisions.
The study’s preliminary findings backed up this theory. The researchers looked at data from a prior set of tests in which three rhesus monkeys were asked to choose between two rewards: a lot of pleasant juice or a little. These investigations were carried out by Dr. Rudebeck while he was a postdoctoral researcher at the National Institute of Mental Health. The monkeys consistently chose more juice, and on average, they made this decision faster while their hearts were racing, supporting the theory that a heightened mood promotes higher performance.
The researchers then looked at the electrical activity recorded from neurons in the orbitofrontal cortex and the dorsal anterior cingulate cortex, two of the brain’s decision regions.
They discovered that the activity of around a sixth of the neurons in each location was related to heart rate changes. In other words, if an animal’s heart rate changes, the activity of these cells changes as well, either increasing or decreasing. This behavior seems to be unaffected by the judgments made on the various prizes given to the monkeys. The activity of the remaining cells in each area, on the other hand, appeared to be predominantly focused on the decision-making process.
“According to brain scanning research, physiological arousal affects the activity of these decision-making areas. Our findings confirm this theory on a molecular level and show that some of these neurons’ main function is to monitor the body’s internal, or interoceptive, states “According to Dr. Fujimoto. “What might happen during the type of heightened arousal states seen in patients suffering from anxiety, addiction, and other mental disorders?” was the following inquiry.
The data collected after the amygdala, the brain’s emotional center, was surgically switched off in each animal was evaluated to answer the question. Heart rates increased by up to 15 beats per minute as a result of this. The faster the animals’ hearts beat in this higher arousal condition, the slower they were to choose a reward. This shows that raising the animals’ arousal level actually impaired their decision-making ability.
The team discovered something much more intriguing when they examined the brain activity. The neurons’ responsibilities during decision-making appeared to change as the arousal level increased. The researchers discovered evidence of a decline in the number of neurons engaged in decision-making in both brain areas. Furthermore, the number of neurons that appeared to track internal states increased slightly in the dorsal anterior cingulate cortex. As though arousal had “hijacked” the brain signals for decision making, the balance of information displayed in this area had shifted.
“While our findings aren’t conclusive, they do show that a high arousal state weakens and takes control of the brain’s decision-making circuits,” Dr. Rudebeck stated. “We want to learn more about how arousal affects higher brain functions and how this affects psychiatric diseases.”