How a beating heart may affect the circuits in the brain that make decisions

The decision-making process can be hijacked by neurons that monitor body status.

Anxiety, addiction, and other psychiatric diseases are frequently characterised by high episodes of what scientists refer to as arousal: the heart beats faster, blood pressure measurements rise, breathing shorter, and “poor” decisions are made as a result of the disorder. Scientists at the Icahn School of Medicine at Mount Sinai examined data from a prior research on non-human primates in an attempt to better understand how these states influence the brain’s decision-making processes. Scientists have discovered that neurons in two of the brain’s decision-making regions appear to be completely dedicated to monitoring the body’s internal dynamics. Furthermore, a high level of arousal appeared to rewire one of the brain’s decision-making areas, causing some of the neurons to function as internal state monitors instead.

“Our findings show that the brain’s decision-making circuits are built to constantly monitor and integrate information about what is going on inside the body, according to the researchers. Consequently, fluctuations in our level of arousal can have an impact on the way these circuits function “Peter Rudebeck, PhD, Associate Professor in the Nash Family Department of Neuroscience and Friedman Brain Institute at Mount Sinai, and the senior author of the study published in PNAS, explained how the study was conducted (Proceedings of the National Academy of Sciences). “We believe that these findings will aid researchers in their efforts to get a deeper understanding of the brain regions and fundamental cellular processes that underlie a variety of psychiatric diseases.”

Atsushi Fujimoto, MD, PhD, an Instructor in Dr. Rudebeck’s lab who has previously investigated how the brain controls risk-taking, was in charge of the study. Dr. Rudebeck was also involved.

Scientists have known for years that the relationship between arousal and decision-making performance is characterised by a “U-shaped curve.” On the whole, a small amount of arousal — such as that experienced after drinking a cup of coffee — may be sufficient to promote optimal performance. However, too much or too little arousal raises the likelihood that the brain may make decisions that are slow or wrong.

The preliminary findings of this study supported this hypothesis. The researchers looked at data from a prior series of tests in which they assessed the capacity of three rhesus monkeys to choose between receiving a large amount of tasty juice or a small amount of tasty juice. At the time of the tests, Dr. Rudebeck was working as a post-doctoral associate at the National Institute of Mental Health. The monkeys consistently selected to drink more juice, and on average, they made this decision faster when their hearts were beating faster, supporting the notion that being in a highly aroused state promotes higher performance.

They next examined electrical activity recorded from neurons in two of the brain’s decision-making centres, known as the orbitofrontal cortex and the dorsal anterior cingulate cortex, to see how they differed from one another.

Specifically, they discovered that the activity of around one-sixth of the neurons in either location was associated with changes in heart rate. In other words, if the heart rate of an animal varied, the activity of these cells would alter as well, either increasing or decreasing in pace. This activity did not appear to be influenced by the judgments made about the varied prizes that the monkeys were getting, which was surprising given the circumstances. The activity of the remaining cells in each area, on the other hand, appeared to be largely concerned with the decision-making procedure.

“Researchers have discovered that physiological arousal changes the activity of these decision-making areas, according to brain scanning studies. Both at the cellular and systemic levels, our findings confirm this hypothesis, and they show that the sole function of certain of these neurons is to track the body’s interior or interoceptive states “Dr. Fujimoto expressed himself. A second question was posed to the team: “‘What might happen during the type of elevated arousal states that are seen in people who suffer from anxiety, addiction, and other psychiatric disorders?'” they explained.

Using data collected after the amygdala, the brain’s emotional centre, was surgically removed from each animal, the researchers attempted to address the question. Heart rates were elevated by up to 15 beats per minute as a result of this. During this increased arousal state, the animals’ hearts beat quicker and they were slower to choose a reward, which indicated that they were more focused on the task at hand. This shows that when the animals’ arousal levels were raised, it actually impeded their ability to make decisions.

However, when the researchers examined the brain activity, they discovered something much more interesting.. The increased level of arousal appeared to have an effect on the roles that the neurons played during the decision-making process. The researchers discovered evidence of a decline in the number of neurons participating in the decision-making process in both of the brain’s decision-making centres. Furthermore, the number of neurons in the dorsal anterior cingulate cortex that appeared to track internal states increased somewhat in the study. It was as if arousal had “hijacked” the brain signals that were used for decision-making in this region, altering the balance of information represented there.

“Although not conclusive, our findings show that a high level of arousal weakens and takes control of the decision-making circuits in the brain,” Dr. Rudebeck said. “We intend to continue investigating how arousal affects higher brain functions and how this contributes to the development of psychiatric diseases.”

National Institutes of Health (MH110822), the National Institutes of Health’s Brain Initiative (MH117040), the National Institute of Mental Health’s Intramural Research Program (MH002886), the Takeda Science Foundation, and the Brain and Behavior Research Foundation Young Investigator Grant (#28979) provided support for this research.

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