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Last week, we celebrated Halloween by sharing how we bring the spooky season into our lives with skulls and skeletons and science—oh, my! This week, we’re looking at another fascinating piece of anatomy: the brain. In this first in a new series in which we look a bit closer at a headline in today’s science news, we’ve got an interesting—yet perhaps not terribly surprising—bit of news for you: Under states of heightened arousal characteristic of people with anxiety, addiction, and other psychiatric disorders, the brain’s ability to make good decisions appears to become hampered.
In other words, the brain may become hijacked during times of heightened stimulation.
It seems to logically follow that in times of duress, our ability to make decisions might be affected. Who hasn’t had an extra cup of coffee and been able to think about little else than the way their hands shake over the keyboard or felt that deer-in-the-headlights paralysis after almost hitting—or being hit by—another vehicle? Whether we’re entirely conscious of it or not, our brain clearly suppresses certain circuits that allow us to have complete control over our thoughts or actions during times like these.
How specifically might heightened arousal—for example, states of heart racing, high blood pressure, or shortness of breath—affect the ability to make decisions? Scientists at the Icahn School of Medicine at Mount Sinai analyzed the results of an earlier study led by Atsushi Fujimoto, an instructor in Peter Rudebeck’s lab at the Nash Family Department of Neuroscience and Friedman Brain Institute. This study looked at how a higher heart rate affected rhesus monkeys’ decisions to select between two rewards: a little juice or a lot of juice. In short, the results showed that when the monkeys’ hearts were beating faster, they more quickly made the better decision of more juice.
These results coincide with scientists’ current understanding of how arousal affects performance, which can be illustrated with a U-shaped curve: While a small amount of arousal may lead to peak performance, too much can, in fact, hamper it; worse, it can lead to the brain making slower or incorrect decisions.
To get at why these results came about, the scientists next looked at the electrical activity of neurons in the brain associated with its two decision-making centers, the orbitofrontal cortex (OFC) and the dorsal anterior cingulate cortex (dACC). They found that about a sixth of the neurons in either of these centers were associated with the animal’s heart rate. In other words, a change in the speed of the heart rate would result in a change in the speed of the firing of the neurons. The activity of these neurons did not appear to be affected by the decisions the monkeys made when choosing an award. The remaining neurons in these centers of the brain were devoted to processing decision-making.
After analyzing the results from this study, the researchers next asked themselves a timely question: “What might happen during the type of heightened arousal states seen in patients who suffer from anxiety, addiction, and other psychiatric disorders?” (The Mount Sinai Hospital, 2021).
The idea that we make riskier decisions when in states of heightened arousal is not new (see, e.g., Mobbs & Kim, 2015; Herman et al., 2018; and Rushworth et al., 2011). However, what role neurons play in this process is not entirely known. To get closer to an answer, researchers turned to the amygdala, a key part of our brain's emotional responses. Monkeys who experienced damage to the amygdala showed an increase in heart rate by up to 15 additional beats per minute, effectively inducing a heightened state of arousal. At this higher state of arousal, the animals were slower to choose a reward, suggesting that heightened arousal was a cause for their slower decision making.
And when the researchers again looked at the neurons in the OFC and dACC, they found evidence that the number of neurons involved in decision making had decreased; furthermore, in the dACC, the number of neurons tracking the internal state had risen. These results suggest that in times of high stress or arousal, our brain focuses more on monitoring how we're doing rather than making the best decisions, and scientists can now point to the part of the frontal cortex responsible for this effect.
Over the course of the past couple years, as humans are experiencing higher states of anxiety, depression, addiction, and other negative effects of the COVID-19 pandemic; the general state of unrest due to social and racial injustice; and the looming, seemingly unavoidable effects of climate change, learning more about how our day-to-day decisions might be affected by these changes in our bodies can provide small comfort. If we can identify how our bodies are changing as a result of being subjected to higher levels of arousal, we’re one step closer to finding ways to not only calm ourselves but also, perhaps, reduce the suffering of others as they struggle with debilitating psychiatric disorders.
Are you or someone you know interested in neuroscience? Check out hBARSCI’s human-sized brain models here and here. Or, download this printable coloring page to teach your kids about the different areas of the brain. hBARSCI even has single, prepared microscope slides with a mammalian brain tissue section, which are great for biology classrooms to explore structure-function connections per Next Generation Science Standards.
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