Does anxiety cause your heart to beat faster or does having a fast heartbeat make you anxious?
“It was a chicken-and-egg question that has been the subject of debate for a century,” according to Karl Deisseroth, a neuroscientist at Stanford University in California, of whether emotions drive bodily functions or if those functions drive emotions.
A study authored by Deisseroth and others that was published Wednesday in the Nature journal shows that the answer is… both.
To study the question, Deisseroth and his team used optogenetics and mice bioengineered to have heart muscle that are sensitive to light. Optogenetics is a method that “involves using light to control cell activity,” said an article in Nature.
“The authors also designed tiny vests for the animals that emitted red light, which could pass through the rodents’ bodies all the way to their hearts,” the article explained. “When a mouse’s vest emitted a pulse of light, the animal’s engineered heart muscles fired, causing the heart to beat.”
With this system, the team was able to raise the rodents’ heartbeats from 660 beats per minute to 900. They were also able to train the mice to expect a shock if they pressed a lever for a water reward.
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“When their hearts started racing, mice became less willing to press the lever or to explore open areas, suggesting that they were more anxious,” said the article. “But for animals in other contexts, the externally increased heart rate had no effect, suggesting that the brain and the heart worked together to produce anxiety.”
Researchers also found that a region of the brain associated with emotion and the processing of bodily signals “became more active when the heart rate increased if the animal was acting anxious.” This finding suggests that the region, called the insula, “is in charge of integrating signals from the heart with threats from the environment before passing the information on to areas involved in higher cognition.”
“I just love this paper so much,” said Sarah Garfinkel, a neuroscientist at University College London,” of the study. “You can’t just look at the brain if you want to understand fear,” she added.
Hugo Critchley, a psychiatrist at Brighton and Sussex Medical School in Sussex, U.K., also said the work “is a major advance in terms of methodology,” and Sahib Khalsa, a psychiatrist at the Laureate Institute for Brain Research in Tulsa, Okla., said it could have implications for how anxiety disorders are treated in the future.
“I think that it’s really important to know that we think about mental health, I think there’s still a stigma attached to it,” Dr. Kevin Chapman told Audacy podcast “Something Offbeat” last summer. “In many ways people think that you could just get over conditions like anxiety and whatnot. And that, obviously, is not the case, especially for somebody who has a diagnosable anxiety condition.”
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Going forward, Deisseroth plans to use optogenetics to look at the connection between the brain, behavior and body systems by stimulating other organs. These could include the gut, skin cells that raise an animal’s hairs when it confronts a threat, and facial muscles that are used to make expressions.
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