- Researchers have investigated whether increasing heart rate could induce anxiety in mice.
- They found that increased heart rate induces anxiety-like behavior in mice in risky environments.
- Further research is needed to know if these findings translate to humans.
Physiological theories of emotion proposed over a century ago suggest that emotions may arise from the body as well as the brain.
While the topic has been greatly discussed, until now, researchers have not had the experimental means to test the theory.
Recently, researchers used optogenetics to assess how increasing heart rate affects behavior in mice. Optogenetics involves bioengineering cells so they can be controlled by light.
The researchers found that increasing the heart rate induces anxious behavior in mice. The study appears in
Dr. Luana Marques, associate professor at Harvard Medical School, not involved in the study, told Medical News Today:
“This is a great study that pushes further the methodology that can help us to begin exploring the question of circuits that are involved in anxiety, but given [the] preliminary nature of the study, it will need replication and extension to humans to be able to be conclusive.”
To begin with, the researchers bioengineered muscle cells in the rodents’ hearts to make them sensitive to light. They then fitted the rodents with tiny vests that emitted red light that could pass through the body to control their heart rate. Each time the vest emitted a pulse of light, their heart muscles fired, causing a beat.
To test whether intermittent changes in heart rhythm could influence behavior, the researchers increased the mice’s heartbeat from 660 beats per minute (bpm) to 900 bpm for 500 milliseconds every 1,500 milliseconds.
They found that these intermittent changes did not alter behavior or pain perception when in a familiar space.
However, when the mice were placed in a maze, those with increased heart rates were less explorative than control mice, suggesting that the increased heart rate made them more anxious.
In further tests, the researchers trained mice to press a lever for water and then introduced random shocks when the mice pressed the lever.
They found that mice whose heart rates were increased were less willing to press the lever. This, they noted, means that increased heart rate may generate anxiety in stressful — but not relaxing — contexts.
To understand how the heart and brain work together to produce anxiety, the researchers next measured the rodents’ brain activity.
They found that the insula — a brain region linked to both emotion and processing bodily signals — became more active when the heart rate increased, and animals became anxious.
Dr. David Feifel, emeritus professor of psychiatry at the University of California, San Diego, not involved in the study, noted that scientists have thought for centuries that the heart-brain connection is very likely a two-way street.
“Some scientists, going back as far as the 19th century, proposed that emotions may, in fact, be the brain’s response to specific changes in the body and not the other way around,” he told us.
“This is plausible since there are nerve signals that travel from all areas of the body, including the heart, to the brain, keeping the brain apprised about what is going on in the body,” he explained.
“Our brain will respond to an increased heart rate, which can be interpreted as danger, and that can produce anxiety. In mice, the increased heart rate alone didn’t seem to create the anxiety, unless the mouse was in a stressful situation such as receiving an electric shock when it pushed a lever to obtain water. The combination of the stressful situation, along with the artificially increased heart rate produced the anxiety.”
MNT also spoke with Dr. Jay Trambadia, a licensed clinical psychologist, who was not involved in the study. He told us that the mind-body connection is key to understanding how anxiety happens during the fight-or-flight response.
“When you experience a racing heart, it can be a sign that your body is in a state of high arousal and stress, which can be a signal to your brain that something is wrong,” he explained. “This can activate your fight-or-flight response, which is your body’s natural response to perceived threats.”
“When your fight-or-flight response is activated, it also activates the sympathetic nervous system, which influences physical and psychological components such as a racing heart or negative self-talk,” noted Dr. Trambadia.
Stress hormones may act as the mediators, he added:
“In addition, your body releases stress hormones like cortisol and adrenaline, which can cause a range of physical symptoms, including a racing heart, sweating, and shortness of breath. These symptoms can then trigger a feedback loop that leads to more anxiety, as you become more aware of your physical sensations and start to worry about what might be causing them.”
The researchers who conducted the study wish to use this new technology to investigate how the brain and behavior are affected by different bodily systems — including the gut, skin cells, and facial muscles.
Dr. Jonathan Fialkow, a cardiologist at Baptist Health Miami Cardiac & Vascular Institute, not involved in the study, told MNT that the study’s biggest limitation is that it was conducted on mice and not humans.
He noted that mouse physiology differs from human physiology in important ways. For example, the heart rate of mice is ten times faster than humans.
He added that anxiety measures may not reflect anxiety in humans, as of course, the researchers could not ask the mice how they were feeling.
Dr. Stephen Pickett, a cardiologist at Memorial Hermann in Houston, TX, also not involved in the study, further cautioned that “[f]eeling anxious can be due to many factors, and I don’t think this paper means to imply that all anxiety is related to tachycardia.”
“It is not certain that risk-averse behaviors in mice necessarily correlate with the same emotional experience that people describe as anxiety. The particular arrhythmia they provoked is a specific problem and is not the same as having a high resting heart rate,” said Dr. Pickett.
“We have often told patients that they can feel anxiety just from having a rapid heart rate, or from an arrhythmia or electrical, short circuit of the heart, and the study actually correlates specific findings in this animal model that suggests that there is a direct correlation between the increase heart rate, and the brains perception of anxiety,” Dr. Shephal Doshi, cardiac electrophysiologist and director of cardiac electrophysiology and pacing at Providence Saint John’s Health Center in Santa Monica, CA, not involved in the study, told MNT.
“This may help patients understand that the anxiety that they are experiencing is real and common when patients have arrhythmias or rapid heartbeats,” he explained.
Dr. Feifel added that “[o]ne implication of this [study finding] is that we may be able to develop treatments for anxiety and other emotional extremes, such as clinical depression, by interrupting the physiological states associated with those emotions.”
“In fact, there are already some established treatments that utilize this approach,” he noted. “For example, if a person who experiences debilitating anxiety whenever they must give a presentation or talk in front of an audience — a condition referred to as ‘performance anxiety’ — seeks help from a psychiatrist, they are likely to get a prescription for a beta-blocker, which is cardiac medication that puts the brake on heart rate.”