A racing heart makes the mind race, too, mouse study finds

A new study published today disentangles this link in mice, showing that speeding up a mouse’s heart rate made otherwise calm animals act more anxious. The finding indicates heart activity can influence mental state—and finding ways to lower heart rate may be a way to treat mood disorders such as anxiety and depression.

The finding shows that “clearly, the body can trigger an emotion,” says Nadine Gogolla, a neuroscientist at the Max Planck Institute of Psychiatry who was not involved with the study.

Scientists have long suspected the crosstalk between the heart and the brain could affect mental health. In the past, researchers have tested this link by giving individuals drugs such as isoproterenol , which, like naturally occurring adrenaline, can safely speed up the heart rate. Scientists then used brain imaging to look at brain activity and asked people whether they felt anxious or panicked. However, because these drugs tend to act on the entire body, scientists had not been able to activate only the heart and isolate its role in the heart-brain axis.

Karl Deisseroth, a neuroscientist at Stanford University and the leader of the new study, was aware of this research—and during his psychiatric training saw an unusual correlation: Patients with panic disorder also often had cardiac problems. One typical sign of anxiety and a panic attack is tachycardia, or a heart rate of more than 100 beats per minute (bpm). And at least one study found people with anxiety had a 26% increased risk of coronary artery disease .

To try to isolate the brain-heart connection, Deisseroth’s group took advantage of a light-sensitive protein called ChRmine , which was originally found in algae. It works like a gate, controlling the flow of charged particles into cells. The ChRmine gate is usually closed, but when the protein is exposed to light the gate opens and charged particles, mainly potassium ions, flow into cells.

The research team introduced ChRmine into heart muscle cells of live mice whose torsos were fitted with a vest equipped with a micro–light-emitting diode bulb. Light from the bulb then penetrated the skin of the mice to activate ChRmine within the cardiac cells. The result: a small, noninvasive pacemaker that made the animals’ hearts beat faster.

Because the team could just turn the light on and off, “we were now able to control heart rates using this wearable,” said Ritchie Chen, a bioengineer at Stanford and an author of the study.

A mouse’s resting heart rate is usually about 600 bpm, but to induce tachycardia the team bumped up the rate to about 900 bpm. The researchers also put the mice in a maze with one open and one closed arm. Mice tend to show anxietylike behaviors by avoiding open areas, and during the experiment the mice with sped-up hearts preferred to stay in the closed arm. That maze test made it clear “that increasing the heart rate worsened the anxietylike behaviors,” Deisseroth said.

The team then looked at the mouse brains for signals—either the activation of a gene or electrical activity—indicating a brain region was turned on when the heart rate was elevated. They found that increasing the heart rate activated areas involved with analyzing physiological information from the body, particularly the insular cortex. That region is known for, among other things, maintaining emotional regulation. When researchers used a similar light-sensitive protein to block nerve signals from the insular cortex, the mice began to explore the open arm of the maze, suggesting a calmer mental state, even though their heart rate was still skyrocketing.

In the future, Deisseroth and his team want to induce tachycardia for periods longer than used in the current experiment to see whether increased heart rate over weeks or months can lead to an increase or worsening of anxiety or depressionlike behaviors.

If the findings can be replicated in other settings, particularly with people, they could have implications for treating mental health conditions. Current medications are not foolproof and often take months to work. Going through the heart may be a quicker, more effective alternative. “Manipulating the heart is much easier than manipulating the brain,” Gogolla says. “We may actually unravel new treatment strategies for patients with anxiety or depressive disorder.”