[Reading Science] Body vs Mind... What Determines Behavior?

Emotions Generally Trigger Physical Responses
Stanford University Team Proves Opposite Also True
Increasing Heart Rate in Mice Induces Anxiety

Animal behavior is usually determined by the brain, which collects external information. Physical activities are influenced by emotions such as anxiety, joy, and sadness. However, a study has shown that emotions can also be triggered by the movements of organs like the heart. While anxiety makes the heart beat faster, it is also possible that a fast-beating heart can trigger anxiety.

Heart. Stock photo.

On the 1st (local time), the international academic journal Nature reported this recent research result published by a research team from Stanford University in the United States. It is well known that there is a close connection between animal emotions and physical responses. When hearing a scary sound, fur stands on end. When hearing bad news, the stomach sinks. However, the research team proved through animal experiments that the opposite is also possible.

The research team used optogenetics, a technique that controls cell activity with light. First, using biotechnology, they made the heart muscles of mice sensitive to light. When exposed to light, the heart would beat faster. They also made a small vest that could shine red light on the heart through the mouse’s body and put it on the mouse. Then, every time the mouse pressed a lever to drink water, the heart was stimulated with light to increase the heartbeat. Normally, the heart beats 660 times per minute, but they increased it to 900 times.

As a result, the mice showed anxious and fearful behavior when their heart rate increased without any other environmental changes. It was observed that the willingness to press the lever to drink water decreased and the desire to explore empty spaces significantly diminished. This suggests, according to the research team, that the increase in the mice’s heart rate worked together with the brain to induce anxiety.

To identify the exact mechanism, the research team examined the insula region of the mouse brain, which is responsible for processing emotions and bodily signals. The results showed that the insula region became more active when the heart rate increased. The research team explained, "This suggests that the insula integrates signals from the heart with threats coming from the external environment before transmitting information to higher cognitive areas." The mouse brain and heart evolved to process danger signals more quickly. In other words, when a potential threat is recognized, the heart rate increases before the brain fully perceives the situation and sends signals, thus warning the brain first.

Sahib Khalsa, a researcher at the Loriart Brain Institute in Oklahoma, USA, said, "Deliberately slowing a patient’s heart rate could help reduce anxiety," but also pointed out that challenges remain. He said, "The exact mechanism by which anxiety reduction works has not yet been identified," adding, "It is unclear whether acute fear, such as from a foot shock, operates in the same body-brain circuits as chronic anxiety. Especially in humans, chronic anxiety involves many more brain regions than acute anxiety, so this needs to be clarified."

Meanwhile, the research team plans to conduct further studies on how the states of other organs such as the stomach and skin cells affect the brain and behavior using optogenetics.