The most important key to Professor Terasawa's research is "interoception."

While the five senses are for knowing the world outside the body, interoception refers to the sense for knowing the state inside the body. Specifically, it means the sense of feeling things such as heartbeat, breathing, gastrointestinal movement, and changes in body temperature.

Professor Terasawa positions interoception as an "inner compass" that indicates one's internal direction. There are individual differences in how this sense arises; if the sense becomes hypersensitive or too dull, the richness of emotions can be impaired, or conversely, vulnerability to stress can increase. In other words, if the inner compass does not work well, it becomes difficult for us to steer ourselves in a direction that leads to a good state.

"The body is constantly sending signs. How the brain receives those small voices—the 'accuracy of that interpretation'—determines our mental stability," says Professor Terasawa.

Her motivation to study this connection between mind and body was a classical theory of emotion known as the "James-Lange theory," which she learned about as a university student. Proposed in the 1880s, this theory argues that when we perceive an event that excites us, changes first occur in the body, and emotions are born by sensing those changes. Today, it is called the "peripheral theory." The example mentioned at the beginning—that we don't "cry because we are sad," but rather "we are sad because we cry"—is one such instance.

"We experience on a daily basis that our hearts beat faster when we are nervous and our breathing becomes shallow when we are anxious. If this were the cause rather than the result of emotion, wouldn't our minds be more directly connected to our bodies?"

This realization drew her into the path of research.

The famous case of Phineas Gage, which occurred at a 19th-century railroad construction site, also provided a major hint for her research. Gage was a man who miraculously survived a tragic accident in which an iron rod pierced his head (frontal lobe) during an explosion. Before the accident, he had a gentle and sincere personality, but after the accident, he changed drastically into a very short-tempered, irresponsible person who could not follow social norms.

What further piqued Professor Terasawa's interest was that in cases of injuries to the same brain region as Gage, not only personality and emotions changed, but even bodily reactions such as sweaty palms changed, and this was related to changes in behavior.

"I thought that bodily reactions were having some kind of influence on emotions, but until then, there was no way to investigate it. However, with the development of cognitive neuroscience, we can now see brain activity, and we are in an era where we can simultaneously collect data on bodily reactions and emotions, so I wanted to deepen this research."

A breakthrough in continuing her research was encountering the psychological trait called "alexithymia."

Alexithymia is translated as "shitsukanjoushou" in Japanese, but in the original Latin, it means "losing words for emotions," referring to a trait where it is difficult to recognize and verbalize one's own emotions.

It is not that they have no emotions at all. When they have some kind of vague, fuzzy feeling, they cannot put into words whether it is anger, anxiety, or sadness. Even though they are carrying mental and physical stress, they cannot communicate those emotions well to those around them.

For example, even if stress is being generated because of a workplace situation, they do not look toward approaches to improve it, but instead focus only on physical ailments, taking medicine or relying on alcohol.

Professor Terasawa conducted an experiment in which people with eating disorders, who are said to have high alexithymic tendencies, and healthy individuals were asked to imagine and draw what kind of bodily reactions were linked to four emotions: "fear," "anger," "sadness," and "joy."

The results were surprising even to Professor Terasawa. While healthy individuals perceived the four emotions separately and had different images of bodily reactions, it was found that there was little difference in how people with eating disorders drew their images. This showed that they were unable to match words with bodily reactions, and the categorization of emotions was not working well.

This discovery indicates not only that there are individual differences in the link between emotions and bodily reactions, but also that in people with eating disorders, a "malfunction" is occurring in the circuit that delivers the body's voice to the brain. This provides a major hint for helping people suffering from unexplained physical ailments, which are common in modern society.

Professor Terasawa's deep awareness of the issues led to a further groundbreaking discovery. Through joint research with Atsushi Sekiguchi, then-Head of the Psychosomatic Research Laboratory at the National Center of Neurology and Psychiatry, she demonstrated that training to focus attention on interoception can change "brain circuits" and potentially improve mental health issues.

To begin with, the brain achieves prediction and control through the coordinated work of regions such as the insular cortex and the brainstem. It is said that people who tend to feel strong anxiety have prediction pathways that are too strong, causing them to feel "short of breath" even when their breathing is not actually that shallow.

Professor Terasawa's group thought that being able to balance these two regions through the adjustment of interoception might be the key to reducing anxiety tied to bodily reactions like shortness of breath, and they attempted an experiment.

First, 14 university students underwent training for one week, 80 times a day, focusing on their own heartbeat for about 10 to 20 seconds each time. Subjects answered whether the "beep, beep, beep" sounds coming from a speaker matched or were out of sync with the heartbeat they felt.

In the experimental program, the speaker sounds were intentionally shifted or matched with the subject's heartbeat. If the subject could not guess correctly, it was marked as an "incorrect answer."

Among the subjects, some improved their accuracy rate by receiving feedback on correct and incorrect answers. When the brains of these people were examined, it was found that the connectivity between the activities of the insular cortex and the brainstem became stronger, showing that changes had occurred in the brain due to the training.

Furthermore, when asked about their physical and mental state before and after the training, complaints of physical symptoms decreased and anxiety was also reduced after the training. In other words, scientific evidence was obtained that interoception can be tuned, and that the active action of listening to one's own body changes the functioning of the brain itself and eases anxiety.

Although this experiment is positioned as a "model study" with a limited number of 14 subjects, it has attracted attention from overseas. Professor Terasawa is looking to develop this research further, with a view toward creating a smartphone app for training interoception.

Professor Terasawa's research teaches us, who live in a stressful society, scientific coping methods for facing ourselves.

For example, many people have a fuzzy feeling of discomfort but cannot put into words what kind of feeling it is. However, giving them advice like "It's just your imagination" or "It's all in your head" can be off the mark. Even if no physical ailment is visible, some kind of stress may exist, and they may simply be unable to put it into words.

When Professor Terasawa counseled people with "irritable bowel syndrome," which involves repeated constipation and diarrhea related to psychological and social stress, there were people who suffered because they were told "It's just your imagination." On the other hand, at the hospital where she was involved in counseling, they provided mental care and gastrointestinal prescriptions simultaneously, leading to symptom improvement by looking at both the mind and body.

In fact, Professor Terasawa herself had a period in high school when the balance between her mind and body was lost for unknown reasons, making it difficult for her to go to school. She says that became the starting point for her to study the mind and body comprehensively at university.

Professor Terasawa explains that instead of trying to solve mental problems only inside the head, it is important to first correctly notice the small signs the body is emitting and guide them so they can be processed appropriately.

Currently, Professor Terasawa is putting particular effort into a research project on women's health issues such as premenstrual syndrome (PMS) and premenstrual dysphoric disorder (PMDD).

The project focuses on the relationship between changes in the autonomic nervous system associated with the menstrual cycle and how interoception is felt. Previous research has shown that people who tend to focus their attention on interoception on a daily basis tend to have stronger PMS and PMDD, and are more likely to experience mental and physical discomfort during the "luteal phase" before menstruation.

While such people can feel calm by focusing on their heartbeat and breathing during the "follicular phase" (from the start of menstruation to ovulation) when they are in good physical and mental condition, they cannot feel this calmness before menstruation due to the disturbance of the autonomic nervous system derived from hormone secretion, leading to anxiety and irritability. It is expected that simply knowing such mechanisms will provide clues for dealing with oneself.

Regarding the relationship between the brain and the body, the BMI (Brain-Machine Interface) research being advanced by Professor Junichi Ushiba of the Faculty of Science and Technology, introduced in "Part 1," is also attracting worldwide attention.

While Professor Ushiba's research aims to reconstruct the "output" of taking brain signals outside to move paralyzed bodies, Professor Terasawa's research focuses on the "input" of the brain reading minute changes in the body.

The research of both—"from the brain to the outside" and "from the body to the inside"—appears contrasting, but is there any common ground? Professor Terasawa says:

"I sometimes see the idea that 'if we understand the brain, we might understand everything about the human mind,' or conversely, 'brain research is not very useful for knowing the mind.' But the mind, body, and brain are closely connected. Although the approaches are different, I think there is a point of connection in that we both believe the link between the brain and the body is the key to understanding humans."

Composition: Toru Tamakawa, Editor-in-Chief of Asahi Shimbun GLOBE+

Interview/Text: Kaori Sawaki

Photography: Hidehiro Yamada