Interoception, including visceral sensations, is a sensory system for perceiving one’s own physiological conditions within the body. It is considered essential for maintaining homeostasis and fundamentally important for human health.
Significance in Psychosomatic Medicine and Psychosomatics
The main significance of the interoception in psychosomatic medicine includes the following:
The centripetal interoceptive sensation is involved alongside centrifugal autonomic and endocrine functions as roots of psychosomatic correlation, highlighting the importance of the interoceptive sensation system in the mechanism of psychosomatic correlation.
It serves as the physiological basis for “awareness of mind and body”, characteristic of psychosomatic disorders such as alexithymia and alexisomia. This awareness is related to self-coping in daily life and is crucial for symptom self-control.
It is involved in the sensitivity of symptoms such as pain thresholds and physical symptom amplification.
The neuroscience mechanisms of interoception have gradually become clearer, with reports on its relationship with psychological and emotional functions, physiological functions such as the autonomic nervous system, and mental functions and decision-making. Research on its relationship with various psychosomatic interventions such as mindfulness and meditation is also progressing.
We are advancing studies on several psychosomatic issues from the perspective of interoception.
Kanbara, K., Fukunaga, M. Links among emotional awareness, somatic awareness and autonomic homeostatic processing. BioPsychoSocial Med 10, 16 (2016). https://doi.org/10.1186/s13030-016-0059-3
Kanbara, K., Fukunaga, M. Links among emotional awareness, somatic awareness and autonomic homeostatic processing. BioPsychoSocial Med 10, 16 (2016). https://doi.org/10.1186/s13030-016-0059-3
Emotional Process is a process that connects the mind, emotions, and body. “Emotion” refers to something that is similar to “feeling”, but more difficult to verbalize, vague, and undifferentiated than feeling. Simply put, it is the function that lies between the mind and the body and connects them.
Alexithymia (lack of awareness of one’s own feelings) is considered one of the abnormalities in emotional processes. There are many reports on the relationship between this Alexithymia and Autonomic Nervous System function, and overall, it is believed that there are abnormalities in autonomic nervous system function (autonomic function) and deviations in autonomic nervous system stress response in Alexithymia. In other words, emotions and their awareness are closely related to physiological functions such as the autonomic nervous system.
This emotional process is mainly carried out by a part of the brain called the limbic system (for details, please refer to “Functional Levels of the Brain and Psychosomatic Medicine”). The autonomic nervous system, which maintains homeostasis in the body, is also carried out by this limbic system. Therefore, there is an inseparable relationship between emotional processes and the autonomic function.
Interoceptive Awareness and Autonomic Function
Alexithymia is a tendency to lack “awareness of emotions,” but this is thought to be based on (or closely related with) “awareness of the body.” Awareness of the body means accurately grasping one’s own physical condition, whether it is good or bad. It is known that in psychosomatic disorders, awareness of emotions and the body is decreased.
The physiological basis of this bodily awareness is interoceptive awareness (the function of perceiving the physiological state of the body). There are also numerous reports on the relationship between interoceptive awareness and autonomic function, especially stress responses. The autonomic nervous system has a centripetal function (sensory function from the body to the brain), which is the entrance of interoception, so it can be easily inferred that interoceptive awareness and autonomic function are closely related, similar to centrifugal function (function from the brain to the body).
Hypothetical Model of the Relationship between Emotional Awareness and Autonomic Stress Response
So, what is the specific relationship between emotional and bodily awareness and the autonomic function?
We have proposed a hypothesis about the relationship between emotional and bodily awareness and autonomic function by integrating various previous research results, literature knowledge, physiological mechanisms, and our previous research on stress responses.
In healthy individuals, there is moderate fluctuation in physiological/ autonomic tone, but in stress-related disorders, there is a tendency for a high physiological/ autonomic tone (typically sympathetic tone) and a attenuated stress response. This suggests that the attenuated stress response or fluctuation may lead to a decrease in emotional and bodily awareness (or conversely, a decrease in awareness may lead to a decrease in stress response or fluctuation).
Relationship between Emotional Process and Autonomic Nervous System Function
A reduced stress response or fluctuation of the autonomic nervous system hinders flexible adaptation to various stresses. Just as a soft, flexible object is more resistant to external forces and less likely to break than a rigid object. Reduced flexibility due to physiological tension interferes with awareness of the mind and body, which may lead to psychosomatic and other stress-related disorders.
Emotional Awareness and the Vagal Response Feedback Loop
There is a model of a negative feedback loop in which the vagus nerve is hyperactive when emotional awareness occurs. This model also supports the hypothesis that awareness of one’s emotions leads not only to emotional regulation but also to a physical relaxation response.
The process of homeostatic regulation by the autonomic nervous system is closely related to body-mind awareness and the interoception, and further research is expected to combine central brain imaging studies with evaluation of peripheral autonomic function.
