The Brain-Body Connection in Emotions

Our emotions and our relationship with them are an important part of our health and well-being. Because of their importance in understanding human behavior, psychologists have long been striving to understand the root cause of emotions. One common feature of emotions is that they cause changes in brain activity, body function, and behavior. However, there has been debate for more than a hundred years about how the relative sequence of brain and body changes is related to the emotional experience itself.

Theories of Emotion

A well-known psychological account of emotion from the 19^th century called the James-Lange theory puts forth the idea that it is physical changes inside the body that cause emotions, and our subjective experience of emotions (the feeling) comes from our brain detecting these changes. For example, if you see a bear, your heart rate will increase, your palms will sweat, and your muscles will tense up. According to the James-Lange theory, you will then interpret these physiological changes as fear.

In the earlier half of the 20^th century, the Cannon-Bard theory posited that bodily change and emotion occur at the same time. For example, if you see a bear, you will start to feel afraid, and your heart rate will increase at the same time. However, according to the Cannon-Bard theory, your fear does not cause your heart rate to increase, and your heart rate increase does not cause your fear. Of course, brain activity is necessary for detecting stimuli that induce emotions, and more modern theories of emotion recognize that there is crosstalk between the brain and body.

Top-down and bottom-up control

Indeed, the brain and the body are intimately connected. The brain sends signals to the organs and skeletal muscles to control their functions, a process that is known as top-down control (going from brain to body). However, it is important to recognize that the body is constantly monitored by the brain, and changes in organ function can alter brain activity. These changes in organ function can have strong effects on emotions and behavior through what is known as bottom-up processing (going from body to brain).

Precisely testing the relative role of top-down and bottom-up processing in human emotions is difficult because of ethical restraints on experiments using human subjects. To circumvent this difficulty, scientists turn to non-human animal models to understand the brain-body connection in emotions. However, in animal models, it has been difficult to precisely measure heart activity during behavior, and what is even more difficult is finding ways to control the activity of the heart experimentally.

Recent research

Two recent studies add important knowledge to our understanding of the brain-body connection during emotions. These studies used mice subjected to different behavioral tests to study the emotions of fear and anxiety.

To better understand complex emotional responses, Signoret-Genest et al. developed an innovative way to precisely measure cardiac activity in the mouse. This technique allowed them to measure heart function during different fear and anxiety tasks. These studies demonstrated that fear and anxiety states are composed of a complex set of changes to both the activity of the heart and fear-related behavior. While this may seem to be an intuitive finding, this was the first time this was achieved in the laboratory.

An especially important finding from this study was that emotional responses are not the same all the time and instead change with experience, and they also depend on the environment the animal is in. Similar types of work can now be done in animal models of mental illness to provide insights that can be translated to humans.

To understand the role of bottom-up processing in emotion, a recent paper by Hsueh, Chen et al. developed a clever method for testing the effects of elevated heart rate on behavior. They were able to control the activity of the heart using a technique called optogenetics. This innovative technique uses genetics and molecular biology to allow scientists to control the electrical activity of cells with light, and it is a widely used tool in neuroscience. Because the cells of the heart are electrical, the authors were able to develop a method that allowed them to use optogenetics to control heart rate.

This approach allowed them to increase the mouse’s heart rate during different behaviors, including some of the same tests used by Signoret-Genest et al. Interestingly, Hsueh, Chen, et al. found that increasing heart rate caused anxiety-like behavior, but only in situations that were already anxiety-inducing. The authors then discovered that an area of the brain called the insula was activated during these events.

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Both studies add important knowledge to our understanding of the brain-body connection in emotions. They help us better define what an emotion is, and they add to our understanding of the brain-body connection. Together, they demonstrate that both top-down and bottom-up information is important for emotions. They are excellent examples of how important technological advances are in science.

Limitations and Future Directions

Although these studies increase our understanding of emotions and the brain-body connection, there may be some difficulty in translating these findings to humans. One limitation being that it is unethical to elicit actual fear in human subjects like we can in non-human animals. Therefore, we cannot test whether these same findings happen in people.

Another difficulty is that while emotional research in non-human animals can measure brain activity, physiological reactions, and behavior, these studies cannot tell us how the research subjects feel. We must infer their subjective emotional state from what we observe in their brain and body. There is currently quite some debate in the field about whether the subjective feeling of emotion that humans can describe with language is equivalent to the emotion itself.

A final note worth mentioning is that understanding the brain-body connection in emotional research could lead to developing better ways of attaining cognitive control over our emotions. For example, mindfulness practices and breathing techniques are two ways that individuals can gain control over their emotions through conscious regulation of their bodily processes. It will be fascinating to see how a greater understanding of the brain-body connection will help us develop other emotional regulation techniques.