Motivation and emotion/Book/2024/Gut-brain axis and emotion

Gut-brain axis and emotion:
What is the gut-brain axis and how does it influence emotion?

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Overview

Have you ever heard that some emotions are stored in your gut? Or had "butterflies in your stomach"? Maybe you got home from a rough day, were feeling down, so you get your favourite nutritious meal and things start to feel a little bit better. Or maybe you got some greasy fast food and sugary snacks, then ended up feeling not so great the next day. Are these feelings surface level, or is there some deeper explanation for all of this? This is a new question in the field of psychology, and these feelings are connected to the gut-brain axis.

Overview: one to four paragraphs inbetween the scenario and focus questions. Suggested 180 to 330 words.

• The gut acts as our second brain, directing the digestion of food through the body and absorption of nutrients. (Figure 1)
• Does the communication between the gut and the brain influence emotions?
• Mental health challenges related to the gut-brain axis.
• Optimising positive emotion and mood through the gut-brain axis.
• Integral to understand how the gut influences emotion to avoid dysregulation of emotion.

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Focus questions: How do the gut and brain communicate? How does the gut influence the brain? What happens when the gut-brain axis is dysfunctional? Can emotions be manipulated by manipulating the gut environment? How?

Understanding the gut-brain axis

To understand how to gut-brain axis influences our emotions, we first have to understand how it works, as well as how the gut can communicate with the brain and vice versa.

Key components and mechanisms of communication

- Autonomic nervous system: The ANS consists of parasympathetic, sympathetic, and enteric (ENS) nervous systems. The ENS is embedded in the gut wall, so is the starting point for information from the gut to go to the brain. The parasympathetic and symapthetic nervous systems send information to the gut, telling it when to digest, or when to slow down and conserve energy.

- Vagus nerve: Think of the vagus nerve like the main highway between the gut and the brain. This is were most messages go back and forth. The ENS sends information to the vagus nerve, which goes up the spinal cord and to the brain.

- Hypothalamic pituitary adrenal axis (HPA Axis) releases cortisol which is sent to the gut to slow digestion (Appleton, 2018).

- Central nervous system (CNS): the brain sends messages to the gut through the CNS (Martin et al., 2018).

- However, there are many more components in this complex system such as hormonal, immune, and metabolic pathways

The microbiome

But what factors influence the messages the gut sends to the brain? The microbiome is an ecosystem of bacteria that is collected in the gut across the lifespan. These bacteria (microbes) help us digest food and assist in the development of our immune system, and a more diverse microbiome is associated with better physiological and emotional outcomes for the individual.

Similar to the bi-directional communication between the brain and gut, there is also a bi-directional communication between the microbiome and the gut-brain axis (Carabotti et al., 2015). Microbes produce many of the neurotransmitters sent to the brain, such as dopamine, norepinephrine, serotonin, and GABA. Animal studies have shown that microbiome interventions can also alter the levels of such neurotransmitters in the brain (Strandwitz, 2018). Recent research has found the microbiome to be increasingly influential in the gut-brain communication system, with some now referring to the system as the microbiome-gut-brain axis. Have a further look here about how the microbiome can influence emotions.

Gut-brain axis, neurotransmitters, hormones, and emotions

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In this bidirectional communication system, it is well known the gut can respond to neurotransmitters and hormones produced and sent by the brain. Surprisingly to many, the microbiome can also produce it's own neurotransmitters to send to the brain. In fact, more than 90% of the body's serotonin is synthesised in the digestive tract, and over 50% of dopamine is produced in the gut (Liu et al., 2020).

• Lee. et, al, (2020) found stress and anxiety were significantly associated with reduced microbiome diversity, while favourable social environments as well as the trait of openness were associated with increased microbiome diversity. Overall, they found increased microbiome diversity is positively associated with emotional well-being.

• Ke. et, al, (2023) Found linkages of emotions and emotion regulation processes to the gut microbiome in a sample of women.

• The gut can also influence emotion through hormone secretion. A diverse gut microbiome regulates the secretion of leptin, grehlin, and insulin by the gut cells.

1 The microbiome can produce it's own neurotransmitters:

	True
	False

2 Microbiome diversity causes stress and anxiety:

	True
	False

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Dysregulation of the gut-brain axis.

• Microbiome dysbiosis as a disruption in the normal functioning of the microbiome resulting in dysfunction in the normal functioning of the gut-brain axis.
• Lower serotonin, which can be a result of microbiome dysbiosis, seen in those with major depressive disorder (MDD).
• Anxiety- depressive behaviours associated with microbiome dysbiosis (Carabotti et al., 2015).

• Association found between gut microbiome dysbiosis and autism spectrum disorder (ASD), with most patients with ASD suffering from some sort of gastro intestinal disorder (Taniya et al., 2022).

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Modulating the gut-brain axis

• Biodiversity of the microbiome
• Psychobiotics/ Psychomicrobiotics/ Probiotics proven effective as non-toxic psychiatric interventions for depressive symptoms (Appleton, 2018).
• Vagus nerve stimulation: Johnson & Steenbergen (2022) found stimulation of the vagus nerve reduced emotional reactivity in participants. It has also been used to treat some cases of severe depression.
• Diet reconstruction as an accessible solution.

Conclusion

• Bidirectional Influence: The gut-brain axis involves complex, bidirectional communication. Both systems influence eachother through neural, chemical, immune, and hormonal pathways. This interaction plays a crucial role in regulating and influencing emotions.
• Microbiota's Role: Gut microbiota significantly impacts the gut-brain axis by modulating neurotransmitter production. Dysbiosis in the gut microbiome has been linked to emotional dysfunction causing anxiety, depression, and autism.
• Therapeutic Potential: Understanding and manipulating the gut-brain axis through diet, pro/pre/psychobiotics, and other interventions may be promising avenues for improving mental health and emotional well-being, highlighting the need for further research and clinical applications in this emerging field.

Take home message: By taking care of your gut—through a whole food diet, probiotics, prebiotics and stress management—you can positively impact your emotions and overall well-being.

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See also

• Digestive system and emotion (Book chapter, 2015)
• Emotion (Wikipedia)
• Gut-brain axis (Wikipedia)
• Junk food and psychological distress (Book chapter, 2019)

References

Appleton, J. (2018). The Gut-Brain Axis: Influence of Microbiota on Mood and Mental Health. Integr Med (Encinitas), 17(4), 28-32.

Carabotti, M., Scirocco, A., Maselli, M. A., & Severi, C. (2015). The gut-brain axis: interactions between enteric microbiota, central and enteric nervous systems. Ann Gastroenterol, 28(2), 203-209.

Johnson, K. V. A., & Steenbergen, L. (2022). Gut Feelings: Vagal Stimulation Reduces Emotional Biases. Neuroscience, 494, 119-131. https://doi.org/https://doi.org/10.1016/j.neuroscience.2022.04.026

Ke, S., Guimond, A. J., Tworoger, S. S., Huang, T., Chan, A. T., Liu, Y. Y., & Kubzansky, L. D. (2023). Gut feelings: associations of emotions and emotion regulation with the gut microbiome in women. Psychol Med, 53(15), 7151-7160. https://doi.org/10.1017/s0033291723000612

Lee, S.-H., Yoon, S.-H., Jung, Y., Kim, N., Min, U., Chun, J., & Choi, I. (2020). Emotional well-being and gut microbiome profiles by enterotype. Scientific Reports, 10(1), 20736. https://doi.org/10.1038/s41598-020-77673-z

Liu, T., Feenstra, K. A., Heringa, J., & Huang, Z. (2020). Influence of gut microbiota on mental health via neurotransmitters: A review. Journal of Artificial Intelligence for Medical Sciences, 1(1-2), 1-14. https://doi.org/10.2991/jaims.d.200420.001

Martin, C. R., Osadchiy, V., Kalani, A., & Mayer, E. A. (2018). The Brain-Gut-Microbiome Axis. Cell Mol Gastroenterol Hepatol, 6(2), 133-148. https://doi.org/10.1016/j.jcmgh.2018.04.003

Strandwitz, P. (2018). Neurotransmitter modulation by the gut microbiota. Brain Res, 1693(Pt B), 128-133. https://doi.org/10.1016/j.brainres.2018.03.015

Taniya, M. A., Chung, H. J., Al Mamun, A., Alam, S., Aziz, M. A., Emon, N. U., Islam, M. M., Hong, S. S., Podder, B. R., Ara Mimi, A., Aktar Suchi, S., & Xiao, J. (2022). Role of Gut Microbiome in Autism Spectrum Disorder and Its Therapeutic Regulation. Front Cell Infect Microbiol, 12, 915701. https://doi.org/10.3389/fcimb.2022.915701

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External links

• More than a gut feeling: how your microbiome affects your mood (Stanford Lifestyle Medicine)
• Do gut microbes control your personality? (Ted)

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