Motivation and emotion/Book/2024/Vagus nerve and stress

Vagus nerve and stress:
What role does the vagus nerve play in the stress response?

Multimedia presentation (3 min)

Overview

Figure 1. Stressed human waiting for exam Scenario You’re sitting in a crowded lecture hall, about to take an important final exam. The pressure is mounting—weeks of studying come down to this moment. Your heart pounds, your palms are sweaty, and your mind is racing through everything you’ve crammed. You feel the familiar grip of anxiety tightening. As you start to read over the questions, you take a slow, deep breath. Your heart rate begins to steady, your muscles relax, and your overthinking stops. This is your vagus nerve taking effect, activating your parasympathetic nervous system (PNS). Signalling to your body that the immediate threat is over, helping your body ease out of the fight or flight response from panic to focus. Allowing you to concentrate and take the exam.

When our bodies are in stress mode, our thoughts focus on getting away from things that we don’t like. For example, waiting for an exam (see Figure 1) or even avoiding people. These are stress responses and can trigger our fight or flight response. This is not beneficial when making important life and career decisions. Research has shown that our IQ is reduced, there is an increased heart rate and there is an increase in blood glucose concentrations when in this stress state. It is not a healthy state to be in for more than a few minutes.

This book chapter provides an understanding of the role the vagus nerve plays in stress response and brings awareness of the physical and mental risks when the body undergoes stress.

Focus questions: Which nervous system activates the vagus nerve? What is the relationship between the vagus nerve and stress? What happens to the body during a fight or flight response? What neurotransmitter does the vagus nerve release?

Definition and concepts

Overview of the vagus nerve and stress

The vagus nerve, the 10th cranial nerve, has an important role in maintaining homeostasis of the body's stress response by controlling the parasympathetic nervous system, also referred to as the "rest and digest" system. It goes through the brainstem, neck, chest, and abdomen, innervating various immediate organs such as the gastrointestinal tract, heart, and lungs.

In the context of Paleo Stress Management (2023), the vagus nerve is viewed as integral to ancient, evolutionary conserved mechanisms that help manage stress. Techniques like deep breathing, meditation, and cold exposure are often emphasised to stimulate the vagal system, enhancing it's calming effects and promoting resilience to modern stressors.

Key theories

One major theory is the Cognitive Appraisal Theory which proposes that stress is a result of how an individual perceives and appraises a situation, rather than the situation itself. Stress arrises when a person evaluates a situation as threatening or demanding, while also feeling that their resources to cope are insufficient. The two main concepts of appraisal include primary appraisal, the evaluation of an event as either a threat or a challenge, and secondary appraisal, which involves assessing the available coping resources and options to manage the stressor.

The second major theory is the General Adaption Syndrome (GAS). This model addresses the body's response to ongoing stress and is broken down into three stages. The first stage is the alarm stage, where the body recognises a stressor and starts the activation of the sympathetic nervous system, releasing stress hormones like cortisol and adrenaline. The second stage is the resistance stage, this is when the body attempts to withstand or adapt towards the stressor by maintaining high levels of stress hormone production and physiological readiness. Lastly, there is the exhaustion stage, in which continuous exposure to stressors leads to the depletion of the body's agents, resulting in reduced immune function, fatigue, and potentially stress-related illness.

Comparatively, the cognitive appraisal and GAS both offer valuable insights into how individuals respond to stress, but they significantly differ in their focus. Cognitive appraisal theory emphasises the subjective interpretation of stressors, proposing that an individual’s perception of a situation determines whether it is deemed stressful. In contrast, GAS takes a more biological approach, outlining a universal, physiological response to stress that occurs regardless of personal appraisal. While cognitive appraisal highlights the mental and emotional evaluation—where stress arises if one feels they lack sufficient resources—GAS focuses on the body’s automatic response over time, showing how prolonged stress can lead to physical exhaustion and illness. Cognitive appraisal suggests that stress can be mitigated by changing how an individual perceives and interprets events, implying that cognitive interventions could reduce stress. Meanwhile, GAS underlines the importance of managing stress to prevent the body from reaching the exhaustion stage, underscoring the need for interventions like relaxation techniques that target the physiological stress response. Together, these theories present a holistic understanding of stress, one emphasizing mental strategies for appraisal and the other focusing on the biological toll of prolonged stress exposure.

Importance of understanding the stress response

Understanding the stress response is crucial for several reasons:

• Health and well-being: Chronic stress can result in a range of mental and physical health problems, such as impaired immune function, depression, cardiovascular disease, and anxiety. Understanding how the body reacts to stress aids in identifying effective coping strategies and interventions.
• Resilience building: Insight into the physiological and psychological aspects of stress allows individuals to build resilience. Techniques like mindfulness, relaxation, and improving vagal tone can enhance adaptive responses to stress.
• Clinical and therapeutic application: Stress management is key in therapies aimed at reducing anxiety, treating Post Traumatic Stress Disorder (PTSD), and managing chronic conditions. Understanding how stress impacts both the body and mind informs better therapeutic outcomes.
• Performance and productivity: In fields like work and academics, understanding stress can help optimise performance by teaching people to manage stressors effectively, preventing burnout and fostering a balanced lifestyle.

This knowledge helps integrate stress theories and models into real-life strategies to maintain better health and mental clarity.

Gut-brain axis

The gut-brain axis is the two-way communication network linking the gastrointestinal system and the brain, incorporating neural, hormonal, and immune pathways. This connection primarily operates through the vagus nerve, which sends nerve signals from the gut to the brain, influencing mood, cognition, and stress responses. Tan et al., 2022 , highlight how gut microbiota can influence brain function and mood through the vagus nerve, impacting immune responses.The gut microbiota, the grouping of microorganisms in the digestive system, also plays a key role by producing neurotransmitters like serotonin and influencing inflammation. Disruptions in the axis have been associated with conditions such as stress, depression, anxiety, and irritable bowel syndrome, highlighting it's importance in both mental and physical health. Read this Wikipedia article to gain a better understanding of this topic.

Relevance in everyday life

The relief of stress through the vagus nerve is crucial and relevant in everyday life for several reasons. First and foremost, chronic stress can result in multiple adverse health effects, such as depression, cardiovascular disease, anxiety disorders, and digestive issues. By effectively regulating the parasympathetic nervous system, the 10th cranial nerve promotes a state of calm and relaxation, counteracting the "fight or flight" response triggered by stress. This regulation not only helps to lessen the immediate effects of stress but also contributes significantly to preventing the long-term consequences associated with chronic stress.

Furthermore, the vagus nerve is involved in emotional and physiological stability, influencing mood and overall mental health. Its ability to enhance emotional regulation allows individuals to respond more adaptively to stressors, thereby improving resilience and coping mechanisms. In a fast-paced world where stressors are ubiquitous, harnessing the power of the vagal system can enhance an individual's quality of life, foster better relationships, and improve productivity.

Practices that stimulate the vagal pathway, such as mindfulness, deep breathing, and physical exercise, are not only accessible but can also be easily integrated into daily routines, as seen in Kopplin and Rosenthal (2022) research. This accessibility makes the vagus nerve a relevant target for stress relief strategies that are sustainable over time. Ultimately, the importance of the vagal system in stress relief lies in its ability to enhance both mental and physical health, promoting a balanced, healthy lifestyle that is essential for navigating the complexities of modern life.

History

The vagus nerve has been recognised since ancient times due to its critical role in various body functions. Its name originates from the Latin word “vagus” meaning "wandering," which reflects its extensive reach from the brainstem to multiple organs throughout the body. The first detailed anatomical descriptions of the nerve were provided by Porras-Gallo et al. (2018). The research details how the discovery and understanding of the vagal system evolved over centuries, beginning with Galen, who first identified and described it in the 2nd century. Over time, advances in anatomy and physiology from figures like Vesalius and Willis expanded knowledge about the vagus nerve's extensive role in parasympathetic regulation. By the 21st century, the nerve's influence on multiple organ systems and its significance in stress regulation and therapeutic interventions were well-established.

Research

• Vagus nerve stimulation

Figure 2. Vagus nerve stimulation

In the study of vagal nerve stimulation for stress-related psychological disorders, (Bremner et al., 2020) investigates the use of non-invasive vagal nerve stimulation (VNS) as a treatment for stress-related psychiatric disorders, such as Major Depressive Disorder (MDD) and PTSD. They demonstrate that VNS can modulate regions of the brain responsible for emotional regulation, such as the amygdala and prefrontal cortex, by activating the parasympathetic nervous system. This stimulation helps reduce stress and improve mood by rebalancing autonomic function. The findings emphasise the potential of VNS as a personalised and a minimally invasive approach for managing psychiatric conditions related to chronic stress (see Figure 2).

• How the brain and gut respond to stress

In a study conducted by (Hou et al., 2020) they explored how the brain and gut respond to stress through the GABAergic system and the gut-vagus-brain pathway. The study highlights the role of GABA (gamma-aminobutyric acid), an inhibitory neurotransmitter, in regulating stress responses. The research emphasises that specific GABAergic neuron subpopulations in the brain, along with the gut microbiota, influence vagus nerve activity, affecting mood and stress resilience. Dysregulation in this pathway can contribute to anxiety, depression, and other stress-related disorders, demonstrating the significance of gut-brain communication in stress regulation.

• Automatic nervous system in regards to PTSD

In a meta-analysis and review, Siciliano et al. (2022) explored the link between the autonomic nervous system (ANS) and post-traumatic stress disorder (PTSD) in young people. They found that PTSD symptoms were associated with heightened sympathetic nervous system activity and reduced parasympathetic function, implicating an imbalance between these systems in trauma responses. This imbalance, specifically the decreased activity of the vagus nerve, highlights its role in the physiological regulation of stress. Improving vagal tone through therapeutic interventions could be beneficial in mitigating PTSD symptoms by restoring autonomic balance.

Quiz 1

What is the primary role of the vagus nerve in the body?

	To increase heart rate
	To regulate the parasympathetic nervous system
	To promote muscle tension
	To decrease oxygen intake

Relationship between the vagus nerve and stress

Which nervous system is activated?

When stress occurs, the sympathetic nervous system is activated, releasing cortisol and adrenaline, which are hormones released during stress. This engages the "fight or flight" response, increasing energy, glucose levels, respiratory rate, blood pressure, and heart rate to prepare the body to face a threat. The parasympathetic nervous system, primarily controlled by the vagus nerve, helps the body return to a state of rest after the threat has passed. It reduces heart rate, promotes digestion, and calms the nervous system, facilitating recovery from stress. Vagus nerve stimulation directly enhances parasympathetic activity, reducing the physiological markers of stress, such as heart rate and cortisol levels. This stimulation, achieved through techniques like deep breathing or electrical impulses, helps promote relaxation, emotional regulation, and resilience to stress, improving overall mental and physical health.

What is the relationship between the vagus nerve and stress?

The relationship between the vagus nerve and stress is that the nerve helps counteract the stress response. It is activated by the sympathetic nervous system (fight or flight) by lowering the heart rate, reducing inflammation, and promoting relaxation and recovery.

Approaches used to stimulate the vagal tone during stress

Vagal nerve stimulation (VNS) consists of administering electrical impulses to the vagus nerve to regulate bodily functions such as heart rate and mood. It's primarily used to treat epilepsy and depression, demonstrating efficacy in reducing seizures and improving mood when other treatments fail​. Transcutaneous vagal nerve stimulation (tVNS) serves as a non-invasive technique that engages the vagal system through the skin, often utilising electrodes on the ear. tVNS has been shown to enhance vagal tone, promoting relaxation and reducing both anxiety and stress, as seen in Coy et al. (2023) study. Both approaches leverage the vagus nerve's role in the autonomic nervous system, offering potential benefits for stress and mental health management.

Causes of stress

Figure 3. Woman feeling emotional stress

• Life pressure: High expectations from work, university, family, or personal commitments can overwhelm an individual, leading to stress as they try to meet demanding standards or deadlines.
• Change: Major life changes like, moving, starting a new job, or experiencing a loss, disrupt routine and create uncertainty, which is often a trigger of stress.
• No control of an outcome or situation: A lack of security over events, such as waiting for medical results or dealing with uncomfortable circumstances, can heighten stress as individuals feel helpless.
• Emotional stress: Intense feelings of anger, sadness, or frustration can create psychological pressure, particularly in relationships or personal conflicts, leading to chronic stress over time. (see Figure 3)

Consequences of stress

Case study: Jenny Jenny is a student in her third year of university, currently studying full-time and working part-time at an after-school care. Jenny is a high achiever and has a history of chronic stress due to her academics and job demands. Jenny has reported feeling constantly anxious, and overwhelmed, suffering insomnia and has increased digestive issues. Her stress levels have been significantly high for the last two years, impacting her relationships. She has become more irritable and less patient with her family, resulting in conflicts at home. Jenny is withdrawn and avoids social gatherings that she used to enjoy. She feels trapped in an endless cycle of stress, with little to no time to engage in activities that previously brought her joy.

A major consequence of stress is Chronic stress, which occurs when an individual is exposed to stressors over an extended period. This causes an ongoing ignition of the body's stress response system. Unlike acute stress, which is short-term and often manageable, chronic stress can lead to significant health problems, including cardiovascular issues, weakened immune function, anxiety, and depression. Persistent stress keeps the body in a heightened state of alert, with elevated levels of stress hormones like cortisol, which can disrupt sleep, digestion, and overall well-being, making stress management crucial for long-term health. In a systematic review, Noushad et al. (2021) identify key physiological biomarkers associated with chronic stress, including alterations in cortisol levels and heart rate variability. The study emphasises how these biomarkers can provide insights into the physiological changes due to prolonged stress and highlights the importance of monitoring them to understand stress-related health implications.

What happens to the body during a fight or flight response?

Physical health

• Increase in heart rate: Stress engages the sympathetic nervous system, which causes the heart to pump faster to prepare the body for "fight or fight", which can strain cardiovascular health overtime.
• Increase in blood pressure: Increased levels of stress hormones, like cortisol, lead to the constriction of blood vessels, resulting in higher blood pressure and an increased risk of hypertension.
• Increased muscle tension: Chronic stress keeps muscles tense, especially in areas like the neck, shoulders, and back, leading to pain and discomfort.
• Irregular breathing: Under stress, breathing patterns often become rapid and shallow, reducing oxygen flow and contributing to feelings of anxiety and discomfort.
• Irregular sleep: Stress disrupts normal sleep patterns by keeping the mind in a hyper aroused-state, leading to insomnia or poor-quality sleep.
• Memory: Chronic stress can impair cognitive functions, particularly memory, as high cortisol levels affect the hippocampus, the part of the brain essential for learning and memory.

Mental health

• Chronic stress: Activates the body's autonomic nervous system, leading to a sustained "fight or flight" response. This prolonged activation can cause physiological changes, which negatively impact overall health.
• Depression: Dysregulation in the autonomic nervous system caused by chronic stress. It can encourage more frequent feelings of hopelessness, sadness, and a lack of desire in previously enjoyable hobbies or tasks, significantly impairing daily functioning and quality of life.
• Anxiety: Characterised by excessive worry and fear, often exacerbated by chronic stress. This heightened state of arousal can result in physical symptoms, such as rapid heartbeat and shallow breathing, creating a cycle that reinforces feelings of anxiety and contributes to mental health disorders.

In research conducted by, Blase et al. (2021) explores the interrelationship between stress, depression, and anxiety through a neurophysiological lens. They discuss how chronic stress can lead to dysregulation of the autonomic nervous system, and highten symptoms of depression and anxiety. The authors expand on the potential for self-regulation techniques, such as biofeedback and mindfulness, to help individuals manage their stress responses, improve emotional regulation, and reduce the severity of anxiety and depression. This approach underscores the importance of understanding the physiological mechanisms behind these mental health conditions.

Quiz 2

Which hormone is primarily released in response to chronic stress?

	Adrenaline
	Insulin
	Cortisol
	Serotonin

The benefits of the vagus nerve and stress response

There are numerous benefits of the vagus nerve; starting with, it is a vital component of the autonomic nervous system, which plays a vital role in maintaining the body’s stress response and enhancing relaxation. It is also called the "wandering nerve" due to its impressive reach throughout the body, it is instrumental in facilitating the "rest and digest" response. This state counteracts the detrimental effects of chronic stress, supporting not only physical health but also mental health. Understanding the benefits of the 10th cranial nerve and its influence on the stress response can empower individuals to adopt practices that enhance relaxation, resilience, and overall quality of life.

The vagus nerve helps lower heart rate and promotes a state of calm. Activation of the vagal pathway induces a parasympathetic response, leading to vasodilation and reduced blood pressure. This process is essential for recovery after stressors and for maintaining cardiovascular health. The "rest and digest" response initiated by vagal stimulation promotes optimal digestive function. When the body is in a relaxed state, digestive enzymes and bile production are increased, facilitating nutrient absorption. Additionally, it enhances gut motility, reducing issues like bloating and constipation. It is linked to the regulation of emotions and stress levels. Activation of the vagal system can enhance mood and decrease anxiety by promoting the release of neurotransmitters, such as serotonin and acetylcholine. Leading to improved emotional resilience and a decline in symptoms associated with both anxiety and depression. The 10th cranial nerve also influences the immune system by regulating inflammation. When the body is in a relaxed state, the vagal pathway can reduce the production of pro-inflammatory cytokines, promoting an anti-inflammatory response. This is vital for overall health and can mitigate the effects of chronic stress on the immune system. The vagal pathway is involved in the physiological underpinnings of social behaviour. When activated, it promotes feelings of safety and connection, facilitating social engagement and bonding. This social support is crucial for mental well-being and can serve as a buffer against stress.

What neurotransmitter does the vagus nerve release?

The neurotransmitter released is called acetylcholine, which has significant implications for both psychiatric and inflammatory disorders. According to research by (Breit et al., 2018), it can be determined that acetylcholine released by the vagus nerve reduces inflammation by attaching to receptors on immune cells, thereby reducing the production of cytokines that drive inflammation. The vagus nerve's influence on acetylcholine also facilitates parasympathetic activation, promoting relaxation and recovery by slowing heart rate and supporting digestion. The vagus nerve's ability to release acetylcholine is important to maintain both mental and physical health, particularly in the context of stress-related and inflammatory disorders.

Stress response and the "rest and digest" approach:

In the framework of chronic stress, the activation of the vagus nerve is essential for counteracting the effects of the stress response. When stressors are perceived, the body enters a sympathetic state characterised by the release of adrenaline and cortisol, leading to increased heart rate, heightened alertness, and reduced digestive activity. Over time, this can lead to various health issues, including anxiety, digestive disorders, and cardiovascular problems.

Activation of the nervous system and physiology:

Chu et al. (2024) discuss the physiological underpinnings of the stress response, deepening the interplay between the nervous system and various body systems. The article outlines when the hypothalamic-pituitary-adrenal (HPA) axis is activated, it prompts the secretion of cortisol, and other stress hormones, which play crucial roles in managing stress. Additionally, the authors highlight the significance of the vagus nerve in regulating the parasympathetic nervous system, promoting recovery from stress. This comprehensive overview underscores the complex interactions involved in the stress reaction and its health implications.

Activation of the vagus nerve enhances the parasympathetic nervous system, facilitating a calming response that counteracts the effects of stress. This leads to a reduction in blood pressure and heart rate, presenting a state of relaxation and recovery. The vagal system is integral to various bodily functions, including digestion and immune response, thereby helping to maintain homeostasis during periods of stress. By mitigating the stress response, the vagal pathway contributes to overall well-being and resilience against stress-related disorders.

Implementing practices that stimulate the vagus nerve—such as yoga, meditation, deep breathing, and engaging in enjoyable activities—can assist the body from a sympathetic (stress) state to a parasympathetic (rest and digest) state. These practices encourage relaxation and recovery, promoting a sense of well-being and resilience against stressors.

Quiz 3

1 What neurotransmitter does the vagus nerve release?

	Acetylcholine
	Dopamine

2 What triggers the vagus nerve?

	Calmness
	Stress

Conclusion

The vagus nerve serves as a crucial mediator in the physiological reaction to stress, aiding the transition from a state of heightened stress in the brain to one of content. As illustrated through the scenarios and case studies, chronic stress can significantly impact both mental and physical health, underscoring the importance of understanding the vagus nerve's role in promoting the "rest and digest" response. By actively engaging in practices that stimulate the vagal pathway—such as deep breathing, meditation, and mindfulness—individuals can enhance their emotional regulation, improve digestion, and increase their immune function. This knowledge empowers us to take control of our stress responses, leading to improved resilience, wellness, and overall life quality. Emphasising the significance of the vagus nerve in stress management provides a pathway for healthier living, helping individuals navigate the pressures of daily life while fostering deeper connections and enhancing their overall mental and physical health.

Answers for the focus questions

Answers for the focus questions Which nervous system activates the vagus nerve? - Parasympathetic nervous system What is the relationship between the vagus nerve and stress? - The vagus nerve, helps regulate relaxation and recovery during stress. Higher vagal tone is linked to better stress resilience, while lower tone can increase stress and anxiety. What happens to the body during a fight or flight response? - The body experiences increased heart rate, elevated blood pressure, and heightened alertness, preparing it to confront or escape a threat. What neurotransmitter does the vagus nerve release? - Acetylcholine

See also

• Emotion (Wikipedia)
• Hunger motivation (Book chapter, 2010)
• Stress and health (Book chapter, 2010)
• Vagus nerve stimulation (Wikipedia)

References

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Breit, S., Kupferberg, A., Rogler, G., & Hasler, G. (2018). Vagus nerve as modulator of the brain–gut axis in psychiatric and inflammatory disorders. Frontiers in Psychiatry, 9(44). https://doi.org/10.3389/fpsyt.2018.00044

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Swarna Buddha Nayok, Vanteemar Sathyanaryana Sreeraj, Venkataram Shivakumar, & Ganesan Venkatasubramanian. (2023). The vagus nerve in psychiatry: From theories to therapeutic neurostimulation in neuropsychiatric disorders. Indian Journal of Physiology and Pharmacology, 67, 151–162. https://doi.org/10.25259/ijpp_401_2022

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Vanderhasselt, M.-A., & Ottaviani, C. (2021). Combining top-down and bottom-up interventions targeting the vagus nerve to increase resilience. Neuroscience & Biobehavioral Reviews. https://doi.org/10.1016/j.neubiorev.2021.11.018

External links

• Psychological stress reactivity and future health and disease outcomes: A systematic review of prospective evidence (Psychoneuroendocrinology)
• The gut-brain axis and cognitive control: A role for the vagus nerve (Seminars in Cell & Developmental Biology)
• Vagus Nerve Stimulation and the Cardiovascular System (Cold Spring Harbor Perspectives in Medicine)