Post by Elisa Guma
Our first breath
Our first breath at birth marks one of the most profound changes in our physiology. We transition from having fluid-filled lungs in the womb to suddenly filling them with oxygen. Hormonal changes occurring during labor stimulate the removal of fluid from the lungs. Once the baby enters the world, the sensation of air on the skin as well as rising carbon dioxide levels signal to the brain that it's time to initiate breathing. As the baby’s lungs begin to fill with air, increased oxygen in their system stimulates the closure of blood vessels in the heart called the ductus arteriosus, which are important in the womb for diverting blood away from the lungs. After birth, breath continues to influence our physiology throughout our lifespan.
Neural control of respiration
The neural control of involuntary breathing occurs mainly in the brainstem. This is necessary for sustaining life when voluntary respiration is not possible, such as during sleep. The medulla oblongata sends signals to respiratory muscles to induce breathing, with one portion signaling expiratory movements (exhaling), and another stimulating inspiratory movements (inhaling). This structure is also responsible for coughing, sneezing, swallowing, and vomiting reflexes. The pons, situated just below the medulla, is responsible for controlling the rate of involuntary respiration. In contrast, voluntary respiration occurs under conscious control and is important for higher functions such as voice control. This type of breathing is controlled by the motor cortex, which sends signals via the spinal cord to activate the diaphragm and accessory muscles of respiration. This can be overridden by various limbic structures of the brain, such as the hypothalamus. For example, in periods of perceived danger or intense emotional stress, signals from the hypothalamus cause an increase in respiratory rate in order to facilitate the fight or flight response.
Breath and mindfulness
The practice of ‘pranayama’ is a core component of many ancient practices such as yoga, meditation, and tai chi. This involves focusing one’s attention on the breath in order to reach a more calm and meditative state. The practitioner aims to slow the rate of breathing and often synchronizes breath with steady movement, increasing the link between the internal body and external world. This type of breathing increases oxygen uptake and activates the parasympathetic nervous system (‘rest and digest’) to allow us to enter a more relaxed state. Additionally, it activates brain regions beyond the brainstem involved in emotion, attention, and body awareness.
In addition to focused breathing, many of the contemplative traditions discussed above focus on mindfulness. Mindfulness is defined as the basic human ability to be fully present, aware of where one is in space and what one is doing, without interpretation or judgement. Breathing techniques are often employed in order to achieve this state, so it may be difficult to disentangle the benefits of intentional breathing from those of mindfulness.
Possible health benefits
In recent decades there has been increased scientific interest in these mind-body practices and the proposed benefits on physical and mental health. When attention is drawn to the breath, breathing is slowed, and as one elongates their exhale, decreased heart rate, blood pressure, and even inflammation have been observed. Improvement in symptoms of depression, as well as reduced anxiety, stress, and chronic pain have also been reported. Further, mindfulness practice has been shown to improve emotional regulation and reduce stress. Some of these effects may be mediated by activation of fronto-limbic brain networks involved in attention control, emotion regulation, and self-awareness during mindfulness meditation. However, many of the underlying mechanisms of these benefits are still unclear.
The link between breath and mental state
The link between involuntary breathing mechanisms and our ability to use breath to regulate our mental state from aroused or frantic to calm and contemplative are slowly becoming clearer. Recently, a small cluster of neurons in the brainstem, referred to as “respiratory pacemaker”, linking respiration to relaxation, attention, excitement, and anxiety has been identified. Within this cluster of neurons, termed the pre-Bötzinger complex, there are more than 60 different neuronal subtypes responsible for different aspects of breathing.
Leveraging genetic knockout technology in rodent models, the roles of many of these neuronal subpopulations have been identified. The most exciting discovery pertained to two specific subpopulations (identified by the presence of Gdh9 and Dbx1 genes) that, when eliminated from the brain, produced mice that were exceptionally calm in experimentally induced stressful situations, producing fewer fast or sniffing breaths and more slow breaths. However, researchers realized that rather than regulating breathing, these neurons were relaying information back to the locus coeruleus, a brain region that projects to almost every part of the brain, driving arousal and alertness, as well as anxiety and distress. This seminal study demonstrates that information about stress states is normally relayed from breathing centers to the rest of the brain and provides evidence for the relationship between breath and mental states. Importantly, this region identified in the mouse also exists in the human brain.
Another possible pathway for the connection between breath and mental state could be the vagus nerve. This cranial nerve can slow down heart rate through its direct projections to the heart and may also suppress inflammation by exerting control on the sleep and anti-inflammatory pathways in the body. This interesting pathway has received some attention recently but remains largely unexplored.
What’s next?
Interestingly, ancient practitioners were well aware of the connection between breath and mental states, despite not understanding the underlying physiology. Over the last few decades, our scientific understanding of these mechanisms has significantly improved. However, future work is needed to better understand how the central and peripheral nervous systems modulate the changes in our physiology and mental states associated with breath and mindfulness. In turn, understanding how to leverage this practice to help individuals suffering from mental health crises will be beneficial, as it is free, non-invasive and easy to disseminate.
References
Tang YY et al., The neuroscience of mindfulness meditation. Nature Reviews. 2015. Access to the publication can be found here.
Zaccaro A et al., How Breath-Control Can Change Your Life: A Systematic Review on Psycho-Physiological Correlates of Slow Breathing. Frontiers in Neuroscience. 2018. Access to the publication can be found here
Shi Y et al., A brainstem peptide system activated at birth protects postnatal breathing. Nature. 2021. Access to the publication can be found here
Gerritsen RJS & Band GPH. Breath of Life: The Respiratory Vagal Stimulation Model of Contemplative Activity. Frontiers in Human Neuroscience. Access to the publication can be found here.
