Hearts to Brains: Communication, Emotions, Biology
Introduction
In 1990, takotsubo cardiomyopathy, better known as the “broken heart syndrome”, was discovered; it is when extreme emotional distress mimics heart attack symptoms. The effects of a broken heart (both literally and not) is a showcase of the impact of emotions on the heart. With the two-way dialogue between the brain and the heart, our hearts and heads influence one another, affecting our cognitive functions, emotions, stress, and cardiovascular and physical health.
Historical Context & Research
For centuries, stories, folklore, and tales alike have shared notions of human emotional states affecting one’s physical health. The theories of heart-to-brain (and vice versa) belong to a field known as psychophysiology. One of the earliest observations in this field was the examination of the heart-brain interactions by John and Beatrice Lacey during the 1960s and 1970s, an extension to the research by Cannon. The research done by the Laceys found that the heart sent meaningful messages to the brain, which were deciphered, understood, and obeyed by the brain.
Walter Bradford Cannon was the first modern scientist to truly explore the heart-brain connection, where he coined the term “fight or flight” in 1915. His “fight or flight” concept theorises that when aroused, the mobilising part of the nervous system (sympathetic) energises us for either fight or flight. Conversely, during peace and quiet, the parasympathetic nervous system slows down the heart rate. Thus, the theory relies on the idea that the nervous system and its related physiological responses (be it the heart, the body, etc) will move alongside the brain’s response to a stimulus. In his research, he reviewed cases in tribal communities, where healthy individuals died within a few days of being accused of misdeeds. Cannon proposed that emotional stress could cause the “sympathetico-adrenal complex” to constrict the blood vessels.
Figure 1: A diagram of the fight-or-flight nervous system. (Source: Getty Images)
Heart-Brain Dialogue
Heart-brain communication occurs in four major pathways: neurologically (via the transmission of nerve impulses), biochemically (using hormones and neurotransmitters), biophysically (by pressure waves), and energetically (which are electromagnetic field interactions).
Facilitating the complex communication between the heart and brain is the heart-brain axis (HBA). The heart-brain axis theory follows the inter-relationship between the heart and brain, where the reciprocal connection between the two influences mood disorders, psychological states, and physical health. Historically, the brain has been considered the primary component of the relationship; this notion has since been disproved by studies finding dynamic coupling between the heart and brain. A crucial part to the HBA is the autonomic nervous system (ANS), which anatomically connects the central nervous system of the brain to the circulatory system of the heart via interoception frameworks. In fact, the ANS acts as the foundation that links the heart and the brain, allowing them to engage in bidirectional communication and information exchange using interoceptive pathways. To dive a little further, interoception is essentially the perception of internal signals from the body, referring to the way peripheral visceral information is relayed to the brain and thus influences the brain function (Critchley et al., 2013). The interoception framework and pathways through the ANS is key for physiological regulation and behavioural modulation.
Figure 2: A diagram conveying partially the heart-brain communication. (Source: The Campbell Lab)
During the unconscious state, the heart autonomously generates intrinsic electrical activity despite the disconnect from the brain, thus regulating the cardiac cycle through the central nervous system. At the same time, continuous information is relayed from the heart to the brain through an ascending interoceptive pathway. To clarify the distinction, ascending interoception refers to information flowing from the body to the brain, whereas descending interoception explains the opposite. Overall, the core of the HBA is a neuroanatomical pathway between the heart and brain, which involves the autonomic and central nervous system. Here, it is then interconnected with the ANS (including the sympathetic and parasympathetic nerves) to allow regulation. Thus, the HBA’s physiological connection ties together autonomic nerves, hormones, and cytokines, in turn facilitating the transfer of information between the two central systems within our bodies.
Furthermore, a main part of the ANS is the vagus nerve. The vagus nerve, otherwise known as the pneumogastric nerve, is the longest nerve of the ANS. It controls autonomic functions, such as breathing, heart beating, and so on. Its sensory functions can be divided into two kinds: somatic and visceral. Somatic components are the sensations on the skin and muscles; visceral components are the sensations felt internally in the organs. As it plays a significant role in physiological homeostasis, it also helps with reflex pathways to do with the regulation of cardiac function. The heart’s cardiac muscle cells and conductive pathways are supplied with vagus nerve cells and fibres. With the stimulation of the nerve, the cells will experience negative chronotropic, dromotropic, or inotropic action affecting the heart. For example, the sinoatrial node will experience a lower heart rate due to negative chronotropic action when the vagus nerve is activated. Hence, the vagus nerve acts as a conduit for signals between the heart and the brain, particularly for reflex and autonomous actions. The nerve has sensory neurons taking information from the body to the brain, as well as motor neurons going the opposite direction. Additionally, research has found that the vagal tone is associated with emotional regulation (Porges, 2001).
Feelings On The Heart
Heart activity is strongly impacted by our emotions. Some ordinary responses include fear inducing a sped up heart rate or calmness slowing down the heart rate. According to a study by Prkachin et al., the findings suggested that different emotions elicited different cardiovascular responses. Heart rate increased more in negative emotions compared to positive emotions. Besides that, there are even differences between men and women in their stress responses.
In addition to the cardiovascular responses triggered by psychological emotions, emotional states even lead to increased risks for onset of cardiovascular disease. Many early studies have found that strong emotional upsets precipitate heart failure, thus linking psychological emotions to human health in terms of the heart and the rest of the physical body. For instance, day-to-day stress is correlated with an increased risk of heart attack and stroke. Long-term mental disorders, such as depression and anxiety, are commonly associated with heart disease. Particularly, depression (due to its being an emotional stressor) has higher risks of ventricular arrhythmias and sudden cardiac death (Lambiase, 2023).
Figure 3: Diagram depicts the effects of stress and its transmission through the brain, nervous system and to the heart. (Source: Nature)
Moreover, our heart rhythms can act as a marker for stress. The patterns of our heart rhythms convey information about current emotional states. Heart rate variability (HRV) is the variation in time between heartbeats; its slight fluctuations are indicators of possible stress, emotions, and heart disease. HRV is controlled by the ANS, reflected in the sympathetic (fight-or-flight) and parasympathetic (relaxation) nerves. Therefore, HRV can indicate imbalances in the ANS, demonstrating how variation tends to be lower in systems in a fight–or-flight state. Typically, high HRV suggests that the individual has greater stress resilience and cardiovascular health. Numerous research studies consistently found that reduced HRV and an elevated heart rate are associated with depression and anxiety (Alvares et al, 2016; Chalmers et al., 2014). On the other hand, experiencing emotions like gratitude can also lead to immediate improvements in HRV, aiding emotional resilience and improving physical health (Fredrickson, 2001).
Aside from that, HRV is also linked to emotion regulation (Thayer and Lane, 2009; Appelhans and Luecken, 2006; Thayer and Brosschot, 2005). It is discovered that those able to better regulate their emotions show greater levels of resting HRV while HRV levels also increase in concert with successful performance on emotion regulation tasks.
Due to emotions provoking stress responses, the self-regulation of our emotions is an important task. Since bidirectional neural connections allow information exchange between the emotional centers – the amygdala and body – and neocortex, emotion-related input and cognitive processing both have a hand in brain activity and emotional processing. As a result, counteracting emotional stressors, especially negative ones, are essential to individual health to reduce cardiovascular risks. Through various techniques, including meditation, yoga, etc, you can improve biomarkers of cardiovascular risk.
Conclusion
Our physical well-being and emotional ones are clearly in connection with one another. With the heart and the brain communicating to one another via neurones, hormones, cytokines, and electrical signals, it is evident that our emotions influence our heart health significantly. The HBA demonstrates the dynamics between the heart and brain in terms of information exchange as well as the respective impacts. Hence, it is key to manage your emotions through self-regulation techniques to prevent long-term stress from increasing risks of heart disease.
Article prepared by: Estelle Sia Yu Qi, MBIOS R&D Director 24/25
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References
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