Motivation and emotion/Book/2018/Autonomic nervous system and emotion
What role does the ANS play in the experience of emotion?
Sometimes when anxious it is so intense that the body begins to respond by a pounding heart beat. Or when extremely afraid the body responds by sweating and shaking. Or when angry it feels as if heat is radiating off the skin. Strong emotion has long been thought to have a physiological response that enhances the experience of a stimulus. This response is dictated by the central nervous system where the emotion begins in the brain, and is enhanced by one of two mechanisms. The first is the endocrine system, and the second is the nervous system. Involuntary emotional responses of the nervous system are often dictated by the Autonomic Nervous System (ANS). The ANS is strongly suggested to be key in this link between physiological responses and emotion. Which many researches deducing this to an evolutionary purpose that enabling people to do incredible things. For example, when scared walking down a spooky alley way, the body prepares to jump into action and run away at the faintest of sounds. This book chapter will explore the role of the ANS in experiencing emotion as well as some of the hindrances this poses for human nature.
1. To determine what role the ANS plays in the experience of emotion?
2. To understand the basic properties of the ANS.
3. To discover how the role of the ANS in experiencing emotions.
4. To identify the differences between the parasympathetic nervous system and sympathetic nervous system.
The Autonomic Nervous System
The Autonomic Nervous System (ANS) is the division that controls most subconscious physiological functions, of the body like heart rate, tidal breathing, circulation etc. The two divisions of the ANS are the sympathetic nervous system (SNS) and parasympathetic nervous system (PNS) divisions which work together to regulate bodily functions in a state of tone. Providing a homeostatic equilibrium in response to brain output. Strong emotions felt can at times be seen in changes to physiological functions in the body.
To maintain a stable environment for optimal function, homeostasis is used to keep body systems in equilibrium. This is done by feed back mechanisms to the brain, and specifically the hypothalamus. This optimal functioning enables stability from pH levels in the blood to heart rate, therefore ensuring the seven hallmarks of ageing do not occur prematurely. Where through conscious or unconscious emotions the body adjust its homeostatic mechanisms in an effort to prepare the body for what the emotions dictate might happen. Which overall has an evolutionary purpose for not only preventing premature ageing but for survival (O’Callaghan, 2015).
Neural Pathways and Physiology
A specific feature to the ANS is the way information is passed through the body. It is unique and differs from other motor neural networks in the information that is projected (neurotransmitter) and the effect on the organ or target cell (receptors). Specific only to the ANS, are a preganglionic neurons and postganglionic neurons with a synapse in between. Both kinds of neurons differ in length, according to whether they belong to the PNS or SNS. These differences determine how an organ will respond to the signal presented, through excitation or inhibition of organ response. Together both systems create tone within organs between excitation and inhibition, causing a physiological dance of what system takes the lead. This is further described by figure 3. showing how the PNS and SNS are divided to create tone with in an organ. Furthermore due to neurons' splitting signals down different pathways causes the inhibition and or excitation of several target cells/organs at the same time. Emotions can change this physiological mechanism through relationship with emotional anatomy of the brain and the prefrontal cortex, and therefore prepares the body when a stimulus causes an intense emotion (Byku, Douglas, Mann, 2016). Theoretical concepts of emotion describe this relationship further.
In the baroreceptor reflex, mechanoreceptors pick up a change in blood pressure. Causing messages to be sent to the brain that increases or decreases heart rate, change the diameter of blood vessels and can change in breathing rate. With constant feedback from the PNS and SNS, allows increase or decrease in all the organs previously mentioned . Causing tone within the heart, circulatory system and lung function, all subconsciously (Byku, Douglas, Mann, 2016) .
The definition of emotion is seen to be controversial though out the study of psychology and other disciplines (Hagemann, Thayer, Waldstein, 2003). However, how these recent theories relating to the ANS have caused this link to become more clear. Classical researchers have investigated how the physiology and the mind relate, for example the mind-body problem. More recently many of these concepts have been integrated into current investigations and trends in emotion research. Where many theorists attempt to provide modern solutions for old problems. Focusing on the innate mechanisms of physiology and psychology holistically. Many of these theories have become heavily criticised for how appropriate the evidence is (Peters, 2013). However, with further understanding of the emotional centres of the brain the Hypothalamus, Amygdala, Cingulate Gyrus and Hippocampus, and links being drawn to the ANS, evidence is becoming more valid and reliable.
James-Lange Theory (1884)
James-Lange theory was first proposed by William James (1884), with the simple concept of the mind has a bodily expression. This was done by identifying changes in the vascular system when different emotions were on display. Specifically how the role of anxiety produces a bodily effect as an overall sensation. Attributing these occurrences to a reflection to conscious behaviour changes as predisposed by emotion. These concepts provided stability for further research in both the ANS and emotion. (Levenson, 2014)
Ekman and Colleagues (1983), pursued multiple theories on the role of the ANS. His findings show that in accordance to the classification of basic emotions, there was differences in heart rate and finger temperature. The basic emotions used were anger, fear, sadness, happiness, surprise and disgust. The finding showed that there was increased heart rate for anger, fear and sadness in comparison to happiness, surprise and digest. The finger temperature was greater for anger than any other emotion. With this understanding there is evident homeostatic mechanisms of heart rate and temperature that are involved in emotion. Ekamn and colleagues (1983), also used facial reactions to determine these basic emotions, and attributed them to being innate for an evolutionary purpose.
Evolutionary perspective looked to define the mind by addressing physical characters (Peters, 2013). Historically Charles Darwin (1872) was pivotal in creating debate around the evolutionary purpose of emotion. Now theorists attributed a bottom-up process of emotion and the ANS instead of a top-down process. Where all aspects of emotion and the ANS provide an evolutionary purpose, for survival and maintaining the human race (Levenson, 2014). Where basic emotions such as fear and disgust are important for avoiding potentially harmful scenarios though learning. In combination with the James-Lange Theory (James, 1884), this debate became a controversial topic in the psychological and neuroscience world (Berntson, Cacjoppo, Norman, 2014)
Neurobiology and Psychophysiology Today
Current research in psychology and neurobiology as branches of the study of emotion investigate the physiological mechanisms, and attribute them to changes in the brain. This is done by attempting to discover the physiological neural networks that elicit certain emotions (Hagemann, Thayer, Waldstein, 2003). Research discussing this relationship has turned into controversy of theory discussing two fundamental ideas; the specificity in emotion of role of the ANS and the coherence between systems (Levenson, 2014). Unlike the theories by James (1884) , Ekmann and colleagues (1983) show the difficulty in determining specific emotions in the physiological response.
Emotions and the Autonomic Nervous System
Although there is theoretical support for the link between emotion and the ANS, it is still unclear if this is a causal relationship. Showing that the ANS does not react specifically to a singular emotion. Due to not following a specific response pattern, it is difficult to divide the ANS in how it will respond. Hence there being a multitude of theoretical frameworks that seek to understand how this relationship occurs (Kreiberg, 2010).
By applying the theories of emotion to the ANS, there is an ability to reflect on what physiologically happens in the body when emotions are experienced. The theoretical frame works from a variety of literature give a range of emotions that have the possibility for discussion. Ekmans and colleagues (1983) model of emotions is widely used and featured in discussion and research, which is why these basic emotions are able to be applied to the workings of the ANS. Some of the ways many of the emotions have an effect on the physiological out put can be seen in figure 3. which describes the relationship of the PNS and SNS. Application of Ekmans and colleagues (1983) basic emotions to these areas, show observable physiological changes that occur for each emotion in finger temperature and heat rate. In this way the body reacts for survival. Which has be categorised based on as affectionally termed "rest and digest" or "fight or flight".
In Ekmans research there is a clear distinction between emotions that increase and decrease heart rate (1983). From this analysis, emotions can be divided into anger, fear, and sadness, which increase heart rate and, happiness, surprise and disgust which heart rate is unchanged. With this distinction comparisons can be made with other autonomic functions to give a description of the physiological response to each emotion. Unlike the terms "rest and digest" and "fight or flight", this is based in research specific to emotion.
No Change of Heart Rate
At rest the ANS uses the PNS to regulate the majority of functioning. with slight changes being made by the SNS to establish tone and maintain homeostasis. Emotions that are consistent with this aspect of the ANS according to Ekmans theory are happiness, surprise and disgust (1983) . In this case these emotion are considered positive, as an advantageous way in dividing the physiological attributes. Where these emotions might not necessarily illicit positive effects on the body physiology, they pose minimal health risks due to the ANS being pressured (Fox, Kop, Newell, Schmidt, Synowski, Waldstein, 2011).
Happiness is considered a positive emotion, that has physiological side effects that promotes health (Fox, et al., 2011). Maintenance of happiness is associated with a reduced risk of cardiovascular disease and promotion health in physiological mechanisms. This is attributed to maintaining body functions in a healthy range, without pressure on organs. Findings that showed that heart rate was higher than that of disgust but still far lower than that of anger, fear and sadness. Which supports findings that happiness helps in preventing cardiovascular disease and is advantageous for survival (Fox, et al. 2011).
Disgust, had very limited ANS response, where there is no change across heart rate, or any other characteristic of other specific emotions (Cacippo, Bernston, Larson, Poehlmann, Ito, 2000). However Ekman (1883), still considers this a core emotion. This is due to it being an evolutionary response, where learning enables avoidance of harmful things. With out disgust is the signal that an item is safe. For example potentially harmful food an individual has ingested in the past might illicit the disgust response.
Current findings in surprise show that in comparison to boredom and pain, there are moderate changes in heart rate (Jang, Kim, Park, Sohn, 2015,). Which contradicts Ekmans (1983), theory of relatively no change therefore having a similar response to happiness and disgust. Surprise can be divided into multiple categories, and perhaps linking to one of these caused a change in results. Where current findings initiating a 'startle' response while one classical studies another category of surprise. Evolutionary surprise enables a rapid response to an unexpected event, this initial response being in preparation for any situation (Ekman, Cordaro, 2011).
Changes in Heart Rate
The ANS response to anger, fear and sadness, are often strong and intense. Which in some cases are a "fight or flight" response preparing the body for action. According to the American Psychological Association (2018), when under stress there are physiological changes that occur across the body including respiratory increases, heart rate increase, release of stress hormones and disregulation of the gastrointestinal system. In extreme cases these emotions can result in myocardial infarction and lead to death. These extreme ANS responses, are due to a mass discharge in the SNS, which are invoked in fear, anger and sadness. Drawing a parallel with Ekman and colleagues (1983), model.
Fear has been associated with the "fight of flight" mechanism for a long time. Which evolutionarily is a primal response to get away from a threat or to fight the threat. To do this the ANS needs to be activated by, increasing heart rate, dilating pupils and changing blood vessels, all for an impending threat as a result of fear. However, fear is not the only emotion that we can attribute this response to. Experiences in attraction, anxiety and other emotions can elicit the same physiological phenomena. It is the interpretation of these symptoms that causes people to attribute this response to an emotion, and in this case fear is a strong antecedent.
Anger has classically been associated with health risks that include coronary heart disease, bulimia and diabetes (Cutov, Staicu, 2010). This has been associated with the constant strain on ANS. Resulting in measurable increases in both heart rate and finger temperature (Ekman, 1983). Evolutionary this preparation is consistent with the 'fight' aspect of 'fight or flight', in readying the body to enter action. Although, heart rate is high and is a constant with fear and sadness, this change is far more dramatic (Ekman, 1983). From this showing that there is increased risk of myocardial infarction and other disease, if anger is prolonged.
In the experience of sadness, the physiological state does not change according to the type of stimulus. Where regardless meaning, there is an increase in overall physical response, which invokes feelings of powerlessness, and the cause of chest ache and tears (Shirai, Suzuki, 2017). In Ekmans, original study (1983), findings show that there is a increase in heart rate when experiencing sadness. Which accompanied by other physiological changes encompasses the physical response of pain. Poetically it has no specific evolutionary purpose, but none the less is a quality that is possessed by most of humanity.
So with all this knowledge, what happen when there is psychological distress that causes loss of emotional control? When the ANS represents aspects of psychological disorders, there can be observable problems. These problems can begin with emotions and development of the mind, or changes which have occurred over the lifetime. This is a premise which polyvagal theory attempts to understand. By attributing emotional dysregulation to the dysfunction of specific cranial nerves, that control physiological responses like heart rate. Or does this strain begin with emotional input as long suggest by psychological theorists? So what happens when the body and the mind is under constant stress, that causes strain on the ANS?
Due to anxiety having a strong correlation with cardiovascular disease and hypertension, there is a direct link to the ANS. It has been found that there is a reduced heart rate in individuals with anxiety (Chen, Chen, Chi, Hsiao, Hui Lee, Tsai, Yang, Yeh, 2016). Often times this is accompanied by an increased level of respiration, which would cause the decrease in heart rate (Averell, Bondarenko, Dickson, Dunkley, Fullern Hodgson, Nalivaiko, Sominsky, 2013) . The overall experience of the psychological and the physiological response, causes great stress on the individual. Which is not beneficial for overall heath, and effects quality of life for long periods of time. The ANS does not necessarily cause anxiety but it gives a physiological aspect across the body, that intensifies associated emotions. Which perhaps was due to its role in evolution, which is not helpful in this situation.
Attention-Deficit/Hyperactivity Disorder (ADHD)
The dysregulation of emotion and the ANS is considered to be an aspect of ADHD. There is unconfirmed hypothesis that are currently seeking to find a link between the dysfunction to the ANS, that may be related to the presentation of ADHD. With a depiction that the SNS, specifically has a role in changing the physiological response to emotions (Musser, Backs, Schmitt, Ablow, Nigg, 2011). Polyvagl theory argues that the dysregulation of the SNS, is the cause for the physiological changes associated with ADHD (Beauchaine, Gatzke-Kopp, Mead, 2007)
- Future research suggestions
- With a clear undetermined link between emotion and the ANS, future research would be invaluable for progress in this field. Where with potential findings could help in understanding and treatment for disorders that are associated with a disregulation of the ANS. Such as that discussed of anxiety and the many more that are associated with a combination of ANS and emotion regulation.
- Potential research could also bring understanding to old philosophical questions, like the mind-body problem. To find a definitive answer to what drives and dictates human emotion. In which much of modern day science has been centered around. Bringing solutions to long unanswered questions, which satisfy the intrigue of humanity for centuries. Providing limitless potential for not only neuroscience and biological psychology, but to many disciplines of study.
- There are several theoretical frameworks that seek to link emotion and the ANS. Many of which argue an evolutionary perspective where emotions are derived from the need for survival, with Ekman (1983) being at the forefront with his theory of six basic emotions. These emotions can be analyzed in accordance to heart rate, and other physiological responses.
- With a complete overview of the relationship between emotion and the ANS, research dictates that there is a correlative relationship. Where there is no specific physiological response for every specific emotion. However, in response to strong emotional response the body responds without specificity to a singular emotion, and there is considerable similarity between the responses to several emotions.
- Evolutionary theory of emotion (Book chapter, 2018)
- Emotion regulation in children (Book chapter, 2018)
- Anxiety Neurobiology (Book chapter, 2018)
- Stress Physiology (Book chapter, 2015)
- The 'fight, flight, and freeze system' and emotion (Book chapter, 2014)
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