Cannon’s Theory of Emotion and Stress Explained

Cannon-Bard's Theory of Emotion and Stress

We all experience different types of emotions such as anger, fear, love, and hate in our everyday life. Generally, emotions are defined as our responses or behavioural changes to the various outward stimuli. The American Psychological Association defines emotions as “a complex reaction pattern, involving experiential, behavioural, and physiological elements.” The emotions felt by an individual depend upon the various components like psychological evolutions, subjective experiences, and physiological factors, which is why different people show different emotions when they face similar situations. Over the years, various psychologists, philosophers, and researchers have proposed a variety of theories related to emotions that explain the various factors related to emotions, and how people experience emotions. Here in this article, we will focus on Cannon-Bard’s theory of emotion and stress.

Historical Background

Walter Bradford Cannon (1871-1945) was an American physiologist and neurologist. He was the first person who began the use of X-rays in various physiological researches. In 1896, he completed his graduation and was awarded a Harvard Scholarships for his excellent academic skills. He earned a Master of Arts degree (1897) and Doctorate in Medicine (1900) from Harvard University, and after his doctorate, he worked as a professor at Harvard University. He is also one of the other researchers who tried to explain the factors related to human emotions. In the late 1880s, the James-Lange Theory of emotions, proposed by William James and Carl Lange, was very popular. This theory states that any outward stimuli cause physiological changes such as sweating, muscle tension, faster heartbeat, and trembling, and these changes are detected by the brain, and the limbic system of the brain recognizes these changes as emotions, i.e., the person experiences the emotions after the physiological changes detected by the brain. For example, if a person is walking on the road and suddenly, a street dog starts barking (outward stimuli) at that person, this may result in the rapid breathing, high heart-beat, and trembling (physiological changes) of the person, and his brain perceives these physiological changes, and the person feels the emotion of fear, i.e., the person experiences fear because of the physiological changes.

James-Lange's Theory of Emotion

This image represents “James-Lange’s Theory” that the person experiences the emotion of fear after the physiological arousal.

However, Cannon criticized James-Lange’s theory that emotions are the result of the physiological changes perceived by the brain. He emphasized that both the physiological and emotional changes occur at the same time on encounter with any outward stimuli, and both these reactions are independent of each other, i.e., the person can still feel the emotional changes even if the bodily responses information has not yet been received by the brain. One of Cannon’s doctoral students, Phillip Bard (1898-1977), also acknowledged his idea, and he continued his research along with the cannon. They together proposed Cannon-Bard’s theory of emotion in 1927.

Cannon-Bard’s Theory of Emotion

According to Cannon-Bard’s theory of emotion, any outward stimuli trigger both the emotional and the physiological reactions of the person at the same time. He stated that both these reactions simultaneously originate in the thalamus. Thalamus is a small structure present between the midbrain and cerebral cortex (near the centre of the brain), and it has nerve fibre connections with both the midbrain and cerebral cortex. This theory is also referred to as the ‘thalamic theory of emotions’ because the thalamus is responsible for the experience of emotions, and its main functions involve motor control, transmitting visual/auditory signals, and sensory signals to the amygdala, the cerebral cortex, and to the sympathetic nervous system (SNS) if the person encounters any triggering event. The amygdala is an important part of the limbic system of the brain; it is located in the temporal lobe, which is responsible for processing various emotional responses. The cerebral cortex (the brain’s largest part) performs various information processing functions like perception, sensation, memory, and controlling conscious thoughts or actions. The signals transmitted to the autonomic nervous system are responsible for various physiological changes such as sweating, muscle tensing, and trembling.

Important Parts of the Brain Responsible for the Emotions Processes

Parts of the Brain responsible for the experience of emotions

Let’s understand with an example when a dog barks or growls at a person (stimulus), the thalamus of the person gets activated, and it simultaneously sends signals to both the cerebral cortex and to the autonomic nervous system, this results in the physiological changes like rapid breathing, high heart-beat, and trembling, and it instils the emotion of fear in the person. He also emphasized that the physiological responses of the person toward any triggering event are not the accurate measure of their emotions. The increased heart rate of the person does not always mean that the person is experiencing the anger emotion; it could also be due to excitement or stress.

Cannon-Bard's Theory of Emotion

This image represents the “Cannon-Bard’s Theory” that the thalamus sends the triggering event’s (growling dog) signals, and both the physiological arousal and experience of emotion occur at the same time.

Cannon also observed that the thalamus is responsible for the emotional processes, but the person can try to suppress their emotions with the help of the cerebral cortex. For example, remember when you were watching a horror movie, and suddenly that scary monster flashed on your screen? According to Cannon-Bard’s theory, the processed information (seeing the monster) is transferred to the thalamus, which further sends signals to the other parts of the limbic system that are responsible for experiencing the emotions (experiencing fear) and physiological (sweating, high heartbeat) responses. If you ever tried to not let others know that you are scared of the horror movies by assuring yourself that the monster is not real or it’s just a movie, you still get the signals from the thalamus, but the cerebral cortex helps in suppressing the emotion of fear.

Research Model of Cannon-Bard’s Theory of Emotion

Cannon-Bard’s theory of emotion states about the occurrence of both the physiological change and emotional response at the same time, and their independent nature, i.e., individuals have the ability to feel the emotions even before the bodily response to any outward triggering stimuli. To prove his argument, Cannon conducted a study on the cats. He surgically removed the cat’s sympathetic nervous system and studied their various emotional responses to the forced outward stimulus. He thoroughly studied every aspect of this experiment and presented his model of the theory of emotion as a replacement to the James-Lange theory of emotion. In his experiment, he found that the cats when triggered with any outward stimuli were still showing various emotions of pleasure, fear, and anger even in the absence of the sympathetic nervous system. He suggested that the experience of emotions involves the transmission of the signals to the autonomic nervous system (physical or physiological responses- arousal) and the cerebral cortex (information-processing functions- emotions), and both these parts simultaneously receive the signals from the thalamus. However, James-Lange Theory states that the signals received by the autonomic nervous systems are responsible for the emotional processing by the cerebral cortex. Cannon stated that the brain takes much more time to act for the bodily responses than experiencing the emotional change in the presence of triggering stimuli. Phillip Bard further researched Cannon’s experiment. He conducted various researches to understand the parts of the brain that are more responsible for the experience of emotion. When Bard conducted the experiment on the cats and removed their cerebral cortex, he observed that the decorticate cats (cats with the absence of cerebral cortex) were showing ‘sham rage’ (highly emotional and violent reaction produced by the animals whose cerebral cortex is being removed). When the cat was prompted, it showed various physiological responses like growling and erect hair. However, when the lower posterior region of the thalamus of the cats was removed, the cats showed lesser sham rage. Hence, based on all the findings, he concluded, the thalamus was responsible for the emotional responses shown by the cats in the absence of the cerebral cortical, and he proposed that the thalamus plays the most crucial part in the processing of emotions.

Bard's Experiment on a Cat

Understanding Cannon’s Theory of Stress

Walter Cannon is one of the pioneers in studying the body’s physiological responses to stress. He described the concept of flight or fight response to explain the stress. The flight or fight response is also known as an acute stress response or hyperarousal; it is an automatical physiological response (survival instinct) to the perceived threat that allows people to rapidly act on the threat. Cannon’s stress theory highlights that the various hormones are responsible for the feeling of stress. According to his theory, when you face any threatening situation, the amygdala present in your brain processes the threatening situation, and it gets activated and sends signals to the hypothalamus, which further sends messages to the adrenal gland that alerts the sympathetic nervous system. Due to the pumping of adrenaline glands through the individual’s veins, he/she feels various physiological responses like rapid breathing, increased heartbeat, and blood pressure. All these physiological responses prepare you to take necessary actions, and it takes place so rapidly that you instantly act on the flight or fight response. Hence, the release of the stress hormones due to the signals sent by the amygdala activates the flight or fight response, i.e., it activates the survival instinct in the body to either fight with the situation or runs away (Cannon, 1932). Both the endocrine system and the sympathetic nervous system get activated during the fight or flight mode, and the arousal of both these systems helps to tackle the perceived threat. Cannon stated that the flight or fight response helps in maintaining the state of homeostasis; a homeostasis state is a built-in mechanism of the body at which the various physiological factors like respiration, digestion, blood pressure, and temperature are balanced according to the optimum survival conditions. Hence, due to the adaptive nature of the fight or flight mode, people become able to tackle the perceived threat, both internally as well as externally, and enabling them to survive. For example, imagine you are alone in a jungle, and you saw a wild animal approaching you, instead of wasting time thinking about the right decision to make when encountering a wild animal, your brain instantly gives you signals to run away to survive due to the action of fight or flight response.

Fight or Flight Response in Cannon's Theory of Stress

Drawbacks of Flight or Fight Response

Fight or flight response is a great survival mechanism that helps to immediately act on any threatening situation, but this mechanism could also become a problem if the person is constantly dealing with the threatening situation. The individual’s fight or flight mode will get activated even in normal or less threatening situations. This may lead to both mental and physical health problems. The chances of the person to suffer from chronic stress will become very high if the stress is not managed properly. The other drawback is the severe impact on the nervous system of your body due to the excessive release of stress hormones. Some tips suggested by Cannon to manage the fight or flight responses involves analyzing the amount of time you spent stressing about things and do some relaxation techniques like breath-in & breathe-out and training your mind to stay relax and respond with less eagerness if you are experiencing the fight or flight response in normal daily life conflicts.

Drawbacks of Flight or Fight Response

Support of Cannon-Bard’s Theory of Emotion

After Cannon-Brad proposed their theory of emotions, various other researchers explored their findings, and they conducted various studies. Almost all of these studies showed that to experience any emotions, physiological or physical changes of the body do not play a much crucial role. Numerous studies found that the animals still displayed various types of emotions even when their various parts responsible for the physiological actions were removed. Some popular studies include Sherrington’s (1900) study on dogs in which the spinal cord of the dogs was removed, and Dana’s (1921) study on an individual, who had a damaged spinal cord, all these studies demonstrated that one can still show emotions even in the absence of physiological responses.

Support of Cannon-Bard's Theory of Emotion

Criticism of Cannon-Bard’s Theory of Emotion

  • To prove their theory of emotions, Cannon and Bard conducted a study on decorticated cats. The results obtained by this study may be valid on the cats or other animals, but it does not assure that these results will apply to humans too. Hence, the findings of Cannon-Bard’s study are doubtful to be generalized on the emotions of humans.
  • The main criticism of Cannon-Bard’s theory is that it does not consider the influence of various physiological or physical reactions on emotions. Various studies have proven the impact of different facial expressions (physical reactions) on emotions. One of these studies showed that when the subjects were asked to make a specific facial expression, then most subjects showed the emotions related to that specific facial expression, i.e., they felt the anger emotion when they made the scowl expression, and they felt happiness emotion when they made a smiling facial expression.
  • Some critics say that the Cannon-Bard theory overemphasized the role of the thalamus in the emotional processes, and he did not much consider the role of other structures of the limbic system of the brain in the emotional processes.
  • When both James Lange’s theory and Cannon-Bard’s theory of emotion were compared, the Cannon-Bard theory was regarded as more accurate than James Lange’s theory by most of the researchers; however, some recent researches have shown the influence of physiological responses on emotions, and Jame-Lange’s theory is gaining more acceptance over the Cannon-Bard’s theory.

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