The Cannon-Bard theory of emotion states that a person’s emotions originate from a stimulus that triggers feelings and physical reactions at the same time, but separately. This theory originates from Walter Cannon, a physiologist at Harvard University, and Philip Bard, one of Cannon's doctoral students. The pair felt that the thalamus in the brain played the largest role in creating emotion. As such, the theory is also called the thalamic theory of emotion.
At its core, the Cannon-Bard theory of emotion suggests that emotions occur when the thalamus communicates with other parts of the brain in response to stimuli, causing a physiological reaction. A person sees a shark, so they are afraid and begin to shake. The theory states the physical effect (shaking) and the emotional effect (fear) occur simultaneously but do not rely on each other.
The Cannon-Bard theory does not only apply to negative emotions. While those are perhaps the most obvious examples, the theory also applies to positive emotional reactions. As an example, a person is going on a date, so they simultaneously experience feelings of happiness and have a physical reaction of a rapid heartbeat.
Cannon asserted that stimuli trigger receptors send impulses to the brain’s cortex. Once the impulses arrive, they follow pre-existing processes that determine a response. This response then stimulates the thalamus, which fires neurons in specific patterns to achieve different emotional expressions. As these neurons discharge, they activate muscles and nerves.
The key part of this theory is that when the thalamus discharges neurons, the physical effects occur separately from the emotional experience. However, both effects take place simultaneously.
Cannon largely relied on animal experiments to form and test his assertions. He and Bard developed their theory to challenge the dominant emotion model of the time: the James-Lange theory. The basic premise of the James-Lange model is that physiological arousal triggers the experience of emotion. For example, a person who is crying realizes they must be sad.
Cannon outlined some key issues with the James-Lange theory, much of which he discovered after his animal experiments:
In one procedure, Cannon kept cats healthy and alive after removing their sympathetic nervous systems. This had little to no effect on the animals’ emotions, disproving the James-Lange theory. He also injected adrenaline to mimic the physiological effects of intense emotional states, suggesting that the physical changes do not influence emotions.
Perhaps the most influential experiments on Cannon’s theories involved the thalamus. Removing the cerebrum anterior portion of the brain did not affect emotion, but removing the thalamus caused all emotional reactions to cease.
James and Lange also argued that there were either unique centers for the cerebral processes that accompany emotion, or that the processes occurred in the known motor and sensory centers of the cortex. Cannon responded to this by outlining a couple of ideas involving two sources of cerebral emotion processes.
He felt that emotion must be independent of the cortex because a person cannot always control their emotions. Cannon’s animal experiments proved his points, allowing him to assert that the optic thalamus is responsible for the organization of emotions.
People with certain lesions in the thalamus region tend to react excessively to stimuli. For example, a pinprick might cause significantly more pain on one side of the body than the other. Cannon’s experiments removed the thalamus from cortical control, leading to stronger emotions. This led him to believe that the thalamic region is the source of emotional sensation.
One of the main criticisms that the Cannon-Bard theory faces is that it assumes physical reactions do not influence emotion. However, a significant amount of research disproves this.
A person who makes a particular facial expression is more likely to begin feeling the emotion related to that expression — there is science behind smiling to improve mood. Additionally, Cannon’s fixation on the thalamus caused him to overemphasize its effects while downplaying the roles of other areas of the brain.
A variety of other emotional models and theories exist. The influential Papez-Maclean theory states that connections of the limbic system are responsible for emotion.
Stanley Schachter and Jerome E. Singer proposed the two-factor theory of emotion. According to this theory, when a person feels emotion, physiological effects occur and then the individual searches their environment for emotional cues to label the effects.
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