Cannon–Bard theory

The main concepts of the Cannon–Bard theory are that emotional expression results from the function of hypothalamic structures, and emotional feeling results from stimulations of the dorsal thalamus. The physiological changes and subjective feeling of an emotion in response to a stimulus are separate and independent; arousal does not have to occur before the emotion. Thus, the thalamic region is attributed a major role in this theory of emotion. The theory is therefore also referred to as the thalamic theory of emotion. The main concepts of the Cannon–Bard theory are that emotional expression results from the function of hypothalamic structures, and emotional feeling results from stimulations of the dorsal thalamus. The physiological changes and subjective feeling of an emotion in response to a stimulus are separate and independent; arousal does not have to occur before the emotion. Thus, the thalamic region is attributed a major role in this theory of emotion. The theory is therefore also referred to as the thalamic theory of emotion. Walter Bradford Cannon (1871–1945) was a physiologist at Harvard University, who is perhaps best known for his classic treatise on homeostasis. Philip Bard (1898–1977) was a doctoral student of Cannon's, and together they developed a model of emotion called the Cannon–Bard Theory. Cannon was an experimenter who relied on studies of animal physiology. Through these studies, Cannon and Bard highlighted the role of the brain in generating physiological responses and feelings; a role that is important in their explanation of emotion experience and production. A dominant theory of emotion of Cannon's time was the James–Lange theory of emotion, and Cannon recognized that to test this theory, an examination of emotional expression with no visceral afferent feedback was required. This was necessary because the link between visceral changes and the feedback required to stimulate cerebral manifestations of an emotion would no longer be present. To do so, Cannon experimented with severing afferent nerves of the sympathetic branch of the autonomic nervous system in cats. Cannon compiled his experimental results in 1915, then refined and expanded them, and finally proposed his model of emotion as a challenge and alternative to the James–Lange theory of emotion. The James–Lange theory relies on the backflow of impulses from the periphery to account for unique emotional experiences; impulses that William James assumed to come from all parts of the organism, including the muscles, skin, and the viscera. The viscera were attributed a major role by James. The viscera are composed of smooth muscle and glands. Cannon identified and outlined five issues with the James–Lange theory's notion of the vasomotor center as the explanation of emotional experience. William James argued that there were either special centers for cerebral processes that accompany emotion, or they occurred in the ordinary motor and sensory centers of the cortex. Cannon responded by positing that there may not be one or the other, that there may be cortical processes and special centers that accompany emotional responses. He outlined two ideas regarding the existence of two sources of cerebral processes of emotions. Cannon summarized research done by Bechterev regarding emotional expression. In this research, it was argued that emotional expression must be independent of the cortex because the expression of emotions cannot always be inhibited or controlled (e.g. laughing from being tickled) because visceral changes occur independent of our control, and because these responses, which cannot be inhibited, are seen soon after birth before cortical management is developed. Furthermore, after cerebral hemispheres were removed from animal test subjects, correct affective responses could be elicited by appropriate stimulations. These emotional effects were no longer present when the optic thalamus was removed from the animals; thus, it was concluded that this region plays a significant role in the expression of emotions. To further support the assertion that emotional expression results from action of subcortical centers, Cannon and Britton performed further experimental research with cats. Cats were decorticated, and after a period of recovery they spontaneously displayed the behaviours characteristic of intense fury. This response, referred to as sham rage, continued to be displayed after ablation of all brain regions anterior to the diencephalon. However, once the lower posterior portion of the thalamic region was removed, the display of sham rage by the cats subsided. Based on this finding, it was concluded that the thalamus was a region from which, in the absence of cortical control, impulses are discharged which evoke an extreme degree of 'emotional' activity, both muscular and visceral.Based on these findings and observations, Cannon asserts that the optic thalamus is a region in the brain responsible for the neural organization for the different emotional expressions. There are numerous reported and cited cases of patients with unilateral lesions in the thalamus region who have a tendency to react excessively to affective stimuli. For example, pin pricks, painful pressure, and excessive heat or cold all cause more distress on the damaged side of the body as compared to the normal side. Similar results can be observed from agreeable stimuli: warmth stimuli may cause intense pleasure, demonstrated by facial expressions of enjoyment and exclamations of delight by the individual. The increased influence of stimuli resulting in excessive responses was attributed to the release of the thalamus from cortical inhibition. When the thalamus is released from cortical control, the affective states and responses are increased; thus, it was concluded that the thalamic region is occupied with the affective component of sensation.