Theories of Emotions
Researchers have developed several theories of how human emotions arise, and they investigate how each is represented in the brain.
The James-Lange theory of emotion states that the self perception of bodily changes produces emotional experience (Figure 1). For example, you are happy because you are laughing, or you feel sad because you are crying. Alternatively, when a person sees a spider, he or she might experience fear. One problem, according to this theory, is that it is not clear what kind of processing leads to the changes in the bodily state, and whether this process can be seen as a part of the emotion itself.
When an individual is presented with an emotional object, it first stimulates the appropriate sensory organs. These afferent signals are then sent to the cerebral cortex, triggering variously combined ordinary motor-sensorial brain processes. According to James, it is the afferent proprioceptive signals from bodily changes, especially fluctuation of visceral responses, mediated by signaling from these motor and sensory centers that account for the emotional experience. Proprioception refers to the sense of the position of parts of the body, relative to other neighboring parts of the body.
The Cannon-Bard theory states that emotional expression results from action of the subcortical centers of the brain (Figure 2). This theory determined that the optic thalamus is a region in which the neural organization for the different emotional expressions resides. An individual's sensory organs take in the emotional stimulus, and then the stimulus is relayed to the cerebral cortex. It is in the cortex where impulses are associated with conditioned processes, which determine the direction of the response, which therefore stimulate the thalamic processes.
Singer-Schachter and Two Factor Theories
The two factor theory (otherwise known as the Singer-Schachter theory of emotional experience) views emotion as a compound of two factors: physiological arousal and cognition (Figure 3). This theory is based on labels in response to physiological stimulation. Cognitive factors are thought to be major determinants of emotional states. The individual senses the particular emotional object of the situation through the sense organs, and an induced form of autonomic stimulation then follows this perception. Accompanying this excitation is a specific cognitive label, which allows one to interpret the state in terms of characteristics related to the situation. Additionally, past experience provides the framework within which one understands and labels his or her feelings.
Singer and Schachter injected participants in their research with adrenaline (epinephrine), which causes a number of effects like increased blood flow to the muscles and increased heart rate. The result was that the existence of the drug in the body did not lead to experiences of emotion. Contrary to the James-Lange theory, this study suggests that bodily changes can only support conscious emotional experiences but do not create emotions. Therefore, the interpretation of a certain emotion depends on the physiological state in correlation to the subject's circumstances.