A reaction, both psychological and physical, experienced subjectively in a felt response to specific stimuli such as interactions, perceptions, or events.
Emotion has been defined in many ways and often described in conjunction with mood, temperament, personality, disposition, and motivation. It has been called an instinctive or intuitive response rather than one derived from reasoning or knowledge. Emotions involve feelings associated with physiological and psychological changes that, in turn, influence behavior. Even though it is possible to exert some measure of control over one's emotions, they are not initiated purposefully and usually arise in response to stimuli. The physiological activity influenced by emotions involves arousal of the central nervous system and will vary according to the specific emotion elicted. The psychological changes that occur with emotion involve the individual's subjective experience, cognitive process, motivation and subsequent behavior.
In contrast to moods, which are generally longerlasting, emotions are transitory, with relatively welldefined beginnings and endings. They also have valence, meaning that they are either positive or negative. Emotions are experienced subjectively as passive phenomena. Objectively, emotions involve internal physiological responses and expressive outward displays that are both learned and innate. Certain primary emotions are considered to be innate, including joy, anger, sadness, fear, and love, while complex emotions such as altruism, shame, guilt, and envy, seem to arise more from social learning.
The first theory of emotion that influenced modern scientific thought was the James-Lange theory, which was formulated independently in the 1880s by American psychologist and philosopher William James (1842–1910) and Danish physiologist Carl Lange (1834–1900). These scientists suggested that the physiological manifestations of emotion precede the subjective ones. For example, rather than trembling because we are afraid, we are afraid because we tremble. Even though the brain responds to a threatening situation by activating peripheral responses, we do not consciously experience the emotion until these responses are activated. Thus, the central nervous system itself does not actually produce the emotion. Over the following decades, this theory drew widespread response and criticism.
In the early twentieth century, an alternative model of emotional experience was formulated by Harvard physiologist Walter Cannon (1871–1945), who proposed that emotions originate in the central nervous system, beginning with nerve impulses passing through the thalamus, then the cerebral cortex, which directly creates the experience of fear or other emotion, depending on the stimulus. Later Cannon and Phillip Bard (1898–1977) (the Cannon-Bard theory) described the psychological and physiological components of emotion as occurring simultaneously, with nerve impulse activity occuring in the thalamus and cerebral cortex at the same time as physiological responses pass through the hypothalamus. This theory continued to support the idea that the experience of emotion comes directly from the central nervous system.
It was not until the mid-twentieth century that significant research shed new light on the emotions. Many theories were suggested by independent studies, which differed mainly on the question of whether emotions are learned, the result of cognitive processes, or biologically determined. More recent theories propose that the psychological construction of emotion involves clusters of components that may include subjective experience, cognitive processes, motivation, expressive behavior, and psychophysiological changes, but no single component produces emotion, and emotion is not a cause of the components. This contradicts the idea that only one component is responsible for emotion as suggested years earlier by James and others. While scientists generally agree that emotion is multicomponential, different scientific disciplines catorize the components differently. In psychology and philosophy, the components of emotion include subjective experience, psychophysiological expression, biological reactions, and mental states. Physiologists describe the components as physiological with cultural or emotional origins, expressive body actions, and individual appraisal of situations and contexts.
Areas of the brain that have been found to participate in development of emotions include the reticular formation, the limbic system, and the cerebral cortex. The reticular formation of cells within the brain stem receives and filters sensory information before passing it on to the limbic system and cortex. The limbic system includes the hypothalamus, which produces most of the peripheral responses to emotion through its control of the endocrine and autonomic nervous systems; the amygdala, which is associated with fear and aggressive behavior; the hippocampus; and parts of the thalamus. The frontal lobes of the cerebral cortex receive nerve impulses from the thalamus and actively contribute to the experience and expression of emotions. Recent research in neuroscience indicates the involvement of each of these brain areas in the experience and expression of emotions.
While the physiological changes associated with emotions are triggered by the brain, they are carried out by the endocrine and autonomic nervous systems, which produce hormones and neurotransmitters in response to stimuli. For example, in response to confronting danger, the brain signals the pituitary gland to release a hormone called ACTH, which in turn causes the adrenal glands to secrete cortisol. Cortisol is the anxiety hormone (adrenalin) that triggers what is known as the fight-or-flight response. In response to danger or fear, fight or flight is a combination of physical changes that prepare the body for action. The heart beats faster, respiration is more rapid, the liver releases glucose into the bloodstream to supply added energy, fuels are mobilized from the body's stored fat, and the body generally goes into a state of high arousal. The pupils dilate, and perspiration increases while secretion of saliva and mucous decreases, hairs in follicles of the skin become erect, causing“goosepimples,” and the digestive system slows down as blood is diverted to the brain and skeletal muscles. These changes are carried out with the aid of the sympathetic nervous system, one of two divisions of the autonomic nervous system. When the crisis is over, the parasympathetic nervous system, which conserves the body's energy and resources, returns body processes to their normal resting state.
Emotional arousal in ordinary daily life may have beneficial or disruptive effects, depending on the situation and the intensity of the emotion. Arousal of the central nervous system through emotions may increase an individual's energy and efficiency, while intense emotions, whether positive or negative, may interfere with individual performance because central nervous system responses are channeled in too many directions at once. The effects of arousal on performance also depend on the difficulty of the task at hand; emotions interfere less with simple tasks than with more complicated ones.
Research on emotions is ongoing in many fields of study, including psychology, neuroscience, endocrinology, sociology, and computer science. New theories are still attempting to explain the origin of emotion, including the invesigation of materials and events that stimulate or elicit emotions and related behavior. Imaging techniques such as positron emission tomography (PET scans) and magnetic resonance imagine (MRI) are being used to study processes in the brain that are associated with emotion.
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