Emotion is complex, and the term has no single universally accepted definition. Emotion is, however, closely related to motivation and can sometimes provide motivation (as, for example, a student's fear of failing provides motivation for studying). Psychologists do agree that emotions are reaction patterns that include
Theorists differ on the order of appearance of the reaction patterns.
The autonomic nervous system. The autonomic nervous system (ANS) has two components, the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). When activated, the SNS prepares the body for emergency actions; it controls glands of the neuroendocrine system (thyroid, pituitary, and adrenal glands). Activation of the SNS causes the production of epinephrine (adrenaline) from the adrenal glands, increased blood flow to the muscles, increased heart rate, and other readiness reactions. Conversely, the PNS functions when the body is relaxed or at rest and helps the body store energy for future use. PNS effects include increased stomach activity and decreased blood flow to the muscles.
The reticular activating system. The reticular activating system (RAS) is a network of neurons that runs through the core of the hind‐brain and into the midbrain and forebrain. It has been demonstrated that electrical stimulation of the RAS causes changes in the electrical activity of the cortex (as measured by an electroencephalogram) that are indistinguishable from changes in electrical activity seen when external stimuli (such as loud sounds) are present. The RAS is believed to first arouse the cortex and then to stimulate its wakefulness so that it may more effectively interpret sensory information.
The limbic system. The limbic system includes the anterior thalamus, the amygdala, the septal area, the hippocampus, the cingulate gyrus, and structures that are parts of the hypothalamus (Figure ). The word limbic means “border” and describes this system because its structures seem to form a rough border along the inner edge of the cerebrum. Studies have associated the limbic system with such emotions as fear and aggression as well with as drives, including those for food and sex.
The Limbic System
Lie detectors (polygraphs). Lie detectors, or polygraphs, rely upon the physiological arousal of the emotions. Concomitant measurements are taken of the heart rate, blood pressure, respiration rate, and galvanic skin response (GSR). (The GSR is a measure of the skin's electrical conductivity, which changes as the sweat glands increase their activity.) Polygraph recordings are used to see if a person is not telling the truth (lying), which usually creates emotional arousal. Because of polygraphs' high error rates, however, their findings are generally not accepted as evidence in the courts.