Learning Objectives

The word emotion can mean several things. Most of the time, it refers to positive or negative feelings that are produced by particular situations. Emotions consist of patterns of physiological responses and species-typical behaviors. Most of us use the word emotion to refer to the feelings, not to the behaviors. It is behavior, that has consequences for survival and reproduction.

This chapter is divided into four major sections:

1. The patterns of behavioral and physiological responses that constitute emotions. The nature of the response patterns, their neural control, and the perception of situations that give rise to emotions; it includes a discussion of prefrontal lobotomy and other types of psychosurgery.
2. The communication of emotions-their expression and recognition
3. The nature of the feelings that accompany emotions.
4. The neural and hormonal control of aggressive and defensive behaviors.

An emotional response consists of three types of components: behavioral, autonomic, and hormonal. The behavioral component consists of muscular movements that are appropriate to the situation that elicits them. Autonomic responses facilitate the behaviors and provide quick mobilization of energy for vigorous movement. The activity of the sympathetic branch of the autonomic nervous system increases while that of the parasympathetic branch decreases. As a consequence, heart rate increases, and changes in the size of blood vessels shunt the circulation of blood away form the digestive organs toward the muscles. Hormonal responses reinforce the autonomic responses. The hormones secreted by the adrenal medulla-epinephrine and norepinephrine-further increase blood flow to the muscles and cause nutrients stored in the muscles to be converted into glucose. In addition, the adrenal cortex secretes steroid hormones, which also help to make glucose available to the muscles.

Special behaviors that serve to communicate emotional states to other animals, such as the threat gestures that precede an actual attack and the smiles and frowns used by humans. Negative emotions receive much more attention than positive ones. Most of the research on the physiology of emotions has been confined to fear and anxiety.

Stimulation of various parts of the brain can induce an animal to attack another one or can cause it to make vigorous attempts to escape. In other words, the stimulation can produce the behaviors associated with anger or fear. The overt behaviors, the autonomic responses, and the hormonal secretions associated with these emotional reactions are controlled by separate neural systems. The integration of these responses appears to be controlled by the amygdala.

Researchers in several different laboratories have shown that single neurons in various nuclei of the amygdala become active when emotionally relevant stimuli are presented. The amygdala is involved in the effects of pheromones on reproductive physiological and behavior.

The amygdala ( or more precisely, the amygdala complex) is located within the temporal lobes. It consists of several groups of nuclei, each with different inputs and outputs-and with different functions. The major parts of the amygdala are the medial nucleus, the lateral/basolateral nuclei, the central nucleus, and the basal nucleus.

The medial nucleus consists of several subnuclei that receive sensory input (including information about the presence of odors and pheromones from the main and accessory olfactory bulbs) and relay the information to the medial basal forebrain and to the hypothalamus.

The lateral/basolateral nuclei receive sensory information from the primary sensory cortex, association cortex, thalamus, and hippocampal formation. Theses nuclei project to the ventral striatum ( a region involved in the effects of reinforcing stimuli on learning) and to the dorsomedial nucleus of the thalamus, whose projection region is the prefrontal cortex. They also provide sensory input to the central nucleus, which is the part to the amygdala that will most concern us.

The central nucleus projects to regions of the hypothalamus, midbrain, pons, and medulla that are responsible for the expression of the various components of emotional responses.

The basal nucleus consists of several subnuclei that, like the central nucleus, receive sensory input form the lateral and basolateral nuclei and relay information to other amygdala nuclei and to the periaqueductal gray matter of the midbrain.

The central nucleus of the amygdala is the single most important part of the brain for the expression of emotional responses provoked by aversive stimuli. When threatening stimuli are presented, both the neural activity of the central nucleus and the production of Fos protein increase. Damage to the central nucleus (or to the lateral/basolateral nuclei, which provide it with sensory information) reduces or abolishes a wide range of emotional behaviors and physiological responses. After the central nucleus id destroyed, animals no longer show signs of fear when confronted with stimuli that have been paired with aversive events. The animals blood levels of stress hormones are lower. In contrast, when the central amygdala is stimulated by means of electricity or by an injection of an excitatory amino acid, the animal shows physiological and behavioral signs of fear and agitation, and long –term stimulation of the central nucleus produces stress-induced illnesses such as gastric ulcers. These observations suggest that the autonomic and endocrine responses controlled by the central nucleus are among those responsible for the harmful effects of long-term stress.

The central amygdala is particularly important for aversive emotional learning. A few stimuli automatically produce fear reactions-for example, loud unexpected noises, the approach of large animals, heights, or (for some species) specific sounds or odors. Even more important, however, is the fact that we can learn that a particular situation is dangerous or threatening.

A conditioned emotional response is produced by a neutral stimulus that has been paired with an emotion-producing stimulus.

Briefly, classical conditioning occurs when a neutral stimulus is regularly followed by a stimulus that automatically evokes a response.

If an organism learns to make a specific response that avoids contact with the aversive stimulus (or at least minimizes its painful effect), most of the nonspecific "emotional" responses will eventually disappear. If the organism learns a successful coping response- a response that terminates, avoids, or minimizes an aversive stimulus-the emotional responses will no longer occur.

Behavioral arrest- a species-typical defensive response called freezing.

They found that lesions of the lateral hypothalamus interfered with the change in blood pressure, whereas lesions of the periaqueductal gray matter interfered with the freezing response. Thus, two different mechanisms, both under the control of the central nucleus of the amygdala, are responsible for the autonomic and behavioral components of conditioned emotional responses.

Some of the effects of anxiolytic (anxiety-reducing) drugs appear to be produced through the central nucleus. The amygdala contains a high concentration of benzodiazepine receptors- especially the basolateral nucleus, which projects to the central nucleus-and the central nucleus itself contains a high concentration of opiate receptors. The infusion of either opiates or benzodiazepine tranquilizers into the amygdala decreases both the learning and the expression of conditioned emotional responses (Kapp et al., 1982; Davis, 1992a). In addition , Sanders and Shekhar found that an injection of a benzodiazepine antagonist into the basolateral nucleus blocked the anxiolytic effects of an intraperitoneal injection of chlorodiazepoxide(Librium). Thus, tranquilizers appear to exert their anxiolytic effect in the basolateral amygdala. Even after their amygdala is destroyed, benzodiazepines still have some anxiolytic effect.

Some investigators have suggested that anxiety disorders are caused by hyperactivity of the central nucleus of the amygdala, perhaps as a result of increased secretion of endogenous anxiety-producing ligands for the GABA receptor, of which the benzodiazepine receptor is a part. Whether the primary cause of the increased anxiety lies within thesecircuits or elsewhere in the brain (or in people’s environments and past histories) has yet to be determined.

The amygdala is involved in behaviors associated with another negative emotion-disgust. When an animal becomes nauseated as a result of eating tainted food the animal develops an aversion to the flavor of the last thing it ate or drank before the nausea. This form of learning is abolished by lesions of the basolateral amygdala.

A considerable amount of evidence indicates that the amygdala is involved in emotional responses in humans. These studies found that stimulation of parts of the brain produced autonomic responses that are often associated with fear and anxiety but that only when the amygdala was stimulated did people also report that they actually felt afraid (White, 1940; Halgren et al., 1978; Gloor et al., 1982).

Lesions of the amygdala decrease people’s emotional responses. People with lesions of the amygdala showed impaired acquisition of a conditioned emotional response, just as rats do. Startle response of a man with a localized lesion of the right amygdala was not increased by the presence of an unpleasant emotion.

Damage to the amygdala interferes with the effects of emotions on memory. Normally, when people encounter events that produce a strong emotional response, they are more likely to remember these events. A patient with amygdala damage showed no such increase in memory.

Several imaging studies have shown that the human amygdala participates in emotional responses. The activity of the right amygdala increased while the subjects recalled the neutral ones. When well motivated people work on such tasks, they tend to become tense and unhappy and usually report feelings of frustration. A PET scanner showed that the blood flow in the amygdala increased while the subjects were working on the unsolvable anagrams but now when working on the solvable ones.

The analysis of social situations involves much more than sensory analysis; it involves experiences and memories, inferences and judgments. But one region of the brain-the orbitofrontal cortex-plays a special role.

The orbitofrontal cortex is located at the base of the frontal lobes. It covers the part of the brain just above the orbits-the bones that form the eye sockets-hence the term orbitofrontal. The orbitofrontal cortex receives direct inputs from the dorsomedial thalamus, temporal cortex, ventral tegmental area, olfactory system, and amygdala. Its outputs go to several brain regions, including the Cingulate cortex, hippocampal formation, temporal cortex, lateral hypothalamus, and amygdala. Finally, it communicates with other regions of the frontal cortex. Thus, its inputs provide it with information about what is happening in the environment and what plans are being made by the rest of the frontal lobes, and its outputs permit it to affect a variety of behaviors and physiological responses, including emotional responses organized by the amygdala.

The fact that the orbitofrontal cortex plays an important role in emotional behavior is shown by the effects of damage to this region. Before Phineas Gage’s injury he was serious, industrious, and energetic. Afterward, he became childish, irresponsible, and thoughtless of others. He was unable to make or carry out plans, and his actions appeared to be capricious and whimsical. His accident largely destroyed the orbitofrontal cortex (Damasio et al ., 1994).

In general, damage to the orbitofrontal cortex reduced people’s inhibitions and self-concern; they became indifferent to the consequences or their actions. In addition, although they remained sensitive to noxious stimuli, the pain no longer bothered them-it no longer produced an emotional reaction.

Radical removal of the frontal loves in a human patient (performed because of a tumor) did not appear to produce intellectual impairment-thus, people could presumably get along without their frontal lobes. These two reports suggested to Moniz that "if frontal-love removal…eliminates frustrational behavior, why would it not be feasible to relieve anxiety states in man by surgical means?" in fact, Moniz persuaded a neurosurgeon to do so, and approximately one hundred operations were eventually performed under his supervision. (In 1949 Moniz received the Nobel Prize for the development of this procedure.)

Since that time, tens of thousands of people have received prefrontal lobotomies, primarily to reduce symptoms of emotional distress, and many of these people are still alive. Although patients did perform well on standard tests of intellectual ability, they showed serious changes in personality, becoming irresponsible and childish. They also lost the ability to carry out plans, and most were unemployable. And although pathological emotional reactions were eliminated, so were normal ones. Because of these findings, and because of the discovery of drugs and therapeutic methods that relieve the patients symptoms without producing such drastic side effects, neurosurgeons eventually abandoned the prefrontal lobotomy procedure (Valenstein, 1986).

A transorbital leucotome, shaped like an ice pick, was introduced into the brain by passing it beneath the upper eyelid until the point reached the orbital bone above the eye. The instrument was hit with a mallet, driving it through the bone into the brain. The end was then swept back and forth so that it cut through the white matter.

The fact that it was so easy and left no external signs other than a pair of black eyes may have tempted its practitioners to perform it too casually.

But the fact remains that the surgery did reduce people’s emotional suffering, or it would never have become so popular. Primarily, the surgery reduced anxiety, observations, and compulsions. People’s groundless fears disappeared, and they no longer felt compelled to perform rituals to ward off some (imaginary) disastrous events.

Some procedures approached the frontal lobes from the base of the brain, primarily cumin their connections with the diencephalon and temporal lobes. Other procedure approached the frontal lobes form above and disconnected the orbitofrontal cortex from the Cingulate gyrus. In either case the patients’ emotional distress was usually reduced.

What, exactly, does the orbitofrontal cortex do? One possibility is that it is involved in assessing the personal consequences of what is currently happening. People whose orbitofrontal cortex has been damaged by disease or accident are still able to accurately assess the significance of particular situations, but only in a theoretical sense. For example, Eslinger became unable to distinguish between trivial decisions and important ones, spending hours trying to decide where to have dinner but failing to use good judgment in situations that concerned his occupation and family life. Thus, it appears that the orbitofrontal cortex is not directly involved in making judgments and conclusion about events but has a role in translating these judgments not appropriate feelings and behaviors.

The word emotion refers to behaviors, physiological responses, and feelings. This section has discussed emotional response patterns, which consist of behaviors that deal with particular situations and physiological responses (both autonomic and hormonal) that support the behaviors. The amygdala organizes behavioral, autonomic, and hormonal responses to a variety of situations, including those that produce fear, anger, or disgust. In addition, it is involved in the effects of odors and pheromones on sexual and maternal behavior. It receives inputs from the ol-factory system, the association cortex of the temporal lobe, the frontal cortex, and the rest of the limbic system. Its outputs go to the frontal cortex, hypothalamus, hippocampal formation, and brain stem nuclei that control autonomic functions and some species-typical behaviors. Damage to specific brain regions that receive these outputs will abolish particular components of emotional response patterns. Electrical recordings of single neurons in the amygdala indicate that some of them respond when the animal perceives particular stimuli with emotional significance. Stimulation of the amygdala leads to emotional responses, and it destruction disrupts them. Receptors in the amygdala are largely responsible for the anxiolytic effects of the benzodiaaepine tranquilizers and the opiates. Studies of people with amygdala lesions and PET and functional MRI studies with humans indicate that the amygdala is involved in emotional reactions in our species, too.

The orbitofrontal cortex plays an important role in emotional reactions. People with orbitofrontal lesions are able to explain the implications of complex social situations but are unable to respond appropriately when these situations concern them. Thus, this region does not appear to be necessary for making judgments about the personal significance of social situations, but it does appear to be necessary for transpersonal significance of social situations, but it does appear to be necessary for translating these judgments into actions and emotional responses. The orbitofrontal cortex, receives information from other regions of the frontal lobes, from the temporal pole, and form the amygdala and other parts of the limbic system via the mediodorsal nucleus of the thalamus. It produces emotional reactions through its connections with the amygdala and the cingulate gyrus.

Between the late 1930’s and the late 1950’s many

people received prefrontal lobotomies, which involved cutting the white matter in the ventromedial frontal lobes. Although the operations affected many parts of the frontal lobes the most important region was probably the orbitofrontal cortex. The surgery did often relieve emotional anguish and the suffering caused by pain, but it also mad people become largely indifferent to the social consequences of their own behavior and to the feelings of others, and it interfered with their ability to make and execute plans. Prefrontal lobotomies are not longer performed.

Charles Darwin (1872/1965) suggested that human expressions of emotion have evolved form similar expressions in other animals. He said that emotional expressions are innate, unlearned responses consisting of a complex set of movements, principally of the facial muscles. Thus, a human’s sneer and a wolf’s snarl are biologically determined response patterns, both controlled by innate brain mechanisms, just as coughing and sneezing are.

No matter how isolated people are, they show the same facial expressions of emotion, then these expressions must be inherited instead of learned.

Because the same facial expressions were used by people who had not previously been exposed to each other, Ekman and Friesen concluded that the expressions were unlearned behavior patterns. In contrast, different cultures use different words to express particular concepts; production of these words dos not involve innate responses but must be learned.

Thus, both the cross-cultural studies and the investigations with blind children confirm the naturalness of these expressions. Researchers have not yet determined whether other means of communicating emotions, such as tone of voice or changes in body posture, are learned or are at least partly innate.

• Effective communication is a two-way process. That is, the ability to display one’s emotional state by changes in expression is useful only if other people are able to recognize them. They found that happy situations (such as making a strike while bowling, seeing the home team score, or experiencing a beautiful day) produced only small signs of happiness when the people were alone. However, when the people were interacting socially with other people, they were much more likely to smile.
• We recognize other people’s feelings by means of vision and audition-seeing their facial expressions and hearing their tone of voice and choice of words. Many studies have found that the right hemisphere plays a more important role than the left hemisphere in comprehension of emotion. For example, many investigators have found a left-ear and a left-visual-field advantage in recognition of emotionally related stimuli.
• In studies of hemispherical differences in visual recognition, stimuli are usually presented to the left or right visual field so rapidly that the subject does not have time to move his or her eyes. Many studies have shown that the left hemisphere is better than the right at recognizing words or letter strings but that the right hemisphere is better at detecting differences in facial expressions of emotion. These results suggest that when a message is heard, the right hemisphere assesses the emotional expression of the voice while the left hemisphere assesses the meaning of the words.
• Patients with right hemisphere damage had difficulty producing or describing mental images of facial expressions of emotions.
• Subjects’ regional cerebral blood flow with the PET scanner while they listed to some sentences and identified their emotional content. The investigators found that comprehension of emotion from word meaning increased the activity of both frontal lobes, the left more than the right.
• Observations of people with brain damage are consistent with the studies with normal subjects. Patients with right hemisphere damage judged the emotion being expressed less accurately.
• Damage to the visual association cortex can cause prosopagnosia- inability to recognize particular faces. Just as recognition of the meaning of words and the emotion expressed by tone of voice are accomplished by different brain functions, so are recognition of particular faces and facial expressions of emotions.
• The amygdala plays a special role in emotional responses. It may play a role in emotional recognition as well. Several studies have found that lesions of the amygdala (the result of degenerative diseases or surgery for sever seizure disorders) impairs people’s ability to recognize facial expressions of emotion- especially expressions of fear report the case of a woman with bilateral amygdala lesions who had normal hearing but had difficulty recognizing emotions-particularly fear and anger- expressed in a person’s tone of voice.

• That genuinely happy smiles, in contrast to false smiles or smiles people make when they greet someone else, involve contraction of a muscle near the eyes, the lateral part of the orbicularis oculi-now sometimes referred to as Duchenne’s muscle.
• Volitional facial paresis, is caused by damage to the face region of the primary motor cortex or to the fibers connecting this region with the motor nucleus of the facial nerve. The interesting thing about volitional facial paresis is that the patient cannot voluntarily move the facial muscles but will express a genuine emotion with those muscles.
• In contrast, emotional facial paresis is caused by damage to the insular region of the prefrontal cortex, to the white matter of the frontal lobe, or to parts of the thalamus.
• Volitional facial paresis. Difficulty in moving the facial muscles voluntarily; caused by damage to the face region of the primary motor cortex or its subcortical connections.
• Emotional facial paresis. Lack of movement of facial muscles in response to emotions in people who have no difficulty moving these muscles voluntarily; caused by damage to the insular prefrontal cortex, subcortical while matter of the frontal lobe, or parts of the thalamus.
• People with this disorder can move their face muscles voluntarily but do not express emotions on the affected side of the face. These two syndromes clearly indicate that different brain mechanisms are responsible for voluntary movements of the facial muscles and automatic, involuntary expression of emotions involving the same muscles.
• The right hemisphere plays a more significant role in recognizing emotions in the voice or facial expressions of other people- especially negative emotions. They found that the left halves were more expressive than the right ones. Because motor control is contralateral, the results suggest that the right hemisphere is more expressive than the left.
• The left side of their faces appeared to make stronger expressions of emotions. They confirmed these results in the laboratory by analyzing videotapes of people telling sad or humorous stories.
• Rhesus monkeys, like humans, express emotions more strongly in the left sides of their faces
• Left hemisphere lesions do not usually impair vocal expressions of emotion. For example, people with Wernicke’s aphasia usually modulate their voice according to mood, even though the words they say make no sense. In contrast, right-hemisphere lesions do impair expression of emotion, both facially and by tone of voice.
• Interesting information about hemispherical specialization in the expression of emotion has been obtained during the Wada test. The Wada test (named after its developer) is performed before a person receives surgery for removal of a seizure focus. Ross, Homan, and Buck (1994) asked people who were about to be evaluated for seizure surgery about experiences they had had that caused an intense emotion. The subjects narrated their experiences and described their feelings at the time. Then, while the right hemisphere was anesthetized with a fast-acting barbiturate injected into the right carotid artery, the subjects were asked about these experiences again. This time, most of the subjects described less intense emotions. For example, one subject described an accident in which he had wrecked his car. Before the injection, he said, "I was scared, scared to death. I could have run off the road and killed myself or someone else….. I was really scared." During the right hemisphere anesthesia he said that after the accident he felt "silly…. silly." Another patient described an accident with a truck as the scariest situation he had ever experienced. While his right hemisphere was anesthetized, he said he was "sort of scared" but denied that the accident was the scariest event in his life. Another patient said he was very angry when he learned that his wife was having an affair and threw a phone across the room. During the anesthesia he said that he had become "a little angry" and "kind’s tossed the phone."
• Colleagues suggest that the right hemisphere play a role in what the call primary emotions, most of which are negative. The left hemisphere, they believe, is involved in modulating emotional displays controlled by the right hemisphere and organizing social displays of positive emotions, such as the quick smile we flash when we meet someone we know. Unfortunately, it is not possible to query people about their emotional responses while the left hemisphere is anesthetized, because the anesthesia of the speech mechanisms in the left hemisphere prevents them from speaking or understanding the speech of other people.
• Wada test. A test often performed before brain surgery; verifies the functions of one hemisphere by testing patients while the other hemisphere is anesthetized.

• We (and members of other species) communicate our emotions primarily through facial gestures. Darwin believed that such expressions of emotion were innate- that these muscular movements were inherited behavioral patterns. Ekman and his colleagues performed cross-cultural studies with members of an isolated tribe in New Guinea. Their results supported Darwin’s hypothesis.
• Recognition of other people’s emotional expressions involves the right hemisphere more than the left. Studies with normal people have shown that people can judge facial expressions or tone of voice better when the information is presented to the right hemisphere than when it is presented to the left hemisphere. PET scans made while people judge the emotions of voices show that such judgements activate the right hemisphere more than the left. Studies of people with left or right hemisphere brain damage corroborate these findings. In addition, they show that recognition of particular faces involves neural circuits different from those needed to recognize facial expressions of emotions. Finally, the amygdala plays a role in recognition in emotions; lesions of the amygdala disrupt this ability, and PET scans show increased activity of the amygdala while engaging in this task.
• Facial expressions of emotions (and other stereotypical behaviors such as laughing and crying) are almost impossible to stimulate. For example, only, a genuine smile of pleasure causes the contraction of the lateral part of the orbicularis oculi (Duchenne’s muscle). Genuine expressions of emotion are controlled by special neural circuits. The best evidence for this assertion comes from the complementary syndromes of emotional and volitional facial paresis. People with emotional facial paresis can move their facial muscles voluntarily but nut in response to an emotion, whereas people with volitional facial paresis show the opposite symptoms. In addition, the left halves of people’s faces- and the faces of monkeys- tend to be more expressive than the right halves. While the right hemisphere is anesthetized during the Wada test, the emotional feelings that accompany people’s recollection of memories generally become less intense.

• So far, we have examined two aspects of emotions: the organization of patterns of responses that deal with the situation that provokes the emotion, and the communication of emotional states with other members of the species. The final aspect of emotion to be examined, the subjective component: feelings of emotion.

• William James (1842-1910), an American psychologist, and Carl Lange (1834-1900), a Danish psychologist, independently suggested similar explanations for emotion, which most people refer to collectively as the James-Lange Theory. Basically, the theory states that emotion-producing situations elicit an appropriate set of physiological responses, such as trembling, sweating, and increased heart rate. The situations also elicit behaviors, such as clenching of the fists or fighting. The brain receives sensory feedback from the muscles and from the organs that produce these responses; it is this feedback that constitutes our feeling of emotion.
• James-Lange theory. A theory of emotion that suggests that behaviors and physiological responses are directly elicited by situations and that feelings of emotions are produced by feedback from these behaviors and responses.
• James says that our own emotional feelings are based on what we find ourselves doing and on the sensory feedback we receive from the activity of our muscles and internal organs. Thus, when we find ourselves trembling and fell queasy, we experience fear.
• James’s description of the process of emotion might strike you as being at odds with your own experience. Many people think that they experience emotions directly, internally. Or did you ever find tears coming to your eyes while watching a film that you did not think was affecting you?
• A well-known physiologist, Walter Cannon, criticized James’s theory. He said that the internal organs were relatively insensitive and that they could not respond very quickly, so feedback form them could not account for our feelings of emotions. He observed that cutting the nerves that provide feedback from the internal organs to the brain did not alter emotional behavior.

• Cannon cited the fact that cutting the sensory nerves between the internal organs and the central nervous system does not abolish emotional behavior in laboratory animals. However, this observation misses the point.
• James’s theory is difficult to verify experimentally because it attempts to explain feelings of emotion. Some anecdotal evidence supports the theory. The man-a music lover-reported that the shivering sensation he felt while listening to music now occurred only on the unoperated side of his body. He still enjoyed listening to music, but the surgery altered his emotional reaction.
• In one of the few tests of James’s theory, Hohman (1966) collected data from people with spinal cord damage. He asked people about the intensity of their emotional feelings. If feedback is important, one would expect that emotional feelings would be less intense if the injury were high (that is, close to the brain) than if it were low, because a high spinal cord injury would make the person become insensitive to a larger part of the body.

• From the earliest times, people recognized that emotions were accompanied by feelings that seemed to come from inside the body, which probably provided the impetus for developing physiological theories of emotion. James and Lange suggested that emotions were primarily responses to situations. Feedback from the physiological and behavioral reactions to emotion-producing situations gave rise to the feelings of emotion; thus, feeling are the results, not the causes, of emotional reactions. Hohman’s study of people with spinal cord damage supported the James-Lange theory; people who could no longer feel the reactions from most of their body reported that they no longer experienced intense emotional states.

• Almost all species of animals engage in aggressive behaviors, which involve threatening gestures or actual attack directed toward another animal. Aggressive behaviors are species-typical; that is, the patterns of movements (for example, posturing, biting, striking, and hissing) are organized by neural circuits whose developmental is largely programmed by animal’s genes. Many aggressive behaviors are related to reproduction. For example, aggressive behaviors that gain access to mates, defend territory needed to attract mates or to provide a site for building a nest, or defend offspring against intruders can all be regarded as reproductive behaviors. Other aggressive behaviors are related to self-defense, such as that of an animal threatened by a predator.
• Aggressive attacks can consist of actual attacks, or they may simply involve threat behaviors, which consist of postures or gestures that warn the adversary to leave or it will become the target of an attack. The threatened animal might show defensive behaviors-threat behaviors or an actual attack against the animal threatening it-or it might show submissive behaviors-behaviors that indicate that it accepts defeat and will not challenge the other animal. In the natural environment most animals display far more threats than actual attacks. Threat behaviors are useful in reinforcing social hierarchies in organized groups of animals or in warning intruders away from an animal’s territory. They have the advantage of not involving actual fighting, which can harm one or both of the combatants.
• Predation is the attack of a member of one species on that of another, usually because the latter serves as food for the former. While engaged in attacking a member of the same species or defending oneself against attack, an animal appears to be extremely aroused and excited, and the activity of the sympathetic branch of its autonomic nervous system is high. In contrast, the attack of a predator is much more "cold-blooded"; it is generally efficient and not accompanied by a high level of sympathetic activation.

• The neural control of aggressive behavior is hierarchical.
• Predation is not accompanied by a strong display of rage.
• Although a cat looks excited when it pounces on a rat and bites it, it does not show signs of "rage." The attack appears cold-blooded and ruthless.
• Defensive behavior A species-typical behavior by which an animal defends itself against the threat of another animal.
• Threat behavior A stereotypical species-typical behavior that warns another animal that it may be attacked if it does not flee or show a submissive behavior.
• Submissive behavior A stereotyped behavior shown by an animal in response to threat behavior by another animal; serves to prevent an attack.
• Predation Attack of one animal directed at an individual of another species on which the attacking animal normally preys.
• Panksepp observed a significant difference in rats’ preference for receiving electrical brain stimulation that elicits predatory attack or defensive attack. If he turned on the stimulation that produced defensive attack but permitted the rats to press a lever to turn it off quickly learned to do so. Thus, brain stimulation that elicits defensive attack appears to be aversive. In contrast, rats quickly learned to press a lever that turned on stimulation that elicited predatory attack.
• Defensive behavior and Predation can be elicited by stimulation of different parts of the PAG and that the hypothalamus and the amygdala influence these behaviors through excitatory and inhibitory connections with the PAG. They found that the three principal regions of the amygdala and two regions of the hypothalamus affect defensive rage and Predation, both of which appear to be organized by the PAG.
• Brain regions other than the amygdala, hypothalamus, and periaqueductal gray matter are involved in aggressive behavior. In general, increased activity of serotonergic synapses inhibits aggression. For this reason some clinicians have used serotonergic drugs to treat violent behavior in humans. Destruction of serotonergic axons in the forebrain facilitates aggressive attack, presumably by removing an inhibitory effect. (Vergnes et al., 1988).
• A group of researchers has studied the relation between serotonergic activity and aggressiveness in a free-ranging colony of rhesus monkeys. They assessed serotonergic activity by capturing the monkeys and removing a sample of cerebrospinal fluid and analyzing it for 5-HIAA, a metabolite of serotonin (5-HYT).
• The investigators found that young male monkeys with the lowest levels of 5-HIAA showed a pattern of risk-taking behavior, including high levels of aggression directed toward animals that were older and much larger than themselves. They were much more likely to take dangerous, unprovoked long leaps from tree to tree at a height of more than 7m (27.6ft.). they were also more likely to pick fights that they could not possibly win. Of 49 preadolescent male monkeys that the investigators followed for four years, 46 percent of those with the lowest 5-HIAA levels died, while all of the monkeys with the highest levels survived. Most of the monkeys were killed by other monkeys. In fact, the first monkey to be killed had the lowest level of 5-HIAA and was seen attacking two mature males the night before it death.
• It is clear that serotonin does no simply inhibit aggression; rather, it exerts a controlling influence on risky behavior, which includes aggression.
• The monkeys who received the serotonin agonist became dominant, while the status of those who received the antagonist declined.
• The monkeys with low levels of serotonergic activity showed the lowest levels of social competency.
• Several studies have found that serotonergic neurons play an inhibitory role in human aggression.
• A history of aggressiveness in psychological test scores indicating antisocial tendencies was related to low levels of CSF 5-HIAA in a group of naval recruits.
• They found that the men with the lowest serotonergic activity were more likely to have close relatives with a history of similar behavior problems.

• As we saw, many instances of aggressive behavior are in some way related to reproduction. For example, males of some species establish territories that attract females during the breeding season. To do so, they must defend them against the intrusion of other males. Even in species in which breeding does not depend on the establishment of a territory, males may compete for access to females, which also involves aggressive behavior. Females, too, often compete with other females for space in which to build nests or dens in which to rear their offspring.
• Many forms of aggressive behavior are, like mating, affected by hormones.

• Adult males of many species fight for territory or access to females. In laboratory rodents, androgen secretion occurs prenatally, decrease, and then increases again at the time of puberty. Intermale aggressiveness also begins around the time of puberty, which suggests that the behavior is controlled by neural circuits that are stimulated by androgens. Indeed, many years ago, Beeman (1947) found that castration reduced aggressiveness and that injections of testosterone reinstated it.
• The secretion of androgens early in development modifies the developing brain, making neural circuits that control male sexual behavior become more responsive to testosterone. Similarly, early androgenization has an organizational effect that stimulates the development of testosterone-sensitive neural circuits that facilitate Intermale aggression.