c? ON HIGHER BRAIN AREAS
HYPOTHALAMUS
AMYGDALA
RESPONSE DEPENDENT ON PAG BUT NOT THE AMYGDALA RESPONSE DEPENDENT ONTHE PAG AND HYPOTHALAMUS
Figure 1 0.4. Hierarchical control of RAGE in the brain. Lesions of higher areas do not diminish responses from lower areas, while damage of lower areas compromises the functions of higher ones.
subtle refinements to the orchestration that is elaborated in the PAG of the mesencephalon. For instance, various irritating perceptions probably get transmitted into the system via thalamic and cortical inputs to the medial amygdala, while more basic physiological "irritations,"
such as hunger and basic hormonal/sexual int1uences, eriter the system via medial preoptic and hypothalamic inputs.
Since the primary evolved function of anger is to motivate individuals to compete effectively for environ*
mental resources, we would anticipate that reciprocal relations would exist between the SEEKING and RAGE systems (see Figures 3.5 and 1 0 . 1 ). Indeed, as men�
tioned earlier, animals are less likely to bite during "re�
warding" lateral hypothalamic stimulation, but they tend to bite more at the offset of such stimulation. In addition, frustration, a major precipitant of anger, seems to be elaborated largely within frontal cortical areas, where neurons register conditional stimuli that predict forthcoming rewards.46 These neurons can track reward
relevant stimuli, so that when CS+ and CS- (i.e., the conditional stimuli predicting reward presence or ab�
sence) are reversed, the neurons reverse their firing patterns to follow the new reward relationships. Neu
rons within the temporal lobes, which also exhibit similar initial discrimination of conditional reward associations, do not readily exhibit response patterning reversals when the valences of the conditional stimuli are reversedY It is not clear which type of brain tissue is more important for the generation of frustration, but presumably frustration emerges from the ability of such cognitive systems to monitor the probability of forth�
coming rewards. If an expected reward is not registered, the higher cell assemblies send out opponent process
REWARD EVALUATION
messages that invigorate activity within the RAGE sys
tem. Does the relevant neuroanatomy support such a scenario?
Detailed maps have now been constructed of the brain interconnectivites of the executive system for RAGE which ultimately terminate in the PAG. Both the retrograde and anterograde maps of these brain sites yield a provocative set of connections.48 PAG sites that support rage behaviors receive inputs primarily from six areas of the brain (Figure 10.5), including several areas of the cortex, the medial hypothalamus, and sev�
eral zones of the lower brain stem. The six major areas, with their potential psychobehavioral functions are as follows: ( 1 ) The highest brain areas sending direct information to the PAG emerge from the frontal cor
tex-primarily from medial areas that contain reward�
relevance neurons, as well as from a more lateral area called the frontal eye fields, which help direct eye movements to especially prominent objects in the en�
vironment. It seems appropriate that the basic anger circuits receive information from brain systems that regulate these important integrative areas. (2) Another set of inputs comes from the orbitoinsular cortex, es
pecially the insular area, where a multitude of senses converge, especially ones related to pain and perhaps hearing. These areas presumably code the affective content of certain irritations, including vocalizations, and may give specific sounds direct access to · RAGE circuitry, For instance, it is not an uncommon human experience that an angry tone of voice directed at you activates your own anger in return. (3) Powerful inputs emerge from the medial hypothalamus. Not only is this brain area part of the trajectory of the anger system itself, but it also elaborates energy homeostasis (see
RETROGRADE & ANTEROGRADE CONNECTIVITIES OF RAGE SYSTEM
Figure 10.5. The anterograde and retrograde connectivities of mesencephalic RAGE sites in the cat brain. (Adapted from Bandler, 1988; see n. 4 1 .)
198 BASIC EMOTIONAL AND MOTIVATIONAL PROCESSES
Chapter 9) and sexual matters (see Chapter 12); thus it is an ideal area where those influences come to modify anger. For instance, both hunger and testosterone are capable of sensitizing the anger circuit, while satiety and estrogen are able to quell activity within this system.
Inputs from lower areas include ( 4) the vestibular com
plex, which may help enrage animals when their bodily orientation is disrupted; (5) amine cell groups such as the locus coeruleus and raphe, which are known to exert nonspecific modulatory control over all behaviors (see Chapter 6); and (6) the nucleus of the solitary tract, which collects visceral information via the vagus nerve and probably is important for apprising the anger sys
tems of the tone of peripheral autonomic processes such as heart rate and blood pressure. It is important to em
phasize that most of these connections are reciprocat
ing two-way avenues of interdependent control (i.e., they reflect reciprocating feedback mechanisms).
Indeed, it is known that some peripheral inputs can control the sensitivity of rage systems. For instance, increased activity in baroreceptors of the carotid arter
ies monitors levels of blood pressure and can facilitate the sensitivity of RAGE circuitry. When blood pressure goes up, the sensitivity of RAGE systems does, too.49 Probably the most important brain area for the actual integration of the overall anger response is in the PAG, an area that also sends reciprocal' efferent feedback to most of the systems mentioned previously. This reci
procity indicates that the RAGE system remains in
formed of its activities at all of the hierarchical levels of the basic control circuitry. This, of course, makes considerable adaptive sense.
Quiet-Biting Attack
As already indicated, the major brain areas that yield predatory aggression during ESB overlap remarkably with brain areas where self-stimulation is obtained, al
though quiet-biting attack has typically been studied in cats, while rats have been the species of choice for self
stimulation studies. If both self-stimulation and preda
tory attack actually emerge from a homologous basic brain function, it is understandable why cats are so rarely used in self-stimulation research. Cats do not acquire self-stimulation behavior as readily as rats, and when they do, they do not behave in a rapid, agitated way like rats. Presumably, this is because a eat's typi
cal food-aquisition strategy is stealthy hunting that re
quires considerable motor inhibition. Rats, on the other hand, acquire the behavior rapidly and behave energeti
cally, probably because their natural foraging style, which is accompanied by vigorous activity and object manipulation, fits nicely with vigorous lever pressing.
Conversely, it is much easier to obtain quiet-biting attack from cats than from rats, probably because rats normally harvest energy by searching and scavenging for their food rather than hunting. In one of the first
studies to map out aggression circuits in the rat brain, it proved remarkably difficult to demonstrate quiet
biting attack until subjects were preselected for the ten�
dency to exhibit predatory intent. 50 In other words, predatory attack could be obtained easily only in those individual animals that had a preexisting strong ten
dency to approach and vigorously investigate potential prey objects such as mice. In these animals, brain stimu
lation at lateral hypothalamic sites would eventually induce systematic pursuit and attack of available mice.st However, if mice were not available, the same animals would readily exhibit one of the other stimulus-bound behaviors, such as eating or drinking, that is typically evoked from the lateral hypothalamus (see Chapter 8), There was no reason to suppose that quiet-biting attack was aroused from different circuits than those alterna�
tive behaviors (even though the terminal behavioral component obviously requires some different circuitry in the brain stem and spinal cord for the differential patterning of the final behavioral output). In short, ESB
induced quiet-biting attack could be obtained readily only from those animals that already exhibited some predisposition to attack. Accordingly, it seems that quiet-biting attack is simply one behavioral product of the SEEKING system. Even though this behavior has been extensively studied within the context of aggres
sion, from the animal's point of view, there is no ap
parent anger involved in this food-seeking response.
Indeed, it has always been more reasonable to assume that the emotive pattern was, in fact, accompanied by positive affect, since cats, just like rats, readily exhibit feeding during low-intensity stimulation of those lat
eral hypothalamic sites where higher levels of stimula
tion provoke predatory attack. 52
Moreover, it should be noted that many of the per
ceptual sensitivity changes that have been obtained in stimulus-bound aggression studies on felines are re
stricted to quiet-biting atta�k rather than affective at
tack circuitry. For instance, during application of this kind of brain stimulation, the perioral regions of cats are sensitized, so that light touch along the lip line is more likely to evoke orientation and biting than it is without the brain stimulation (Figure I 0.6).53 The stron
ger the current, the broader the area of sensitization. A similar phenomenon is obtained in rats with lateral hy
pothalamic stimulation that sustains stimulus-bound appetitive behavior, 54 which further affirms the com
monality of these systems in the two species. In a simi
lar way, this type of stimulation sensitizes the skin of the eat's paws, so that mild touch is more likely to pro
voke a vigorous striking reflex. 55 Again, the more in
tense the stimulation, the broader the area of sensitiv
ity. In neurological terms, the more intense stimulation recruits more dermatomes along the forearm (i.e., der
rnatomes are skin zones served by the individual spi
nal sensory nerves).
Another fascinating aspect of brain stimulation is that it provokes a predatory temperament only on the
Figure 10.6. Animals stimulated in quiet-biting attack areas exhibit a clear sensitization of various sensory fields, especially that around the lip line and around the muzzle. The area of sensitization increases with increasing stimulation intensity.
Similar changes may occur at brain sites that produce affective attack, but that is not clear from the available literature.
side of the brain that is stimulated directly, and this is reflected in the sensitization of the corresponding visual fields. Specifically, ESB applied to the right side of the brain makes an animal exhibit predatory aggres
sion in its left visual field but not in the right (please note that information from the right visual field is trans
mitted to the left cerebral hemisphere because of the way the optic nerves cross in the optic chiasm). Conversely, stimulation of the left side of the brain leads to attack directed at target animals in the right visual field. In other words, lateral hypothalamic stimulation sensitizes sensory processing within the ipsilateral cerebral hemi
sphere, which sensitizes the animal's response to in
formation coming in through the contralateral sensory fields.56 Accordingly, a prey moving across one half of a subject animal's visual field will provoke attack, but when it reaches the opposite visual field, attack behav
ior ceases. 57 A similar unilateral sensitization of higher areas has been demonstrated for self-stimulation cir
cuitry in rats, 58 again reinforcing the relationship of that circuitry to predatory aggression. Comparable types of brain effects have yet to be demonstrated with electrode placements that generate affective rage, but they may well exist once studies are done.
lntermale Aggression and Dominance
In nearly all mammalian species, males fight more than females. In neural terms, this is the case because males possess more active aggression circuits, at least those types of aggression circuits that were evolutionarily designed to assure reproductive success. Females pos
sess the more precious reproductive resource (the egg and gestational abilities), so it has been left for males to compete for the sexual favors of females. Some have
NATURE RED IN TOOTH AND CLAW 199
even speculated that male assertiveness is a selection process driven by the female, whereby the most vigor
ous males within a breeding population are allowed preferential access to reproductive opportunities. 59 To put it bluntly, from the female' s point of view, a male that can trounce his rivals is more likely to be carrying competitive, winning genes.
In virtually all mammals, male sexuality requires an assertive attitude, so that male sexuality and aggressive
ness normally go together. Indeed, these tendencies are intertwined throughout the neuroaxis, and to the best of our limited knowledge, the circuitry for this type of aggression is located near, and probably interacts strongly with, both RAGE and SEEKING circuitries.
Our knowledge about the intermale aggression system remains preliminary, but the general neurogeography of the system is highlighted by the high density of tes
tosterone receptors running from the medial amygdala, through the preoptic, anterior hypothalamic area, and down into the PAG of the brain stem (which is really quite distinct from the trajectory of the RAGE system).
One can dissociate intermale social aggression from the other types in various ways, including the types of brain damage that affect them. For instance, many forms of brain damage (including lateral septum, nucleus ac
cumbens, medial hypothalamus, and raphe) intensify aggressive responses directed toward experimenters and prey objects but tend to reduce fighting between males.60 Thus, brain manipulations that appear to inten
sify anger and predatory aggression, such as ventrome
dial hypothalamic damage, do not necessarily intensify social aggression, suggesting that they are indepen
dently controlled in the brain.
An especially critical question from both philosophi
cal and empirical points of view is to what extent neu
rons "irritated" by testosterone in the service of sexual arousal (see Chapter 12) also participate in aggressive arousaL Are these extensively or only mildly overlap
ping systems? This question is actually more philo
sophical than practical because testosterone emanating from the testes would affect both systems simulta
neously. It would be of practical interest, however, to discover whether the systems are extensively indepen
dent and capable of independent modulation. If they are essentially a single system in the human brain, then the only hope for tempering the negative aspects of this neural dilemma would be through education-namely, cognitive specification as to what is acceptable and unacceptable behavior. Although we do not have an answer for humans, the question is partly answered for hamsters. Using cfos visualization of neural activity, it is known that many neurons in the amygdala that are aroused by aggressive encounters are also aroused by sexual activity. 61
Although there is no longer much dispute that, in most natural circumstances, males are more aggressive than females (with a few exceptions, such as spotted hyenas), the brain mechanisms for this difference have
only recently been revealed. Testosterone has power�
ful effects on the expression of several brain neuro
chemical system�. The most extensively studied is the neuropeptide arginine-vasopressin (A VP). There are extensive A VP-based systems in the brain; major nuclei are situated in the anterior hypothalamus, with projec
tions to the hippocampus, septal areas, and downward through the diencephalon, to the midbrain PAG (see Figure 6.7).62
Testosterone sustains the genetic expression of A VP in a large number of these circuits. Accordingly, males have more extensive vasopressinergic circuits than fe
males.63 When male rats are castrated, A VP is mark
edly reduced in approximately half of their vasopres
sinergic circuits. This is paralleled by a decline in both sexuality and aggressiveness.64 If one replaces testoster
one directly into the brain via microinjections into the appropriate hypothalamic tissues, these behavioral ten�
dencies return. Several experiments have now directly manipulated the A VP systems, revealing that elevating A VP levels by direct central administration increases intermale aggression in rats.65 In hamsters, centrally administered AVP markedly increases territorial mark
ing behavior, even in the absence of other males.66 If one places an A VP receptor antagonist into the brain, both of these behavioral tendencies are markedly re
duced.67 Thus, it would seem that A VP is certainly one factor that promotes intennale aggression; as we will see in Chapter 12, it is also a powerful factor in promot
ing male sexuality and the fonilation of social memo
ries. Thus, we can speculate that a molecule such as A VP that can facilitate intermale aggression may only do so because it increases a more generalized male ten
dency such as behavioral persistence-the relentless and single-minded pursuit of a goal. Clearly, we have much more to learn about this aggressive system in the brain that plays a key role in the elaboration of social dominance. At an affective level, we might expect that the initial motivation for intermale aggression is posi
tive, since both combatants readily enter the fray; it is only later, when frustration occurs and defeat is immi
nent, that more negative emotions begin to intervene.
There is a distinct possibility that brain systems that mediate social play (see Chapter 15) are highly interre
lated with intennale aggression systems, which would be another reason for seeking linkages to positive affect within intermale aggression circuits.
Although testosterone can clearly increase intermale aggression, we should also briefly consider how those processes relate to RAGE circuits. Although evidence is sparse, the present supposition is that they are largely independent but highly interactive systems. It is pos
sible that testosterone modulates activity in the RAGE system in a way quite comparable to its effects on the intermale aggression systems,68 but the evidence is not definitive. There is little reason to believe that testoster
one promotes anger independently of its effects on male assertiveness and the potential conflicts and problems
that can lead to. lntermale aggression is an ideal behav
ioral circumstance where anger could be evoked. Because of such interactions, we cannot be certain that testoster
one is directly sensitizing RAGE circuits. For instance, human studies have not provided unambiguous evidence that testosterone increases feelings of irritability. Indeed, some recent human work indicates that testosterone ad
ministration does not facilitate such feelings, and human males given·supplementary testosterone typically tend to feel better than those who received placebos.69
Learning and Aggression
As with any emotional system, a great deal of aggres
sive behavior is learned. Animals can be trained to be more aggressive or more passive. They can be trained to be winners or losersJ0 However, it is remarkable how the hormones that promote intermale aggression also provide feedback and reinforce the learning of status. One series of recent findings has shown that victory in a variety of forms leads to increased secretion oftestoster
one in male animals as well as humans. In humans, such vi�tories as the completion of law or medical school or military training increase plasma testosterone levels.71 Victo1y on the tennis court can have the same effect.72 To what extent these hormone changes help reinforce future assertive behavior remains to be evaluated, but it
one in male animals as well as humans. In humans, such vi�tories as the completion of law or medical school or military training increase plasma testosterone levels.71 Victo1y on the tennis court can have the same effect.72 To what extent these hormone changes help reinforce future assertive behavior remains to be evaluated, but it