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Human aggression - introduction
Pages 3 - 4
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- 7 - 8
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Evolution of aggression - introduction
Pages 9 - 10
- 11 - 12
- 13 - 14
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Brain mechanisms of aggression - introduction
Pages 15 - 16 -
17 - 18 -
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Dynamics of aggression - introduction Pages 21 - 22 - 23
When I began work on aggressive behavior, it was my hypothesis that the study of the brain mechanisms of aggression would make possible a more secure understanding of the evolution of aggression and a more secure classification of aggression in both animals and humans. The previous two sections of this book are offered as evidence that the hypothesis has been confirmed. From studies of the brain structure of aggression, it is proposed that there is a central motivational mechanism that varies little during the course of evolution and which forms a stable basis to classify aggression from one animal species to another. It confirms the proposition, expressed in the Author's Response in the the 1979 review and confirmed in the 2006 update reprinted in this section that "a classification of behaviors ought to be based upon the neural circuitry involved."
To classify aggressive behaviors, it is important to begin from the fact that there are three different types of aggression clearly distinguished by the techniques of lesions and electrical stimulation of the brain: offense, defense and predation. These are the conclusions of the first three papers reprinted here. As pointed out in the previous section, offense is further subdivided into two sub-systems for competitive and territorial fighting.
Defense and offense (called 'territorial behavior" at that earlier date) may be differentiated by brain lesions of the hypothalamus in rats. This is the conclusion of the paper reprinted here from Nature in 1971. Lesions of the lateral hypothalamus abolish offense, while not affecting defensive boxing in response to foot shock. Lesions of the medial hypothalamus enhance the defensive boxing, while not affecting offense. And when the lesions are combined, destroying the entire hypothalamus in cross-section, there is a combination effect: offense is abolished while defense is enhanced.
Offense can be differentiated from both predation and defense by brainstem lesions in the rat, as described in the second paper. Lesions of the ventromedial tegmentum abolish offense while leaving both predation and defense unaffected.
Defense can be differentiated from both offense and predation by lesions of the midbrain central gray. Lesions which destroy the central gray and adjoining tegmentum totally abolish all aspects of defense in the rat, as documented in the fifth paper reprinted in this section. Neither offense nor predation are abolished by central gray lesions, although previous studies have shown that the final killing bite of predation may be interrupted.
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