Brain Stem Regulation Of Aggression

Pontine and mesencephalic nuclei coordinate full-fledged aggressive behaviors in rodents but only fragments of aggressive behavior in primates. Inputs

Hypothalamus: and object choice

Stereotyped aggression

Figure 1 Critical sites in the hierarchical, multiregional neural system regulating aggression. Portions of the left temporal and orbitofrontal regions are cut away in this midsagittal view of the human brain to optimize visualization. [Reproduced with permission from Saver et al., 1996, Neuropsychiatry of aggression. In: Neuropsychiatry: A Comprehensive Textbook (Fogel, B. S., Schiffer, R. B., Rao, S. M., Eds.) p. 532. Williams & Wilkins, Baltimore].

Hypothalamus: and object choice

Stereotyped aggression

Figure 1 Critical sites in the hierarchical, multiregional neural system regulating aggression. Portions of the left temporal and orbitofrontal regions are cut away in this midsagittal view of the human brain to optimize visualization. [Reproduced with permission from Saver et al., 1996, Neuropsychiatry of aggression. In: Neuropsychiatry: A Comprehensive Textbook (Fogel, B. S., Schiffer, R. B., Rao, S. M., Eds.) p. 532. Williams & Wilkins, Baltimore].

to the system include spinoreticular proprioceptive and nociceptive sensory circuits. Outputs incorporate pontine (facial) and descending motor centers, leading to stereotypic movements. Electrical stimulation of upper brain stem nuclei in subhuman primates produces different fragments of aggressive facial expressions and vocalizations, dissociated from offensive or defensive behavior. Other brain stem circuits contribute to somatomotor patterns for gestures and approach and avoidance behaviors. Medullary sympathetic and parasympathetic nuclei exert direct autonomic effects on cardiovascular, respiratory, and gastrointestinal peripheral organ systems. In humans, however, full-fledged aggression-related behavior patterns are not produced at the brain stem level. Response coordination and decision making are carried out at higher processing stations. As a result, brain stem lesions, although sometimes disturbing fragments of aggressive behavioral output, generally do not produce major syndromes of altered aggressivity.

However, an important clinical aggression syndrome does arise from disruption of brain stem regulation of sleep-wake states—the rapid eye movement (REM) sleep behavior disorder. In normal individuals, neurons in the vicinity of the locus ceruleus actively inhibit spinal motorneurons during REM sleep, preventing the expression of motor programs being actively generated in the motor cortex. In the cat, bilateral pontine tegmental lesions compromise REM sleep muscle atonia, permitting the enactment of oneiric behaviors, including frequent biting and other attack conduct. In humans, focal or degenerative lesions in the pontine tegmentum similarly produce the REM sleep behavior disorder, in which affected individuals physically perform their dream movements. Although normal dreaming subjects report an extremely diverse array of movements and activities fictively performed in dreams, violent actions comprise the overwhelming preponderance of behaviors actually enacted by individuals with REM sleep behavior disorder. Most commonly, middle-aged men experience a violent dream in which they are attacked by animals or unfamiliar people. In response, the dreamer engages in vigorous, coordinated motor acts that are often violent in nature. Individuals may jump off the bed, smash furnishings, or attack their bed partner, with frequent resulting injury to both patient and spouse. It is likely that aggressive responses generated in the forebrain during REM dreaming produce more powerful descending motor outputs than feeding, sexual, or other drive-related activities and disproportionately override the partial residual muscle atonia in these patients.

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