There is no unanimity of opinion concerning the morphophysiologic substrates that underlie abnormal aggressive behavior in animals or man. Lack of unanimity in current thought reflects the diversity, quality, and incompleteness of data gathered in many disciplines and the number of potentially different interpretations that these data generate. Nevertheless, there was general agreement that derangements of behavior probably have morphophysiologic substrates that involve, in some differential and selective fashion, predominantly brain structures rostral to the rhombencephalon. In general terms, portions of the neuraxis caudal to the midbrain may be regarded as being concerned largely with neural mechanisms that maintain and support essential biological functions (ie, respiration, cardiovascular regulation), and control, regulate, and supply effector mechanisms. Portions of the central nervous system rostral to the rhombencephalon appear to contain neural substrates concerned with goal-directed behavior and the motivational and emotional concomitants that make such behavior possible. Stated broadly and simply,