Organization of brainstem behavioral systems

A review of recent literature suggests that the brainstem may play a more fundamental role in the elaboration of adaptive behaviors than has often been assumed. This view is indicated by current reports documenting the substantial behavioral repertoire of decerebrate animals and by the recent findings that electrical stimulation of localized areas in all major levels of the brainstem can induce complex and coordinated behaviors, including eating, grooming and attack. Indeed, behaviors elicited from sites in the caudal brainstem evidence unexpected goal specificity and stimulus control over response topography. Additional neuroanatomical and behavioral data are reviewed which further implicate caudal brainstem networks in process of reward and aversion. From these and other findings it is argued that integrating mechanisms for the expression of many aspects of species-characteristic behaviors are intrinsic to the brainstem. In line with this view, rostral hypothalamic-limbic mechanisms, while perhaps contributing refinement to the integration of behaviors, may best be viewed as phylogenetically newer control mechanisms making the expression of species-characteristic behaviors subordinate to additional class of exteroceptive and interoceptive stimuli.