ABSTRACT
This chapter presents some aspects of the anatomical and functional organization of spinal pathways that convey nociceptive information. The existence of a restricted area within the ventrolateral quadrant (VLQ) which contains the main pathways responsible for the transmission of nociceptive information responsible for pain has also been demonstrated in both electrophysiological and behavioral studies in animals. The role of the caudal brainstem as a relay for nociceptive signals has been suggested for a long time, as the majority of VLQ ascending axons, in both animals and man, terminates within the medullary reticular formation. Several groups have shown that brainstem reticular areas, most notably the gigantocellular reticular nucleus and surrounding regions, contain neurons responsive to noxious stimuli and that focal stimulation of some of these areas can elicit escape behavior. The alteration of sensory modulatory mechanisms could contribute to the dysesthesias and pain that sometimes appear following cordotomies and more often following mesencephalic tractotomies.
