ABSTRACT
A large number of studies published over the last 75 years indicate that, in addition to blocking pain, ventral lateral cordotomies (surgical disruption of the ventral lateral funiculus) also consistently block the sensation of itch. Such studies are taken as evidence supporting an important role for the spinothalamic tract (STT) in pruriception since its axons ascend within the VLF. Banzet (1927) first reported that cordotomy abolished pruritus. He noted that severe itch caused by irritation of the vulva was completely relieved following a ventral lateral cordotomy and recommended cordotomy as a treatment for the problem. Hyndman and Wolkin (1943) carefully studied the responses of ten cordotomy patients to the pruritic compound cowhage. They found that cowhage did not produce itch in the areas rendered analgesic in any of the patients but did produce itch in areas in which pain sensation was normal. These authors concluded that “it can be said with certainty that the sensation of itch is mediated through the spinothalamic tract” (Hyndman and Wolkin 1943, p. 130). White et al. (1950) reported that a patient who had undergone a cordotomy did not experience itch in the analgesic area of the body even following contact with poison ivy. These authors also noted that in another patient severe itching caused by a intramedullary neoplasm of the spinal cord was abolished by a cordotomy and that their patients were not “annoyed by the itch” following the bite of a mosquito. Foerster (1936), Graf (1960), and Taren and Kahn (1966) also reported that cordotomies blocked the sensation of itch. Therefore, these clinical studies showed that, in addition to information related to pain and temperature sensation, axons in the ventral lateral funiculus (VLF) convey information that is necessary for production of the sensation of itch. It should be noted that electrophysiological studies of neurons in other spinal pathways that send ascending axons within the VLF, such as the spinoparabrachial, spinomesencephalic, spinoreticular, and spinohypothalamic tracts, have not yet been carried out. Axons in any, or all, of these pathways may also carry pruriceptive
22.1 Psychophysical Studies of Scratch ................................................................ 376 22.2 Inhibition on Interneurons in the Spinal Cord .............................................. 378 22.3 Pruriceptive STT Neurons are Inhibited by Scratching during Itch ............ 382 22.4 Scratching on the Skin, Itching in the Brain ................................................384 22.5 Circuitry of Relief ......................................................................................... 386 References .............................................................................................................. 387
information to any number of areas of the brain and thereby contribute to sensorydiscriminative, autonomic, affective, or modulatory systems related to itch.
