[Transmission of nociceptive information along the spino-cervico-thalamic component of the lemniscal system]

Noxious heating (up to 44-60 degrees) of the skin of the foot facilitated the primary cortical responses (PRs) evoked by threshold stimulation of spinocervical tract (SCT) neurones receiving information from the heated skin area. The facilitation reached its maximal level 3-4 minutes after the beginning of the heating when the amplitude of PRs increased 2-4 times. The facilitation is completely due to an increase in excitability of SCT neurones, since PRs to stimulation of the exons of these neurones in the dorsolateral funiculus did not change. In view of the fact that PRs, at least their early components, are evoked by impulses reaching the cerebral cortex through the lemniscal system, the findings suggest that the lemniscal system transmits not only tactile, as for many years has been generally accepted, but also nociceptive information. When it is considered that the lemniscal system, contrary to the extralemniscal pathways, shows a high degree of topographic organizations, the above suggestion should be viewed as having a paramount importance for understanding the animal's ability for an exact localization of the site of pain stimulation.