Electrophysiological identification of neurons in ventrolateral medulla sending collateral axons to paraventricular and supraoptic nuclei in the cat

In recent studies, it has been reported that high-frequency stimulation restricted to A alpha beta fibers in man can be perceived as painful and evoke a nociceptive flexion reflex. These results would indicate that some patterns of activity in low-threshold mechanoreceptors can lead to painful sensations. Because of the theoretical importance of this question, the above studies were extended by recording the evoked neural activity with the technique of percutaneous microneurography. Painful sensations and the nociceptive reflex did not appear unless the evoked nerve response contained activity in A delta fibers. The results support the theory that painful sensations occur in normal man only when nociceptor afferents are activated.