Nociceptors function to protect tissue from potential damage by thermal, mechanical, and chemical stimuli. The central terminals of primary nociceptive mechanical and thermal afferents (C/A fibers) converge in superficial laminae I and II in the dorsal horn of the spinal cord. Nociceptive information is processed by excitatory and inhibitory interneurons in the dorsal horn of the spinal cord before being relayed to projection neurons in lamina I that transmit the information to higher brain centers that mediate the experience of pain (Koch et al., 2018)(Fig. 1).

Light touch does not normally evoke pain, but after nerve injury, innocuous light touch can evoke a pain-like response called allodynia. Information about light touch is carried by low-threshold mechanical primary afferents (A fibers) that synapse in laminae II-IV in the dorsal horn (Fig. 1). In inner lamina II, A fibers synapse directly onto excitatory interneurons that express the isoform of protein