The greater occipital nerve (GON), which derives most of its fibers from the C2 dorsal root, is the primary sensory nerve of the occipital region. The response to GON blockade was not simply dependent on the direct local anesthetic effect of the injection . The mechanism of action might have been via changes in brain nociceptive pathways. Another possible explanation for these findings is, therefore, that GON injections initiated diffuse noxious inhibitory controls, independent of anesthetic effect . Neurophysiological and clinical data suggest there is a functional connection between the sensory occipital segments and the trigeminal nociceptive system in humans.
