Somatotopic organization of brainstem analgesic circuitry

The lateral periaqueductal gray (lPAG) evokes somatotopically appropriate defensive behaviors, including an analgesia that allows the animal to escape or fight unimpeded. Whether the lPAG and its descending targets are also able to drive somatotopically specific analgesic responses is not known. In this work, we performed ultrahigh-field functional magnetic resonance imaging of the lPAG in 93 participants during a placebo analgesia paradigm performed at different body locations. We found that analgesic responses are somatotopically organized in the lPAG and its descending outputs to the rostral ventromedial medulla. These data show that the PAG can regulate analgesic responses in a highly spatially localized manner and thus has the ability to mediate body site-selective control over pain.