Functional representation of trigeminal nociceptive input in the human periaqueductal gray

The periaqueductal gray (PAG) is located in the mesencephalon in the upper
part of the brainstem and as part of the descending pain modulation is
considered a crucial structure for pain control. Its modulatory effect on
painful sensation is often seen as a systemic function affecting the whole
body similarly. However, recent animal data suggest some kind of
somatotopy in the PAG. This would make the PAG capable of
dermatome-specific analgesic function. We electrically stimulated the
peripheral dermatomes of the trigemino-cervical complex consisting the
three branches of the trigeminal nerve and the greater occipital nerve in
sixty-one humans during optimized brainstem fMRI. We provide evidence for
a fine-grained and highly specific somatotopic representation of
nociceptive input in the PAG in humans and a descending functional
connectivity between the individual representations of the peripheral
nerves in the PAG and the brainstem nuclei of these nerves. Our data
suggest that the downstream antinociceptive properties of the PAG may be
rather specific down to the level of individual dermatomes. This study was
preregistered at clinicaltrials.gov: NTC03999060 and primary outcomes
already published elsewhere.