Nociceptive responses of neurons in the posterior group of nuclei and medial thalamus.

Anatomical studies have shown that fibers of the spinothalamic tract terminate in both the posterior group of nuclei (PO) and the nuclei of the medial thalamus. Only the PO receives fiber terminations from the spinocervicothalamic and dorsal column-medial lemniscal projections. This difference in connectively is reflected in the functional differences between the neurons in the PO and those in the medial thalamus. Although both PO and medial thalamus contain a large proportion of nociceptive neurons, only the PO contains neurons that have "lemniscal" response properties. Lesion studies have demonstrated the importance of the spinothalamic tract in mediating A and C fiber input to nociceptive neurons in the PO and medial thalamus. These studies showed that the nociceptive neurons in PO also receive A fiber input from the dorsal column-medial lemniscal projection and A and C fiber input from the spinocervicothalamic projection.