Nociceptive responses of trigeminal neurons in SII-7b cortex of awake monkeys

A cluster of trigeminal nociceptive neurons was located in the lateral sulcus on the upper bank of the frontoparietal operculum in a region bordering between cortical areas SII and 7b. These neurons were isolated in cortical cell layers IV and V-VI. All nociceptive neurons responded exclusively to noxious mechanical stimulation of cutaneous receptive fields on the face/head or intraoral tissue. Sustained noxious mechanical stimulation elicited slowly adapting responses that accurately encoded the duration of the stimulation. Prolonged discharges following removal of noxious stimulation were not observed. These nociceptive specific neurons poorly encoded graded noxious stimuli. Trigeminal somatosensory neurons within and surrounding the SII-7b cluster were not topographically organized according to divisions of the trigeminal nerve, laterality of receptive fields, or division of face/head and intraoral receptive fields. The thalamocortical, corticocortical and indirect corticolimbic connectivities of SII and area 7b and the possible role of SII-7b nociceptive neurons in learning, memory and avoidance behaviors are discussed.