Response Properties and Organization of Nociceptive Neurons in Area 1 of Monkey Primary Somatosensory Cortex

Abstract

The organization and response properties of nociceptive neurons in area 1 of the primary somatosensory cortex (SI) of anesthetized monkeys were examined. The receptive fields of nociceptive neurons were classified as either wide-dynamic-range (WDR) neurons that were preferentially responsive to noxious mechanical stimulation, or nociceptive specific (NS) that were responsive to only noxious stimuli. The cortical locations and the responses of the two classes of neurons were compared. An examination of the neuronal stimulus-response functions obtained during noxious thermal stimulation of the glabrous skin of the foot or the hand indicated that WDR neurons exhibited significantly greater sensitivity to noxious thermal stimuli than did NS neurons. The receptive fields of WDR neurons were significantly larger than the receptive fields of NS neurons. Nociceptive SI neurons were somatotopically organized. Nociceptive neurons with receptive fields on the foot were located more medial in area 1 of SI than those with receptive fields on the hand. In the foot representation, the recording sites of nociceptive neurons were near the boundary between areas 3b and 1, whereas in the hand area, there was a tendency for them to be located more caudal in area 1. The majority of nociceptive neurons were located in the middle layers (III and IV) of area 1. The fact that nociceptive neurons were not evenly distributed across the layers of area 1 suggested that columns of nociceptive neurons probably do not exist in the somatosensory cortex. In electrode tracks where nociceptive neurons were found, approximately half of all subsequently isolated neurons were also classified as nociceptive. Low-threshold mechanoreceptive (LTM) neurons were intermingled with nociceptive neurons. Both WDR and NS neurons were found in close proximity to one another. In instances where the receptive field shifted, subsequently isolated cells were also classified as nociceptive. These data suggest that nociceptive neurons in area 1 of SI are organized in vertically orientated aggregations or clusters in layers III and IV.

Cortical representation of first and second pain sensation in humans

“…8 and 33; for most recent studies, see refs. [34][35][36]. Thus, our finding of strong first pain-related but a virtual lack of second pain-related activation of S1 probably reflects the different perceptual characteristics of first and second pain.…”

Cortical Processing of Noxious Somatosensory Stimuli in the Persistent Vegetative State

“…Of the cerebral areas commonly identified by human neuroimaging studies, only the anterior cingulate shows a consistent response during the experience of pain . Traditionally, S1 is considered to be involved in the sensorydiscriminative component of pain processing (Bushnell et al, 1999) and single neurons in monkey S1 code for stimulus intensity, location, and duration (Kaas, 1993;Kenshalo et al, 2000). In neurological patients, somatosensory stimuli below threshold for conscious sensation elicited activation of S1 but not of downstream areas (Libet et al, 1967) and isolated electrical stimulation of S1 did not evoke the sensation of pain (Penfield and Jasper, 1954).…”

Vicarious responses to pain in anterior cingulate cortex: Is empathy a multisensory issue?

“…The sensory-discriminative dimension is associated with nociceptive pathways ascending through the lateral thalamic nuclei and projecting to somatosensory cortices, including hand areas 3b and 1 (Kenshalo, Iwata, Sholas, & Thomas, 2000;Schnitzler, Seitz, & Freund, 2000;Timmermann et al, 2001).…”