Central Representation of Somatic Sensations in the Parietal Operculum (SII) and Insula

Abstract

Four subjects with small restricted cerebral cortical infarcts have been examined. One had a lesion confined to the parietal operculum (SII), while in the second the SII lesion also encroached on the posterior insula; in the third subject, both banks of the sylvian fissure and the dorsal insula were involved, while in the fourth the lesion involved the upper bank of the sylvian fissure. In all cases, the postcentral gyrus (SI) was intact. Subjects 1 and 2 had mild spontaneous pain, but subjects 3 and 4 had never had spontaneous pain. In the affected areas, none could feel mechanical (skinfold pinch) pain. The 2 subjects with spontaneous pain could not discriminate sharpness (pinprick), but this was unimpaired in the third and fourth subjects. Warmth, cold, and heat pain were impaired in the 2 subjects with spontaneous pain, but not in those without; however warm-cold difference was greater in the affected regions of all subjects. The possibility must nevertheless be considered that the presence of central pain in some way alters the cortical mechanisms for the perception of thermal stimuli. Certainly, as we had earlier observed, spontaneous pain only occurs when there is interference with thermal sensation. Functional MRI (fMRI) studies following thermal stimulation in subjects 1 and 2 showed these areas, particularly SII, to be concerned with the reception of innocuous and noxious thermal stimuli, mechanical (skinfold pinch) pain and sharpness (pinprick), implying that SI is principally concerned with the reception of low-intensity mechanical stimuli, although it was activated in 1 of our fMRI-studied subjects by innocuous cooling.

Somatic Sensation and the Insular-Opercular Cortex: Relationship to Central Pain

“…We have previously suggested that the presence of spontaneous central pain alters cortical mechanisms for the perception of thermal sensations [14]. Here we present further evidence from the 4 patients described in that publication and add data from 2 additional patients.…”

Anteroposterior somatotopy of innocuous cooling activation focus in human dorsal posterior insular cortex

“…Electrical stimulation of the dpIns in awake humans can result in specific thermal sensations (39). A laser-evoked potential study provided evidence that selective warming specifically activates the dpIns (29), and recent fMRI studies provided supplemental data supporting activation of the insular cortex by cooling and "paradoxical heat" (3,18,20). Notably, imaging evidence also indicates strong activation of the human dpIns by noxious cold (8,12,36).…”

“…It incorporates anatomic findings indicating that the dpIns has a major role in the control of homeostatic integration, including direct projections to critical sites in the brain stem. A cardinal (and nearly universal) feature of this syndrome is that such burning pain occurs in the region of the body where the thermosensory dysfunction is most profound (3,16). In order for this cross-modal topographic correspondence to occur, the thermosensory representation in the dpIns (and its forebrain and descending connections) must be somatotopically organized.…”

Functional connectivity of the human insular cortex during noxious and innocuous thermal stimulation

“…Previous studies showed that electrical stimulation in and around the insula produces perception of pain (Afif et al, 2008;Frot and Mauguiere, 2003;Ostrowsky et al, 2002) in the same manner that lesions do e.g. after a stroke involving the operculo-insula region (Bowsher et al, 2004). Despite extensive insular lesions, these patients retained the ability to discriminate between different degrees of evoked pain intensity but with overall increased intensity ratings (Starr et al, 2009).…”