Representation of Pain and Somatic Sensation in the Human Insula: a Study of Responses to Direct Electrical Cortical Stimulation

Abstract

We studied painful and non-painful somaesthetic sensations elicited by direct electrical stimulations of the insular cortex performed in 43 patients with drug refractory temporal lobe epilepsy, using stereotactically implanted depth electrodes. Painful sensations were evoked in the upper posterior part of the insular cortex in 14 patients, mostly in the right hemisphere. Non-painful sensations were elicited in the posterior part of the insular cortex in 16 patients, in both hemispheres. Thus, painful and non-painful somaesthetic representations in the human insula overlap. Both types of responses showed a trend toward a somatotopic organization. These results agree with previous anatomical and unit recording studies in monkeys indicating a participation of the posterior part of the insular cortex in processing both noxious and innocuous somaesthetic stimuli. In humans, both a posterior and an anterior pain-related cortical area have been described within the insular cortex using functional imaging. Our results help to define the respective functional roles of these two insular areas. Finally, lateralization in the right hemisphere of sites where painful sensations were evoked is coherent with the hypothesis of a preponderant role of this hemisphere in species survival.

Brain activity associated with painfully hot stimuli applied to the upper limb: A meta‐analysis

“…A similar lack of electrophysiological data is also the case for the adjacent dorsal insula. Direct stimulation of the insula in humans has elicited painful responses [Ostrowsky et al, 2002], and lesions incorporating S2 and adjacent insula have fundamental effects on the quality of pain sensations evoked by contralateral peripheral stimulation [Greenspan et al, 1999]. The results of the meta-analysis provide further impetus for investigations that will refine our understanding of the role of this region in pain processing.…”

A rat is not a monkey is not a human: comment on Mogil (Nature Rev. Neurosci. 10, 283–294 (2009))

“…A lesion of the ascending lamina I fibres in the middle of the lateral funiculus, a lesion of the VMpo or a lesion of dorsal posterior insula (dpIns) can cause the complete and permanent loss of pain and temperature sensation in a contralateral region of the body [5][6][7][8] . Conversely, micro stimulation in either the VMpo or the dpIns in awake humans can cause a well localized report of either sensation 9,10 . The existence of this pathway has generated debate (for example, see , but there is no comparable evidence in rodents -rodents do not have either of these forebrain structures.…”

The Insular Cortex and the Amygdala: Shared Functions and Interactions

“…In one of these, the over-activation of both areas was reported in patients with anxiety disorder [219], while in another study the ventral agranular frontoinsula was shown to co-activate with the amygdala in social-emotional paradigms [38,45,52,228].…”

“…Such studies include anatomical, electrophysiological, lesion, pharmacological and imaging studies, as well as operatory stimulation techniques which have yielded plausible roles for the IC in dozens of different functions. Several studies indicate that the IC is involved in taste processing [7,8,28,41], viscerosensory information processing [3,20,26,38,42,43], temperature and pain perception [44,45], olfaction [46] auditory processing [47][48][49], somatosensory perception [49,50], drug craving [51], motor tasks [52] and post-stroke motor-recovery functions [53].…”

“…In fact, the rat and human insular cortices have common functional areas -as shown in Figure 2 -which suggests a degree of convergence in overall IC functions (compiled from: Rat IC [7,16,23,32,45,46,[68][69][70]; Human IC [71][72][73][74][75]). …”