Laser-Evoked Potentials Are Graded and Somatotopically Organized Anteroposteriorly in the Operculoinsular Cortex of Anesthetized Monkeys

Abstract

Baumgärtner, Ulf, Wiebke Tiede, Rolf-Detlef Treede, and A. D. (Bud) Craig. Laser-evoked potentials are graded and somatotopically organized anteroposteriorly in the operculoinsular cortex of anesthetized monkeys. J Neurophysiol 96: [2802][2803][2804][2805][2806][2807][2808] 2006. First published August 9, 2006; doi:10.1152/jn.00512.2006. The operculoinsular cortical region has a major role in the representation of noxious stimuli, based on functional imaging observations, clinical lesion studies, and EEG recordings of specifically pain-related laser-evoked potentials (LEPs) in humans. The source of LEPs has not been identified, and several somatic representations and cytoarchitectonic areas may be present in this complex region. To overcome the limitations of human studies, a primate model is needed in which the main LEP generator in this region can be localized and characterized using invasive methods. We obtained EEG recordings of evoked responses to noxious laser stimulation at different intensities and performed dipole source analyses in three anesthetized macaque monkeys. We show that LEPs can be recorded that 1) grade with stimulus intensity, 2) display two distinct responses corresponding to the "late" (A␦-fiber) and the "ultralate" (C-fiber) LEPs recorded in humans, and 3) originate deep within the operculoinsular region, thus establishing a valid primate model for experimental analysis of LEPs. Further, we found that LEPs elicited from the leg, arm, and ear display a global somatotopy organized in the posteroanterior direction (leg posterior and arm and ear anterior), which contrasts starkly with the mediolateral (leg to face) gradient of the somatotopic representations in primary and secondary somatosensory cortices. These results provide evidence that the main generator of pain-related activity in operculoinsular cortex may participate in both the somatic localization and the intensity discrimination of pain sensations, and they indicate that it may be distinct from the traditional somatosensory cortices. I N T R O D U C T I O NThe operculoinsular cortex has been identified as an important nociceptive region in humans by several methods, including EEG recordings of laser-evoked potentials (LEPs) and functional imaging (Apkarian et al. 2005). To investigate the cortical representation of pain, the most specific stimulus available is a noxious heat pulse generated by brief infrared laser stimulation. Laser pulses activate nociceptive A␦-and C-fibers in humans and monkeys, without concomitant activation of tactile afferents, and generate prominent LEPs within the brain that can be recorded from the surface of the cortex or from the scalp in awake humans (Bromm et al. 1984;Treede et al. 1995). The earliest cortical LEP correlates with pain sensation in several ways, and dipole source reconstruction analyses indicate that its main source lies in the contralateral operculoinsular region (Garcia-Larrea et al. 2003;Iannetti et al. 2005;Vogel et al. 2003). This observation is consistent with clinical findings ...

Characterizing the Cortical Activity through Which Pain Emerges from Nociception

“…Since the physical characteristics of perceived and unperceived nociceptive stimuli were matched, our finding suggests that the magnitude of the N1 wave is mainly driven by the magnitude of the eliciting nociceptive input, rather than by the magnitude of pain perception. Consistent with this view, Baumgärtner et al (2006) showed that the N1 wave can be recorded in anesthetized monkeys. Therefore, our results suggest that the correlation between the magnitude of the N1 wave and pain perception that was reported in two of our recent studies did not result from a relationship between the N1 wave and pain perception per se, but instead, was mostly determined by explicit or unavoidable (Iannetti et al, 2005) variations in the strength of the peripheral nociceptive input.…”

MRI-Based Definition of a Stereotactic Two-Dimensional Template of the Human Insula

“…Until now, localization of these functions was only performed by considering an anteroposterior subdivision. This ignored the gyral and sulcal architecture and failed to separate the opercular region from the insula itself [56,57] . Given the diversity of insular functions, it would be interesting to consider their location with respect to the gyral and sulcal anatomy.…”

Nociception and autonomic nervous system

“…However, nociception is not synonymous with pain, which is experienced as a conscious percept. Indeed, nociception can trigger brain responses without necessarily causing the feeling of pain [2][3][4]. On the other hand, pain can occur in the absence of nociceptive input [5].…”