ABSTRACT
Nociceptive processing within the human brain takes place within two distinct and parallel systems: the lateral and medial pain systems. Current knowledge indicates that the lateral system is involved in processing the sensory-discriminative aspects of pain, and that the medial system is involved in processing the affective-motivational aspects of pain. Hemispheric differences in brain activation (lateralisation) during nociceptive processing were studied to further clarify the division of function between the lateral and medial pain systems. Hemispheric lateralisation was studied by applying painful CO(2) laser stimuli of 3-s duration sequentially to the left and right medial lower calves of five normal right-handed human subjects. The resultant brain activity was measured using 3-T functional magnetic resonance imaging, by determining significant changes in blood oxygen level dependent (BOLD) signal and applying a general linear modelling approach. Volumes of interest were defined for the primary and secondary somatosensory cortices (SI and SII), the insular cortex, and the thalamus, on individual subjects' high-resolution structural scans. Hemispheric lateralisation was quantified by comparing the level of activation between brain hemispheres within each volume of interest. In SII, no significant hemispheric difference in activation was detected. In the insula, activation was significantly greater in the left hemisphere than the right. In both SI and the thalamus, activation in response to painful stimulation was significantly greater in the hemisphere contralateral to the stimulus, which is consistent with these areas being involved in processing the sensory-discriminative aspects of pain.
Subject(s)
Brain/pathology , Functional Laterality/physiology , Nociceptors/physiology , Pain/psychology , Adult , Cerebral Cortex/physiology , Female , Hot Temperature/adverse effects , Humans , Image Processing, Computer-Assisted , Lasers , Leg/innervation , Leg/physiology , Linear Models , Magnetic Resonance Imaging , Male , Nerve Fibers, Myelinated/physiology , Nerve Fibers, Unmyelinated/physiology , Oxygen/blood , Psychophysics , Somatosensory Cortex/physiology , Thalamus/physiologyABSTRACT
Electrophysiological studies have revealed a source of laser pain evoked potentials (LEPs) in cingulate cortex. However, few studies have used realistically shaped head models in the source analysis, which account for individual differences in anatomy and allow detailed anatomical localisation of sources. The aim of the current study was to accurately localise the cingulate source of LEPs in a group of healthy volunteers, using realistic head models, and to assess the inter-individual variability in anatomical location. LEPs, elicited by painful CO(2) laser stimulation of the right forearm, were recorded from 62 electrodes in five healthy subjects. Dipole source localisation (CURRY 4.0) was performed on the most prominent (P2) peak of each LEP data set, using head models derived from each subject's structural magnetic resonance image (MRI).For all subjects, the P2 LEP peak was best explained by a dipole whose origin was in cingulate cortex (mean residual variance was 3.9+/-2.4 %). For four out of five subjects, it was located at the border of the caudal division of left anterior cingulate cortex (area 24/32') with left posterior cingulate cortex (area 23/31). For the fifth subject the dipole was centred in right posterior cingulate cortex (area 31). This study demonstrates that the location of the cingulate source of LEPs is highly consistent across subjects, when analysed in this way, and supports the involvement of caudal cingulate regions in pain processing.
