Further characterisation of late somatosensory evoked potentials using EEG and MEG source imaging
Abstract
Beside the well documented involvement of secondary somatosensory area, the cortical network underlying late somatosensory evoked potentials (P60/N60, P100/N100) is still unknown. Electro- and magnetoencephalogram source imaging were performed to further investigate the origin of the brain cortical areas involved in late somatosensory evoked potentials, using sensory inputs of different strengths, and by testing the correlation between cortical sources. Simultaneous high-density electro- and magnetoencephalograms were performed in 19 participants, and electrical stimulation was applied to the median nerve (wrist level) at intensity between 1.5 and 9 x the perceptual threshold. Source imaging was undertaken to map the stimulus-induced brain cortical activity according to each individual brain magnetic resonance imaging, during 3 windows of analysis covering early and late SEPs. Results for P60/N60 and P100/N100 were compared to those for P20/N20 (early response). According to literature, maximal activity during P20/N20 was found in central sulcus contralateral to stimulation site. During P60/N60 and P100/N100, activity was observed in contralateral primary sensorimotor area, secondary somatosensory area (on both hemispheres), premotor and multisensory associative cortices. Late responses exhibited similar characteristics, but different from P20/N20, and no significant correlation was found between early and late generated activities. Specific clusters of cortical activities were activated with specific input/output relationships underlying early and late SEPs. Cortical networks, partly common to and distinct from early somatosensory responses contribute to late responses, all participating in the complex somatosensory brain processing.
