Basic function

Abstract

Magnetoencephalography (MEG) is a powerful noninvasive tool for examining the temporal and spatial aspects of sensory processing in the brain. In this chapter, MEG responses elicited by innocuous and noxious somatic stimuli were reviewed. The development of devices for the selective stimulation of each peripheral receptor (i.e., A-beta mechanoreceptors, A-delta nociceptors, pain-related C nociceptors, and itch-related C nociceptors) enables us to record cortical responses to the activities of a given receptor and compare these responses among somatosensory submodalities. MEG responses to the stimulation of cutaneous A-beta mechanoreceptors suggest a serial mode of processing through the primary and secondary somatosensory cortices. By using the intraepidermal electrical stimulation (IES) method or an electrical itch stimulus, similar serial processing was found for pain and itch systems; however, some differences were observed (e.g., the area 3b sources following IES were absent and the itch stimulus induced a specific activity in the precuneus). These findings can be helpful in further basic studies on the physiology of the somatosensory system and clinical studies to elucidate the pathophysiology of somatosensory dysfunctions.