SY9.1 Painful Brain: Recent Advances of Human Pain Perception Using MEG and fMRI

Abstract

Electrophysiological studies: I will review the recent progress in electrophysiological studies using electroencephalography (EEG) and magnetoencephalography (MEG) on human pain perception. For recording activities following A-delta fiber stimulation relating to first pain, laser stimulation are now widely used, but I will also introduce our new method, epidermal stimulation (ES), which is useful for recording brain activities by the signals ascending through A-delta fibers. For recording activities following C fiber stimulation relating to second pain, but weak CO2 laser stimuli applied to tiny areas of the skin were recently used. EEG and MEG findings following C fiber stimulation were similar to those following A-delta fiber stimulation except for a longer latency. At first, primary somatosensory cortex (SI) contralateral to the stimulation is activated and then secondary somatosensory cortex (SII), insula, amygdala and anterior cingulate cortex (ACC) in the bilateral hemispheres are activated sequentially. Functional magnetic resonance imaging: We analyzed event-related functional magnetic resonance imaging (fMRI) to investigate brain processing of the signals ascending from peripheral C and A-delta fibers evoked by phasic laser stimuli on the right hand in humans. The stimulation of both C and A-delta nociceptors activated the bilateral thalamus, bilateral SII, right (ipsilateral) middle insula, and bilateral Brodmann’s area (BA) 24/32, with the majority of activity found in the posterior portion of the ACC. However, magnitude of activity in the right (ipsilateral) BA32/8/6, including ACC and pre-supplementary motor area (pre-SMA), and the bilateral anterior insula was significantly stronger following the stimulation of C nociceptors than A-delta nociceptors. These findings were probably due to the differences in the emotional and motivational aspects of either pain, which are mainly related to the aACC, pre-SMA, and anterior insula.