Perception of pain coincides with the spatial expansion of electroencephalographic dynamics in human subjects

The dynamics of cortex driven by painful median nerve stimulation were inve stigated in event-related oscillation (ERO). We applied a wavelet time-freq uency analysis to differentiate the brain dynamics between painful and non- painful somatosensory stimulation. The observed pattern to pain-induced eff ects exhibited a stepwise decrease of frequencies over time, starting aroun d 26 ms over somatosensory cortex at 80 Hz, intermediate oscillations at 40 and 20 Hz around 40 ms, and reaching down to 10 Hz after 160 ms. This step -wise frequency decrease of ERO, coincident with spatial shift from the con tralateral somatosensory area at 80 Hz to the centro-frontal brain at 40/20 Hz and final spatial expansion to the large region of centro-parietal area s at 10 Hz, may represent the cortical processes necessary to transfer sens ory information from perceptual stages to subsequent cognitive stages in co nsciousness. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.