Cortical oscillatory changes occurring during somatosensory and thermal stimulation.

Brief somatosensory stimuli are followed by amplitude decreases (event-related desynchronization, ERD) of the 10 and 20 Hz oscillations over the bilateral primary sensorimotor cortices, and by post-stimulus synchronization (event-related synchronization, ERS) of the 20 Hz oscillations in the contralateral primary sensorimotor cortex and in the supplementary motor area (SMA). The 10 and 20 Hz ERD differentiate weak and strong somatosensory stimuli but not fine intensity gradations, and the ipsilateral ERD is especially sensitive to habituation. Stimulus anticipation, motor imagery, action viewing as well as voluntary movements modulate the stimulus-related changes of cortical oscillations. Noxious laser stimuli, selectively activating Adelta and/or C fibers, and innocuous warm and cold stimuli are associated with 10 and 20 Hz ERD but not with the post-stimulus 20 Hz ERS suggesting that the post-stimulus ERS is only related to neuronal transmission in the lemniscal system. It is proposed that phase-unlocked cortical oscillations modulate the preparedness of a particular sensory channel for upcoming somatosensory processing.