Modulation of motor-cortex oscillatory activity by painful Aδ- and C-fiber stimuli

Spontaneous similar to20-Hz oscillations, arising predominantly from the primary motor cortex (MI), are readily observed by magnetoencephatography (MEG). Prior studies have indicated that the level of the similar to20-Hz rhythm reflects the functional state of the MI cortex: increased 20-Hz level is associated with increased inhibition and suppression of the rhythm with excitation of MI Close interaction is suggested between pain and the motor system by the association of chronic pain with motor dysfunction and by the alleviation of pain by motor-cortex stimulation. We therefore explored the effect of noxious input on motor-cortex functions by recording MEG signals from nine healthy subjects during selective laser stimulation of Adelta- and C-fibers of the hand. The similar to20-Hz level was suppressed in the contralateral MI cortex in all nine subjects after painful Adelta- and C-fiber stimuli (P < 0.001). The suppression started 180 +/- 10 ms (mean +/- SEM) after Adelta-fiber stimuli and 820 +/- 30 ms after C-fiber stimuli, and peaked 160-170 ms later. Similar. but about 50% weaker, suppression of the similar to20-Hz oscillations occurred in seven out of nine subjects in the ipsilateral MI. These results suggest automatic, lateralized, excitation of the MI cortex by noxious Adelta- and C-fiber input. (C) 2004 Elsevier Inc. All rights reserved.