Chronic pain is associated with motor dysfunctions, and stimulation of the motor cortex has been shown to alleviate chronic pain. Recently Nakata et al. [Pain 107 (2004) 91-98] showed differentiated patterns of neuromagnetic evoked fields following painful laser stimulation during phasic movements of stimulated and non-stimulated hand. Phasic movements and static contractions differ in their functional activation of the motor cortices. Therefore, we decided to analyze the effects of isometric contractions of intrinsic right and left hand muscles on cortical sources of somatic-evoked potentials related to a painful galvanic stimulation of the right middle finger. Using spatio-temporal source dipole analysis of 111 electroencephalographic signals in 10 right-handed men, source activities were evaluated in the left primary somatosensory cortex (S1), left (S2(L)) and right (S2(R)) secondary somatosensory cortex, anterior cingulate cortex (ACC) and posterior cingulate cortex (PCC). Ipsilateral hand muscle contraction was associated with a decrease of source activity in S1 and with subsequent increases in S2(L) and the PCC. Contralateral hand muscle contraction was accompanied by a decrease of source activity in bilateral S2 cortices followed by decreases in the S1 and anterior cingulate cortex. Results suggest early suppression of source activity in S1 during ipsilateral hand muscle contractions and in bilateral S2 during contralateral hand muscle contractions.

Department of Normal Pathological and Clinical Physiology 3rd Faculty of Medicine Charles University Prague Ke Karlovu 4 120 00 Prague Czech Republic