Background and aims: 
Experimental acute pain stimulation is challenging in magnetoencephalographic (MEG) brain imaging because of the recording equipment is highly sensitive to electrical noise. We tested an intracutaneous electrical stimulation method to elicit acute pain-related fields. Our aim was to identify pain-related magnetic fields in somatosensory brain areas and localize their generators.

Methods:
We recorded ten participants with 306-channel MEG (Elekta Neuromag® Triux™). Participants showed no depressive symptoms, had no contraindications to MEG recording and signed informed consent. We used a rare intracutaneous electrical stimulation for nociceptive stimulation adapted from Kochs et al., (1996). Participant's right hand third finger was stimulated. Superﬁcial layers of the glabrous skin were removed with a small drill. A copper tip electrode was placed to the skin hole. A return electrode was placed in the metacarpo-phalangeal joint of the third ﬁnger. Participants described each stimulus as a stinging pain. Stimulus intensity was set individually so that it was subjectively rated as moderately painful, 6-7 on a visual-analog scale. Data was analyzed in Brainstorm following commonly accepted steps.

Results:
Grand averages of evoked fields revealed two clearly identifiable waveform components: ~45ms and ~101ms. The generators were localized in contralateral primary somatosensory cortex and in secondary somatosensory cortices in both hemispheres. 

Conclusions:
Our intracutaneous stimulation produced stinging pain sensation. Relatively slow current arrival in primary somatosensory cortex supports A-delta fiber activation. Later activations of secondary somatosensory areas are compatible with reports on brain processing of pain stimuli.

UNIQUE ELECTRICAL STIMULATION FOR ACUTE PAIN STUDIES COMPATIBLE WITH MAGNETOENCEPHALOGRAPHY