Effects of external trigeminal nerve stimulation (eTNS) on laser evoked cortical potentials (LEP): A pilot study in migraine patients and controls.

Background Transcutaneous external supraorbital nerve stimulation has emerged as a treatment option for primary headache disorders, though its action mechanism is still unclear. Study aim In this randomized, sham-controlled pilot study we aimed to test the effects of a single external transcutaneous nerve stimulation session on pain perception and cortical responses induced by painful laser stimuli delivered to the right forehead and the right hand in a cohort of migraine without aura patients and healthy controls. Methods Seventeen migraine without aura patients and 21 age- and sex-matched controls were selected and randomly assigned to a real or sham external transcutaneous nerve stimulation single stimulation session. The external transcutaneous nerve stimulation was delivered with a self-adhesive electrode placed on the forehead and generating a 60 Hz pulse at 16 mA intensity for 20 minutes. For sham stimulation, we used 2 mA intensity. Laser evoked responses were recorded from 21 scalp electrodes in basal condition (T0), during external transcutaneous nerve stimulation and sham stimulation (T1), and immediately after these (T2). The laser evoked responses were analyzed by LORETA software. Results The real external transcutaneous nerve stimulation reduced the trigeminal N2P2 amplitude in migraine and control groups significantly in respect to placebo. The real stimulation was associated with lower activity in the anterior cingulate cortex under trigeminal laser stimuli. The pattern of LEP-reduced habituation was reverted by real and sham transcutaneous stimulation in migraine patients. Conclusions The present results could suggest that the external transcutaneous nerve stimulation may interfere with the threshold and the extent of trigeminal system activation, with a mechanism of potential utility in the resolution and prevention of migraine attacks.

A comparative study of cortical responses evoked by transcutaneous electrical vs CO(2) laser stimulation.

OBJECTIVES: A novel non-invasive method for nociceptive electrical stimulation of the skin has been recently introduced by using a planar concentric stimulating electrode (CE). We compared the cortical potentials induced by a CE vs laser stimulator in healthy subjects using a multichannel recording. METHODS: Cortical potentials were recorded in 11 healthy subjects by 54 scalp electrodes, stimulating the skin of the right hand and the right supra-orbital zone by the CE and laser stimulator settled two levels above the individual pain threshold. RESULTS: The latency difference between N1, N2, and P2 evoked by the CE vs laser stimulator was larger than the receptor activation time of 40 ms and larger following stimulation of the upper limbs than of the head. The amplitudes and topographic distribution of the cortical waves did not differ between the two stimulation types. CONCLUSIONS: A-beta fibre co-activation may be induced by CE electrodes, as suggested by latency gaps. Nevertheless, CE-evoked potentials showed similarity in amplitude, morphology and topographic representation with laser-induced ones. SIGNIFICANCE: At present, CE-evoked potentials cannot be considered a reliable measure of nociceptive pathway function.