Facilitation of late somatosensory evoked potentials by electrical train stimuli

Somatosensory evoked potentials (SSEP) may reflect synaptic events and could be suitable to characterise the short-time plasticity of synaptic potentials (SP). For this purpose, the left superficial radial nerve was stimulated in 7 subjects with single or trains of 3 stimuli (C4' against Fz, time interval 500 ms, 1 Hz or 0.4 Hz). The within train interstimulus intervals (ISI) were varied from 2 ms to 10 ms. N20, N1 and N2 displayed a significant gain in amplitude following train stimuli compared with single stimuli. Short ISIs of 2-4 ms led to higher amplitudes of N20, N1 and N2 compared with longer ISIs of 7-10 ms. In general, larger amplitude values were observed with 0.4 Hz stimulus repetition compared with 1.0 Hz. This data reflects synaptic facilitation and refractoriness/habituation. Our results could be helpful to non-invasevely investigate synaptic decay dynamics by late SSEP in diseases of the central nervous system such as migraine or epilepsy.