Facilitation dynamics of late somatosensory evoked potentials after sural nerve stimulation

•Electrical sural nerve train stimuli significantly facilitate late somatosensory evoked potentials.•The magnitude of this facilitation was inversely related to the within train interstimulus interval.•Train stimuli may constitute a novel tool to investigate cerebral synaptic plasticity.

ObjectiveSomatosensory evoked potentials (SSEPs) could be suitable for elucidating the properties of synaptic potentials (SPs). Two experiments were designed for this purpose.Methods1st experiment: the sural nerve was stimulated in 13 subjects with single or trains of 3 stimuli (1 Hz or 0.4 Hz), the within train interstimulus interval (ISI) was stepwise extended from 2 to 10 ms. Cz′ against Fz, time interval 500 ms. 2nd experiment: Gating was investigated in a paired stimulus paradigm with intervals of 0.7, 1, 2, 5 s in 15 subjects after single and train stimuli (ISI 3 ms) with equal stimulus and recording positions.Results1st experiment: N1-P1, P1-N2a, and P2-N2b but not N37-P40 displayed a significant gain in amplitude following train stimuli compared with single stimuli. Significantly larger N1-P1 amplitude values were observed with 0.4 Hz stimulus repetition compared with 1.0 Hz. Short ISIs of 2-4 ms led to higher N1-P1 amplitudes than obtained with longer ISIs of 7-10 ms. 2nd experiment: recovery of the habituated N1-P1 amplitude was complete when the 2nd of 2 stimuli followed after 2 s.ConclusionsSSEP vertex potential amplitudes (especially N1-P1) recorded after train stimuli presumably reflect the decay dynamics of excitatory postsynaptic potentials. Recovery of the habituated N1 (2nd experiment) was complete within 2 s.SignificanceOur study may be relevant to study properties of excitatory synaptic potentials in diseases of the central nervous system such as e.g. epilepsy or migraine.