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.