Normative data of laser evoked potentials using Nd:YAP laser

To establish a robust multi-centre normative database for Nd:YAP laser-evoked potentials (LEPs) across distal and proximal stimulation sites, and to quantify the impact of laser spot size (energy density) and demographic factors on LEP parameters.

One hundred nine healthy adults (57 females) were recruited from three centres (Geneva, Lyon, Saint-Etienne). Nd:YAP laser pulses were delivered with a 3-mm beam (Centre 1) or 4-mm beam (Centres 2-3). LEPs were recorded from standard EEG sites (including Fz/Cz/Pz and contralateral temporal leads). Stimulation sites included hand dorsum (n = 109), foot dorsum (n = 80), thigh and upper neck (both n = 43). N1, N2, and P2 latencies and amplitudes were measured and normal limits estimated as mean ± 99.9% confidence interval. ANCOVA (age-corrected) tested spot-size effects; repeated-measures ANOVA tested site effects; correlations assessed age/height associations.

The vertex N2-P2 complex was consistently recorded across centres and sites (100% for hand, thigh, neck; ∼97% for foot). N1 detection was less consistent, particularly with larger spot size and at the foot. Smaller spot size (higher energy density) yielded shorter N2/P2 latencies and larger N2-P2 amplitudes for hand stimulation, and shorter P2 latency for foot stimulation. Sex and height showed no significant effects. Increasing age was associated with longer N2/P2 latencies and reduced N2-P2 amplitudes for distal sites, with minimal age effects at proximal sites.

This study provides the most comprehensive Nd:YAP LEP normative dataset to date, including distal and proximal sites and spot-size-specific reference limits.

These data support standardized, high-specificity clinical interpretation of LEPs for assessing small-fibre and spinothalamic pathway dysfunction.