Stimulus artifact removal to detect trigeminal sensory evoked potentials

OBJECTIVE: Large stimulus and myogenic artifacts usually prevent detection of sensory evoked potentials to electrical stimulation in trigeminal sensory territory (t-SEP). Stimulus Artifact (SA) removal can be obtained by means of two stimulating modes (Dual Mode Stimulation - DMS) having in common a fixed cathode alternatingly referred to opposed anodes, resulting in SAs of opposite polarity. Opposite SAs progressively cancel each other out during averaging, without interaction with the underlying bio-electrical events. METHODS: Using DMS, dermatomal t-SEP were recorded from C5/C6 scalp sites in 24 healthy volunteers after selective, electrical stimulation of five trigeminal nerve areas: supraorbital, infraorbital, superior alveolar, inferior alveolar and auriculotemporal. RESULTS: Reproducible t-SEPs were obtained after stimulation at all sites and showed the classical W shape, without significant differences related to the stimulated area. Cortical responses were formed by a sequence of individual peaks labelled, according to polarity and mean latency, as P8, N13, P19, N27, P38. A later, less stable component followed (N55-P67), poorly defined or absent in about one third of subjects. CONCLUSIONS: The described technique represents a novel approach, within reach of any neurophysiological unit, to record dermatomal SEPs to electrical stimulation of several, discrete areas of significant clinical interest, covering the whole trigeminal sensory territory. SIGNIFICANCE: DMS represents a simple and robust tool to remove SA as the main drawback that has so far prevented recording of t-SEPs in daily clinical practice.