Prepulse effects of supraorbital nerve stimuli

Trigeminal blink reflex (TBR) modulation, usually accomplished using either paired-pulse supraorbital nerve (SON) stimulation or prepulses delivered to peripheral nerves, has a long tradition in clinical neurophysiology. We investigated whether SON stimuli may themselves serve as prepulses for the TBR and for the somatosensory blink reflex (SBR) following digital nerve stimulation.

In 26 participants we recorded TBRs and SBRs in orbicularis oculi muscle (OOc) either alone or preceded by SON prepulses of low or high intensity. The recordings were obtained in three experimental conditions and encompassed interstimulus intervals (ISIs) between -10 and 500 ms.

SON stimuli induced profound prepulse inhibition (PPI) of both SBR and TBR. PPI with low-intensity SON prepulses reached the same (SBR) or almost the same (TBR) levels obtained with high-intensity SON prepulses. The temporal profile of OOc response suppression was similar for TBR and SBR, but SBR suppression was more pronounced than TBR suppression at short ISIs.

SON stimuli exert prepulse effects on both SBR and TBR over a wide range of stimulus intensities, from subthreshold to reflex-eliciting stimuli. The temporal profiles of the effects are in accord with the distance, hence time lags, between the brainstem and the respective stimulation sites of both prepulses and reflex-eliciting stimuli.

SON stimuli generate prepulse effects irrespective of the elicitation of a motor response, suggesting that paired-pulse stimulation paradigms represent a variant of a more generalized modulatory effect of a prepulse stimulus on the response to a subsequent reflex-eliciting stimulus.