A measure of individual differences in the parametric sensitivity of the trigeminal blink reflex

The trigeminal blink response is an easily evoked brainstem reflex. Despite extensive investigation, there has been limited study of how parametric manipulation of the intensity of stimulation modulates the evoked response. The goal of this study was to measure the psychometric trigeminal reflex sensitivity function, test the resulting model parameters for differences between contralateral and ipsilateral reflex responses, and test for individual differences in sensitivity. We measured blink responses in 17 healthy, adult participants using airpuffs delivered to the cornea at five different, log-spaced intensities (3.5 - 60 PSI). Lid position over time was decomposed into amplitude, velocity, and shape components. We found that variation in blink amplitude was well fit with a two-parameter Weibull cumulative density function of log stimulus intensity. There was a reliable decrease in threshold sensitivity of the contralateral as compared to ipsilateral blink response. This decrease was consistent across participants despite substantial individual differences in the threshold and slope of the overall sensitivity function, suggesting that the laterality effect arises in the neural circuit subsequent to individual differences in sensitivity. We conclude that a parametric measure of trigeminal reflex sensitivity is a promising tool for examining neural mechanisms that modulate this response.