Demographics-robust spontaneous eye blinking slowing in patients with severe acquired brain injury

This study aimed to explore whether spontaneous eye blinking features from a brief vertical electro-oculogram recording can distinguish patients with severe acquired brain injury from healthy volunteers. Given evidence for shared neurobiological substrates in blinking control and attention, we expected altered blinking features in patients. In this observational cross-sectional study we extracted eye blink rate, amplitude, rise time, fall time, duration, and blink-blink interval variability from electro-oculography in 19 patients with severe acquired brain injury and 21 healthy controls during resting state and an auditory oddball task. We tested group differences with Kruskal-Wallis and Conover-Iman post-hoc comparisons. Differences covarying age and sex were assessed with Wald tests for odds ratios from logistic regression. Univariate Kruskal-Wallis testing showed longer rise time and duration and smaller amplitude in patients relative to healthy controls. When considering demographics as covariate, we show that amplitude is strongly confounded by demographics whereas rise time, duration and, to a lesser extent, fall time, are associated to the brain injury condition regardless of age or sex. Eye blink rate and blink-blink interval variability did not show statistically significant differences. Condition moderated effects: group contrasts were strongest at rest and attenuated during oddball. We found preliminary evidence that rise time and total duration are prolonged in patients independently of demographic factors, although with no difference between different levels of consciousness. Our results suggest a general slowing of blink dynamics consistent with altered basal ganglia dopaminergic activity, contributing physiological information relevant for monitoring and rehabilitation planning in brain injury.