Abstract

In 22 human subjects we measured microsaccade count across 60 brief fixation trials both pre- and post- administration of 300mg of caffeine. There was a statistically significant reduction in average microsaccade count post-caffeine administration, with a moderate effect size (Cohen’s d of 0.42). Microsaccade count was stable within individuals across time points (Pearson’s r of 0.89). Sensitivity analysis suggests that the pre/post caffeine effect size is robust to choice of parameters used to identify microsaccades. Bootstrap resampling suggests that both the pre/post-caffeine difference and the across-time stability within individuals could be reliably assessed with far fewer trials. The results support the use of microsaccade count as both a trait measure of individual differences and a state measure of caffeine response. We discuss the results in the context of the theory that the superior colliculus is central to the generation of microsaccades and hence that microsaccade rate may be a useful assay for at least some drug-induced changes at the level of the colliculus: a potentially useful tool in the development of therapies for disorders that may involve collicular dysfunction such as ADHD.

Highlights

  • IntroductionMicrosaccades are miniature fixational eye movements approximately 6 to 25-milliseconds in duration, through 1-120 arcminutes (up to 2 full degrees of rotation), that occur at a rate of about 1-2 per second

  • Microsaccades are miniature fixational eye movements approximately 6 to 25-milliseconds in duration, through 1-120 arcminutes, that occur at a rate of about 1-2 per second

  • There was no significant correlation between the ADHD SelfReport Scale (ASRS) score of Attention Deficit Hyperactivity Disorder (ADHD) traits and either preadministration microsaccade count or reduction in microsaccade count (r = 0.18, -0.13 respectively, p = 0.43, 0.57)

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Summary

Introduction

Microsaccades are miniature fixational eye movements approximately 6 to 25-milliseconds in duration, through 1-120 arcminutes (up to 2 full degrees of rotation), that occur at a rate of about 1-2 per second. Electrophysiological studies have demonstrated the role of the rostral pole. Received January 4, 2019; Published October 3, 2019. Microsaccade rate as a measure of drug response.

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