Boosting multifocal VEP responses from the central visual field with pattern onset stimulation

Abstract

 

Purpose: Multifocal VEPs [1] allow to measure functional correlates of the cortical representation of the visual field in a spatially resolved manner. They might therefore provide a powerful tool for both an objective visual field perimetry and for the assessment of visual pathway abnormalities. However, cortical convolution and its variability cause signal loss at variable visual field locations and therefore introduce spurious scotomata [2]. Methods: We here compared pattern-reversal and pattern-onset stimulation in their efficacy to activate the visual cortex and recorded mVEPs to 60 locations comprising a visual field of 44 diameter from 6 subjects using VERIS 4.8 (EDI). Results: We report three main findings: (1) Pattern-onset compared to pattern-reversal stimulation enhances the amplitude by 30% for stimulation of the central visual field (<10 radius), but evokes 30% less response in the periphery (>15 ). (2) While pattern-onset and pattern-reversal responses markedly differ in their eccentricity dependence, they have a similar topographical distribution. (3) Combining both stimuli reduces the number of false positives in objective visual field perimetry. Conclusion: We conclude that pattern-onset and pattern-reversal activate identical visual areas but target different neuronal mechanisms within these areas. Furthermore, pattern-onset stimulation greatly enhances the sensitivity of the mVEP to assess the cortical representation of the central 10 of the visual field.