Pattern-onset stimulation boosts central multifocal VEP responses.
Multifocal visual evoked potentials (VEP) allow one to assess whether stimulation at specific visual field locations elicits cortical activity; it might therefore enable us to conduct objective visual field perimetry. However, due to the cortical folding, which differs markedly between subjects, a particular electroencephalogram generator may fail to project signal on some recording electrodes. This may lead to false alarms for potential scotomata. Here we compare pattern-reversal and pattern-onset stimulation in their efficacy to activate the visual cortex and recorded mfVEPs to 60 locations comprising a visual field of 44 degrees diameter. We report three main findings: (1) Pattern-onset compared to pattern-reversal enhances the amplitude by 30% for stimulation of the central visual field (<10 degrees radius), while evoking 30% less response in the periphery (>15 degrees ). (2) Although pattern-onset and pattern-reversal responses differ markedly in their eccentricity dependence, they have a similar topographical distribution. (3) By combining both stimuli, the number of false positives was reduced to less than 1.5% of the visual field locations tested. We conclude that pattern-onset and pattern-reversal activate identical visual cortical areas but target different neural mechanisms within these areas. Furthermore, pattern-onset stimulation greatly increases the sensitivity of the mfVEP to assess the cortical representation of the central 10 degrees of the visual field.
Hoffmann
Michael B
MB
Visual Processing Lab, Universitäts-Augenklinik, Freiburg, Germany. hoffmann@aug.ukl.uni-freiburg.de
Straube
Sirko
S
Bach
Michael
M
D000328:Adult; D005074:Evoked Potentials, Visual / Q000502:physiology*; D006801:Humans; D010364:Pattern Recognition, Visual; D014793:Visual Cortex / Q000502:physiology*; D058609:Visual Field Tests; D014794:Visual Fields / Q000502:physiology*