Pattern-pulses and pattern-reversals evoke different cascades of cortical sources in the multifocal visual evoked potential

In this study, we used grand average retinotopy from functional magnetic resonance imaging to study the cortical sources underpinning the pulse and reversal mVEP. In doing so, we found that although the pulse mVEP was dominated by activity in V1 throughout its time course, the reversal mVEP was initially dominated by activity in extrastriate areas with V1-dominated activity following afterwards. This suggests a substantive difference in the visual processing cascade for stimuli that are pulsed on and off compared with stimuli that are reversed in contrast pattern but remain otherwise unchanged. Although these differences do not impact the clinical use of mVEPs to identify visual field defects where the pathophysiology lies before entry to the cortex, studies that use the mVEP to study cortical visual (dys-) function should take these differences into account.