Brain correlates of single trial visual evoked potentials in migraine: more than meets the eye.

Background: Using conventional visual evoked potentials (VEPs), migraine patients
were found to be hyperresponsive to visual stimulus. Considering that a significant
portion of neuronal activity is lost for analysis in the averaging process of conventional
VEPs, in this study we investigated visual evoked responses of migraine patients and
healthy volunteers using a different approach: single trial analysis. This method permits
to preserve all stimulus-induced neuronal activations, whether they are synchronized or
not. In addition, we used MRI voxel-based morphometry to search for cortical regions
where gray matter volume correlated with single trial (st) VEP amplitude. Finally, using
resting-state functional MRI, we explored the connectivity between these regions.
Results: stVEP amplitude was greater in episodic migraine patients than in healthy
volunteers. Moreover, in migraine patients it correlated positively with gray matter volume
of several brain areas likely involved in visual processing, mostly belonging to the ventral
attention network. Finally, resting state functional connectivity corroborated the existence
of functional interactions between these areas and helped delineating their directions.
Conclusions: st-VEPs appear to be a reliable measure of cerebral responsiveness
to visual stimuli. Mean st-VEP amplitude is higher in episodic migraine patients
compared to controls. Visual hyper-responsiveness in migraine involves several
functionally-interconnected brain regions, suggesting that it is the result of a complex
multi-regional process coupled to stimulus driven attention systems rather than a
localized alteration.