Abnormal inhibition-excitation imbalance in migraine

Abstract

Background: People with migraine show increased surround suppression of perceived contrast, a perceptual analogue of centre-surround antagonistic interactions in visual cortex. A proposed mechanism is that cortical 'hyperexcitability' or 'hyperresponsivity', a prominent theory in the migraine literature, drives abnormal excitatory-inhibitory balance to give increased local inhibition. The purpose of this cross-sectional study was to determine whether cortical hyperresponsivity and excitatory-inhibitory imbalance manifests in the visual cortical response of migraine sufferers.

Methods: Interictal steady-state visual evoked potentials (VEPs) in response to 0 to 97% contrast were recorded in 30 migraine participants (15 without aura, 15 with aura) and 21 non-headache controls. Monotonicity indices were calculated to determine response saturation or supersaturation. Contrast gain was modelled with a modified saturating hyperbolic function to allow for variation in excitation and inhibition.

Results: A greater proportion of migraine participants (43%) than controls (14%) exhibited significant VEP supersaturation at high contrast, based on monotonicity index (chi-square, p = 0.028). Supersaturation was also evident by the trend for greater suppressive exponent values in migraine compared to control individuals (Mann-Whitney rank sum, p = 0.075).

Conclusions: Supersaturation in migraine is consistent with excess excitation (hyperresponsivity) driving increased network inhibition and provides support for excitatory-inhibitory imbalance as a pathophysiological disturbance in migraine.

Keywords: Inhibition; electrophysiology; excitation; migraine; supersaturation; vision.