The oblique effect in migraine

Abstract

There has been recent interest in orientation discrimination in migraine. To date, however, performance has been tested at a single orientation only and group differences have either failed to emerge, or have been found to depend on the spatial frequency of the stimulus. Consequently, it is unclear whether elevated thresholds in migraine are due to precortical dysfunction, or abnormal patterns of orientation tuning at cortical loci. A reduced sensitivity to oblique stimuli (the oblique effect) is thought to reflect cortical processing, eg a population bias at V1 and/or narrower tuning of cells tuned to cardinal stimuli due to recurrent intracortical synaptic connections. Orientation discrimination thresholds were calculated by using explicitly-drawn Gabor patches at cardinal (08) and oblique (458) orientations. In parallel, participants made orientation judgments using non-explicit (virtual) lines defined by two widely spaced circles that could not stimulate V1 receptive fields. Twenty migraine and twenty matched control participants were tested. Relative to the control group, the migraine group exhibited orientation-specific sensitivity losses on explicit and virtual judgments: orientation discrimination thresholds were significantly elevated in migraine about the oblique axis only. These findings reflect abnormal function of the striate and extrastriate cortex in migraine