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Source: Cao Y, et al. Functional MRI-BOLD of visually triggered headache in patients with migraine. Arch Neurol 1999; 56:548-554.
As neuroimaging advances, so does our understanding of the underlying neurophysiologic events in migraine. Cao and associates used a functional MRI-BOLD oxygenation level dependent contrast (fMRI-BOLD) to study occipital cortex perfusion and activation during visual stimulation of 10 migraine with aura (MwA) patients, two migraine without aura patients (MwoA), and six controls. fMRI-BOLD technique measures relative changes in oxygenation of blood and can, therefore, be used to study brain activation and, indirectly, blood flow. Visual stimulation attempted to trigger migraine using an alternating red-green projected checkerboard through MRI, compatible mirrored goggles. Six MwA patients developed headache. Only two of the six experienced visual changes associated with the headache. Two MwoA patients developed headache and neither had visual changes. The mean time from visual stimulation to the onset of the headache was 7.3 ± 5.2 minutes. Suppression of occipital cortical activation was recorded in six of the eight triggered headache subjects, which included one person in the MwoA group. Suppression of activation was noted to be both bilateral and unilateral and did not correlate to the intensity of the headache or the location of the head pain. The rate of propagation of the suppression ranged from 2.9 to 6.0 mm/min (mean ± SD, 4.1 ± 1.3). It was noted that four of six subjects with headache and no visual changes still recorded spreading activation. In six of eight triggered headache subjects the occipital cortical neuronal suppression was associated with an increase in the baseline intensity. The increase in baseline intensity on BOLD images reflects vasodilation and hyperoxia.
fMRI-BOLD imaging proves to be another valuable technique in unlocking the neurophysiologic and neuro-vascular secrets of migraine. Cao et al make several important conclusions that are worth reiterating. First, visually triggered headache in migraine patients is associated with spreading suppression. The rate of this change is consistent with the 2 mm/min cortical spreading depression of Leao and the clinically observed spreading scotoma of Lashley. It is interesting to note that six of the eight subjects with spreading suppression did not report visual changes. Cao et al also observed that the spreading suppression was associated with initial activation in the occipital cortex. However, the question of whether the origin of this phenomenon is neuronal or vascular remains unanswered by the current techniques. —jr