Migraine is a common, multifactorial, disabling, recurrent, hereditary neurovascular headache disorder. It usually strikes sufferers a few times per year in childhood and then progresses to a few times per week in adulthood, particularly in females. Attacks often begin with warning signs (prodromes) and aura (transient focal neurological symptoms) whose origin is thought to involve the hypothalamus, brainstem, and cortex. Once the headache develops, it typically throbs, intensifies with an increase in intracranial pressure, and presents itself in association with nausea, vomiting, and abnormal sensitivity to light, noise, and smell. It can also be accompanied by abnormal skin sensitivity (allodynia) and muscle tenderness. Collectively, the symptoms that accompany migraine from the prodromal stage through the headache phase suggest that multiple neuronal systems function abnormally. As a consequence of the disease itself or its genetic underpinnings, the migraine brain is altered structurally and functionally. These molecular, anatomical, and functional abnormalities provide a neuronal substrate for an extreme sensitivity to fluctuations in homeostasis, a decreased ability to adapt, and the recurrence of headache. Advances in understanding the genetic predisposition to migraine, and the discovery of multiple susceptible gene variants (many of which encode proteins that participate in the regulation of glutamate neurotransmission and proper formation of synaptic plasticity) define the most compelling hypothesis for the generalized neuronal hyperexcitability and the anatomical alterations seen in the migraine brain. Regarding the headache pain itself, attempts to understand its unique qualities point to activation of the trigeminovascular pathway as a prerequisite for explaining why the pain is restricted to the head, often affecting the periorbital area and the eye, and intensifies when intracranial pressure increases.

Light makes migraines worse. The authors show that this effect can be mediated by intrinsically photosensitive retinal ganglion cells projecting onto thalamic neurons that also receive nociceptive input from the dura mater. The perception of migraine headache, which is mediated by nociceptive signals transmitted from the cranial dura mater to the brain, is uniquely exacerbated by exposure to light. We found that exacerbation of migraine headache by light is prevalent among blind individuals who maintain non–image-forming photoregulation in the face of massive rod/cone degeneration. Using single-unit recording and neural tract tracing in the rat, we identified dura-sensitive neurons in the posterior thalamus whose activity was distinctly modulated by light and whose axons projected extensively across layers I–V of somatosensory, visual and associative cortices. The cell bodies and dendrites of such dura/light-sensitive neurons were apposed by axons originating from retinal ganglion cells (RGCs), predominantly from intrinsically photosensitive RGCs, the principle conduit of non–image-forming photoregulation. We propose that photoregulation of migraine headache is exerted by a non–image-forming retinal pathway that modulates the activity of dura-sensitive thalamocortical neurons.

Attacks of migraine with aura represent a phenomenon in which abnormal neuronal activity in the cortex produces sensory disturbances (aura) some 20–40 min before the onset of headache. The purpose of this study was to determine whether cortical spreading depression (CSD)—an event believed to underlie visual aura—can give rise to activation of nociceptors that innervate the meninges—an event believed to set off migraine headache. CSD was induced in anesthetized male rats by stimulation of the visual cortex with electrical pulses, pin prick, or KCl; single-unit activity of meningeal nociceptors was monitored in vivo in the rat before and after CSD. Regardless of the method of cortical stimulation, induction of CSD was recorded in 64 trials. In 31 of those trials, CSD induced a twofold increase in meningeal nociceptor firing rate that persisted for 37.0 ± 4.6 min in trials in which activity returned to baseline, or >68 min in trials in which activity remained heightened at the time recording was interrupted. In two-thirds of the trials, onset of long-lasting neuronal activation began ∼14 min after the wave of CSD. The findings demonstrates for the first time that induction of CSD by focal stimulation of the rat visual cortex can lead to long-lasting activation of nociceptors that innervate the meninges. We suggest that migraine with aura is initiated by waves of CSD that lead up to delayed activation of the trigeminovascular pathway.

Information provided to patients is thought to influence placebo and drug effects. In a prospective, within-subjects, repeated-measures study of 66 subjects with episodic migraine, we investigated how variations in medication labeling modified placebo and drug effects. An initial attack with no treatment served as a control. In six subsequent migraine attacks, each participant received either placebo or Maxalt (10-mg rizatriptan) administered under three information conditions ranging from negative to neutral to positive (told placebo, told Maxalt or placebo, told Maxalt) (N = 459 documented attacks). Treatment order was randomized. Maxalt was superior to placebo for pain relief. When participants were given placebo labeled as (i) placebo, (ii) Maxalt or placebo, and (iii) Maxalt, the placebo effect increased progressively. Maxalt had a similar progressive boost when labeled with these three labels. The efficacies of Maxalt labeled as placebo and placebo labeled as Maxalt were similar. The efficacy of open-label placebo was superior to that of no treatment. Relative to no treatment, the placebo, under each information condition, accounted for more than 50% of the drug effect. Increasing “positive” information incrementally boosted the efficacy of both placebo and medication during migraine attacks. The benefits of placebo persisted even if placebo was honestly described. Whether treatment involves medication or placebo, the information provided to patients and the ritual of pill taking are important components of care.