A migraine attack is not simply a bad headache. It is a cascade of events in the brain that begins hours before pain arrives, driven by abnormal activation of deep brain structures, a surge of inflammatory signaling molecules along pain-carrying nerves, and a nervous system that, in susceptible people, processes sensory information differently from the start. Why certain people experience this cascade repeatedly while others never do comes down to a tangle of inherited genetic variants, hormonal fluctuations, and a brain that stays in a state of heightened readiness between attacks.
Where an Attack Actually Starts
For decades, migraine was thought to begin with blood vessels constricting and then expanding inside the skull. That vascular theory turned out to be wrong. Brain imaging showed that headache pain can begin while blood flow is still reduced, and that blood-flow changes during an attack do not line up with when the pain starts or stops.1PubMed Central. Cerebral blood flow and arterial responses in migraine: history and future perspectives The real origin lies deeper, in the hypothalamus, a small region at the base of the brain that regulates sleep, appetite, mood, and stress responses. Brain scans captured during spontaneous migraine attacks showed hypothalamic activation for the first time, confirming what clinicians had long suspected from the warning signs many patients experience before pain hits.2PubMed. Hypothalamic activation in spontaneous migraine attacks
Those warning signs, often called the premonitory phase, can include yawning, food cravings, neck stiffness, irritability, and fatigue. They appear hours or even a day before the headache and are thought to reflect the hypothalamus shifting into a different functional state. This early activity also involves signaling molecules like orexin and neuropeptide Y, which regulate wakefulness and pain modulation in overlapping circuits.3F1000Research. Chronobiological Mechanisms and Temporal Regulation in Migraine: A Conceptual Review The fact that migraine attacks cluster at specific times of day and often follow disrupted sleep patterns fits neatly with a hypothalamic trigger, since the hypothalamus is the brain’s master clock.
Aura and the Wave Across the Cortex
About a quarter to a third of people with migraine experience aura, a brief period of visual disturbances, tingling, or sometimes difficulty speaking that typically precedes the headache by 20 to 60 minutes. The underlying event is a phenomenon called cortical spreading depression, a slow wave of intense nerve-cell firing followed by a period of electrical silence that rolls across the surface of the brain at roughly two to three millimeters per minute. The visual hallucinations of aura, such as shimmering zigzag lines or expanding blind spots, map onto the path of this wave as it moves through the visual cortex.4PubMed Central. Migraine Visual Aura and Cortical Spreading Depression-Linking Mathematical Models to Empirical Evidence
Cortical spreading depression is more than a curiosity. It activates pain pathways by irritating the meninges, the membranes surrounding the brain, and in rare cases the prolonged reduction in blood flow that accompanies it can cause a migrainous stroke.5PubMed Central. Migrainous Infarction and Cortical Spreading Depression For most people with aura, the wave passes without lasting damage, but it serves as a visible marker of how profoundly the migraine brain’s electrical activity differs from normal during an attack.
How the Pain Gets Generated
The headache itself comes from the trigeminovascular system, a network of nerve fibers that wraps around the blood vessels of the meninges. When these fibers are activated, whether by cortical spreading depression, hypothalamic signaling, or other upstream triggers, they release a flood of inflammatory neuropeptides at their nerve endings. The result is local inflammation around the meningeal blood vessels, which the brain registers as throbbing, one-sided head pain.6PubMed Central. Migraine and the trigeminovascular system-40 years and counting
The most studied of these neuropeptides is CGRP (calcitonin gene-related peptide). It is abundant in the trigeminal nerve cells that supply the meninges, and when released from nerve endings, it triggers a chain of events including blood-vessel dilation, increased production of nitric oxide, and further sensitization of the surrounding nerves.7PubMed Central. CGRP and the Trigeminal System in Migraine This creates a feedback loop where the initial pain signal amplifies itself. Drugs that block CGRP or its receptor, the class of medications marketed as gepants and anti-CGRP antibodies, work by interrupting this loop, which is why they have been effective for many patients.
CGRP is not the only player. Another neuropeptide called PACAP (pituitary adenylate cyclase-activating peptide) shares many of the same functions: it is found in sensory nerve fibers, it dilates cranial arteries, and infusing it into migraine patients triggers attacks.8PubMed. Role of PACAP in migraine: An alternative to CGRP? Researchers are investigating whether blocking PACAP could help people who do not respond well to CGRP-targeted treatments, since both peptides can independently induce migraine-like episodes and light-aversive behavior in animal models.9PubMed Central. CGRP and migraine: could PACAP play a role too?
A Brain That Never Fully Relaxes
One of the most consistent findings in migraine research is that the brains of people with migraine behave differently even between attacks. In people without migraine, when the brain is exposed to a repetitive stimulus, like a flashing light or a repeated sound, the neural response gradually quiets down through a process called habituation. In people with migraine, this dampening does not happen. Their sensory cortices continue to react strongly to repetitive stimuli instead of tuning them out.10PubMed. Habituation and migraine This is not a subtle laboratory finding; it helps explain why bright lights, strong smells, and loud sounds are so intolerable for many migraine patients, and why sensory overload can nudge a vulnerable brain toward an attack.
Imaging studies have also found abnormal connectivity between the thalamus and the cortex in people with migraine. The thalamus acts as a relay station for virtually all incoming sensory information, and when its connections to the cortex are dysregulated, the brain may fail to properly filter and prioritize signals.11PubMed Central. Abnormal thalamocortical network dynamics in migraine Together, the lack of habituation and the thalamocortical abnormalities paint a picture of a nervous system that is perpetually on a higher alert setting, processing more sensory input more intensely than the situation warrants. This elevated baseline is thought to lower the threshold at which an attack can be triggered.
The Genetics of Susceptibility
Migraine runs in families, and twin studies suggest that genetics accounts for a substantial share of a person’s risk. The genetic architecture, though, is complex. For common migraine, large-scale genomic studies have identified more than 180 genetic variants that each contribute a small amount of added risk. These variants cluster in pathways related to nerve-cell signaling, blood-vessel function, and the regulation of inflammation, confirming that migraine is a disorder spread across multiple biological systems rather than a single broken gene.12PubMed Central. Genetics of migraine: where are we now?
There are, however, rare and dramatic exceptions. Familial hemiplegic migraine is a severe inherited form in which attacks include temporary paralysis on one side of the body. It can be caused by mutations in genes coding for ion channels, the protein structures that control the flow of charged particles in and out of nerve cells. In roughly half of affected families, the culprit is a mutation in CACNA1A, a gene for a calcium channel in the brain.13PubMed. The clinical spectrum of familial hemiplegic migraine associated with mutations in a neuronal calcium channel Other families carry mutations in a sodium channel gene, SCN1A.14PubMed Central. Divergent sodium channel defects in familial hemiplegic migraine A third gene, ATP1A2, encodes a sodium-potassium pump. All three mutations share a common downstream effect: they make nerve cells more excitable than they should be, essentially lowering the ignition point for a cortical spreading depression wave and, by extension, a migraine attack.15PubMed. Familial hemiplegic migraine and episodic ataxia type-2 are caused by mutations in the Ca2+ channel gene CACNL1A4
These rare monogenic forms are instructive because they spotlight the kinds of biological processes that matter in common migraine as well. The 180-plus common risk variants do not individually break a single channel or pump, but in combination they nudge the same systems toward hyperexcitability, which is why people with a heavy genetic load tend to have more frequent and more severe attacks.
Hormones and the Estrogen Connection
Before puberty, migraine rates are roughly equal between boys and girls. After puberty, women develop migraine at roughly three times the rate of men, and this gap persists until menopause, after which it narrows. The driving factor is estrogen. A drop in circulating estrogen, such as the one that occurs in the late luteal phase of the menstrual cycle, can trigger attacks of migraine without aura, while higher and more stable estrogen levels tend to be protective.16Nature Reviews Neurology. Hormonal influences in migraine — interactions of oestrogen, oxytocin and CGRP This explains why many women report that their migraines worsen around menstruation and sometimes improve during pregnancy, when estrogen levels are high and relatively steady.
Estrogen does not work in isolation. It interacts with the same CGRP pathway described earlier, influencing how much of the peptide gets released and how sensitive nerve cells are to it. It also modulates oxytocin, another hormone with pain-modulating properties. The complexity of these hormonal interactions is one reason why migraine in women can be unpredictable: the same woman might have menstrual migraines reliably for years and then find the pattern changes after starting or stopping hormonal contraception.
Triggers, Thresholds, and the Let-Down Effect
People with migraine often keep detailed trigger logs, tracking things like red wine, chocolate, weather changes, skipped meals, and stress. But the relationship between triggers and attacks is more complicated than a simple cause-and-effect list. A given trigger might provoke an attack one week and have no effect the next, because what matters is the cumulative load on a nervous system whose threshold shifts from day to day. Sleep deprivation, hormonal fluctuations, and ongoing stress can each lower the threshold independently, so that a stimulus that was harmless yesterday pushes the brain over the edge today.
One of the more counterintuitive findings is the “let-down” migraine. A study tracking migraine patients’ daily stress and headache diaries found that it was not the period of high stress itself that predicted attacks, but the drop in stress afterward. A decline in perceived stress from one evening to the next was associated with about a 50 to 90 percent increase in the odds of a migraine beginning over the following six to eighteen hours.17PubMed Central. Reduction in perceived stress as a migraine trigger: testing the “let-down headache” hypothesis This may explain why weekend and vacation migraines are so common: the brain had been holding itself together during high-demand periods, and the sudden relaxation destabilizes the system.
When Attacks Become Chronic
Most people with migraine have episodic attacks, a few per month at most. But in some, the frequency escalates until headache is present on 15 or more days per month, a condition called chronic migraine. Central sensitization is thought to be a major driver of this progression. As repeated migraine attacks bombard the trigeminal nerve pathway with inflammatory signals, the neurons handling those signals become increasingly sensitive. Eventually, stimuli that would normally be painless, such as light touch on the skin or combing hair, start to register as pain. This phenomenon, called cutaneous allodynia, has been observed in about 60 percent of people with migraine and up to 90 percent of those with chronic migraine.18PubMed Central. Central Sensitization in Migraine: A Narrative Review
Allodynia is a useful clinical marker because its presence during an attack signals that the pain system has already become sensitized, which has practical implications for treatment timing. Triptans and other acute medications tend to work much better when taken before allodynia develops. Once central sensitization has set in during an attack, the window for aborting the headache narrows considerably. This is one of the strongest arguments for treating migraine early rather than waiting to see if an attack will resolve on its own.
Energy Supply and the Mitochondrial Angle
The brain is the most metabolically demanding organ in the body, consuming a disproportionate share of the body’s energy. There is growing evidence that the migraine brain may have difficulty meeting its own energy needs. Mitochondrial dysfunction, which affects how efficiently nerve cells produce energy, has been linked to several features of migraine: disrupted calcium regulation inside cells, excessive production of damaging free radicals, and a lower threshold for the kind of intense nerve-cell firing that can initiate cortical spreading depression.19PubMed Central. Energy metabolism disturbance in migraine: From a mitochondrial point of view
This energy-deficit hypothesis helps explain why common migraine triggers, like fasting, poor sleep, and intense exercise, all have one thing in common: they stress the brain’s energy supply. It also provides a rationale for why supplements like riboflavin (vitamin B2) and coenzyme Q10, both of which support mitochondrial function, have shown modest benefit in migraine prevention trials. The effect sizes are not dramatic, but they are consistent enough to appear in clinical guidelines as options for patients who prefer non-pharmaceutical approaches.
The Gut-Brain Connection
An emerging area of research links the gut microbiome to migraine. Migraine has long been associated with gastrointestinal conditions like irritable bowel syndrome and celiac disease, and researchers have begun exploring whether the connection runs through the gut lining. When the balance of gut bacteria is disrupted, the intestinal barrier can become more permeable, allowing bacterial toxins to leak into the bloodstream. These toxins activate inflammatory pathways that may ultimately increase inflammation around pain-sensing nerves in the brain.20PubMed Central. Migraine and the Gut–Brain Axis—The Role of Microbiome-Targeted Biotics Early clinical trials testing probiotics in migraine patients have explored whether restoring gut-barrier integrity could reduce attack frequency, though the results remain preliminary.21European Journal of Clinical Nutrition. The effects of a multispecies probiotic on migraine and markers of intestinal permeability–results of a randomized placebo-controlled study
The gut-brain axis is not likely to be the primary driver of migraine for most people, but it may be a contributing factor that tips a genetically susceptible brain past its threshold. For patients who notice that their migraines correlate with digestive symptoms, this line of research at least offers a plausible biological explanation rather than a vague hand-wave about “mind-body connections.”
Epigenetics and How the Environment Reshapes Risk
Genetics sets the stage, but the environment can rewrite parts of the script. Epigenetic modifications, chemical changes that affect how genes are read without altering the DNA sequence itself, are influenced by factors like chronic stress, diet, and alcohol use. In migraine, researchers have found that deficiencies in B vitamins and folate, which are needed for a key step in gene regulation called DNA methylation, can shift gene expression in ways that may increase susceptibility to attacks.22IP Indian Journal of Neurosciences. Epigenetics in migraine: A review This adds another layer to the question of why two siblings with similar genetic risk can have very different migraine histories: their environments, diets, and stress exposures may have left different epigenetic marks on the same genes.
Why Evolution Kept Migraine Around
Given how disabling migraine is, you might wonder why natural selection has not weeded it out. Migraine is ancient, widespread, and possibly becoming more common, which suggests that the genes behind it may carry survival advantages in other contexts. Several theories have been proposed. One frames migraine as a defense mechanism, essentially a forced withdrawal from harmful environmental exposures when the brain detects that its limits are being approached. Another treats it as a trade-off: the same neural hyperexcitability that predisposes someone to migraine might also confer heightened alertness, sharper sensory perception, or faster reaction times in less extreme circumstances.23PubMed. What is the evolutionary advantage of migraine? A third possibility is that migraine is simply a byproduct of novel environmental pressures, including artificial lighting, processed foods, and chronic psychological stress, that the brain’s ancient wiring was never designed to handle. None of these explanations have been definitively proven, but they reframe migraine susceptibility as something other than a straightforward malfunction, which may be closer to the truth.