The migraine process starts in your nervous system, not in blood vessels
A migraine is not simply a bad headache caused by tight blood vessels. Instead, it involves a cascade of changes in your brain's chemistry and electrical activity. The process begins when something—a trigger like stress, certain foods, hormonal shifts, or sleep changes—causes your trigeminal nerve (a major nerve in your face and head) to become overactive. This nerve then releases chemicals that inflame the tissues around your brain and blood vessels, creating the throbbing pain you feel.
Researchers have learned that migraines involve a spreading wave of electrical and chemical activity across your brain's surface, called cortical spreading depression. This wave moves slowly across your brain tissue, changing how neurons fire and altering blood flow. The wave itself does not cause pain, but it triggers the release of inflammatory substances that irritate nerves and blood vessel walls. This is why migraines feel different from other headaches—the pain comes from a specific biological process, not just muscle tension or dehydration.
Key Takeaways
- Migraines involve overactivity of the trigeminal nerve, which releases chemicals that inflame tissues around your brain and blood vessels.
- A spreading wave of electrical activity moves across your brain during a migraine, triggering the release of inflammatory substances.
- Serotonin, a chemical messenger in your brain, plays a central role in migraines, which is why certain medications target serotonin levels.
- The four phases of a migraine—prodrome, aura, headache, and postdrome—reflect different stages of this biological process.
- Migraine triggers activate this cascade in people whose brains are genetically predisposed to respond this way.
How the trigeminal nerve sets off the migraine cascade
The trigeminal nerve is one of the largest nerves in your head, with branches that reach your eyes, forehead, cheeks, and jaw. When this nerve becomes overactive, it releases chemical messengers called neuropeptides, including one called calcitonin gene-related peptide (CGRP). These chemicals cause blood vessels to dilate (widen) and trigger inflammation in the protective layers surrounding your brain, called the meninges.
This inflammation is the source of migraine pain. The inflamed tissues become sensitive, and the widened blood vessels pulse with each heartbeat, creating the characteristic throbbing sensation. The trigeminal nerve also sends pain signals to the brainstem and higher brain regions, which amplify the sensation and can trigger nausea, sensitivity to light and sound, and other migraine symptoms. Understanding this mechanism led to the development of newer migraine medications that specifically block CGRP, preventing the nerve from triggering this inflammatory cascade.
Why serotonin matters in migraines
Serotonin is a chemical messenger in your brain that regulates mood, sleep, and pain perception. During a migraine, serotonin levels fluctuate abnormally. Early in the migraine process, serotonin levels spike, then drop sharply. This drop is thought to trigger the trigeminal nerve activation and the release of CGRP. Low serotonin also makes you more sensitive to pain signals, amplifying the headache sensation.
This serotonin connection explains why certain medications work for migraines. Triptans, a common migraine medication, work by mimicking serotonin and binding to serotonin receptors on nerve cells. By restoring serotonin signaling, triptans can constrict blood vessels, reduce inflammation, and block pain signals from reaching your brain. Preventive medications like selective serotonin reuptake inhibitors (SSRIs) work differently—they keep serotonin in circulation longer, stabilizing serotonin levels and making your nervous system less reactive to triggers.
The four phases of a migraine and what happens in each
Migraines typically unfold in four distinct phases, each reflecting different changes in your brain chemistry and blood flow. The prodrome phase occurs hours or even a day before the headache starts. During this time, you might feel unusually tired, crave certain foods, or notice mood changes. These symptoms reflect early changes in serotonin and other neurotransmitters, signaling that your brain is becoming unstable.
The aura phase happens next in about one-third of people with migraines. Auras are visual disturbances—flashing lights, zigzag lines, or blind spots—that last 20 to 60 minutes. Auras are caused by the spreading wave of electrical activity moving across your visual cortex at the back of your brain. This wave temporarily disrupts normal nerve firing, creating the visual symptoms. Not everyone experiences aura, and some people have aura without a headache following.
The headache phase is when the throbbing pain peaks, usually lasting 4 to 72 hours. During this phase, the trigeminal nerve is maximally active, blood vessels are dilated, and inflammation is at its height. This is when you experience sensitivity to light, sound, and movement, along with nausea or vomiting. The pain is often one-sided and worsens with physical activity.
The postdrome phase occurs after the headache subsides. You might feel exhausted, foggy, or emotionally drained for hours or even a day. Your brain is recovering from the intense neurological activity, and neurotransmitter levels are normalizing. This phase is sometimes called a "migraine hangover" because the fatigue and cognitive effects can be as disabling as the headache itself.
How genetic predisposition makes your brain more reactive
Migraines run in families because you inherit a tendency toward nervous system instability. If one or both of your parents have migraines, your risk is significantly higher. This genetic predisposition does not mean you will definitely have migraines, but it means your brain's pain-processing systems and neurotransmitter regulation are wired differently.
People with migraines have brains that are more excitable—their neurons fire more readily, and their nervous systems are more sensitive to changes in their environment. This hyperexcitability makes the trigeminal nerve more likely to activate in response to triggers. Researchers have identified several genes involved in migraine susceptibility, many of them related to ion channels (which control how electrical signals move across nerve cells) and neurotransmitter regulation. However, genetics alone does not cause migraines; triggers are still necessary to set off the cascade.
What role inflammation plays beyond the initial trigger
Inflammation is central to migraine pain, but it works differently than inflammation from an injury. When the trigeminal nerve releases CGRP and other neuropeptides, they cause blood vessels to leak fluid into surrounding tissues and activate immune cells. These immune cells release their own inflammatory chemicals, amplifying the irritation of nerve endings and blood vessel walls.
This inflammatory process can become self-sustaining. The more inflamed the tissues become, the more pain signals are sent to your brain, which can intensify the migraine. This is why anti-inflammatory medications like NSAIDs (nonsteroidal anti-inflammatory drugs) can help if taken early, before inflammation becomes severe. It also explains why some preventive medications work by reducing overall inflammation in the nervous system, making the trigeminal nerve less likely to trigger a full migraine cascade.
How triggers activate this biological process
Migraine triggers are highly individual, but common ones include stress and stress relief, hormonal changes (especially in people who menstruate), skipped meals, dehydration, sleep disruption, bright lights, strong smells, and certain foods like aged cheeses or processed meats. Each trigger works by destabilizing your nervous system in some way, making the trigeminal nerve more likely to become overactive.
Stress, for example, causes your body to release cortisol and adrenaline, which affect serotonin levels and blood vessel tone. Hormonal changes alter the sensitivity of pain-processing pathways in your brain. Skipped meals cause blood sugar fluctuations that affect neurotransmitter production. Dehydration concentrates electrolytes in your blood, changing how nerve cells fire. None of these triggers directly causes a migraine in someone without the genetic predisposition, but in someone whose brain is primed for migraines, they can tip the balance toward activation of the trigeminal nerve and the cascade that follows.
Frequently Asked Questions
Are migraines caused by blood vessel problems?
Blood vessel changes are part of the migraine process, but they are not the primary cause. The trigeminal nerve activation and the release of inflammatory chemicals come first, and blood vessel dilation is a consequence of that nerve activity. Early migraine theories focused on blood vessels, but modern research shows the nervous system is the driver.
Can stress alone cause a migraine?
Stress can trigger a migraine in someone predisposed to them, but it does not cause migraines in people without the genetic tendency. Stress activates the nervous system and alters serotonin levels, which can push a susceptible brain over the threshold into a migraine cascade. This is why stress management is a common prevention strategy.
Why do some people get aura and others don't?
Aura occurs when the spreading wave of electrical activity crosses the visual cortex at the back of your brain. Not everyone's migraines involve this wave, or the wave may not reach the visual areas. The underlying trigeminal nerve activation and inflammation can happen without aura, producing a migraine headache alone.
Does caffeine help or hurt migraines?
Caffeine can work both ways. It narrows blood vessels and can help pain relief medications work better, which is why it is included in some migraine drugs. However, regular caffeine use can lower your migraine threshold, and sudden caffeine withdrawal can trigger a migraine. The key is consistency—either use it regularly or avoid it, rather than varying your intake.
Why do migraines get worse with movement and light?
During a migraine, your brain's sensory processing is amplified. The inflamed tissues around your brain and the overactive trigeminal nerve make your visual and balance systems hypersensitive. Movement triggers more pain signals from your inner ear and neck muscles, and light overstimulates your already-sensitive visual system. This is why dark, quiet rest is often the most effective immediate response.