As someone who has suffered chronic migraine throughout the majority of her life, my focus has generally been on identifying triggers as well as seeking effective treatment to combat the debilitating pain.

Now that my migraine frequency has reduced somewhat, it’s given me space and time to ponder, what exactly are migraines? What is the mechanism by which they occur? Why are migraines so uniquely painful? And what is happening in my body when the dreaded head throb begins?

The following blog post will discuss this complex, often misunderstood, neurological phenomena and outline common symptoms associated with the condition.

What are migraines?

A broad definition of migraine is that it’s a complex sequence of physiological events that unfold over hours to days inside the brain after being triggered (1). They are a reaction of sorts, similar to that of a fever or a sneeze.

However, unlike sneezes and fevers, it’s not entirely clear what problems migraines are solving. Instead, this common disorder has been likened to a biological glitch rather than serving any biological purpose, which is quite the evolutionary conundrum given that migraine is such a common human affliction (conditions that impair function generally lead to poorer survival of an individual and eventual elimination of the trait in the population). Helping to curtail this confusion, science has put forward some evolutionary explanations as to why migraines persist in society.

Because migraine is a physiological reaction to a trigger, they can occur in any brain. But why do only some people suffer from them? New research suggests people who suffer migraines may not only have brains that function differently, but have structural differences in pain-related areas of the brain also (6).

What happens in the brain during a migraine?

While migraines appear to occur in one continual process, it can be helpful to think of them in the following phases:

Prodrome (can last a few hours to a couple of days)

Because the prodrome is the phase in which the very first symptoms of migraine are experienced, it’s thought that the area of the brain responsible for the prodrome is also the area responsible for initiating the whole migraine process. This migraine generating area in our brain is known as the hypothalamus, a small yet vital structure wedged between the thalamus (“hypo-” meaning beneath) and the pituitary gland (involved in regulating hormones), which regulates the activity of the pituitary, maintaining homeostasis in the body.

Homeostasis refers to bodily processes that actively maintain stable conditions necessary for survival. Our body has evolved a variety of mechanisms which ensure our body stays within these narrow ranges, and the hypothalamus can be likened to the big kahuna, regulating things like temperature, breathing, blood pressure, digestion, energy balance, etc. so we can stay alive. The hypothalamus can activate certain processes in the body through our endocrine system (hormones), autonomic nervous system and through our feelings, all of which have different ways of helping to achieve homeostasis.

When migraine occurs, the hypothalamus malfunctions (2), generating feelings usually triggered by changes in the environment in order to maintain homeostasis (think initiating sweating or the feeling of lethargy to help lower body temperature when it’s hot outside).

Migraine occurs when the hypothalamus is activated at the wrong time, initiating homeostatic mechanisms when it shouldn’t. For example, why, when you have a migraine, you might feel thirsty when you don’t actually need to drink or tired when you are well rested; an explanation for symptom contradictions which can be observed below (irritability or euphoria, constipation or diarrhoea, etc.)

Aura (usually lasts under an hour, typically 30-45 minutes)

During the aura phase, a temporary disturbance in brain function occurs, believed to be caused by Cortical Spreading Depression (CSD) (3) which can be thought of as a wave-like motion that moves from one spot of the brain spreading outwards. The wave is known as “a wave of depolarisation” or the firing of neurons that occurs at a very specific rate followed by a period of subdued neural activity in the same area. The type of symptoms a person experiences in this phase will depend on where the wave is centred in the brain. The most common place is in the occipital lobe which is responsible for visual images, which accounts for the common symptom of visual disturbances (tunnel vision, area of visual loss, zigzag lines, etc.).

Pain Phase: (4-72 hours, though may last longer in certain circumstances)

During the pain phase of a migraine attack, pain-sensing structures in the brainstem are activated at the wrong time. In the brainstem there are clusters of nerve cells that receive input from nerves that supply the skull and from the blood vessels, a network referred to as the trigeminovascular system.(4).

The trigeminal system is responsible for relaying pain signals to the brain. When functioning normally, the trigeminal nerve transmits touch, temperature and other sensations from the skin to the face, scalp and some of the blood vessels and layers covering the cerebral cortex. However, during a migraine, the threshold for provoking pain is lowered (the pathway becomes sensitized) and sensations that would normally be pain-free, such as light and sound, become painful. This sensitisation is thought to be due to repeated activation of the trigeminovascular system over time (7).

Pain ensues when trigeminovascular neurons are activated and relay the head pain signal from the peripheral (outside the blood-brain barrier) to the central nervous system (inside the blood-brain barrier). When the trigeminal nerve becomes activated (e.g. by food triggers) this results in the release of neuropeptides from the nerve. These neuropeptides cause painful neurogenic inflammation in the brain causing widening of blood vessels, activation of nociceptors (sensory receptors that detect signals from damaged tissue) and mast cell degranulation, all of which contribute to the migraine headache. Inflammation, in turn, activates nerve endings of the trigeminovascular system which relays pain signals back to the brain stem resulting in a vicious cycle. This feed-forward loop explains why migraines tend to build over time, culminating in extreme pain.

When the brain is working optimally, the cluster of nerve cells in the brain stem are there to detect when there is a threat to the head or skull, usually from trauma, a blow to the head or infection. Pain sensing systems are there to alert us if something is wrong so we can do something about it. However, when a migraine occurs, the pain-sensing structures are turned on by the migraine process itself rather than by any actual injury or threat.

Postdrome: (lasting anywhere from 24-48 hours)

Recovering from all the stuff that has just happened, the postdrome is the phase in which the brain tries to restore itself back to equilibrium; to peace.

Note: it’s important to note that not everyone with migraine will experience the above mentioned phases. For example, some may experience a prodrome phase in one migraine attack but not another, while others will experience the same phases with each migraine. It’s just another example of how migraines vary widely from individual to individual.

What are the many types of migraine?

Migraines can be named according to what type of aura a person experiences, what triggers them, their location in the brain and the pattern by which they occur.

Some of the most common migraines are:

• Ocular migraine
• Basilar migraine
• Olfactory migraine
• Vestibular migraine
• Episodal migraine
• Sensory migraine
• Menstrual migraine
• Hormonal migraine
• Weather migraine
• Hemiplegic migraine

The variation in names has led people to think that these migraines are different and thus require a unique approach when in fact they are all part of the same underlying process (5).

How do you know if what you have is a migraine?

Again, we can look at the different phases of migraine and their associated symptoms to help identify if what you are experiencing is likely to be a migraine:

• Prodrome symptoms: fatigue, thirst, repetitive yawning, increase urination, hunger, not wanting to eat, constipation, diarrhoea, depressed mood, irritability, euphoria, mental fogginess
  It’s unlikely a person in the prodrome phase will experience all of these symptoms, instead it’s more likely that they’ll notice one or two symptoms that occur before the pain phase.
• Aura: temporary disturbance in brain function. Can include things like visual disturbances, temporary loss of vision, numbness and tingling on parts of the body, difficulty speaking or understanding
  The symptoms of the aura phase are similar to that of a stroke, which is why many people report to the ER when they experience this phase for the first time, thinking this is what is happening.
  Not everyone will experience an aura as part of their migraine
• Pain Phase: Throbbing pain on one side of the head (can be likened to drilling, icepick stabbing into the head or burning), nausea, vomiting, giddiness, insomnia, nasal congestion, anxiety, depressed mood, sensitivity to light, smell or sound, neck pain and stiffness
• Postdrome: Recovery phase where people don’t typically go back to feeling normal straight away, but may instead experience symptoms such as euphoria, depressed mood, difficulty concentrating, or sensitivity to touch.
  

Resource

The Migraine Miracle, authored by a neurologist who is also a migraineur, is a comprehensive book providing a much more in-depth explanation of how migraines occur and dietary changes which may help reduce migraine frequency. The book is well researched and manages to explain neurological processes in a way that is easy to understand and not at all overwhelming. Highly recommended.

Conclusion

Research has shown that migraines vary widely, often leading to misdiagnosis and ineffective treatment. However, what migraines lack in identical symptoms, they make up for in mutual processes, making improved therapies more attainable than ever before thanks to a clearer understanding of what exactly goes on in the body during a migraine attack. While much has been learnt about what migraines are, gaps still remain. It’s hoped that with better understanding of this complex disorder, preventative treatment will ensue so people will no longer have to endure this painful affliction.

Brigid xx

References

(1) Pescador Ruschel MA, De Jesus O. Migraine Headache. 2021 Aug 30. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 32809622.

(2) May, Arne, and Rami Burstein. “Hypothalamic regulation of headache and migraine.” Cephalalgia : an international journal of headache vol. 39,13 (2019): 1710-1719. doi:10.1177/0333102419867280

(3) Richter F, Lehmenkühler A. Cortical spreading depression (CSD) : Ein neurophysiologisches Korrelat der Migräneaura [Cortical spreading depression (CSD): a neurophysiological correlate of migraine aura]. Schmerz. 2008 Oct;22(5):544-6, 548-50. German. doi: 10.1007/s00482-008-0653-9. PMID: 18483750.

(4) Ashina, Messoud et al. “Migraine and the trigeminovascular system-40 years and counting.” The Lancet. Neurology  vol. 18,8 (2019): 795-804. doi:10.1016/S1474-4422(19)30185-1

(5) Healthy Brain Solutions – Neurology Education. Retrieved February 6, 2022, from https://www.youtube.com/watch?v=anhDtGDMqYY.

(6) Messina R, Rocca MA, Colombo B, Valsasina P, Horsfield MA, Copetti M, Falini A, Comi G, Filippi M. Cortical abnormalities in patients with migraine: a surface-based analysis. Radiology. 2013 Jul;268(1):170-80. doi: 10.1148/radiol.13122004. Epub 2013 Mar 26. PMID: 23533286.

(7) Goadsby, Peter J et al. “Pathophysiology of Migraine: A Disorder of Sensory Processing.” Physiological reviews vol. 97,2 (2017): 553-622. doi:10.1152/physrev.00034.2015