What causes migraine?
The cause of migraine may be malfunctioning of the brain stem nuclei, which are responsible for inhibition of trigeminal nerve, which in turn causes migraine. The brain stem can also cause so-called cortical spreading depression (CSD) associated with aura, which in some patients precedes the attack.
Migraine is classified by the World Health Organization for the four most disabling chronic diseases. It affects 300 million people worldwide, of which two thirds are women aged 15 – 55 years. Its course can be divided into four phases. 60% of patients experience lasting several hours to several days, problems with concentration, fatigue and sensitivity to light and noise. The second stage is an aura, which occurs in 30% of patients. Such people can see the stars and sparks, then blind or dark spots corresponding to the previous sparks. After the aura, which lasts from 20 minutes to an hour follows a migraine attack, whicg reveals a very strong headache, sensitivity to light and sound, nausea, dizziness and vomiting. The attack lasts from 4 hours to 3 days, but 70% of sufferers go through 4 phase during which they are still hypersensitive to light and sound and feel tired and entangled. This stage lasts from several hours to several days. There are a lot of stimuli that can trigger an attack, including alcohol, dehydration, hunger, lack of sleep, exercise, menstruation, stress, weather changes, allergies, height, fluorescent.
Migraines are caused by disorders of the nervous system, probably the oldest part – brainstem. It is accompanied by changes in blood flow in the brain that were once thought to be the cause of migraine pain. The cause of the aura is cortical spreading depression – wave of intense nerve cell activity, which embraces most of all areas of the brain responsible for vision. After a period of increased activity of neurons, follows its inhibition during which neurons are dormant. It is the inhibition of these areas of the visual cortex that have been overstimulated has the effect of dark spots, which replace the spark and stars.
For an attack of ;migraine pain is responsible the so-called trigeminal nerve system. The nerve cells of this system collect the pain signals from the meninges and vessels supplying them with blood and transmit to the trigeminal nucleus in the brainstem. From there, the pain signals are transmitted over the thalamus to the somatosensory cortex, which is responsible for realizing the pain.
There are two hypotheses explaining what activates the trigeminal nerve system in migraine. According to one hypothesis, trigeminal nerves are stimulated by neurotransmitters that are released by cortical spreading depression. In patients who do not have the aura CSD would cover areas of the brain where stimulation does not cause symptoms, for example cortex unrelated to sensory organs. More likely, however, seems second concept, according to which for a migraine is responsible the brainstem. It includes, among others centers of sleep, perception of light and sound, regulation of blood flow through the brain and pain centers. During a migraine attack, and after it three nuclei in the brainstem are active (locus coeruleus, raphe nuclei and periaqueductal gray). Those nuclei operating properly, inhibit neurons in the trigeminal system. Perhaps in migraine brainstem nuclei do not function properly, and inhibition is weakened. The nuclei of the brain stem may also cause cortical spreading depression. The concept of the brainstem supports the fact that the activity of the brainstem nuclei is controlled by behaviour, the cycle of sleep and wakefulness and emotional state, which often are responsible for the occurrence of an attack.
In recent years, scientists have discovered mutations in several genes that are responsible for familial hemiplegic migraine. These mutations cause the malfunction of pumps and ion channels, which regulate the activity of neurons. In all of these genes were also discovered mutations causing epilepsy, which also is related to abnormalities of ion channels.
David W. Dodick, J. Jay Gargus “Nowa aura migreny”, Świat Nauki, 9/2008
Author: Maja Kochanowska