What is a seizure?

February 8, 2022

Written by: Sophie Liebergall

M is a twelve-year-old girl who writes memoirs about her many dolls, and loves her math and science classes in school. She has always been a little shy around her peers, but is very close with her family and loves to speak in the imagined voice of her beagle, Tony. M’s parents were surprised when they received a letter from M’s teacher a few weeks into Seventh Grade. Her teacher reported that M is often distracted and frequently does not respond when asked questions in class. Upon reflection, M’s parents had noticed something similar. Occasionally, they would catch her staring off into the distance, pupils transfixed on a point in the distance. But her seeming jaunts into another dimension never lasted more than a few seconds, so they had always assumed that she was simply daydreaming.

That was, until one day M had a seizure. She had been sitting at the kitchen table working on her homework, when suddenly she fell to the ground, arms and legs convulsing, pupils fixed ahead. The seizure had lasted less than a minute, but it had been the longest minute of M’s family’s life. She had bitten her tongue and injured her shoulder during the event, and M’s parents couldn’t get the image of their daughter’s frightening thrashing out of their mind. When M and her mother went to the emergency room after this incident, they were surprised to learn that it had not been her first seizure. The doctors told her that she had likely been having dozens of seizures every day.

Though M’s story may capture the fear and uncertainty that occurs for many people after a first seizure, it is hardly emblematic of the full range of seizure types or the way that they are experienced by those who have seizures. When most of us think of a seizure, we picture what doctors call a “generalized tonic-clonic” seizure: the person loses consciousness and their entire body starts to violently shake. However, seizures are often more subtle and can present in a dizzying multitude of forms. For example, before her obvious generalized tonic-clonic seizure, M had been having hundreds, if not thousands, of “absence” seizures, in which a person briefly stops what they are doing and stares into space. In other types of seizures, people will experience rhythmic movements in just one part of their body, such as one hand or one foot. In yet another kind of seizure, people will experience the freezing of an entire half of their body. Surprisingly, in some cases people won’t display any outward signs that they are having a seizure, but will instead perceive false sensations before or during the event. People have described hallucinations of flashing lights, ominous buzzing sounds, or the sudden onset of the nauseating scent of burning rubber1.

Given that it can appear in so many forms, what exactly is a seizure? Seizures occur when the brain has trouble keeping its electrical signals under control. Neurons, which are the cells in our brains, communicate with each other by sending electrical signals. Some neurons are very chatty; they send lots of electrical signals to their neighbors, who then pass the fresh gossip to their neighbors. Other neurons instead try to quiet the messages of their neighbors. You can think of the brain as a busy cafeteria during lunch time: lots of neurons are having different conversations at their tables as they try to carry out the normal functions of the brain. But what happens when there’s no teacher or hall monitor to tell all of the neurons to keep their voices down? All of the different conversations between the neurons get louder and louder until suddenly it’s so loud that the cafeteria descends into pandemonium. A similar chaotic chorus occurs in the brain during a seizure: all of the neurons are screaming so loud that the brain can’t make out any of the normal conversations that it needs to function (see Figure 1).

Figure 1. Seizures, which occur when there is synchronous activity of the neurons in the brain, can be captured using electroencephalography (EEG). EEG uses electrodes (usually placed on the patient’s scalp) to eavesdrop on the electrical signals that neurons use to communicate. Prior to a seizure, shown on the left, neurons communicate with either other in a regulated fashion. During a seizure (right), communication becomes dysregulated, leading to simultaneous activation of neurons. Image created with BioRender.

Why does this neural cafeteria sometimes spiral out of control? In the same way that a seizure can appear in many different forms, a seizure can also have many different causes. One common causes of seizures in children is a really high fever. In fact, up to 5% of children will have a fever-induced seizure before the age of five years old2. Seizures can also occur when the brain gets damaged, either by a traumatic brain injury, an infection, a tumor, or a toxic chemical. Some people, like M, can get repeated seizures without any other obvious provoking factor. When someone has repeated seizures where the seizures themselves seem to be the primary problem, it is called epilepsy3. Epilepsy can have its own set of causes, including mutations in the person’s genes or small regions where the anatomy of the brain has developed abnormally.

What are the next steps for someone once they are diagnosed by a physician as having seizures? Because they can come at unexpected times, people who have had a seizure are often advised to avoid activities which could become dangerous if someone were to lose consciousness, such as driving a car or taking a bath alone. Doctors also have treatments that can help reduce the frequency or severity of seizures. Anti-seizure medications can dampen the electrical signals that neurons send to each other, and thus can help to quiet down the neurons when they try to talk over each other. In some people, all of their seizures start in a particular spot in their brain that is abnormal, so they can get a surgery to remove the piece of their brain where the seizures originate. Even cannabidiol (CBD) has been shown to be an effective treatment for some rare genetic forms of epilepsy (read more in this previous post).

M’s neurologist started her on a medication called lamotrigine after she was diagnosed with epilepsy. She now has to be extra careful to make sure that she gets enough sleep and avoids activities that could be dangerous if she were to have a seizure. But she has only had one “big” seizure since she started the medication, and the absence seizures have almost gone away completely. She’s had an easier time following along in the classroom, and has gained confidence when engaging with her peers.  

Though we now have a wide array of treatment options for many people with epilepsy, many questions about what seizures are and why they occur remain unanswered. We have identified a number of gene mutations associated with epilepsy, but we still don’t understand the cause of epilepsy in most patients that are diagnosed. We also don’t understand why, in some forms of epilepsy, people are more likely to have seizures when they’re falling asleep or waking up. Or why high fevers can trigger seizures in children. A long road lies ahead for researchers interested in understanding the exact mechanism of seizures. Further understanding the mechanism of seizures may not only help in the development of new medical therapies, but may also teach us a great deal about the fundamental workings of our brains.


1 Tufenkjian K, Lüders HO.   Seizure Semiology: Its Value and Limitations in Localizing the Epileptogenic Zone.   J Clin Neurol. 2012 Dec;8(4):243-250.   https://doi.org/10.3988/jcn.2012.8.4.243

2 “Febrile Seizures Fact Sheet”, NINDS, Publication date September 2015. NIH Publication No. 15-3930

 3 Bromfield EB, Cavazos JE, Sirven JI, editors. West Hartford (CT): American Epilepsy Society; 2006.

Figure 1 and Cover Image created with BioRender

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