By: Erin Vinson
Seizures are often seen as harmful events characterized by uncontrollable shaking and a loss of consciousness. While this can be the case some of the time, seizures are so much more than just that. They’re the result of abnormal excessive synchronous nerve activity, or electrical firing in the brain and is a main symptom of a condition called epilepsy. A staggering 3.4 million Americans suffer from this, and it’s defined as a condition in which a person has two or more unprovoked seizures more than 24 hours apart. The cause of epilepsy for 50% of people remains unknown, but there are some hypothesized causes, such as brain structural abnormalities, infections within the brain, and head trauma. Risk factors are also involved in someone developing epilepsy, which include older age, autism, a history of strokes, etc. Genetics are also playing an increasing role within epilepsy, though much research still needs to be conducted on this topic. One theory is that the DNA that codes how neurons interact in the brain could be mutated in epilepsy.
As for what we do know, there are two main types of epilepsy: focal and generalized seizures. Focal seizures include different subtypes, which are seizures of the four lobes of the brain. This includes temporal, parietal, occipital, and frontal lobe epilepsy. Depending on the location of the seizure, many different symptoms can arise. See the cool chart to the right for more information on which symptoms stem from seizures impacting the various areas of the brain.
Some fast facts about each type of focal seizures are that temporal lobe seizures are the most common type of epilepsy. It’s normally caused by hippocampal sclerosis, which is otherwise called mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS). An MRI of someone with TLE will reveal mesial temporal sclerosis. Parietal lobe epilepsy accounts for only 5% of seizures, as well as occipital lobe epilepsy, and this type of epilepsy can be mistaken as migraines. Frontal lobe epilepsy is the second most common form, and all of these focal type seizures can be undetectable until more severe seizures occur, at which time epileptic patients are usually diagnosed.
The second type of epilepsy is called generalized seizures, or idiopathic generalized epilepsy, that are categorized by the uncontrollable jerking movements that we often see in movies. This is usually due to the spike in electrical activity occurring in both hemispheres of the brain. It’s been determined that the cause most likely lies within genetics, but these abnormalities are mainly unknown. There are three types of generalized seizures, which are summarized in the chart to the right.
Amazingly enough, we can record seizures on machinery called an EEG, or an Electroencephalogram, which measures electrical activity in the brain. It does this by measuring the postsynaptic potentials (versus action potentials) in large groups of neurons that are active at the same time, which is shown in waves on a chart. Researchers can study these graphs from different patients and it helps determine if they have epilepsy. An MRI is then helpful in seeing the potential cause. These are super useful tools in epilepsy studies and patient care!
Seizures are so much more than how they’re depicted on TV, and the science behind them is absolutely fascinating! Research on this topic is progressing with each day, which helps us know more and more about one of the major phenomena of the human brain.
Q: What are action potentials and what do they have to do with epilepsy?
A: Action potentials are the mechanism by which neurons communicate. Electricity travels down the axons of neurons through action potentials. In epilepsy, the brain experiences a spike in action potentials, increasing the electrical activity of the brain, resulting in mild to severe seizures.
Q: What are postsynaptic potentials and how do they relate to epilepsy?
A: Postsynaptic potentials are changes in the polarization of the membrane of the postsynaptic terminal (the place where the electrical signal ends up after traveling down an axon). Therefore, they can either initiate or inhibit action potentials. In epilepsy, they receive the electrical signals much quicker and at a higher rate, which is a major factor in the increase in electrical activity within the brain before and during a seizure.