Epilepsy | What Happens Inside the Brain During a Seizure?

A focal seizure originates in one specific area of the brain. The brain's nerve cells, known as neurons, communicate using carefully balanced electrical signals. In epilepsy, this balance is disrupted. During a focal seizure, a group of neurons in a localized region begins to fire excessively and in a synchronized manner. This hyperactivity is the "abnormal electrical signal." The term "focal" refers to this point of origin, or focus. The symptoms of a focal seizure are directly related to the function of the affected brain area. For example, if the seizure focus is in the motor cortex, which controls movement, symptoms might include involuntary jerking of a limb. If it's in the temporal lobe, responsible for memory and emotion, a person might experience feelings of déjà vu, anxiety, or sensory hallucinations like smelling a strange odor that isn't there. These seizures are sometimes called partial seizures. They can be simple, where the person remains aware, or complex, where awareness is impaired, and the person may perform automatic, purposeless movements like lip-smacking or fidgeting with their clothes.

Unlike a focal seizure, a generalized seizure involves abnormal electrical discharges that appear to begin in both hemispheres of the brain simultaneously. The networks involved are more widespread from the onset. This doesn't mean the entire brain is seizing at once, but rather that the electrical disruption is not confined to a single starting point and rapidly engages broad neural networks. Because these seizures affect large areas of the brain, they almost always result in a loss of consciousness. There are several types of generalized seizures. "Tonic-clonic seizures," previously known as grand mal, involve a phase of muscle stiffening (tonic) followed by rhythmic jerking (clonic). "Absence seizures," once called petit mal, are characterized by brief episodes of staring into space, like a momentary lapse in awareness, and are more common in children. The widespread nature of the electrical storm in generalized seizures leads to more dramatic and encompassing symptoms compared to focal seizures.

The precise cause of the abnormal signaling that leads to seizures is not always identifiable, but it stems from an imbalance between excitatory and inhibitory forces within the brain's neural circuits. Excitatory signals promote neuron firing, while inhibitory signals suppress it. In epilepsy, this equilibrium is disturbed, leading to excessive excitation. This can be due to various factors, including genetic predispositions that may alter ion channel function—the proteins that control electrical flow in neurons. Structural abnormalities in the brain, such as those caused by a traumatic brain injury, stroke, brain tumor, or infection like meningitis, can create focal points of irritable brain tissue. In some cases, developmental brain malformations that occurred before birth can also be a root cause. Essentially, any condition that damages or alters the brain's intricate wiring can disrupt the normal pattern of electrical activity and increase the risk of seizures.

Yes, abnormal electrical activity can be detected between seizures. This is a key principle in diagnosing epilepsy. The primary tool for this is the electroencephalogram (EEG), a test that records the brain's electrical activity through small electrodes placed on the scalp. A person with epilepsy may show specific abnormal patterns called "interictal epileptiform discharges" on their EEG even when they are not having a seizure. These discharges are brief, sharp bursts of electrical energy that are a biomarker for an irritable or seizure-prone brain. Identifying these signals helps neurologists confirm an epilepsy diagnosis, classify the type of epilepsy (focal or generalized), and determine the location of the seizure focus in the brain. However, a normal EEG between seizures does not rule out epilepsy, as these discharges can be infrequent and may not be captured during the test period.

Medications for epilepsy, known as anti-seizure medications or antiepileptic drugs (AEDs), work by altering the electrical activity of neurons to make them less likely to fire excessively. They do not cure epilepsy but are highly effective at controlling seizures. These drugs primarily act on the brain's neurotransmitter systems or on the ion channels in neuron membranes. One common mechanism is to enhance the effect of the brain's main inhibitory neurotransmitter, GABA (gamma-aminobutyric acid). By boosting GABA's calming influence, these drugs suppress the hyperexcitability that leads to seizures. Another major strategy is to block sodium or calcium channels on the neurons. These channels are crucial for a neuron's ability to fire and send signals. By blocking them, medications reduce the flow of electrical charge into the cell, effectively raising the threshold for a neuron to fire and preventing the rapid, repetitive firing seen in a seizure. The choice of medication depends on the type of seizure, the patient's age, and other individual health factors.