A seizure is a sudden episode involving changes in movement, sensation, or awareness, caused by a temporary, abnormal disturbance in the brain’s electrical signaling. Not every episode that appears to be a seizure is caused by epilepsy, leading to the classification of non-epileptic seizures (NES). The electroencephalogram (EEG) is the standard tool used by neurologists to record the brain’s electrical activity and determine the true cause of these events.
How the EEG Detects Seizures
The electroencephalogram works by using small metal discs, or electrodes, placed on the scalp to detect electrical impulses generated by the brain’s neurons. These signals are amplified and recorded as wavy lines, which represent the collective firing patterns of millions of brain cells. In a healthy brain, these patterns form an organized, rhythmic background activity that changes predictably depending on the person’s state.
An epileptic seizure is caused by an uncontrolled burst of synchronized electrical discharges across a network of neurons. When the EEG records an epileptic event, the normal wavy pattern is suddenly replaced by distinctive, chaotic waveforms. These abnormal signals are known as epileptiform discharges, which often appear as high-amplitude spikes or sharp waves.
These synchronized discharges indicate underlying cortical hyperexcitability, which is the hallmark of epilepsy. By observing the location and pattern of these discharges, a neurologist can gain a clearer understanding of where the seizure activity originates and how it spreads throughout the brain.
The Difference Between Epileptic and Non-Epileptic Events
The fundamental difference between epileptic and non-epileptic events lies in their physiological origin within the brain. Epileptic seizures are a neurological disorder resulting from a structural, genetic, or unknown cause that leads to abnormal, excessive neuronal electrical activity. This electrical malfunction produces the distinctive, chaotic patterns captured by the EEG.
Non-epileptic seizures, conversely, are not caused by this kind of electrical disturbance in the central nervous system. The most common type, psychogenic non-epileptic seizures (PNES), is often classified as a functional neurological disorder. This condition involves physical manifestations that mimic the movements and symptoms of an epileptic seizure, but the root cause is related to psychological or emotional stress.
Other forms of non-epileptic events can be caused by physical conditions outside of the brain, such as metabolic issues like low blood sugar or certain cardiac arrhythmias. The defining feature of all non-epileptic events is the absence of the characteristic, synchronized neuronal firing seen in epilepsy.
What Happens When an EEG is Run During a Non-Epileptic Seizure
Non-epileptic seizures do not appear on an EEG in the context of epileptiform activity. When an individual is undergoing an NES, a simultaneously recorded EEG will typically show a preserved, normal background rhythm. This means the tracing will lack the high-amplitude spikes, sharp waves, or rhythmic, rapidly firing patterns that define an epileptic event.
The absence of these abnormal, synchronized electrical discharges is the definitive diagnostic finding for a non-epileptic seizure. The brain’s electrical activity remains essentially unaffected during the episode, even while the patient is exhibiting dramatic physical symptoms. This contrast between the outward physical manifestation and the inward electrical stability separates NES from true epilepsy.
In some cases, the physical movements during an NES can generate movement artifacts on the EEG tracing. These artifacts appear as large, irregular waves caused by muscle activity or electrode displacement. They are easily distinguishable from genuine epileptiform discharges by an experienced interpreter. The EEG confirms the lack of an electrical seizure by demonstrating a normal brain rhythm underlying the artifact.
The Definitive Diagnostic Process
Since a routine, short-term EEG may miss an episodic event entirely, the gold standard for definitive diagnosis is continuous Video-EEG Monitoring. This specialized test involves continuous recording of the patient’s brain activity (EEG) while simultaneously capturing their physical behavior using a video camera. Patients are typically admitted to a specialized monitoring unit for several days to increase the likelihood of capturing a typical event.
A definitive diagnosis of non-epileptic seizures is confirmed when the video shows the patient experiencing a typical seizure-like episode, but the corresponding EEG tracing remains normal. This simultaneous documentation of a clinical event with a lack of ictal electrical discharge makes the distinction unambiguous and ensures the patient receives the correct, non-antiepileptic treatment.