A spike detected by Persyst is not the same thing as a seizure. Persyst is an automated software system that analyzes EEG (brainwave) recordings, and it flags two distinct types of abnormal electrical activity: spikes and seizures. These are separate categories with different clinical meanings, and seeing “spike” on a Persyst report does not mean a seizure occurred.
What a Spike Actually Is
A spike on an EEG is a brief, sharp burst of electrical activity in the brain. It has a pointed shape, lasts between 30 and 80 milliseconds, rises and falls unevenly, and is usually followed by a slower wave. It stands out clearly from the normal background rhythm of the brain. The whole event is over almost instantly.
These spikes are called “interictal” discharges, which literally means “between seizures.” They represent a tiny, localized electrical hiccup in the brain. Think of it like a spark that flares and dies out on its own. It doesn’t spread, it doesn’t evolve, and it doesn’t cause the sustained disruption that defines a seizure. Most people don’t feel anything when an interictal spike occurs, and there’s no visible change in behavior or consciousness.
How a Seizure Looks Different on EEG
A seizure on EEG is fundamentally different from a spike because it evolves over time. Rather than a single sharp burst, a seizure shows a sustained pattern of abnormal electrical activity that changes in both speed (frequency) and size (amplitude) as it progresses. This evolution is the key feature that separates a seizure from everything else on an EEG, including spikes.
At the start, a seizure often appears as a flattening of normal brain rhythms or as fast, low-voltage activity. Over seconds to minutes, the pattern builds, with electrical discharges becoming more synchronized and intense before the seizure eventually terminates. This sustained, evolving disruption is what produces the clinical symptoms people associate with seizures: altered awareness, involuntary movements, confusion, or loss of consciousness. A single spike, by contrast, is too brief and too localized to produce those effects.
What Persyst Does With Each
Persyst runs two separate detection algorithms. One identifies spikes, and the other identifies seizures. When a neurologist reviews a Persyst report, these are displayed independently. A spike detection means the software found brief, sharp discharges consistent with epileptic activity. A seizure detection means it found a sustained, evolving pattern of abnormal electrical activity.
The software is quite accurate for seizure detection. In clinical studies, Persyst’s seizure detection algorithm achieved 80% sensitivity (it caught 80% of real seizures) and 98% specificity (it rarely flagged something as a seizure when it wasn’t one). However, false positives do occur, particularly when the EEG recording picks up artifacts like muscle movement or electrical interference from equipment. This means even a Persyst seizure detection isn’t a final diagnosis. A neurologist still reviews every flagged event to confirm whether it’s a true seizure.
For spike detections, the stakes are lower. The software is essentially highlighting areas of the EEG that a neurologist should look at more closely. Finding spikes helps localize where abnormal electrical activity originates in the brain, which is useful for diagnosis and treatment planning.
Why Spikes Still Matter
Even though a spike isn’t a seizure, it’s not meaningless. Interictal spikes indicate that a region of the brain has a tendency to produce abnormal electrical discharges. In someone being evaluated for epilepsy, finding spikes on an EEG supports the diagnosis and helps pinpoint where seizures are likely originating. In someone who has already had a seizure, spikes between seizures help confirm the epileptic nature of the event.
That said, spikes are imprecise markers. They tend to show up not just at the exact spot where seizures begin, but also in surrounding brain tissue where the electrical activity has spread. Research on surgical epilepsy patients has shown that removing brain tissue based on spike location alone produces mixed outcomes, with spike-based predictions achieving only about 54% specificity for identifying the true seizure-generating zone. In other words, spikes cast a wide net. They’re helpful for pointing in the right direction, but they don’t pinpoint the problem with high precision.
Some people have spikes on an EEG and never develop clinical seizures. Others have frequent spikes that correlate with a higher seizure burden. The relationship between spikes and seizure risk varies significantly from person to person, and interpreting that relationship is something a neurologist does in the context of your full clinical picture, not something the Persyst software determines on its own.
Reading a Persyst Report
If you’re looking at a Persyst report (or heard results from one), the key distinction is simple. A spike notation means the software detected brief, sharp electrical discharges. These are abnormal but are not seizures. A seizure notation means the software detected a sustained, evolving pattern of electrical activity consistent with a clinical seizure. Both findings are flagged for a neurologist to review and confirm manually.
Persyst is a screening tool that speeds up the process of reviewing hours or even days of continuous EEG data. It highlights events of interest so a human expert can make the final call. No automated detection replaces the neurologist’s interpretation, and the presence of either spikes or seizure flags on a Persyst report is a starting point for clinical discussion, not a standalone diagnosis.