What does a seizure look like on an EEG, and what can the EEG miss? · Grey Matter

During a seizure the trace changes from low, irregular activity to rhythmic discharges that grow in amplitude, change frequency over seconds and spread to neighbouring electrodes, followed after the seizure by slowing.

What does a seizure look like on an EEG, and what can the EEG miss?

During a seizure the trace changes from low, irregular activity to rhythmic discharges that grow in amplitude, change frequency over seconds and spread to neighbouring electrodes, followed after the seizure by slowing. Between seizures, brief sharp waves and spikes in one region can mark tissue prone to seizures. Because the scalp EEG needs several square centimetres of synchronous cortex, a small or deep seizure can be invisible on it, which is one reason electrodes are sometimes placed inside the skull to find where seizures start.