how far back can an eeg detect a seizure

An electroencephalogram (EEG) can detect seizure activity in real-time, but the ability to detect a seizure after it has occurred depends on various factors, including:

1. Type of seizure: EEG is more sensitive to detecting seizures that involve widespread brain activity, such as generalized tonic-clonic seizures. Focal seizures, which affect a smaller area of the brain, may be more challenging to detect.
2. EEG recording duration: The longer the EEG recording, the higher the likelihood of detecting seizure activity. Standard EEG recordings typically last 20-30 minutes, but prolonged recordings (e.g., 24 hours) can increase the chances of detecting seizures.
3. EEG analysis techniques: Advanced analysis techniques, such as quantitative EEG (qEEG) or machine learning algorithms, can help detect subtle changes in brain activity that may indicate a seizure.
4. Post-seizure EEG changes: After a seizure, the brain may exhibit changes in electrical activity, such as post-ictal slowing or suppression, which can be detectable on EEG.

In general, an EEG can detect seizure activity:

• During the seizure: EEG can detect seizure activity in real-time, allowing for immediate diagnosis and treatment.
• Immediately after the seizure: Post-ictal changes can be detectable on EEG for several minutes to hours after the seizure.
• Several hours after the seizure: In some cases, EEG can detect abnormal brain activity, such as focal slowing or spikes, that may persist for several hours after a seizure.
• Days to weeks after the seizure: In rare cases, EEG can detect persistent abnormalities in brain activity, such as focal slowing or seizure-like patterns, that may indicate a higher risk of future seizures.

However, it’s essential to note that EEG is not always able to detect seizures, especially if:

• The seizure is focal or limited to a small area of the brain.
• The seizure occurred in a region of the brain that is not easily accessible by EEG (e.g., deep brain structures).
• The EEG recording is too short or of poor quality.

In summary, while EEG can detect seizure activity in real-time, its ability to detect seizures after they have occurred depends on various factors, and the detection window can range from several minutes to days or even weeks after the seizure.