Classification and parameters of epileptic EEG

by Forrest Sheng Bao

data for healthy people

You can classify them by their brain activities: rest, sleep or cognitive activities.

And you can also classify them by the state of eyes: with eyes open or with eyes close.

Classify EEG data by the sampling place:

EEG data are recorded extracranially or intracranially. The first one is non-invasive and the later one is invasive. The later one is only recorded in a presurgical evaluation of focal epilepsies. The implantable electrodes is carried out to exactly localize the seizure focal, which is termed as epileptogenic zone.

The EEG signal reflecting abnormal neural discharging may source from epileptogenic zone or the opposite hemisphere of the brain.

We can also classify EEG data by the time interval that they are sampled:

EEG data can be recorded during interictal (epileptiform) activities or ictal activity. The ictal data starts from a period (for example 50 min) of pre-ictal data. The interictal period is relatively much longer than pre-ictal period. The interictal period can be up to 24 hours. It can be sampled by the widely used video-EEG recording system.

Here are some frequently-mentioned parameters of EEG data
  • channel number: 24/32/128
  • sampling rate: generally at the level of 100Hz (such as 256Hz)
  • ADC resolution: the number of bits of analog-to-digital converter
  • filters: notch or bandpass filters, and cutoff frequency
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