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The background is normal. Occipital intermittent rhythmic delta activity (OIRDA) may be seen.

CAUTION Generalized slowing is not seen.

CAUTION Focal slowing consistently over one area right arrow consider structural brain abnormality.


There may be generalized spike-and-wave, fragments of generalized spike-and-wave or polyspike-and-wave.

CAUTION Although focal spikes can occur, if they consistently arise in one area right arrow consider structural brain abnormality.

CAUTION Slow spike-and-wave (<2.5Hz) is not seen right arrow consider other epilepsy syndromes.

Example of 3-6Hz generalized spike-and-wave


Generalized spike-and-wave or polyspike-and-wave and clinical absences are provoked by hyperventilation.

CAUTION Where hyperventilation is performed well for three minutes and no generalized spike-and-wave is seen, absence seizures are unlikely.

EEG abnormality is enhanced by sleep deprivation, by sleep and on wakening. Generalized spike-and-wave often becomes fragmented with sleep deprivation or in sleep. Fragmented generalized spike-and-wave can appear focal or multi-focal but usually is not consistently seen in one area. The morphology of the focal spike-and-wave typically appears similar to the generalized spike-and-wave.


Regular 3-6 Hz generalized spike-and-wave or polyspike-and-wave occurs with absence seizures.

With generalized tonic-clonic seizures the ictal EEG is often obscured by artifact. Generalized fast rhythmic spikes are seen in the tonic stage, in the clonic phase bursts of spikes and after-coming slow waves are synchronous with clonic jerks. A postictal period of irregular slow activity follows generalized convulsions.

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