Analyzing the voltage field can help distinguish them from artifacts. Spikes and sharp waves should also have a voltage field, which should make biological sense in regard to the underlying location of the cortical source. Often they disrupt the underlying background activity and can have an aftergoing slow wave, to form a spike-and-wave complex. They are episodic and should clearly stand out from the underlying background activity. Epileptic spikes and sharp waves are commonly surface negative due to the depolarization of the superficial laminae (1). The clinical importance of distinguishing between spikes and sharp waves is uncertain. Sharp waves, by contrast, are not as sharply contoured and last for 70 to 200 ms. In addition, IEDs can also present as intermittent rhythmic focal slowing such as temporal intermittent rhythmic delta activity (TIRDA) in adults or occipital intermittent rhythmic delta activity (OIRDA) in children.Įpileptic spikes are sharply contoured waveforms with lasting between 20 and 70 ms ( Figure 12.1). Interictal epileptiform dischages (IED) can present as single spikes, sharp waves, or complexes that contain spikes and sharp waves that can last for up to a few seconds. In this chapter, interictal and ictal EEG patterns for common types of epilepsies will be discussed.ĮPILEPTIC ACTIVITY-GENERAL CONSIDERATIONS However, despite advances in medical technology, including functional neuroimaging and recording magnetic brain field with magnetoencephalography (MEG), EEG remains the mainstay for the diagnoses and monitoring of epileptic activity.

The EEG recording has limited specificity in terms of localization and spatial analysis as various factors such as dipole orientation, volume conduction, synchronization, and evolution of ictal activity can influence the final recording.

EEG is largely a recording of excitatory and inhibitory postsynaptic potentials generated by the large vertically oriented pyramidal neurons located in layers 3, 5, and 6 of the cerebral cortex.

Absence seizure eeg finding