How is paroxysmal depolarization shift (PDS) characterized in epileptic seizures?

Updated: May 30, 2019
  • Author: David Y Ko, MD; Chief Editor: Selim R Benbadis, MD  more...
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The PDS is characterized by a prolonged calcium-dependent depolarization that results in multiple sodium-mediated action potentials during the depolarization phase, and it is followed by a prominent after-hyperpolarization, which is a hyperpolarized membrane potential beyond the baseline resting potential. Calcium-dependent potassium channels mostly mediate the after-hyperpolarization phase. When multiple neurons fire PDSs in a synchronous manner, the extracellular field recording shows an interictal spike.

If the number of discharging neurons is more than several million, they can usually be recorded with scalp EEG electrodes. Calculations show that the interictal spikes need to spread to about 6 cm2 of cerebral cortex before they can be detected with scalp electrodes.

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