Eeg Sharp Activity: Morphological, Neurophysiological and Biochemical Features

February 2009 Version 10 EEG SHARP ACTIVITY: MORPHOLOGICAL, NEUROPHYSIOLOGICAL AND BIOCHEMICAL FEATURES Spike/sharp waves, morphological features: The spike/sharp wave activity are hypersynchronous discharge pattern of large amount of epileptic neuronal aggregates. Spike A spike is a pointed peak transient clearly distinguished from the ongoing EEG activity. The distinction between the spike and the ongoing activity is based upon the voltage and wave morphology. The spike stands out in clear contrast with the ongoing activity because of their higher voltage compared with the ongoing activity. From the morphological point of view, the spike has a multiphasic feature, being composed of a minor positive, major negative and another minor positive component. The multiphasic characteristic of the spike is related to the fluctuating membrane potentials during the genesis of the hypersynchronous epileptic neuronal discharge. The duration of the spike potentials ranges between 70-100 msec. The spike is usually followed by a large surface negative slow wave. Sharp waves The only difference between spikes and sharp waves lies in their duration. While the spike duration does not exceed 100 msec. The sharp wave duration ranges between 100-200 msec. Otherwise no other differences exist between the spikes and the sharp waves. Both of them are frequently termed sharp activity. From the physiological view point, the sharp activity represents large excitatory post-synaptic potentials (EPSPS) called paroxysmal depolarization shifts (PDS), while the slow waves following them interictally represent inhibitory post-synaptic potentials (IPSPS).