Interictal Spikes as an EEG Biomarker of Cognitive Impairment

Although interictal spikes (IISs) are a well-established EEG biomarker for epilepsy, whether they are also a biomarker of cognitive deficits is unclear. Interictal spikes are dynamic events consisting of a synchronous discharge of neurons producing high frequency oscillations and a succession of action potentials which disrupt the ongoing neural activity. There are robust data showing that IISs result in transitory cognitive impairment with the type of deficit specific to the cognitive task and anatomic location of the IIS. Interictal spike, particularly if frequent and widespread, can impair cognitive abilities, through interference with waking learning and memory and memory consolidation during sleep. Interictal spikes seem to be particularly concerning in the developing brain where animal data suggest that IISs can lead to adverse cognitive effects even after the disappearance of the spikes. Whether a similar phenomenon occurs in human beings is unclear. Thus, although IISs are a clear biomarker of transitory cognitive impairment, currently, they lack sensitivity and specificity as a biomarker for enduring cognitive impairment.