  Seizure and synchronization are related to each other in complex manner.
Altered synchrony has been implicated in loss of consciousness during partial
seizures. However, the mechanism of altered consciousness following termination
of seizures has not been studied well. In this work we used bivariate mutual
information as a measure of synchronization to understand the neural correlate
of altered consciousness during and after termination of mesial temporal lobe
onset seizures. First, we have compared discrete bivariate mutual information
(MI) measure with amplitude correlation (AC), phase synchronization (PS),
nonlinear correlation and coherence, and established MI as a robust measure of
synchronization. Next, we have extended MI to more than two signals by
principal component method. The extended MI was applied on intracranial
electroencephalogram (iEEG) before, during and after 23 temporal lobe seizures
recorded from 11 patients. The analyses were carried out in delta, theta,
alpha, beta and gamma bands. In 77% of the complex partial seizures MI was
higher towards the seizure offset than in the first half of the seizure in the
seizure onset zone (SOZ) channels in beta and gamma bands, whereas MI remained
higher in the beginning or in the middle of the seizure than towards the offset
across the least involved channels in the same bands. Synchronization seems
built up outside the SOZ, gradually spread and culminated in SOZ and remained
high beyond offset leading to impaired consciousness in 82% of the complex
partial temporal lobe seizures. Consciousness impairment was scored according
to a method previously applied to assess the same in patients with temporal
lobe epilepsy during seizure.

Neurons and Cognition