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Stimulation-based state monitoring – new developments S. Kalitzin , D.Velis , F. Lopes da Silva Epilepsy Institute of The Netherlands (SEIN), Medical Physics Department Epilepsy Institute of The Netherlands (SEIN), Department of Clinical Neurophysiology
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Stimulation-based state monitoring – new developments S. Kalitzin, D.Velis, F. Lopes da Silva Epilepsy Institute of The Netherlands (SEIN), Medical Physics Department Epilepsy Institute of The Netherlands (SEIN), Department of Clinical Neurophysiology Swammerdam Institute of Life Sciences, University of Amsterdam, The Netherlands
Phase clustering index (PCI) Complex Fourier amplitudes Triggered response Repetitive stimulus S. Kalitzin, J. Parra, D. Velis, F. Lopes da Silva, Enhancement of phase clustering in the EEG/MEG gamma frequency band anticipates transition to paroxysmal epileptiform activity in epileptic patients with known visual sensitivity, IEEE-TBME, v.49, 11 p 1279-1286, 2002
Decision on stimulation sequence Monophasic Biphasic BiCAP Cyclic Alternating Pattern (CAP) Question 1: how to stimulate and measure the response ?
Non-linear response to direct electric stimulation What is a linear response ? How can we test this ?
CAP – polarity alternation For linear response model: total PCI=0
Example from patient case –MONOCAP Stimulation frequency invariant response Stimulation frequency
Application to interictal localization of the SOS Case: left TLE
Question 2: where to stimulate and where to measure the response ? • Averaged rPCI • Collective PCI
Processing features of the collective response to stimulation in one location Triggered response and correlation Partial correlation Collective phase clustering and bi-local phase coherence
Application to interictal localization of the SOS Case: (predominantly) right TLE
Speculation: going beyond locality (bilateral case) rPCI of non-linear response
What about Seizure prediction ?
Summary & Conclusions: 1. rPCI feature successfully detected the SOS in six new TLE cases. 2 left, 2 right 2 bilateral. 2. BICAP stimulation solves the problem of high PCI due to linear conductance. 3. For interictal localization tasks, the best spatial coding so far is at the stimulation site and the best response measure is the collective response. 4. Bi-local rPCI spread studies deserve attention. 5. Seizure prediction in time remains a statistical observation at best. Electrode size, recording sites and stimulation protocol might be critical. Robustness is therefore crucial.