1. 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

2. 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 , 2002

3. Question 1: how to stimulate and measure the response ?
Decision on stimulation sequence
Biphasic
Monophasic
BiCAP
Cyclic Alternating Pattern (CAP)

4. Non-linear response to direct electric stimulation
What is a linear response ?
How can we test this ?

5. Averaged triggered response analysis

7. Linear Response Model

8. For linear response model: total PCI=0
CAP – polarity alternation
For linear response model: total PCI=0

9. BICAP: Separating PCI of the non-linear response

10. Stimulation in conducting fluid (NaCl)

11. Example from patient case –MONOCAP
Stimulation frequency invariant response
Stimulation frequency

12. Application to interictal localization of the SOS
Case: left TLE

13. Robustness to stimulation frequency

14. Question 2: where to stimulate and where to measure the response ?
Averaged rPCI
Collective PCI

15. 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

16. Application to interictal localization of the SOS
Case: (predominantly) right TLE

17. Collective Impact estimations

18. Speculation: going beyond locality (bilateral case)
rPCI of non-linear response

19. What about
Seizure prediction ?

23. 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.