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Synchronization and topology of ‘brain waves’ in epilepsy
C.J. StamDepartment of Clinical Neurophysiology
VU University Medical CenterAmsterdam, the Netherlands
Brain Waves
Leiden, Lorentz Center 24-6-2009
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Epileptic networks and EEG / MEG
Synchronization and ‘functional connectivity’
Principlesseizures
Network analysisPrinciplesSeizures
Conclusions
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A B
Synchronization:
‘Functional connectivity’
Excessive:seizures
Normal:‘fragile binding’
Diminished:Dysconnection /Cognitive dysfunction
How do distributed systems in the brain integrate theiractivity under normal and pathological conditions?
?
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Montez et al., Neuroimage 2006; 33 : 1117-1125.
Synchronization likelihood
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Hypersynchronous background rhythm‘desynchronous seizures’
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Seizures and synchronization:
Not all seizures are ‘hypersynchronous’Different frequency bands may display different patterns of synchronizationSpatial patterns of synchronization and desynchronization may be relevant
Le van Quyen et al., 2001
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Epileptic networks and EEG / MEG
Synchronization and functional connectivity
Principlesseizures
Network analysisPrinciplesseizures
Conclusions
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Felleman and van Essen 1991How do you analyse
Functional brain networks ?
Anatomy
Network theory
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A
D
E
B
C
F
: vertex : edge
Graph
Cp: Clustering coefficientLp: Pathlength
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Application of graph analysis to EEG:
C
Ldrempel
1 2
3 4
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Epileptic networks and EEG / MEG
Synchronization and functional connectivity
Principlesseizures
Network analysisPrinciplesSeizures
ModelsTLEAbsencesGlioma
Conclusions
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Small-world networks and epilepsy
Netoff et al 2004Hippocampal model Seizure activity corresponds with a small-world regimen of neurons
Percha et al 20052 dimensional lattice model of coupled neuronsAbrupt state transitions in SWN may be a mechanism of seizure development
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SWN and epilepsy ~ Methods
Ponten et al., Clin Neurophysiol 2007;118: 918-927.
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SWN and epilepsy ~ Results
BRD DRD ARD postictal
Cp Lp Cp Lp Cp Lp Cp Lp
1-48 Hz - - - - - - -
1-4 Hz - - - - -
4-8 Hz - - - - -
8-13 Hz - -
13-30 Hz - - - - - - - -
30-48 Hz - - - - - - - -
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SWN and epilepsy ~ Conclusions
During seizure activity the neuronal network changes in the direction of a small-world network
Interictal neuronal network has a more random configuration
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New hypothesis:-brain pathology is associated with network randomisation-random networks have higher synchronizability /
lower seizure threshold
Healthy Epilepsy
Seizure threshold
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Synchronization likelihood coherence
Network changes during absence seizures
pre ictal
ictal
Ponten et al. Exp Neurol 2009
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A
B C
D
L R
Bartolomei et al. Ann Neurol 2006; 59: 128-138
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theta
gamma
Changes of network measures in glioma patients:
C/<C-random> L/<L-random>
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Summary of network changes in glioma patients:-decrease of clustering coefficient C-decrease of pathlength L
Healthy controls have‘small-world’ brainnetworks
Patients have more‘random’ neworks:-relation to cognition?-lower threshold for seizures?
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Summary & Conclusions:
Synchronization / ‘functional connectivity’ are indices of functional interactions between brain regionsSeizures are accompanied by characteristic changes in synchronizationNetwork topology and seizures:
Ictal networks more ‘ordered’Interictal networks more ‘random’: lower seizure threshold?
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Acknowledgements:
Clinical NeurophysiologyR.L.M. StrijersH.E. RonnerA. HillebrandS.C. PontenW. de Rijkelaboranten
NeurologyH.W. BerendseH. BosboomI. BosmaL. DouwJ.J. HeimansM. KleinJ. ReijneveldY.A.L. PijnenburgT. PostmaPh. ScheltensD. StoffersE. Wolters
MEG B.W. van DijkJ.C. de MunckF. BartolomeiT. MontezJ. VerbuntK. CoverI. Zuiderwijk
MOVEA. Daffertshofer
AbroadM Scheltens de BoerC. CalmelsR. FerriS. MicheloyannisG. NolteM. Breakspear