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

Epileptic networks and EEG / MEG

Synchronization and ‘functional connectivity’

Principlesseizures

Network analysisPrinciplesSeizures

Conclusions

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?

?

Montez et al., Neuroimage 2006; 33 : 1117-1125.

Synchronization likelihood

Hypersynchronous background rhythm‘desynchronous seizures’

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

Epileptic networks and EEG / MEG

Synchronization and functional connectivity

Principlesseizures

Network analysisPrinciplesseizures

Conclusions

Felleman and van Essen 1991How do you analyse

Functional brain networks ?

Anatomy

Network theory

A

D

E

B

C

F

: vertex : edge

Graph

Cp: Clustering coefficientLp: Pathlength

Application of graph analysis to EEG:

C

Ldrempel

1 2

3 4

Epileptic networks and EEG / MEG

Synchronization and functional connectivity

Principlesseizures

Network analysisPrinciplesSeizures

ModelsTLEAbsencesGlioma

Conclusions

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

SWN and epilepsy ~ Methods

Ponten et al., Clin Neurophysiol 2007;118: 918-927.

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 - - - - - - - -

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

New hypothesis:-brain pathology is associated with network randomisation-random networks have higher synchronizability /

lower seizure threshold

Healthy Epilepsy

Seizure threshold

Synchronization likelihood coherence

Network changes during absence seizures

pre ictal

ictal

Ponten et al. Exp Neurol 2009

A

B C

D

L R

Bartolomei et al. Ann Neurol 2006; 59: 128-138

theta

gamma

Changes of network measures in glioma patients:

C/<C-random> L/<L-random>

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?

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?

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