Long-term effects of temporal lobe epilepsy on local neural networks: a graph theoretical analysis of corticography recordings.
OBJECTIVE
Pharmaco-resistant temporal lobe epilepsy (TLE) is often treated with surgical intervention at some point. As epilepsy surgery is considered a last resort by most physicians, a long history of epileptic seizures prior to surgery is not uncommon. Little is known about the effects of ongoing TLE on neural functioning. A better understanding of these effects might influence the moment of surgical intervention. Functional connectivity (interaction between spatially distributed brain areas) and network structure (integration and segregation of information processing) are thought to be essential for optimal brain functioning. We report on the impact of TLE duration on temporal lobe functional connectivity and network characteristics.


METHODS
Functional connectivity of the temporal lobe at the time of surgery was assessed by means of interictal electrocorticography (ECoG) recordings of 27 TLE patients by using the phase lag index (PLI). Graphs (abstract network representations) were reconstructed from the PLI matrix and characterized by the clustering coefficient C (local clustering), the path length L (overall network interconnectedness), and the "small world index" S (network configuration).


RESULTS
Functional connectivity (average PLI), clustering coefficients, and the small world index were negatively correlated with TLE duration in the broad frequency band (0.5-48 Hz).


CONCLUSIONS
Temporal lobe functional connectivity is lower in patients with longer TLE history, and longer TLE duration is correlated with more random network configuration. Our findings suggest that the neural networks of TLE patients become more pathological over time, possibly due to temporal lobe changes associated with long-standing lesional epilepsy.
van Dellen
Edwin
E
Department of Neurology, VU University Medical Center, Amsterdam, The Netherlands. E.vanDellen@vumc.nl
Douw
Linda
L
Baayen
Johannes C
JC
Heimans
Jan J
JJ
Ponten
Sophie C
SC
Vandertop
W Peter
WP
Velis
Demetrios N
DN
Stam
Cornelis J
CJ
Reijneveld
Jaap C
JC
D000328:Adult; D001921:Brain / Q000502:physiology; D001931:Brain Mapping / Q000379:methods; D004569:Electroencephalography / Q000379:methods*; D004827:Epilepsy / Q000378:metabolism; D004833:Epilepsy, Temporal Lobe / Q000175:diagnosis* / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009415:Nerve Net; D009474:Neurons / Q000378:metabolism; D013702:Temporal Lobe / Q000473:pathology; D013997:Time Factors