In search of optimal DBS paradigms to treat epilepsy: bilateral versus unilateral hippocampal stimulation in a rat model for temporal lobe epilepsy.

BACKGROUND

In many temporal lobe epilepsy (TLE) patients both hippocampi are seizure onset zones. These patients are unsuitable candidates for epilepsy surgery but may be amenable to hippocampal deep brain stimulation (DBS). The optimal DBS parameters for these patients are unknown. Recent observations suggest that even in patients with a unilateral focus switching from unilateral hippocampal DBS to bilateral hippocampal DBS could improve seizure control.

OBJECTIVE

Compare the effect of unilateral with bilateral hippocampal DBS on seizures in a rat model for TLE.

METHODS

In the post status epilepticus (SE) kainic acid rat model for TLE continuous EEG monitoring was performed for 50 days during which rats were subjected to 10 days of unilateral and 10 days of bilateral Poisson-distributed high frequency hippocampal DBS in a cross-over trial. During bilateral DBS, each hippocampus was stimulated with a separate stimulator and its own generated Poisson distribution with a mean and variance of 1/130 s.

RESULTS

Electrographic seizure rate was 23% lower during bilateral compared to unilateral hippocampal DBS (P < 0.05). No effect of unilateral nor bilateral hippocampal DBS was observed on seizure duration. When bilateral hippocampal DBS was applied, lower stimulation intensities were required to evoke after discharges (P < 0.05), reflecting a higher potency of bilateral hippocampal DBS compared to unilateral hippocampal DBS to affect hippocampal networks.

CONCLUSIONS

Superior outcome in seizure control with bilateral compared to unilateral hippocampal DBS indicates that targeting larger regions of the hippocampal formation with more than one stimulation electrode may be more successful in suppressing seizures in TLE.