Neural adaptation to responsive stimulation: a comparison of auditory and deep brain stimulation in a rat model of absence epilepsy.

BACKGROUND: Responsive deep brain stimulation (rDBS) has been recently proposed to block epileptic seizures at onset. Yet, long-term stability of brain responses to such kind of stimulation is not known.

OBJECTIVE: To quantify the neural adaptation to repeated rDBS as measured by the changes of anti-epileptic efficacy of bilateral DBS of the substantia nigra pars reticulata (SNr) versus auditory stimulation, in a rat model of spontaneous recurrent absence seizures (GAERS).

METHODS: Local field potentials (LFP) were recorded in freely moving animals during 1 h up to 24 h under automated responsive stimulations (SNr-DBS and auditory). Comparison of seizure features was used to characterise transient (repetition-suppression effect) and long-lasting (stability of anti-epileptic efficacy, i.e. ratio of successfully interrupted seizures) effects of responsive stimulations.

RESULTS: SNr-DBS was more efficient than auditory stimulation in blocking seizures (97% vs. 52% of seizures interrupted, respectively). Sensitivity to minimal interstimulus interval was much stronger for SNr-DBS than for auditory stimulation. Anti-epileptic efficacy of SNr-DBS was remarkably stable during long-term (24 h) recordings.

CONCLUSIONS: In the GAERS model, we demonstrated the superiority of SNr-DBS to suppress seizures, as compared to auditory stimulation. Importantly, we found no long-term habituation to rDBS. However, when seizure recurrence was frequent, rDBS lack anti-epileptic efficacy because responsive stimulations became too close (time interval < 40 s) suggesting the existence of a refractory period. This study thus motivates the use of automated rDBS in patients having transient seizures separated by sufficiently long intervals.