Abstracts

Rationale: Single pulse electrical stimulation (SPES) is increasingly utilized in patients with refractory epilepsy who are undergoing pre-surgical intracranial monitoring to map functional connectivity and probe epileptogenic networks. A significant limitation at present is that there is significant variability in the manner in which SPES is conducted between sites. This inconsistency may result in discordant findings that may limit the clinical utility of cortico-cortical evoked potentials (CCEPs). The aim of the present study was to investigate the optimal stimulation parameters for CCEPs for mapping functional and epileptogenic networks.

Methods: We studied 13 patients with refractory focal epilepsy undergoing intracranial EEG monitoring. We systematically titrated the intensity of single-pulse electrical stimulation at multiple sites to assess the effect of increasing current on salient features of CCEPs such as early response amplitude (N1), signal to nose ratio, waveform similarity, and spatial distribution of responses. Responses at each incremental stimulation setting were compared to each other and to a final set of responses at maximum intensity.

Results: We found that at least 2-4 mA is needed to differentiate between non-responsive and responsive sites, and that stimulation currents of 6-7 mA are needed to maximize amplitude and spatial distribution of N1 responses and stabilize waveform morphology.

Conclusions: We determined a minimum stimulation threshold necessary for eliciting CCEPs, as well as a maximum strength at which all response metrics saturate. This titration study provides practical, immediate guidance on optimal stimulation parameters to study specific features of CCEPs, which have been increasingly used to map both functional and epileptic brain networks in humans.

Funding: Please list any funding that was received in support of this abstract.: This work was supported by the NIH NINDS Grant R01 NS115929 and NIH NINDS Grant R01 NS091139.