Intra-stimulation discharges: An overlooked cortical electrographic entity triggered by direct electrical stimulation

• Intra-stimulation discharges (IDs) can occur during language mapping and before after-discharges (ADs).
• High stimulus intensities, long stimulation durations, and presence of baseline epileptiform discharges at the stimulation site increase the probability of triggering IDs, and consequently, ADs.
• Attention to IDs may improve the safety and precision of neurophysiologic mapping.

ObjectiveIntra-stimulation discharges (IDs) can occur during language mapping, are largely unrecognized, and may precede the occurrence of after-discharges (ADs) and seizures. This study aimed to identify predictors of ID occurrence and determine whether IDs increase the probability of triggered ADs.MethodsA total of 332 stimulation events performed during language mapping were analyzed in 3 patients who underwent intracranial EEG recordings during evaluations for epilepsy surgery. IDs were identified in 76 stimulation events. The relationships between IDs and the stimulus current intensity, stimulation duration, and proximity to regions of abnormal cortical excitability [characterized by the presence of baseline epileptiform discharges (BEDs)] were determined using regression analysis.ResultsThe presence of BEDs in close proximity to stimulation, an increase in stimulus intensity by 1 mA, and an increase in stimulation duration by 1 s independently increased the odds of triggering IDs by 7.40, 1.37, and 1.39 times, respectively. All IDs were triggered during stimulations in the temporal lobe. The occurrence of IDs increased the odds of triggering ADs 5-fold.ConclusionsLonger stimulations, higher currents, and the presence of BEDs at the stimulation site increase the probability of ID occurrence, which in turn increases the probability of triggering ADs.SignificanceAttention to IDs may improve the safety and precision of neurophysiologic mapping.