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

Objective: Intra-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.

Methods: A 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.

Results: The presence of BEDs in close proximity to stimulation, an increase in stimulus intensity by 1 mA, and an increase in stimulation duration by 1s 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.

Conclusions: Longer 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.

Significance: Attention to IDs may improve the safety and precision of neurophysiologic mapping.