Extraoperative electrical cortical stimulation: characteristics of motor responses and correlation with precentral gyrus.

Purpose: To characterize properties and stimulation thresholds of extraoperative cortical stimulation with respect to the anatomic area stimulated.

Methods: Analysis of 1,496 bipolar extraoperative cortical stimulations with respect to stimulation threshold, anatomic area stimulated, afterdischarges (ADs), and latencies to observe a clinical sign on video analysis.

Results: Cortical stimulation mapping stimulus thresholds to induce clinical motor responses are lower when compared with stimulus thresholds to induce nonmotor responses (P < 0.01). Motor thresholds vary depending on the anatomic area stimulated with the precentral gyrus, showing lower stimulation thresholds when compared with cortex outside the precentral gyrus (P < 0.001). Afterdischarges are more likely to occur with motor stimulations outside the precentral gyrus (χ = 1; n = 123; P < 0.05), and those stimulations show longer latencies to observe an arm motor response on video analysis when compared with precentral gyrus stimulations (P < 0.05). Within the precentral gyrus, stimulation of the hand knob was achieved with lower stimulation intensities compared with stimulation outside the hand knob (P < 0.001).

Conclusion: Clinical response thresholds, afterdischarge occurrence, and latencies to observe clinical signs during extraoperative cortical stimulation vary depending on the cortex stimulated. Findings provide information about motor cortex organization and might aid interpreting results from extraoperative cortical stimulation in a clinical setting.