J Neurol Surg A Cent Eur Neurosurg 2015; 76(03): 190-198
DOI: 10.1055/s-0034-1396438
Original Article
Georg Thieme Verlag KG Stuttgart · New York

Transcranial Electric Stimulation for Intraoperative Motor Evoked Potential Monitoring: Dependence of Required Stimulation Current on Interstimulus Interval Value

Boban Joksimovic
1   Clinic for Neurosurgery, Clinical Centre of Serbia, Belgrade, Serbia
Aleksandar Damjanovic
2   Clinic for Psychiatry, Clinical Centre of Serbia, Belgrade, Serbia
Aleksandra Damjanovic
2   Clinic for Psychiatry, Clinical Centre of Serbia, Belgrade, Serbia
Lukas Rasulic
1   Clinic for Neurosurgery, Clinical Centre of Serbia, Belgrade, Serbia
› Author Affiliations
Further Information

Publication History

12 March 2014

15 September 2014

Publication Date:
16 January 2015 (online)


Study Objective To evaluate the relationship between stimulus intensity by constant current transcranial electric stimulation and interstimulus interval (ISI) for eliciting muscle motor evoked potentials (MEPs) in three different hand muscles and the tibialis anterior muscles.

Patients/Material and Methods We tested intraoperatively different monophasic constant current pulses and ISIs in 22 patients with clinically normal motor function. Motor thresholds of contralateral muscle MEPs were determined at 0.5 milliseconds (ms) pulse duration and ISIs of 1, 2, 3, 4, 5, and 10 ms using a train of 2, 3, and 5 monophasic constant current pulses of 62 to 104 mA before craniotomy and after closure of the dura mater.

Results The lowest stimulation threshold to elicit MEPs in the examined muscles was achieved with a train of 5 pulses (ISI: 3 ms) before craniotomy, which was statistically significant compared with 2 pulses (ISI: 3 ms) as well as 3 pulses (ISIs: 3 and 10 ms). An ISI of 3 ms gave the lowest motor thresholds with statistical significance compared with the ISIs of 4 ms (2 pulses) and of 1 ms (3 pulses). All current intensity (mA) and ISI (ms) relationship graphs had a trend of the exponential function as y = a + bx + c ρ x , where y is intensity (mA) and x is ISI (ms). The minimum of the function was determined for each patient and each muscle. The difference was statistically significant between 3 and 5 pulses before craniotomy and between 3 and 5 pulses and 2 and 5 pulses after closure of the dura mater.

Conclusion In adult neurosurgical patients with a normal motor status, a train of 5 pulses and an ISI of 3 ms provide the lowest motor thresholds. We provided evidence of the dependence of required stimulation current on ISI.

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