Related Experiment Video
Updated: Jun 8, 2026
A Standardized Protocol for Functional Motor Mapping Using Navigated Transcranial Magnetic Stimulation
Published on: February 27, 2026
Non-invasive preoperative localization of primary motor cortex in epilepsy surgery by navigated transcranial magnetic
Laura Säisänen1, Mervi Könönen, Petro Julkunen
1Department of Clinical Neurophysiology, Kuopio University Hospital, Kuopio, Finland. laura.saisanen@kuh.fi
Background:
Navigated transcranial magnetic stimulation (nTMS) is a non-invasive method to localize the primary motor cortex (M1).
Objective/Hypothesis:
To assess the safety and feasibility of nTMS as a non-invasive preoperative mode of functional localization of M1 in epilepsy surgery candidates with intractable focal epilepsy due to lesions in the vicinity of M1.
Methods:
We mapped the muscle representation areas of M1 with nTMS in 10 patients (age 2 to 55 years) with intractable epilepsy. The lesions were focal cortical dysplasia (n=6), ganglioglioma (n=2) polymicrogyria (n=1) or dysembryoblastic neuroepithelial tumour (n=1). The optimal stimulation sites and motor threshold (MT) of the distal hand or leg muscles were determined in both hemispheres. Cortical areas were mapped with stimulation intensities 100-120% of the MT to localize functional M1. Patients were on their stabile antiepileptic medication, and EEG was continuously monitored. The clinical benefit obtained with the preoperative nTMS mapping in the surgical decision making was scored as (1) essential, (2) beneficial, or (3) not beneficial, depending mainly on the difference between the functional and the presumed anatomic M1.
Results:
The M1 was successfully assessed in all but the 2 youngest patients (aged 2 and 5 years), in whom nTMS was unable to elicit motor responses. nTMS was regarded as essential or beneficial in the localization of M1 in relation to the lesions in 6 out of 10 cases. The optimal motor representation areas were mainly located symmetrically on the precentral gyrus, and corresponded to the presumed location of M1 in MRI. No clinical or EEG evidence of acute epileptogenic adverse effects were observed during the localization procedure. None of the operated patients developed post-operative motor deficits.
Conclusions:
nTMS is a safe and feasible clinical tool for the non-invasive preoperative localization of motor cortex in patients with intractable epilepsy due to focal lesions adjacent or within the presumed M1 in MRI.
