Minimum-Norm Estimation of Motor Representations in Navigated TMS Mappings

Area of Science:

• Neuroscience
• Neurophysiology
• Medical Imaging

Background:

• Navigated transcranial magnetic stimulation (nTMS) is used to map cortical motor representations, crucial for neurosurgery and rehabilitation.
• Conventional nTMS methods may overestimate motor map areas due to the broad electric field (E-field) distribution of the stimulation pulse.

Purpose of the Study:

• To enhance the precision of nTMS-based motor maps by incorporating the E-field distribution of the stimulation pulse.
• To introduce and evaluate the minimum-norm estimate (MNE) method for improved motor representation mapping.

Main Methods:

• Developed and applied the minimum-norm estimate (MNE) method to account for the E-field distribution in nTMS.
• Tested the MNE method on simulated data, followed by application to data from six healthy volunteers and one stroke patient.
• Compared motor map areas derived from the MNE method with those from a previously established interpolation method.

Main Results:

• The MNE method demonstrated comparable hotspots and centers of gravity to the interpolation method.
• The calculated areas of the motor maps were influenced by the chosen thresholds for outlining.
• The MNE method shows potential for refining the definition of cortical motor areas.

Conclusions:

• The minimum-norm estimate (MNE) method offers a promising approach to improve the accuracy of navigated transcranial magnetic stimulation (nTMS) motor mapping.
• Further validation against direct cortical stimulation is recommended to confirm the accuracy of the MNE method in defining cortical motor areas.