• Josep Espadaler, Maja Rogić, Vedran Deletis, Alba Leon, Cesar Quijada, and Gerardo Conesa.
• Department of Clinical Neurophysiology, Hospital Del Mar, Barcelona, Spain.
• Clin Neurophysiol. 2012 Nov 1;123(11):2205-11.

ObjectivesTo establish a methodology for mapping of primary motor cortex (M1) for cricothyroid (CTHY) muscles in a group of healthy subjects using three-dimensional (3D) magnetic resonance imaging (MRI) navigated transcranial magnetic stimulation (nTMS).MethodsTwo independent measurements were performed. Twelve right-handed healthy subjects were included in the study. In the first measurement, mapping of the abductor pollicis brevis (APB) muscle was followed by mapping of the M1 for CTHY. This was performed in 11 subjects. Second, to avoid bias concerning using a hand knob as a landmark, mapping of M1 for CTHY muscle was followed by mapping of M1 for APB. This was performed in three healthy subjects. The nTMS was used, with selective recordings of motor evoked potentials (MEPs) from APB muscle and corticobulbar motor evoked potentials (CoMEPs) from the CTHY muscle. For recording the responses from the CTHY muscle two hook wire electrodes (the size of 76 μm of diametre passing through 27 gauge needle) were inserted in the muscle. For the recording of MEPs from APB muscle, surface electrodes were used.ResultsFirst measurement: Stimulation over the left M1 for APB muscles elicits MEPs in the contralateral APB muscle with a mean latency of 22.8±1.69ms. Stimulation over the left M1 for the CTHY muscle elicits CoMEPs in the contralateral CTHY muscle with a mean latency of 11.89±1.26ms. The distance between the cortical representation for APB and CTHY was 25.19±6.52mm, with CTHY muscle representation lateral to the APB muscle. Second measurement: The results of second measurement of the distance between M1 for CTHY and M1 for APB and their cortical localisation were comparable to the results of the first measurement.ConclusionThis is the first study with the aim to determine the exact cortical localisation of CTHY muscle with nTMS. Mapping of M1 for CTHY and APB muscles by nTMS was successfully performed in all healthy subjects. The exact location of the stimulating points over M1 muscles eliciting responses in CTHY and APB muscles was determined and superimposed over 3D MRI images. The data show that M1 for CTHY muscle is about 25mm more lateral with regard to M1 for the APB muscle.SignificanceMapping of M1 for CTHY muscle might represent an important neurophysiologic marker for facilitating preoperative mapping of motor speech-related cortical areas due to the proximity of motor cortical representation for laryngeal muscles and opercular part of the Broca area.Copyright © 2012 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

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