Functional Mapping and Distance Measurement between Primary Motor Cortex Representation of Cricothyroid and Abductor Pollicis Brevis Muscles with Navigated Transcranial Magnetic Stimulation

1 Laboratory for Human and Experimental Neurophysiology (LAHEN), School of Medicine University of Split, Croatia, 2 Division of Intraoperative Neurophysiology St. Luke’s – Roosevelt Hospital, New York, 3 Department of Clinical Neurophysiology, Hospital del Mar, Barcelona, Spain, 4 Department of Neurosurgery, Hospital del Mar, Spain

Maja Rogić 1, Vedran Deletis 1,2 , Josep M. Espadaler3, Alba León3, Cesar Quijada3, Gerardo Conesa4

(1) Amassian et al. Proceedings of Physiologic Society 1987 (2) Ertekin et al. Clin Neurophysiol 2001 (3) Khedr & Aref. Euro J Neurol 2002 (4) Rödel et al. Laryngoscope 2004 (5) Penfi eld & Boldrey. J Neurol 1937 (6) Penfi eld & Rasmussen. The Macmillan Company, New York 1957 (7) Deletis et al. Clin Neurophysiol 2009; (8) Deletis et al. Clin Neurophysiol 2011

References

Several previous studies used transcranial magnetic stimulation (TMS) to elicit corticobulbar motor evoked potentials (CoMEPs) from laryngeal muscles, but without determining out their exact cortical localization (1, 2, 3, 4). Direct cortical stimulation (mapping) of the human primary motor cortex (M1) for laryngeal muscles (5,6), showed that vocalizations like sounds were elicited from a rather wide part of M1, with the localization more lateral to the representation for the face and lip muscles. Exact cortical distance has never been measured. These authors used 50-60 Hz stimulation and obtain tonic activity of the laryngeal and pharyngeal muscles.The data presented here is an extension of our two recently published methodologies: a) eliciting CoMEPs from the vocal muscles ast er transcranial and direct electrical stimulation (TES and DCS) in anesthetized patients (7), and b) eliciting CoMEPs from CTHY muscle with DCS and TES in patients, as well as with TES in healthy subjects (8).

Objective

Eleven healthy subjects included in the study (7 males, mean age 43 years, range 27-65 years; 4 females; mean age 30, range 25-37 years).Stimulation and recordingnTMS was used for cortical stimulation with recordings of MEPs from APB and CoMEPs from CTHY muscles. In eight subjects stimulation parameters consisted of 20 biphasic stimuli and 1 Hz stimulating rate, while in two subjects 10 Hz and in one 5 Hz was used.For recording CoMEPs from CTHY muscle, two hook wire electrodes were inserted into the muscle percutaneously (Fig 1). For the correct placement of the electrodes into CTHY muscle, the subject has to slightly extend the neck and to produce a high pitch sound. Facilitation of the electrode placement was performed by palpating lateral side of the thyroid and cricoid cartilages and CTHY muscle belly during production of high pitch sound. Correct placement of the electrode was verifi ed by EMG feedback.For recording MEP from APB muscle two surface electrodes were used.The cortical location of the stimulating points over the M1 for CTHY and APB muscles was determined and superimposed over MRI images. The parameters of MEPs from APB muscle were measured when elicited with 110% of the threshold intensity at rest. Euclidian distance between primary motor cortex representation for CTHY and APB muscles was calculated.

Subjects and methodology

Several previous studies used transcranial magnetic stimulation (TMS) to elicit corticobulbar motor evoked potentials (CoMEPs) from laryngeal muscles, but without determining out their exact cortical localization (1, 2, 3, 4). Direct cortical stimulation (mapping) of the human primary motor cortex (M1) for laryngeal muscles (5,6), showed that vocalizations like sounds were elicited from a rather wide part of M1, with the localization more lateral to the representation for the face and lip muscles. Exact cortical distance has never been measured. These authors used 50-60 Hz stimulation and obtain tonic activity of the laryngeal and pharyngeal muscles.The data presented here is an extension of our two recently published methodologies: a) eliciting CoMEPs from the vocal muscles ast er transcranial and direct electrical stimulation (TES and DCS) in anesthetized patients (7), and b) eliciting CoMEPs from CTHY muscle with DCS and TES in patients, as well as with TES in healthy subjects (8).

Introduction

Table 1: Normative values for CTHY Table2: Normative values for APB APB-CTHY

Subject Latency(ms) (R/L)

Amplitude(mV)

Intensity(%TMR)

Dose(V/m)

Single stim (Y/N)

Side(R/L)

Latency(ms)

Amplitude(mV)

Intensity(%)

Dose(V/m)

Euclidian distance(mm) NBS

1 11.3/10.06 0.037/0.2 41/37 112/ 59 Y R,L 22.07.11 0.44 37 74 26.59

2 01.12.83 25 60 88 - R 22.06.11 0.3 40 74 35.57

3 11 0.15 44 112 Y R 25 0.72 39 85 32.05

4 13.18 0.12 45 82 Y R 20.08.11 54 33 71 30.52

5 01.12.68 0.3 65 120 - R 22.04.11 0.36 31 60 25.91

6 12.07.11 0.12 53 109 Y R 24.05.11 0.6 45 76 22.05.11

7 11.02.11 0.21 57 129 - R 23.07.11 01.09.11 50 110 29.43

8 10.03.11 0.59 39 64 Y R 20.07.11 0.25 35 57 19.07.11

9 13.04.11 0.1 58 129 Y R 21.06.11 0.39 50 86 13.23

10 09.06.11 0.15 44 89 Y R 21 01.01.89 40 77 20.57

11 01.12.63 0.36 37 65 Y R 25.04.11 0.57 34 65 22.09.11

Mean ± SDRange

11.89 ± 0.389.6-13.4

0.21 ± 0.050.025-0.59

49.36 ± 2.8837-65

99.9 ± 7.1164-129 22.8 ± 0.51

20.7-25.40.60 ± 0.150.054-1.89

39 ± 1.9633-50

75.9 ± 4.357-110

25.19 ± 1.9713.23–35.05

3 rd International Symposium on Navigated Brain Stimulation, 21st -22nd October, 2001, Berlin, Germany

Cortical location for CTHY and APB muscle was successfully performed in all subjects with high reproducibility (Fig 2). Stimulation over lest M1 for CTHY muscle elicited CoMEPs in the right CTHY muscle with a mean latency of 11.9 ± 0.38 ms (Table 1). Stimulation over lest M1 for APB muscles elicited MEPs in right APB muscle with a mean latency of 22.8 ± 0.51 ms (Table 2). Distance measurement between primary motor cortex representation for CTHY and APB muscles was 25.2 ± 1.97 mm (Fig 3).

This study determined cortical location of CTHY and APB muscles with nTMS and shows that M1 for CTHY muscle is about 3 cm lateral than M1 for APB. The method can be used in preoperative mapping. Furthermore, functional mapping of M1 for CTHY muscle might represent important neurophysiologic marker for facilitating preoperative mapping of motor speech related cortical areas by nTMS.

Results and conclusion

Fig 1. (A) Placement of the recording electrodes. A) lateral view of the anatomy of CTHY; B) Optimal angle of needle insertion (30-40o); C) hook wire electrode consist of 27 gauge size needle and 76μm wire; D)Skin mark indication position of the electrode in the CTHY muscle; E) EMG activity in CTHY muscle during phonation of sound /e/ in high frequency register verifying optimal position of the hook wire electrode.

Fig 3. The 3D location of cortical motor representation for APB (1) and CTHY (2) muscles for subject No 7. Note: Highlighted line represents central sulcus. Each square within the grid represent distance of 5 mm.

Fig 2. Repeatability of MEP recordings from APB and CoMEPs from CTHY muscles and their cortical representation for M1 from subjects No.1. Each square within the grid represent distance of 5 mm.