Navigated Brain Stimulation (NBS) by Nexstim is the only CE marked and FDA cleared noninvasive solution to presurgical mapping of the motor cortex. The NBS System 5 adds navigation to transcranial magnetic stimulation (nTMS), creating a precise map of the eloquent cortex superimposed on a patient specific MRI.
NBS accurately locates the stimulating electric field (E-field) in the cortex, with the proven accuracy of direct cortical stimulation (DCS)1. The stereotactic camera provides visualization of the induced E-field, which is displayed in a 3D rendering of the individual patient’s MRI. Placing surface electrodes on the desired muscles, the 6-channel EMG records motor evoked potentials (MEPs) amplitudes and latencies. As the TMS coil is moved over the patient’s head, the operator can see, in real-time, the E-field location, strength and direction in the 3-D intracranial rendering, creating a map of the cortical somatotopy.
The patient’s motor responses are clearly marked as pegs color coded as a heat scale. Each mapping session can be stored to precisely replicate any session at a later date. NBS 5’s mapping results can be exported via DICOM to planning systems or directly into the neuronavigator. In the OR, NBS maps help optimal placement of DCS electrodes and facilitates surgical guidance.
Introduction: This article explores the feasibility of a novel repetitive navigated transcranial magnetic stimulation (rnTMS) system and compares language mapping results obtained by rnTMS in healthy volunteers and brain tumor patients.
Methods: Fifteen right-handed healthy volunteers and 50 right-handed consecutive patients with left-sided gliomas were examined with a picture-naming task combined with time-locked rnTMS (5-10 Hz and 80-120% resting motor threshold) applied over both hemispheres. Induced errors were classified into four psycholinguistic types and assigned to their respective cortical areas according to the coil position during stimulation
Results: In healthy volunteers, language disturbances were almost exclusively induced in the left hemisphere. In patients errors were more frequent and induced at a comparative rate over both hemispheres. Predominantly dysarthric errors were induced in volunteers, whereas semantic errors were most frequent in the patient group.
Conclusion: The right hemisphere's increased sensitivity to rnTMS suggests reorganization in language representation in brain tumor patients.
Significance: rnTMS is a novel technology for exploring cortical language representation. This study proves the feasibility and safety of rnTMS in patients with brain tumor.
Publication: Clin Neurophysiol. 2014 Mar;125(3):526-36. doi: 10.1016/j.clinph.2013.08.015. http://www.ncbi.nlm.nih.gov/pubmed/24051073
Objective: The aim of this study was to identify neurophysiologic markers generated by primary motor and premotor cortex for laryngeal muscles, recorded from laryngeal muscle.
Methods: Ten right-handed healthy subjects underwent navigated transcranial magnetic stimulation (nTMS) and 18 patients underwent direct cortical stimulation (DCS) over the left hemisphere, while recording neurophysiologic markers, short latency response (SLR) and long latency response (LLR) from cricothyroid muscle. Both healthy subjects and patients were engaged in the visual object-naming task. In healthy subjects, the stimulation was time-locked at 10-300ms after picture presentation while in the patients it was at zero time.
Results: The latency of SLR in healthy subjects was 12.66±1.09ms and in patients 12.67±1.23ms. The latency of LLR in healthy subjects was 58.5±5.9ms, while in patients 54.25±3.69ms. SLR elicited by the stimulation of M1 for laryngeal muscles corresponded to induced dysarthria, while LLR elicited by stimulation of the premotor cortex in the caudal opercular part of inferior frontal gyrus, recorded from laryngeal muscle, corresponded to speech arrest in patients and speech arrest and/or language disturbances in healthy subjects.
Conclusion: In both groups, SLR indicated location of M1 for laryngeal muscles, and LLR location of premotor cortex in the caudal opercular part of inferior frontal gyrus, recorded from laryngeal muscle, while stimulation of these areas in the dominant hemisphere induced transient speech disruptions.
Significance: Described methodology can be used in preoperative mapping, and it is expected to facilitate surgical planning and intraoperative mapping, preserving these areas from injuries.
Publication: Clin Neurophysiol. 2014 Feb 11. pii: S1388-2457(14)00062-5. doi: 10.1016/j.clinph.2014.01.023. http://www.ncbi.nlm.nih.gov/pubmed/24613682
Introduction: Transcranial magnetic stimulation (TMS) is being used in the pre-operative diagnostics of patients with tumors in or near the motor cortex. Although the main purpose of TMS in such patients is to map the functional areas of the motor cortex in spatial relation to the tumor, TMS also provides some numerical neurophysiological measurements of the functional status of the patient's motor system. The aim of this paper is to provide reference values for these neurophysiological measurements from a large and varied clinical sample.
Methods: TMS was used in the pre-operative work-up of patients with various types of tumors in or near the motor cortex during a 3-year period. Data was collected prospectively in 100 patients, yet this is a post hoc report.
Results: Patient characteristics had no influence on the neurophysiological parameters. The response latency time was almost never different in the tumorous versus healthy hemisphere, so clinicians should be suspicious if they find interhemispheric differences for latency. A high interhemispheric ratio of resting motor threshold (RMT) or a low interhemispheric ratio of motor evoked potential (MEP) amplitude appear to suggest immanent deterioration of the patient's motor status.
Conclusion: In addition to topographic cortical mapping, TMS also serves as a neurophysiological assessment of the functional status of the patient's motor system. The results presented here provide clinicians with a set of reference values to contextualize findings in their own tumor patients. Further research is still needed to better understand the full clinical relevance of these neurophysiological parameters
Publication: Acta Neurochir (Wien). 2012 Nov;154(11):2075-81. doi: 10.1007/s00701-012-1494-y. Epub 2012 Sep 5. http://www.ncbi.nlm.nih.gov/pubmed/22948747
Introduction: To 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).
Methods: Two 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.
Results: First 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 localization were comparable to the results of the first measurement.
Conclusion: This is the first study with the aim to determine the exact cortical localization 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.
Significance: Mapping 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.
Publication: Clin Neurophysiol. 2012 Nov;123(11):2205-11. Epub 2012 May 22. http://www.ncbi.nlm.nih.gov/pubmed/22621909
Objectives: To provide a new protocol for a simple determination of resting motor threshold (MT) and assessment of excitation-inhibition balance in motor cortex and pathways.
Methods: Navigated TMS was used to map cortical representation area of the FDI muscle bilaterally in ten healthy subjects. Reference MTs were determined using a threshold hunting paradigm. Subsequently, a novel stimulation protocol was applied which included 70 stimuli (7 intensities, sub- and suprathreshold). The "MT-curve" was constructed by computing the MTs with several threshold amplitudes with the novel protocol. The measurements were repeated. Sensitivity of the MT-curve to stimulus location was also tested.
Results: The reference MTs agreed with those determined with the novel protocol (R=0.96-0.99, p<0.001). Based on coefficient of repeatability derived from non-parametric one-way ANOVA, the repeatability was good (ρ(AO)=0.929, p<0.05). Generally, the mean difference between the repeated MT-curves was <3% of the maximum stimulator output. Coil movement 10mm medially from the optimal stimulus location increased that difference to >7%.
Conclusions: The MTs derived using the MT-curve protocol concurred with the reference MTs. The MT-curve is highly reproducible and sensitive to the exact cortical location of stimulation.
Significance: The MT-curves provide a simple way to assess motor pathway status using a single stimulation train. This may be useful in the follow-up and monitoring of motor pathway recovery e.g. from stroke or trauma.
Publication: Clin Neurophysiol. 2011 May;122(5):975-83. doi: 10.1016/j.clinph.2010.09.005.
The Nexstim NBS System is indicated for noninvasive mapping of the primary motor cortex of the brain to its cortical gyrus. The NBS System provides information that may be used in the assessment of the primary motor cortex for pre-procedural planning.
Nexstim NexSpeech®, when used together with the NBS System, is indicated for noninvasive localization of cortical areas that do not contain essential speech function. NexSpeech® provides information that may be used in pre-surgical planning in patients undergoing brain surgery. Intraoperatively, the localization information provided by NexSpeech® is intended to be verified by direct cortical stimulation.
The Nexstim NBS System and NBS System with NexSpeech® are not intended to be used during a surgical procedure. The NBS System and NBS System with NexSpeech are intended to be used by trained clinical professionals.
1 Preoperative multimodal motor mapping: a comparison of magnetoencephalography imaging,navigated transcranial magnetic stimulation, and direct cortical stimulation By: Phiroz E. Tarapore, M.D., Mitchel S. Berger, M.D., et. al Journal of Neurosurgery. 2012 Aug;117(2):354-62. doi: 10.3171/2012.5.JNS112124