Navigated transcranial magnetic stimulation for presurgical planning--correlation with functional MRI

Navigated Transcranial Magnetic Stimulation Motor Mapping and Diffusion Tensor Imaging Tractography for Diencephalic Tumor in Pediatric Patients

Background. In deep-seated brain tumors, adequate preoperative planning is mandatory to assess the best surgical corridor to obtain maximal safe resection. Functional diffusor tensor imaging (DTI) tractography based on navigated transcranial magnetic stimulation (nTMS) motor mapping has proven to be a valid preoperative examination method in adults. The aim of this paper is to present the application of nTMS and functional DTI tractography in a series of pediatric diencephalic tumors. Material and methods. Three patients affected by thalamic (one) and thalamopeduncular tumor (two) were successfully examined with nTMS motor mapping and DTI tractography between October 2020 and October 2021 (F:M 3:0, mean age 12 years ± 0.8). Cortical representation of leg, hand and mouth were determined in the affected hemisphere and the positive stimulation spots were set as seeds point for tractography. Results. Mapping of the motor cortex and tracts reconstruction for leg and hand were successful in all patients, while facial function was properly mapped in one patient only. In all cases, the procedure was well tolerated and no adverse events were recorded. Spatial relationships between tumor and functional tissue guided the surgical planning. Extent of the resection varied from 96.1% to 100% with a postoperative new motor deficit in one patient. Conclusions. nTMS and DTI fiber tracking is a feasible, effective and well-tolerated method to identify motor pathway in deep-seated lesion in pediatric population.

Navigated transcranial magnetic stimulation mapping of the motor cortex for preoperative diagnostics in pediatric epilepsy

OBJECTIVE

Navigated transcranial magnetic stimulation (nTMS) is a noninvasive technique often used for localization of the functional motor cortex via induction of motor evoked potentials (MEPs) in neurosurgical patients. There has, however, been no published record of its application in pediatric epilepsy surgery. In this study, the authors aimed to investigate the feasibility of nTMS-based motor mapping in the preoperative diagnostic workup within a population of children with medically refractory epilepsy.

METHODS

A single-institution database was screened for preoperative nTMS motor mappings obtained in pediatric patients (aged 0 to 18 years, 2012 to present) with medically refractory epilepsy. Patient clinical data, demographic information, and mapping results were extracted and used in statistical analyses.

RESULTS

Sixteen patients met the inclusion criteria, 15 of whom underwent resection. The median age was 9 years (range 0-17 years). No adverse effects were recorded during mapping. Specifically, no epileptic seizures were provoked via nTMS. Recordings of valid MEPs induced by nTMS were obtained in 10 patients. In the remaining patients, no MEPs could be elicited. Failure to generate MEPs was associated significantly with younger patient age (r = 0.8020, p = 0.0001863). The most frequent seizure control outcome was Engel Epilepsy Surgery Outcome Scale class I (9 patients).

CONCLUSIONS

Navigated TMS is a feasible, effective, and well-tolerated method for mapping the motor cortex of the upper and lower extremities in pediatric patients with epilepsy. Patient age modulates elicitability of MEPs, potentially reflecting various stages of myelination. Successful motor mapping has the potential to add to the existing presurgical diagnostic workup in this population, and further research is warranted.

Pediatric navigated transcranial magnetic stimulation motor and language mapping combined with diffusion tensor imaging tractography: clinical experience

OBJECTIVE

In adults, navigated transcranial magnetic stimulation (nTMS) has been established as a preoperative examination method for brain tumors in motor- and language-eloquent locations. However, the clinical relevance of nTMS in children with brain tumors is still unclear. Here, the authors present their initial experience with nTMS-based surgical planning and family counseling in pediatric cases.

METHODS

The authors analyzed the feasibility of nTMS and its influence on counseling and surgical strategy in a prospective study conducted between July 2017 and September 2019. The main inclusion criterion was a potential benefit from functional mapping data derived from nTMS and/or nTMS-enhanced tractography in pediatric patients who presented to the authors' department prior to surgery for lesions close to motor- and/or speech-eloquent areas. The study was undertaken in 14 patients (median age 7 years, 8 males) who presented with different brain lesions.

RESULTS

Motor mapping combined with cortical seed area definition could be performed in 10 children (71%) to identify the corticospinal tract by additional diffusion tensor imaging (DTI). All motor mappings could be performed successfully without inducing relevant side effects. In 7 children, nTMS language mapping was performed to detect language-relevant cortical areas and DTI fiber tractography was performed to visualize the individual language network. nTMS examination was not possible in 4 children because of lack of compliance (n = 2), syncope (n = 1), and preexisting implant (n = 1). After successful mapping, the spatial relation between lesion and functional tissue was used for surgical planning in all 10 patients, and 9 children underwent nTMS-DTI integrated neuronavigation. No surgical complications or unexpected neurological deterioration was observed. In all successful nTMS cases, better function-based counseling was offered to the families. In 6 of 10 patients the surgical strategy was adapted according to nTMS data, and in 6 of 10 cases the extent of resection (EOR) was redefined.

CONCLUSIONS

nTMS and DTI fiber tracking were feasible for the majority of children. Presurgical counseling as well as surgical planning for the approach and EOR were improved by the nTMS examination results. nTMS in combination with DTI fiber tracking can be regarded as beneficial for neurosurgical procedures in eloquent areas in the pediatric population.

Measurement of Active Motor Threshold Using a Dynamometer During Navigated Transcranial Magnetic Stimulation in a Patient with Postoperative Brain Tumor: Technical Note

BACKGROUND

Navigated transcranial magnetic stimulation (nTMS) is being used for different purposes in patients with brain tumors. However, the procedure requires a positive electrophysiological response. For patients with negative response in rest conditions, active motor threshold (AMT) may be used. However, sometimes it is difficult to obtain AMT measures owing to inability of the patient to sustain steady muscle contraction. Herein, we describe a simple method by using a hand dynamometer to obtain AMT measures during nTMS session.

CASE DESCRIPTION

A woman aged 68 years underwent total removal of a right frontal lobe oligodendroglioma World Health Organization grade II 15 years ago. Cranial magnetic resonance imaging during follow-up revealed local recurrence. In the postoperative period, she developed left upper limb paresis. A postoperative nTMS session was performed for motor electrophysiological evaluation. However, using the standard technique for AMT measurement, the patient was unable to perform sustained muscle contraction as required. A hand dynamometer was used. It allowed sustained muscle contraction for AMT measurement. A counter force for the index finger flexion, the hand support to stabilize hand joints, and a numerical screen serving for both the examiner and the patient as a feedback parameter may explain the success obtained with this simple device.

CONCLUSIONS

Although more studies are necessary to validate the method, the hand dynamometer should be considered for patients unable to sustain muscle contraction during AMT measurement.

Computed tomography-guided navigated transcranial magnetic stimulation for preoperative brain motor mapping in brain lesion resection: A case report

Background:

Navigated transcranial magnetic stimulation (nTMS) is a well establish a noninvasive method for preoperative brain motor mapping. We commonly use magnetic resonance imaging (MRI) to supply the nTMS system. In some cases, MRI is not possible or available, and the use of computed tomography (CT) is necessary. We present the first report describing the association of CT and nTMS motor mapping for brain lesion resection.

Case Description:

CT imaging of a 59-year-old man suffering from acquired immune deficiency syndrome for 17 years, presenting with seizure and right hemiparesis, revealed a small single hypodense ring-enhancing lesion in the left central sulci suggesting cerebral toxoplasmosis. After 3 weeks of neurotoxoplasmosis treatment, due to four consecutive tonic-clonic seizures, a new CT scan was performed and showed no lesion changes. MRI was in maintenance at that time. Infectious diseases department suggested a brain lesion biopsy. Due to lesion’s location, we decided to perform a presurgical nTMS motor mapping. After a small craniotomy, we could precisely locate and safely totally remove the lesion. The pathology report revealed a high suspicious toxoplasmosis pattern. The patient was discharged after 2 days and continued toxoplasmosis treatment. After 6 months follow-up, he showed no signs of any procedure-related deficits or radiological recurrence.

Conclusion:

We report the feasibility and applicability of nTMS motor mapping using CT scan as an image source. It gives neurosurgeons another possibility to perform motor mapping for brain lesion removal, especially when MRI is not available or feasible.

Functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI) maps the spatiotemporal distribution of neural activity in the brain under varying cognitive conditions. Since its inception in 1991, blood oxygen level-dependent (BOLD) fMRI has rapidly become a vital methodology in basic and applied neuroscience research. In the clinical realm, it has become an established tool for presurgical functional brain mapping. This chapter has three principal aims. First, we review key physiologic, biophysical, and methodologic principles that underlie BOLD fMRI, regardless of its particular area of application. These principles inform a nuanced interpretation of the BOLD fMRI signal, along with its neurophysiologic significance and pitfalls. Second, we illustrate the clinical application of task-based fMRI to presurgical motor, language, and memory mapping in patients with lesions near eloquent brain areas. Integration of BOLD fMRI and diffusion tensor white-matter tractography provides a road map for presurgical planning and intraoperative navigation that helps to maximize the extent of lesion resection while minimizing the risk of postoperative neurologic deficits. Finally, we highlight several basic principles of resting-state fMRI and its emerging translational clinical applications. Resting-state fMRI represents an important paradigm shift, focusing attention on functional connectivity within intrinsic cognitive networks.

Safety and tolerability of navigated TMS for preoperative mapping in neurosurgical patients

OBJECTIVE

Navigated transcranial magnetic stimulation (nTMS) is a non-invasive technique for pre-surgical motor and language mapping in patients with brain lesions. This study examines the safety and tolerability of nTMS in a large, multi-center cohort of neurosurgical patients.

METHODS

Functional mapping with monopulse and repetitive nTMS was performed in 733 patients. In this cohort, 57% of patients had left-sided tumors, 50% had frontal tumors, and 50% had seizures secondary to the lesion. Side effects and pain intensity related to the procedure were documented.

RESULTS

Patients undergoing monopulse stimulation underwent an average of 490 pulses while those undergoing repetitive stimulation received an average of 2268 pulses. During monopulse stimulation, 5.1% reported discomfort (VAS 1-3), and 0.4% reported pain (VAS>3). During repetitive stimulation, 23.4% reported discomfort and 69.5% reported pain. No seizures or other adverse events were observed.

CONCLUSIONS

nTMS is safe and well-tolerated in neurosurgical patients. Clinicians should consider expanding nTMS to patients with frequent seizures, but more evaluation is necessary to evaluate this risk fully.

SIGNIFICANCE

nTMS is safe and well-tolerated, even in neurosurgical patients with persistent occasional seizure secondary to a lesion. It should be considered in any patient with a lesion in a presumed peri-eloquent or eloquent brain region.

Principles of surgery for malignant astrocytomas

Malignant astrocytomas constitute the most aggressive and common primary tumors of the central nervous system. The standard treatment protocol for these tumors involves maximum safe surgical resection with adjuvant chemoradiotherapy. Despite numerous advances in surgical techniques and adjuncts, as well as the ongoing renaissance in the genetic and molecular characterization of these tumors, malignant astrocytomas continue to be associated with poor prognosis, with median overall survival averaging 15 months for grade IV astrocytomas after standard-of-care treatment. In this article, the goals, principles, techniques, prognostic factors, and modern outcomes of malignant astrocytoma surgery are reviewed. Particular attention is paid to contemporary methods of neuronavigation and functional mapping, the prognostic significance of the extent of resection, surgically delivered adjunctive therapies, and future avenues of research.

Functional brain mapping of patients with arteriovenous malformations using navigated transcranial magnetic stimulation: first experience in ten patients

BACKGROUND

Intracranial arteriovenous malformations (AVM) are known to be potent inductors of functional plasticity, and their vasculature makes standard functional imaging difficult. Here we conducted functional mapping of both primary motor cortex and speech related areas in patients with AVM using navigated transcranial magnetic stimulation (nTMS), which has been recently proven as a reliable noninvasive modality of preoperative functional brain mapping.

METHOD

nTMS mapping was performed in ten patients with unruptured intracranial AVMs located in or near eloquent areas. Motor mapping was conducted for six patients with AVMs near the rolandic region, and speech mapping was performed for four patients with left perisylvian AVMs. After the examination, all patients were treated with surgery, radiosurgery or observed with best medical treatment on case-by-case basis.

RESULTS

Motor mapping allowed for delineation of the primary motor cortex, even if the anatomy was severely obscured by the AVM in all cases with rolandic AVMs. No plastic relocation of the primary motor cortex was observed. Repetitive stimulation of the left ventral precentral gyrus led to speech impairments in all four cases that underwent speech mapping. Right hemispheric involvement was observed in one out of four cases and potentially indicated plastic changes. No side effects were observed.

CONCLUSION

nTMS allowed for detailed delineation of eloquent areas even within hypervascularized cortical areas. Our observations indicate that nTMS functional mapping is feasible not only in tumorous brain lesions, but also in AVMs.

Intraoperative cortico–subcortical stimulations in surgery of low-grade gliomas

In order to increase the impact of surgery on the natural history of low-grade glioma, resection should be of maximum importance. Nevertheless, since low-grade gliomas are frequently located in eloquent structures, function needs to be preserved. Therefore, studying the functional organization of the brain is mandatory for each patient due to the inter-individual anatomofunctional variability, increased in tumors due to cerebral plasticity. This strategy enables performance of a resection according to functional boundaries. However, preoperative neurofunctional imaging only allows the study of the gray matter. Consequently, since low-grade glioma invades cortical and subcortical structures and shows an infiltrative progression along the fibers, the goal of this review is to focus on the techniques able to map both cortical and subcortical regions. In addition to diffusion tensor imaging, which gives only anatomical information and still needs to be validated, intraoperative direct cortico-subcortical electrostimulation is the sole current method allowing a reliable study of the individual anatomofunctional connectivity, concerning sensorimotor, language and other cognitive functions. Its actual contribution is detailed, both in clinical issues, especially the improvement of the benefit/risk ratio of low-grade glioma resection, and in fundamental applications--namely, a new door to the connectionism and cerebral plasticity.

Language mapping with navigated repetitive TMS: proof of technique and validation

OBJECTIVE

Lesion-based mapping of speech pathways has been possible only during invasive neurosurgical procedures using direct cortical stimulation (DCS). However, navigated transcranial magnetic stimulation (nTMS) may allow for lesion-based interrogation of language pathways noninvasively. Although not lesion-based, magnetoencephalographic imaging (MEGI) is another noninvasive modality for language mapping. In this study, we compare the accuracy of nTMS and MEGI with DCS.

METHODS

Subjects with lesions around cortical language areas underwent preoperative nTMS and MEGI for language mapping. nTMS maps were generated using a repetitive TMS protocol to deliver trains of stimulations during a picture naming task. MEGI activation maps were derived from adaptive spatial filtering of beta-band power decreases prior to overt speech during picture naming and verb generation tasks. The subjects subsequently underwent awake language mapping via intraoperative DCS. The language maps obtained from each of the 3 modalities were recorded and compared.

RESULTS

nTMS and MEGI were performed on 12 subjects. nTMS yielded 21 positive language disruption sites (11 speech arrest, 5 anomia, and 5 other) while DCS yielded 10 positive sites (2 speech arrest, 5 anomia, and 3 other). MEGI isolated 32 sites of peak activation with language tasks. Positive language sites were most commonly found in the pars opercularis for all three modalities. In 9 instances the positive DCS site corresponded to a positive nTMS site, while in 1 instance it did not. In 4 instances, a positive nTMS site corresponded to a negative DCS site, while 169 instances of negative nTMS and DCS were recorded. The sensitivity of nTMS was therefore 90%, specificity was 98%, the positive predictive value was 69% and the negative predictive value was 99% as compared with intraoperative DCS. MEGI language sites for verb generation and object naming correlated with nTMS sites in 5 subjects, and with DCS sites in 2 subjects.

CONCLUSION

Maps of language function generated with nTMS correlate well with those generated by DCS. Negative nTMS mapping also correlates with negative DCS mapping. In our study, MEGI lacks the same level of correlation with intraoperative mapping; nevertheless it provides useful adjunct information in some cases. nTMS may offer a lesion-based method for noninvasively interrogating language pathways and be valuable in managing patients with peri-eloquent lesions.

Preoperative multimodal motor mapping: a comparison of magnetoencephalography imaging, navigated transcranial magnetic stimulation, and direct cortical stimulation

OBJECT

Direct cortical stimulation (DCS) is the gold-standard technique for motor mapping during craniotomy. However, preoperative noninvasive motor mapping is becoming increasingly accurate. Two such noninvasive modalities are navigated transcranial magnetic stimulation (TMS) and magnetoencephalography (MEG) imaging. While MEG imaging has already been extensively validated as an accurate modality of noninvasive motor mapping, TMS is less well studied. In this study, the authors compared the accuracy of TMS to both DCS and MEG imaging.

METHODS

Patients with tumors in proximity to primary motor cortex underwent preoperative TMS and MEG imaging for motor mapping. The patients subsequently underwent motor mapping via intraoperative DCS. The loci of maximal response were recorded from each modality and compared. Motor strength was assessed at 3 months postoperatively.

RESULTS

Transcranial magnetic stimulation and MEG imaging were performed on 24 patients. Intraoperative DCS yielded 8 positive motor sites in 5 patients. The median distance ± SEM between TMS and DCS motor sites was 2.13 ± 0.29 mm, and between TMS and MEG imaging motor sites was 4.71 ± 1.08 mm. In no patients did DCS motor mapping reveal a motor site that was unrecognized by TMS. Three of 24 patients developed new, early neurological deficit in the form of upper-extremity paresis. At the 3-month follow-up evaluation, 2 of these patients were significantly improved, experiencing difficulty only with fine motor tasks; the remaining patient had improvement to 4/5 strength. There were no deaths over the course of the study.

CONCLUSIONS

Maps of the motor system generated with TMS correlate well with those generated by both MEG imaging and DCS. Negative TMS mapping also correlates with negative DCS mapping. Navigated TMS is an accurate modality for noninvasively generating preoperative motor maps.

Cortical mapping with navigated transcranial magnetic stimulation in low-grade glioma surgery

Transcranial magnetic stimulation (TMS) is a promising method for both investigation and therapeutic treatment of psychiatric and neurologic disorders and, more recently, for brain mapping. This study describes the application of navigated TMS for motor cortex mapping in patients with a brain tumor located close to the precentral gyrus.

MATERIALS AND METHODS

In this prospective study, six patients with low-grade gliomas in or near the precentral gyrus underwent TMS, and their motor responses were correlated to locations in the cortex around the lesion, generating a functional map overlaid on three-dimensional magnetic resonance imaging (MRI) scans of the brain. To determine the accuracy of this new method, we compared TMS mapping with the gold standard mapping with direct cortical electrical stimulation in surgery. The same navigation system and TMS-generated map were used during the surgical resection procedure.

RESULTS

The motor cortex could be clearly mapped using both methods. The locations corresponding to the hand and forearm, found during intraoperative mapping, showed a close spatial relationship to the homotopic areas identified by TMS mapping. The mean distance between TMS and direct cortical electrical stimulation (DES) was 4.16 ± 1.02 mm (range: 2.56-5.27 mm).

CONCLUSION

Preoperative mapping of the motor cortex with navigated TMS prior to brain tumor resection is a useful presurgical planning tool with good accuracy.

Navigated Brain Stimulation for Preoperative Cortical Mapping in Paretic Patients: Case Report of a Hemiplegic Patient

BACKGROUND AND IMPORTANCE:

Navigated brain stimulation (NBS) is an emerging technology that can be used for preoperative mapping of the motor cortex. It combines conventional transcranial magnetic stimulation with neuronavigation and achieves high precision by taking into account all relevant physical factors. In contrast to functional imaging technologies, NBS does not rely on voluntary patient movements for cortical mapping. Thus, NBS can be used even on patients with severe motor impairment.

CLINICAL PRESENTATION:

This article presents the case of a hemiplegic elderly woman with a brain tumor in the motor cortex. Preoperative NBS surprisingly demonstrated intact corticospinal tracts in the hemiplegic patient. The results modified the surgical strategy. Direct cortical stimulation was performed intraoperatively. The direct cortical stimulation results were in agreement with the preoperative NBS findings, and the clinical success of the surgery exceeded expectations.

CONCLUSION:

NBS can be used for preoperative mapping in plegic patients. Even more important, this case report discusses why tumor resection surgery based on NBS may sometimes lead to substantially better clinical outcomes than surgery planned according to functional imaging technologies.

Navigated Transcranial Magnetic Stimulation and Functional Magnetic Resonance Imaging: Advanced Adjuncts in Preoperative Planning for Central Region Tumors

BACKGROUND:

Tumor resection in the vicinity of the motor cortex poses a challenge to all neurosurgeons. For preoperative assessment of eloquent cortical areas, functional magnetic resonance imaging (fMRI) is used, whereas intraoperatively, direct cortical stimulation (DCS) is performed. Navigated transcranial magnetic stimulation (nTMS) is comparable to DCS in activating cortical pyramidal neurons.

OBJECTIVE:

To evaluate the reliability of nTMS compared with fMRI and DCS for preoperative resection planning of centrally located tumors.

METHODS:

In a prospective series, 11 patients (ages, 20-63 years; mean, 41.9 ± 14.9 years, 2 women) with tumors located in or adjacent to the motor cortex were evaluated for surgery. fMRI and nTMS were applied for preoperative assessment of the extent of tumor resection. A 3-dimensional anatomic data set with superimposed fMRI data was integrated in the eXimia Navigated Brain Stimulation station for ensuing motor cortex mapping by nTMS. Responses from nTMS were evaluated by electromyographic response. During surgery, the coordinates of each DCS site were unambiguously defined and integrated into neuronavigation. A post hoc comparison of the coordinates of nTMS, fMRI, and DCS was performed.

RESULTS:

Distances from nTMS to DCS (10.5 ± 5.67 mm) were significantly smaller than those from fMRI to DCS (15.0 ± 7.6 mm).

CONCLUSION:

nTMS anticipates information usually only enabled by DCS and therefore allows surgical planning in eloquent cortex surgery.

Group-level variations in motor representation areas of thenar and anterior tibial muscles: Navigated Transcranial Magnetic Stimulation Study

Navigated transcranial magnetic stimulation (TMS) can be used to stimulate functional cortical areas at precise anatomical location to induce measurable responses. The stimulation has commonly been focused on anatomically predefined motor areas: TMS of that area elicits a measurable muscle response, the motor evoked potential. In clinical pathologies, however, the well-known homunculus somatotopy theory may not be straightforward, and the representation area of the muscle is not fixed. Traditionally, the anatomical locations of TMS stimulations have not been reported at the group level in standard space. This study describes a methodology for group-level analysis by investigating the normal representation areas of thenar and anterior tibial muscle in the primary motor cortex. The optimal representation area for these muscles was mapped in 59 healthy right-handed subjects using navigated TMS. The coordinates of the optimal stimulation sites were then normalized into standard space to determine the representation areas of these muscles at the group-level in healthy subjects. Furthermore, 95% confidence interval ellipsoids were fitted into the optimal stimulation site clusters to define the variation between subjects in optimal stimulation sites. The variation was found to be highest in the anteroposterior direction along the superior margin of the precentral gyrus. These results provide important normative information for clinical studies assessing changes in the functional cortical areas because of plasticity of the brain. Furthermore, it is proposed that the presented methodology to study TMS locations at the group level on standard space will be a suitable tool for research purposes in population studies.

The combination of neuronavigation with transcranial magnetic stimulation for treatment of opercular gliomas of the dominant brain hemisphere

OBJECTIVE

The objective of this study is to investigate the application of transcranial magnetic stimulation combined with neuronavigation for preoperative mapping of the language area in neurosurgical interventions on the opercular area of the dominant hemisphere.

METHODS

Five patients were operated upon gliomas in the opercular area. For localization of the speech area a transcranial magnetic stimulator MEDTRONIC-MagPro was used. BrainLAB-VectorVision Neuronavigation system was utilized for precise planning of the operative approach.

RESULTS

Gross total resection was achieved in all patients. Three-month postoperative follow-up was done. Three of the patients had a transient postoperative motor aphasia which resolved within 1 month.

CONCLUSION

This method is useful for preoperative localization of the speech area, as well as preoperative planning of the operative approach and intra-operative planning of the direction of brain retraction and operative corridor.

Two different reorganization patterns after rehabilitative therapy: an exploratory study with fMRI and TMS

We used two complementary methods to investigate cortical reorganization in chronic stroke patients during treatment with a defined motor rehabilitation program. BOLD ("blood oxygenation level dependent") sensitive functional magnetic resonance imaging (fMRI) and intracortical inhibition (ICI) and facilitation (ICF) measured with transcranial magnetic stimulation (TMS) via paired pulse stimulation were used to investigate cortical reorganization before and after "constraint-induced movement therapy" (CI). The motor hand function improved in all subjects after CI. BOLD signal intensity changes within affected primary sensorimotor cortex (SMC) before and after CI showed a close correlation with ICI (r = 0.93) and ICF (r = 0.76) difference before and after therapy. Difference in number of voxels and ICI difference before and after CI also showed a close correlation (r = 0.92) in the affected SMC over the time period of training. A single subject analysis revealed that patients with intact hand area of M1 ("the hand knob") and its descending motor fibers (these patients revealed normal motor evoked potentials [MEP] from the affected hand) showed decreasing ipsilesional SMC activation which was paralleled by an increase in intracortical excitability. This pattern putatively reflects increasing synaptic efficiency. When M1 or its descending pyramidal tract was lesioned (MEP from the affected hand was pathologic) ipsilesional SMC activation increased, accompanied by decreased intracortical excitability. We suggest that an increase in synaptic efficiency is not possible here, which leads to reorganization with extension, shift and recruitment of additional cortical areas of the sensorimotor network. The inverse dynamic process between both complementary methods (activation in fMRI and intracortical excitability determined by TMS) over the time period of CI illustrates the value of combining methods for understanding brain reorganization.

Lessons from brain mapping in surgery for low-grade glioma: insights into associations between tumour and brain plasticity

Surgical treatment of low-grade gliomas (LGGs) aims to maximise the amount of tumour tissue resected, while minimising the risk of functional sequelae. In this review I address the issue of how to reconcile these two conflicting goals. First, I review the natural history of LGG-growth, invasion, and anaplastic transformation. Second, I discuss the contribution of new techniques, such as functional mapping, to our understanding of brain reorganisation in response to progressive growth of LGG. Third, I consider the clinical implications of interactions between tumour progression and brain plasticity. In particular, I show how longitudinal studies (preoperative, intraoperative, and postoperative) could allow us to optimise the surgical risk-to-benefit ratios. I will also discuss controversial issues such as defining surgical indications for LGGs, predicting the risk of postoperative deficit, aspects of operative surgical neuro-oncology (eg, preoperative planning and preservation of functional areas and tracts), and postoperative functional recovery.

Should transcranial magnetic stimulation research in children be considered minimal risk?

OBJECTIVE

Transcranial magnetic stimulation (TMS) is a neurophysiologic technique with research applications. Institutional Review Boards (IRBs) must carefully consider potential risks and possible benefits in research involving children. The purpose of this study is to provide concise information for investigators and IRBs about the safety of single and paired pulse TMS research in children.

METHODS

This paper has 4 sections: (I) Regulations governing research in children are reviewed and applied to the use of TMS. (II) Energy imparted by TMS is assessed in terms of theoretical biological risks to human subjects. (III) Through MEDLINE review, the empirical evidence of risk from TMS is assessed. Reported adverse events, including issues related to risk of seizures and of hearing loss, are summarized. (IV) Safety data are presented from a study of TMS in children with Tourette Syndrome.

RESULTS

No published or empirical evidence was found to suggest that single or paired pulse TMS is associated with more than minimal risk in children.

CONCLUSIONS

IRBs may consider well-designed studies using single and paired pulse TMS protocols similar to those described in this study as bearing minimal risk to children.

SIGNIFICANCE

This manuscript may be useful as a reference to IRBs and TMS investigators.

Focused high frequency repetitive transcranial magnetic stimulation for localisation of the unexposed primary motor cortex during brain tumour surgery

OBJECTIVES

To investigate if intraoperative focused high frequency repetitive transcranial magnetic stimulation (rTMS) can localise the primary motor cortex without exposure of the cortical surface.

METHODS

A high frequency train (357 Hz) of four suprathreshold magnetic stimuli was delivered transcranially to the region of the rolandic area during brain tumour operations in 12 patients. To induce a focal magnetoelectric field, the flat figure of eight coil (outer diameter of each loop 7 cm) was used. Motor evoked potentials (MEP) were recorded in eight muscles of the upper and lower contralateral extremities. The first stimulation site was 2.5 cm behind the bregma, the second site 2 cm, and the third site 4 cm dorsal to the first stimulation site. If no MEP were obtainable, stimulation was repeated in anteroposterior direction at more laterally located sites. Using neuronavigation, each positive stimulation site was correlated with the underlying cortical anatomy.

RESULTS

Stimulation was performed at a total of 42 sites (in two patients, maximum stimulation at the three initial sites failed to evoke a motor response). In four patients, MEP were obtained only from one stimulation site. This site exactly overlayed the primary motor cortex. In eight patients, MEP could be elicited from more than one stimulation site. In seven of the eight patients, the site from which MEP with peak amplitudes were elicited, corresponded to the primary motor cortex. In total, the primary motor cortex was correctly identified on the basis of electrophysiological findings in 11 of 12 patients (92 %). In two patients, only the more lateral stimulation sites permitted MEP recording.

CONCLUSION

Intraoperative focused rTMS is highly sensitive for localisation of the primary motor cortex. Focused rTMS as a localising instrument alleviates the need of motor cortex exposure and, thereby, can contribute to minimise the surgical approach to brain tumours in the rolandic area.

Comparison of representational maps using functional magnetic resonance imaging and transcranial magnetic stimulation

OBJECTIVE

Comparison of functional magnetic resonance imaging (fMRI) representational maps, that were generated during voluntary thumb abduction, hand dorsiflexion and foot elevation to amplitude maps of motor-evoked potentials (MEPs) elicited by single transcranial magnetic stimulation (TMS) administered to cortical motor representation areas of the muscles of the thenar eminence, extensor carpi radialis and tibialis anterior muscles.

METHODS

Stimulus locations that produced maximal motor-evoked potential amplitudes were compared to fMRI activation maxima in three-dimensional (3D)-space and in a 2D-projection using a novel technique that allowed fMRI activation sites to be projected onto the surface of the brain.

RESULTS AND CONCLUSIONS

When analyzing pooled data from all target muscles, the location of projected fMRI and TMS activation maxima on the cortical surface differed by an average 13.9 mm. The differences in 3D distances were particularly large for representation areas of lower leg muscles. 3D distances between fMRI activation maxima and highest MEP site in TMS correlated significantly with higher TMS thresholds. These observations strongly suggest that higher TMS excitation thresholds and lower MEP amplitudes are largely due to the absolute distance between the stimulation site and the excitable cortical tissue targeting this muscle. After the projection 4 out of 5 representation sites as evaluated by TMS were located anterior to the fMRI activation maxima, an observation which may due to the orientation of the magnetic field induced by the current in the coil. The representation sites as evaluated with both methods were specific for the type of movement: distances between representation maxima of the same movements were significantly smaller than those within different movements. Nevertheless, fMRI and TMS provide complementary information, which is discussed on the basis of the functional map observed with both methods.