Neuroscience

Authors: V Rizzo et. al
Publication: Front Neurol. (2021), doi.org/10.3389/fneur.2021.673836

Abstract:

Background: Brain tumors can cause different changes in excitation and inhibition at the neuronal network level. These changes can be generated from mechanical and cellular alterations, often manifesting clinically as seizures.
Objective/Hypothesis: The effects of brain tumors on cortical excitability (CE) have not yet been well-evaluated. The aim of the current study was to further investigate cortical–cortical and cortical–spinal excitability in patients with brain tumors using a more extensive transcranial magnetic stimulation protocol.
Methods: We evaluated CE on 12 consecutive patients with lesions within or close to the precentral gyrus, as well as in the subcortical white matter motor pathways. We assessed resting and active motor threshold, short-latency intracortical inhibition (SICI), intracortical facilitation (ICF), short-latency afferent inhibition (SAI), long-latency afferent inhibition, cortical silent period, and interhemispheric inhibition.
Results: CE was reduced in patients with brain tumors than in healthy controls. In addition, SICI, ICF, and SAI were lower in the affected hemisphere compared to the unaffected and healthy controls.
Conclusions: CE is abnormal in hemispheres affected by brain tumors. Further studies are needed to determine if CE is related with motor impairment.

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Authors: V. Mylius, S.S. Ayache, R. Ahdab, J.P. Lefaucheur, et. al
Publication: NeuroImage (2013), doi:10.1016/j.neuroimage.2013.03.061

Abstract: The optimization of the targeting of a defined cortical region is a challenge in the current practice of transcranial magnetic stimulation (TMS). The dorsolateral prefrontal cortex (DLPFC) and the primary motor cortex (M1) are among the most usual TMS targets, particulary in its “therapeutic” application. This study describes a practical algorithm to determine the anatomical location of the DLPFC and M1 using a three-dimensional (3D) brain reconstruction provided by a TMS-dedicated navigation system from individual magnetic resonance imaging (MRI) data. The coordinates of the right and left DLPFC and M1 were determined in 50 normal brains (100 hemispheres) by five different investigators using a standardized procedure. Inter-rater reliability was good, with 95% limits of agreement ranging between 7 and 16 mm for the different coordinates. As expressed in the Talairach space and compared with anatomical or imaging data from literature, the coordinates of the DLPFC defined by our algorithm corresponded to the junction between BA9 and BA46, while M1 coordinates corresponded to the posterior border of hand representation Finally, we found an influence of gender and possible of age on some coordinates on both rostrocaudal and dorsoventral axes. Our algorithm only requires a short training and can beused to provide a reliable targeting of DLPFC and M1 between various TMS investigators. This method, based on an image-guided navigation system using individual MRI data, should be helpful to a variety of TMS studies, especially to standardize the procedure of stimulation in multicenter “therapeutic” studies.

Publication: NeuroImage (2013), doi:10.1016/j.neuroimage.2013.03.061

Authors: Rosanova M, Gosseries O, Casarotto S, Boly M, Casali AG, Bruno MA, Mariotti M, Boveroux P, Tononi G, Laureys S, Massimini M.
Publication: Brain. 2012 Apr;135(Pt 4):1308-20. doi: 10.1093/brain/awr340. Epub 2012 Jan 5.

Abstract: Patients surviving severe brain injury may regain consciousness without recovering their ability to understand, move and communicate. Recently, electrophysiological and neuroimaging approaches, employing simple sensory stimulations or verbal commands, have proven useful in detecting higher order processing and, in some cases, in establishing some degree of communication in brain-injured subjects with severe impairment of motor function. To complement these approaches, it would be useful to develop methods to detect recovery of consciousness in ways that do not depend on the integrity of sensory pathways or on the subject's ability to comprehend or carry out instructions. As suggested by theoretical and experimental work, a key requirement for consciousness is that multiple, specialized cortical areas can engage in rapid causal interactions (effective connectivity). Here, we employ transcranial magnetic stimulation together with high-density electroencephalography to evaluate effective connectivity at the bedside of severely brain injured, non-communicating subjects. In patients in a vegetative state, who were open-eyed, behaviorally awake but unresponsive, transcranial magnetic stimulation triggered a simple, local response indicating a breakdown of effective connectivity, similar to the one previously observed in unconscious sleeping or anaesthetized subjects. In contrast, in minimally conscious patients, who showed fluctuating signs of non-reflexive behavior, transcranial magnetic stimulation invariably triggered complex activations that sequentially involved distant cortical areas ipsi- and contralateral to the site of stimulation, similar to activations we recorded in locked-in, conscious patients. Longitudinal measurements performed in patients who gradually recovered consciousness revealed that this clear-cut change in effective connectivity could occur at an early stage, before reliable communication was established with the subject and before the spontaneous electroencephalogram showed significant modifications. Measurements of effective connectivity by means of transcranial magnetic stimulation combined with electroencephalography can be performed at the bedside while by-passing subcortical afferent and efferent pathways, and without requiring active participation of subjects or language comprehension; hence, they offer an effective way to detect and track recovery of consciousness in brain-injured patients who are unable to exchange information with the external environment.

Publication: Brain. 2012 Apr;135(Pt 4):1308-20. doi: 10.1093/brain/awr340. Epub 2012 Jan 5. http://www.ncbi.nlm.nih.gov/pubmed/22226806
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3326248/

Authors: Frye RE, Rotenberg A, Ousley M, Pascual-Leone A.
Publication: J Child Neurol. 2008 Jan;23(1):79-96. Epub 2007 Dec 3.

Abstract: Transcranial magnetic stimulation (TMS) is a method for focal brain stimulation based on the principle of electromagnetic induction, where small intracranial electric currents are generated by a powerful, rapidly changing extracranial magnetic field. Over the past 2 decades TMS has shown promise in the diagnosis, monitoring, and treatment of neurological and psychiatric disease in adults, but has been used on a more limited basis in children. We reviewed the literature to identify potential diagnostic and therapeutic applications of TMS in child neurology and also its safety in pediatrics. Although TMS has not been associated with any serious side effects in children and appears to be well tolerated, general safety guidelines should be established. The potential for applications of TMS in child neurology and psychiatry is significant. Given its excellent safety profile and possible therapeutic effect, this technique should develop as an important tool in pediatric neurology over the next decade.

Publication: J Child Neurol. 2008 Jan;23(1):79-96. Epub 2007 Dec 3. http://jcn.sagepub.com/content/23/1/79.abstract - http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2539109/

Authors: V. Mylius, S.S. Ayache, R. Ahdab, J.P. Lefaucheur, et. al
Publication: NeuroImage (2013), doi:10.1016/j.neuroimage.2013.03.061

Abstract: The optimization of the targeting of a defined cortical region is a challenge in the current practice of transcranial magnetic stimulation (TMS). The dorsolateral prefrontal cortex (DLPFC) and the primary motor cortex (M1) are among the most usual TMS targets, particulary in its “therapeutic” application. This study describes a practical algorithm to determine the anatomical location of the DLPFC and M1 using a three-dimensional (3D) brain reconstruction provided by a TMS-dedicated navigation system from individual magnetic resonance imaging (MRI) data. The coordinates of the right and left DLPFC and M1 were determined in 50 normal brains (100 hemispheres) by five different investigators using a standardized procedure. Inter-rater reliability was good, with 95% limits of agreement ranging between 7 and 16 mm for the different coordinates. As expressed in the Talairach space and compared with anatomical or imaging data from literature, the coordinates of the DLPFC defined by our algorithm corresponded to the junction between BA9 and BA46, while M1 coordinates corresponded to the posterior border of hand representation Finally, we found an influence of gender and possible of age on some coordinates on both rostrocaudal and dorsoventral axes. Our algorithm only requires a short training and can beused to provide a reliable targeting of DLPFC and M1 between various TMS investigators. This method, based on an image-guided navigation system using individual MRI data, should be helpful to a variety of TMS studies, especially to standardize the procedure of stimulation in multicenter “therapeutic” studies.

Publication: NeuroImage (2013), doi:10.1016/j.neuroimage.2013.03.061

Authors: Rosanova M, Gosseries O, Casarotto S, Boly M, Casali AG, Bruno MA, Mariotti M, Boveroux P, Tononi G, Laureys S, Massimini M.
Publication: Brain. 2012 Apr;135(Pt 4):1308-20. doi: 10.1093/brain/awr340. Epub 2012 Jan 5.

Abstract: Patients surviving severe brain injury may regain consciousness without recovering their ability to understand, move and communicate. Recently, electrophysiological and neuroimaging approaches, employing simple sensory stimulations or verbal commands, have proven useful in detecting higher order processing and, in some cases, in establishing some degree of communication in brain-injured subjects with severe impairment of motor function. To complement these approaches, it would be useful to develop methods to detect recovery of consciousness in ways that do not depend on the integrity of sensory pathways or on the subject's ability to comprehend or carry out instructions. As suggested by theoretical and experimental work, a key requirement for consciousness is that multiple, specialized cortical areas can engage in rapid causal interactions (effective connectivity). Here, we employ transcranial magnetic stimulation together with high-density electroencephalography to evaluate effective connectivity at the bedside of severely brain injured, non-communicating subjects. In patients in a vegetative state, who were open-eyed, behaviorally awake but unresponsive, transcranial magnetic stimulation triggered a simple, local response indicating a breakdown of effective connectivity, similar to the one previously observed in unconscious sleeping or anaesthetized subjects. In contrast, in minimally conscious patients, who showed fluctuating signs of non-reflexive behavior, transcranial magnetic stimulation invariably triggered complex activations that sequentially involved distant cortical areas ipsi- and contralateral to the site of stimulation, similar to activations we recorded in locked-in, conscious patients. Longitudinal measurements performed in patients who gradually recovered consciousness revealed that this clear-cut change in effective connectivity could occur at an early stage, before reliable communication was established with the subject and before the spontaneous electroencephalogram showed significant modifications. Measurements of effective connectivity by means of transcranial magnetic stimulation combined with electroencephalography can be performed at the bedside while by-passing subcortical afferent and efferent pathways, and without requiring active participation of subjects or language comprehension; hence, they offer an effective way to detect and track recovery of consciousness in brain-injured patients who are unable to exchange information with the external environment.

Publication: Brain. 2012 Apr;135(Pt 4):1308-20. doi: 10.1093/brain/awr340. Epub 2012 Jan 5. http://www.ncbi.nlm.nih.gov/pubmed/22226806
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3326248/

Authors: Petro Julkunena, Anne M. Jauhiainenb, Jari Karhu, et. al
Publication: Journal of Neuroscience Methods 172 (2008) 270–276

Abstract: Our aim was to assess the potential of navigated transcranial magnetic stimulation (TMS)-evoked electroencephalographic (EEG) responses in studying neuronal reactivity and cortical connectivity in Alzheimer’s disease (AD) and in mild cognitive impairment (MCI). We studied 14 right-handed subjects: five patients with AD, five patients with MCI and four healthy controls. Fifty TMS-pulses at an intensity of 110% of individually determined motor threshold were delivered to the hand area of primary motor cortex (M1) with navigated brain stimulation (NBS). Spreading of primary NBS-evoked neuronal activity was monitored with a compatible 60-channel EEG, and analyzed in time, frequency and spatial-domains. We found significantly reduced TMS-evoked P30 (time-locked response 30 ms after the magnetic stimulation) in the AD subjects. This reduction was seen in the temporo-parietal area ipsilateral to stimulation side as well as in the contralateral fronto-central cortex corresponding to the sensorimotor network, which is anatomically interconnected with the stimulated M1. In addition, there was a significant decrease in the N100 amplitude in the MCI subjects when compared with the control subjects. Thus, the combination of NBS and EEG revealed prominent changes in functional cortical connectivity and reactivity in the AD subjects. This pilot study suggest that the method may provide a novel tool for examining the degree and progression of dementia.

Publication: Journal of Neuroscience Methods 172 (2008) 270–276 http://www.brainstimulation.columbia.edu/doc/journal_club/papers/julkunen_j_neuroscience_methods_2008.pdf

Authors: Frye RE, Rotenberg A, Ousley M, Pascual-Leone A.
Publication:

Abstract: Transcranial magnetic stimulation (TMS) is a method for focal brain stimulation based on the principle of electromagnetic induction, where small intracranial electric currents are generated by a powerful, rapidly changing extracranial magnetic field. Over the past 2 decades TMS has shown promise in the diagnosis, monitoring, and treatment of neurological and psychiatric disease in adults, but has been used on a more limited basis in children. We reviewed the literature to identify potential diagnostic and therapeutic applications of TMS in child neurology and also its safety in pediatrics. Although TMS has not been associated with any serious side effects in children and appears to be well tolerated, general safety guidelines should be established. The potential for applications of TMS in child neurology and psychiatry is significant. Given its excellent safety profile and possible therapeutic effect, this technique should develop as an important tool in pediatric neurology over the next decade.

Publication: J Child Neurol. 2008 Jan;23(1):79-96. Epub 2007 Dec 3. http://jcn.sagepub.com/content/23/1/79.abstract -http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2539109/

Authors: S. Ille et al. 
Publication: Brain Stimul. 2021 Jul-Aug;14(4):780-787. 

Abstract:
Background
Navigated repetitive transcranial magnetic stimulation (nrTMS) is effective therapy for stroke patients. Neurorehabilitation could be supported by low-frequency stimulation of the non-damaged hemisphere to reduce transcallosal inhibition.
Objective
The present study examines the effect of postoperative nrTMS therapy of the unaffected hemisphere in glioma patients suffering from acute surgery-related paresis of the upper extremity (UE) due to subcortical ischemia.
Methods
We performed a randomized, sham-controlled, double-blinded trial on patients suffering from acute surgery-related paresis of the UE after glioma resection. Patients were randomly assigned to receive either low frequency nrTMS (1 Hz, 15 min) or sham stimulation directly before physical therapy for 7 consecutive days. We performed primary and secondary outcome measures on day 1, on day 7, and at a 3-month follow-up (FU). The primary endpoint was the change in Fugl-Meyer Assessment (FMA) at FU compared to day 1 after surgery.
Results
Compared to the sham stimulation, nrTMS significantly improved outcomes between day 1 and FU based on the FMA (mean [95% CI] +31.9 [22.6, 41.3] vs. +4.2 [-4.1, 12.5]; P = .001) and the National Institutes of Health Stroke Scale (NIHSS) (−5.6 [-7.5, −3.6] vs. −2.4 [-3.6, −1.2]; P = .02). To achieve a minimal clinically important difference of 10 points on the FMA scale, the number needed to treat is 2.19.
Conclusion
The present results show that patients suffering from acute surgery-related paresis of the UE due to subcortical ischemia after glioma resection significantly benefit from low-frequency nrTMS stimulation therapy of the unaffected hemisphere.
Clinical trial registration

Local institutional registration: 12/15; ClinicalTrials.gov number: NCT03982329

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Authors: Richard L. Harvey, MD , Heidi R. Roth, DHS, PT, Rachel S. Tappan, PT, Rachel Kerman, MD, Jarmo Laine, MD PhD MBA, Jim W. Stinear, PhD, Lynn M. Rogers, PhD
Publication: Abstract 152 Presented at the American Heart Association/American Stroke Association’s International Stroke Conference February 2014, San Diego: Stroke.2014;45:A152

Objective: To determine whether neuro-navigated 1hz rTMS targeted to the non-lesioned hemisphere (NLH) combined with task-oriented occupational therapy (OT) can improve motor function of arm and hand in patients with subacute stroke.

Methods: 30 patients (3-9 months post-stroke) were randomly assigned to sham (n=10) or active 1hz rTMS (n=20) targeted to the wrist extensor representation in the NLH. Patients completed 3 visits per week for 6 weeks that included: 20min pre-functional OT, neuro-navigated 1hz rTMS or sham, and 60 min upper-limb task-oriented OT. Patients returned for 1 week, 1 month, and 6 month follow-up visits. Groups were well matched at baseline but there was a trend toward more severe impairment in the active treatment group on the Upper Extremity Fugl Meyer (UEFM) (23.8+10.2, active; 31.5+15.3, sham: p=0.11).

Results: Patients receiving active rTMS prior to OT made significantly greater gains on the UEFM by 6 months post-intervention than patients receiving sham stimulation (change in UEFM 14.4 + 10.0 vs. 4.1 + 5.5; p=0.013). On ANOVA differences were significant for group, time and group x time (F=5.73, df=2, p=0.006).   Individuals receiving active rTMS were significantly more likely to exceed the published minimal clinical important difference (MCID) on the UEFM at 6 months post (88% vs. 38%, p = 0.002). Similar trends at 1 week and 1 month post were not statistically significant. Ceiling effects were unlikely.

Conclusion: These findings suggest neuro-navigated 1hz rTMS paired with task-oriented OT is more likely to promote clinically important improvements than OT alone. Of note is the finding that significant improvements in impairment were seen 6 months following therapy, suggesting non-invasive brain stimulation as an adjuvant to therapy promotes lasting motor improvement.

Publication: Abstract 152 Presented at the American Heart Association/American Stroke Association’s International Stroke Conference February 2014, San Diego: Stroke.2014;45:A152
http://stroke.ahajournals.org/content/45/Suppl_1/A152?related-urls=yes&legid=strokeaha;45/Suppl_1/A152

Authors: Narayana S, McAfee S, Chaudhri A, Wheless J, Papanicolauo A
Publication: Abstract from International Conference on Functional Mapping of the Human Brain, June 2013, Seattle, WA

Introduction: Evidence of plasticity in neuronal systems, specifically in the motor system is emerging. For example, when the motor cortex is diseased or removed, its action is taken over by residual tissue, and nearby premotor/sensory regions (1). Using transcranial magnetic stimulation (TMS), we investigated the mechanism of functionality in muscles contralateral to the lesion even when the entire motor network (primary motor cortex, premotor cortex, and pyramidal tracts) in the hemisphere has been removed due to injury or surgery.

Methods: Five patients (3F, 11.5±6.4 years) who had undergone complete functional hemispherectomy (H group) for treatment of refractory epilepsy, and five patients (3F, 9.8±3.8 years) with history of epilepsy due to unilateral brain lesions who had also undergone surgical resection (C group) were studied. The demographics and nature of lesions in the patients are detailed in Table 1. Navigated TMS was delivered using a ‘figure 8’ coil (Nexstim Inc.). In both groups, left and right primary hand motor cortices (M1hand) were targeted and single pulses of TMS were delivered while monitoring electromyography in bilateral hand and forearm muscles. Motor evoked potentials (MEP) following TMS were recorded from these muscles and the motor hotspot, resting motor threshold (rMT), and the corticomotor conduction times (CMCT) were determined. Spinal stimulation was performed to examine peripheral conduction. DTO was acquired in three patients in the H group to confirm complete hemispherectomy.

Results: TMS applied to the precentral gyrus of the healthy hemisphere of H group resulted in MEP in both hand muscles in all participants, as shown in Figures 2 and 3. TMS stimulation of the diseased hemisphere did not elicit MEPS. TMS applied to bilateral precentral gyri elicited MEPs with normal corticomotor transit times only in the respective contralateral hand muscles in C group (Figure 1). In three participants in the H group, DTI confirmed complete hemispherectomy with no evidence of contiguous commisural fibers traversing the midline through the corpus callosum. There was no difference in rMT between the groups, or the hemisphere removed/affected.

Conclusions: These data indicate that the motor function is retained in the diseased hemisphere in patients with lesions in the vicinity of the motor cortex, when the rest of the motor network (pyramidal tracts and motor association areas) is intact (as seen in Figure 1). However, in the patients in the H group, the bilateral innervations of the motor system originated from the healthy hemisphere (Figure 2). We hypothesize that this motor plasticity is mediated via the uncrossed corticospinal tracts arising from the healthy primary motor cortex. Normally, at birth the corticospinal tracts project bilaterally at the spinal motor neuron level that becomes contralateral by 2 year of age (2). However, damage to unilateral corticospinal tracts during this period, results in enlargement of the ipsilateral terminal axonal arborization both within spinal gray matter and motoneuronal poos (2), and such plasticity can support functionality in the ipsilateral muscles. MEPS in the hand muscles contralateral to the diseased cortex were elicited by stimulating the spinal nerves ipsilateral pathways. Thereforeearly and intensive physical therapy can improve functional outcome following hemispherectomy by invoking the mechanism of plasticity.

Publication: Abstract from International Conference on Functional Mapping of the Human Brain, June 2013, Seattle, WA

Authors: Machetanz, K. et al. 
Publication: Clin Neurophysiol. 2021 Nov; 132(11):2780-2788. doi.org/10.1016/j.clinph.2021.07.024

Abstract:

Objective: Conventional time-series parameters are unreliable descriptors of motor-evoked potentials (MEPs) in brain tumor patients. Frequency domain analysis is suggested to provide additional information about the status of the cortico-spinal motor system. Aim of the recent study was to describe the time-frequency representation of MEPs and its relation to the motor performance.
Methods: This study enrolled 17 consecutive brain tumor patients with impaired dexterity. After brain mapping of the affected (AH) and non-affected (NAH) hemisphere, TMS was applied to the hotspots of the abductor pollicis brevis muscles (APB). Using a Morlet wavelet approach, event-related spectral perturbation (ERSP) and inter-trial coherence (ITC) of the MEPs were calculated and compared to the Grooved Pegboard Test (GPT). Additionally, inter- and intra-subject reliability was assessed by the intraclass correlation coefficient (ICC).
Results: MEPs were projecting to a frequency band between 30 and 400 Hz with a local maximum between 100 and 150 Hz. There was a significant ERSP and ITC reduction of the AH in comparison to the NAH. In contrast, no interhemispheric differences were depicted in the conventional time-series analysis. ERSP and ITC values correlated significantly with GPT results (r = 0.35 and r = 0.50). Time-frequency MEP description had good inter-and intra-subject reliability (ICC = 0.63).
Conclusions: Brain tumors affect corticospinal transmission resulting in a reduction of temporal and spectral MEP synchronization correlating with the dexterity performance.
Significance: Time-frequency representation of MEPs provide additional information beyond conventional time-domain features.

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Authors: Machetanz, K. et al. 
Publication: Front Neurol. 2021 Feb 5; 11:633224. doi.org/10.3389/fneur.2020.633224

Abstract:

Background: The integrity of the motor system can be examined by applying navigated transcranial magnetic stimulation (nTMS) to the cortex. The corresponding motor-evoked potentials (MEPs) in the target muscles are mirroring the status of the human motor system, far beyond corticospinal integrity. Commonly used time domain features of MEPs (e.g., peak-to-peak amplitudes and onset latencies) exert a high inter-subject and intra-subject variability. Frequency domain analysis might help to resolve or quantify disease-related MEP changes, e.g., in brain tumor patients. The aim of the present study was to describe the time-frequency representation of MEPs in brain tumor patients, its relation to clinical and imaging findings, and the differences to healthy subject.
Methods: This prospective study compared 12 healthy subjects with 12 consecutive brain tumor patients (with and without a paresis) applying nTMS mapping. Resulting MEPs were evaluated in the time series domain (i.e., amplitudes and latencies). After transformation into the frequency domain using a Morlet wavelet approach, event-related spectral perturbation (ERSP), and inter-trial coherence (ITC) were calculated and compared to diffusion tensor imaging (DTI) results.
Results: There were no significant differences in the time series characteristics between groups. MEPs were projecting to a frequency band between 30 and 300 Hz with a local maximum around 100 Hz for both healthy subjects and patients. However, there was ERSP reduction for higher frequencies (>100 Hz) in patients in contrast to healthy subjects. This deceleration was mirrored in an increase of the inter-peak MEP latencies. Patients with a paresis showed an additional disturbance in ITC in these frequencies. There was no correlation between the CST integrity (as measured by DTI) and the MEP parameters.
Conclusion: Time-frequency analysis may provide additional information above and beyond classical MEP time domain features and the status of the corticospinal system in brain tumor patients. This first evaluation indicates that brain tumors might affect cortical physiology and the responsiveness of the cortex to TMS resulting in a temporal dispersion of the corticospinal transmission.

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Authors: Picht T, Strack V, Schulz J, Zdunczyk A, Frey D, Schmidt S, Vajkoczy P.
Publication: Acta Neurochir (Wien). 2012 Nov;154(11):2075-81. doi: 10.1007/s00701-012-1494-y. Epub 2012 Sep 5.

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

Authors: Espadaler J, Rogic M, Deletis V, Leon A, Quijada C, Conesa G.
Publication: Clin Neurophysiol. 2012 Nov;123(11):2205-11. Epub 2012 May 22.

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

Publication: Clin Neurophysiol. 2012 Nov;123(11):2205-11. Epub 2012 May 22. http://www.ncbi.nlm.nih.gov/pubmed/22621909

Authors: Julkunen P, Ruohonen J, Sääskilahti S, Säisänen L, Karhu J.
Publication: Clin Neurophysiol. 2011 May;122(5):975-83. doi: 10.1016/j.clinph.2010.09.005.

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.