Transcranial magnetic stimulation in children

Pediatric stroke: We need to look for it

PURPOSE

This review provides a comprehensive overview of the characteristics and diagnosis of pediatric stroke, emphasizing the importance of early recognition and accurate assessment. Pediatric stroke is a complex condition with diverse etiologies, and its timely diagnosis is critical for initiating appropriate interventions and improving clinical outcomes.

RECENT FINDINGS

Recent advances in neuroimaging techniques, including magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA), have significantly enhanced the diagnostic capabilities for pediatric stroke. Additionally, a better understanding of its underlying etiologies in specific cases, and of the importance of differential diagnosis have improved the outcome and prevention strategies in this vulnerable population. Despite these improvements, though, research still has a long way to go to optimize the management of this condition.

SUMMARY

Timely and accurate diagnosis of pediatric stroke remains a challenge due to its rarity and variability in clinical presentation, and to the presence of many mimic conditions. The integration of clinical evaluation, neuroimaging, and comorbidities analysis is crucial for achieving a precise diagnosis and guiding tailored treatment strategies for affected children.

Exploring new horizons: Emerging therapeutic strategies for pediatric stroke

Pediatric stroke presents unique challenges, and optimizing treatment strategies is essential for improving outcomes in this vulnerable population. This review aims to provide an overview of new, innovative, and potential treatments for pediatric stroke, with a primary objective to stimulate further research in this field. Our review highlights several promising approaches in the realm of pediatric stroke management, including but not limited to stem cell therapy and robotic rehabilitation. These innovative interventions offer new avenues for enhancing functional recovery, reducing long-term disability, and tailoring treatments to individual patient needs. The findings of this review underscore the importance of ongoing research and development of innovative treatments in pediatric stroke. These advancements hold significant clinical relevance, offering the potential to improve the lives of children affected by stroke by enhancing the precision, efficacy, and accessibility of therapeutic interventions. Embracing these innovations is essential in our pursuit of better outcomes and a brighter future for pediatric stroke care.

Dystonia in Childhood: How Insights from Paediatric Research Enrich the Network Theory of Dystonia

Dystonia is now widely accepted as a network disorder, with multiple brain regions and their interconnections playing a potential role in the pathophysiology. This model reconciles what could previously have been viewed as conflicting findings regarding the neuroanatomical and neurophysiological characteristics of the disorder, but there are still significant gaps in scientific understanding of the underlying pathophysiology. One of the greatest unmet challenges is to understand the network model of dystonia in the context of the developing brain. This article outlines how research in childhood dystonia supports and contributes to the network theory and highlights aspects where data from paediatric studies has revealed novel and unique physiological insights, with important implications for understanding dystonia across the lifespan.

Prevalence of Adverse Effects Associated With Transcranial Magnetic Stimulation for Autism Spectrum Disorder: A Systematic Review and Meta-Analysis

Background

A growing number of studies have suggested that transcranial magnetic stimulation (TMS) may represent a novel technique with both investigative and therapeutic potential for autism spectrum disorder (ASD). However, a full spectrum of the adverse effects (AEs) of TMS used in ASD has not been specifically and systematically evaluated.

Objective

This systematic review and meta-analysis was to assess the prevalence of AEs related to TMS in ASD and to further explore the potentially related factors on the AEs.

Methods

A systematic literature research of articles published before 31 December 2020 was conducted in the databases of PubMed, Embase, Cochrane Library, Ovid, PsycINFO, Chinese National Knowledge Infrastructure (CNKI), Chongqing VIP, and WANFANG DATA. AEs reported in the studies were carefully examined and synthesized to understand the safety and tolerability of TMS among ASD. Then, subgroup and sensitivity analyses were performed to examine the potentially related factors on the AEs. PROSPERO registration number: CRD42021239827.

Results

Eleven studies were included in the meta-analysis. The pooled prevalence with 95% confidence interval (CI) of AEs was calculated (overall AEs: 25%, 95% CI 18-33%; headache: 10%, 95% CI 3-19%; facial discomfort: 15%, 95% CI 4-29%; irritability 21%, 95% CI 8-37%; pain at the application site: 6%, 95% CI 0-19%; headedness or dizziness: 8%, 95% CI 0-23%). All reported AEs were mild and transient with relatively few serious AEs and can be resolved after having a rest or medication. In addition, the following variables showed no significant change in overall prevalence of AEs: the purpose of using TMS, mean age of participants, whether the stimulation site was dorsolateral pre-frontal cortex (DLPFC), intensity of TMS, and the number of stimulation sessions.

Conclusion

The overall prevalence of reported AEs of TMS among ASD was 25%. No identified ASD-specific risk factors for TMS-induced AEs were found. Further studies are needed to clarify the variation in the prevalence.

Systematic Review Registration

www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=239827, PROSPERO, identifier: CRD42021239827.

Alteration of cortical but not spinal inhibitory circuits in idiopathic scoliosis

Background: The pathogenesis of adolescent idiopathic scoliosis (AIS), including the role of brain and spinal inhibitory circuits, is still poorly elucidated. The aim of this study was to identify which central inhibitory mechanisms are involved in the pathogenesis of AIS.Design: A prospective neurophysiological study, using a battery of neurophysiological tests, such as cutaneous (CuSP) and cortical (CoSP) silent periods, motor evoked potentials (MEP) and paired-pulse transcranial magnetic stimulation (ppTMS).Settings: Neurophysiological laboratory.Participants: Sixteen patients with AIS (14 females, median age 14.4) and healthy controls.Outcome measures: MEPs were obtained after transcranial magnetic stimulation (TMS) and recorded from the abductor pollicis muscle (APB). ppTMS was obtained at interval ratios (ISI) of 1, 2, 3, 6, 10, 15 and 20 ms. The cortical silent period (CoSP) was recorded from the APB. The cutaneous silent period (CuSP) was measured after painful stimuli delivered to the thumb while the subjects maintained voluntary contraction of the intrinsic hand muscles. The data were analyzed and compared with those from healthy subjects.Results: The CoSP duration was significantly prolonged in AIS patients. A significantly higher amplitude of ppTMS for ISI was found in all AIS patients, without remarkable left-right side differences. No significant difference in MEP latency or amplitude nor in the CuSP duration was obtained.Conclusion: Our observation demonstrates evidence of central nervous system involvement in adolescent idiopathic scoliosis (AIS). Lower intracortical inhibition, higher motor cortex excitability, and preserved spinal inhibitory circuits are the main findings of this study. A possible explanation of these changes could be attributed to impaired sensorimotor integration predominantly at the cortical level.

Biomarkers Obtained by Transcranial Magnetic Stimulation in Neurodevelopmental Disorders

SUMMARY

Transcranial magnetic stimulation (TMS) is a method for focal brain stimulation that is based on the principle of electromagnetic induction where small intracranial electric currents are generated by a powerful fluctuating magnetic field. Over the past three decades, TMS has shown promise in the diagnosis, monitoring, and treatment of neurological and psychiatric disorders in adults. However, the use of TMS in children has been more limited. We provide a brief introduction to the TMS technique; common TMS protocols including single-pulse TMS, paired-pulse TMS, paired associative stimulation, and repetitive TMS; and relevant TMS-derived neurophysiological measurements including resting and active motor threshold, cortical silent period, paired-pulse TMS measures of intracortical inhibition and facilitation, and plasticity metrics after repetitive TMS. We then discuss the biomarker applications of TMS in a few representative neurodevelopmental disorders including autism spectrum disorder, fragile X syndrome, attention-deficit hyperactivity disorder, Tourette syndrome, and developmental stuttering.

Neurostimulation for the treatment of functional neurological disorder: A systematic review

Functional Neurological Disorder (FND), also known as conversion disorder, is characterized by neurological symptoms that are incompatible with any known structural disorder and best explained by a biopsychosocial model. Evidence-based treatments for FND are limited, with cognitive behavioral therapy (CBT) and physiotherapy being the most effective interventions [1]. In recent years, functional neuroimaging studies have provided robust evidence of alterations in activity and connectivity in multiple brain networks in FND. This body of evidence suggests that neurocircuitry-based interventions, such as non-invasive brain stimulation techniques (NIBS), may also represent an effective therapeutic option for patients with FND. In this systematic review, we outline the current state of knowledge of NIBS in FND, and discuss limitations and future directions that may help establish the efficacy of NIBS as a therapeutic option for FND.

Effects of Transcranial Direct Current Stimulation and High-Definition Transcranial Direct Current Stimulation Enhanced Motor Learning on Robotic Transcranial Magnetic Stimulation Motor Maps in Children

Introduction: Conventional transcranial direct current stimulation (tDCS) and high-definition tDCS (HD-tDCS) may improve motor learning in children. Mechanisms are not understood. Neuronavigated robotic transcranial magnetic stimulation (TMS) can produce individualised maps of primary motor cortex (M1) topography. We aimed to determine the effects of tDCS- and HD-tDCS-enhanced motor learning on motor maps. Methods: Typically developing children aged 12-18 years were randomised to right M1 anodal tDCS, HD-tDCS, or Sham during training of their left-hand on the Purdue Pegboard Task (PPT) over 5 days. Bilateral motor mapping was performed at baseline (pre), day 5 (post), and 6-weeks retention time (RT). Primary muscle was the first dorsal interosseous (FDI) with secondary muscles of abductor pollicis brevis (APB) and adductor digiti minimi (ADM). Primary mapping outcomes were volume (mm²/mV) and area (mm²). Secondary outcomes were centre of gravity (COG, mm) and hotspot magnitude (mV). Linear mixed-effects modelling was employed to investigate effects of time and stimulation type (tDCS, HD-tDCS, Sham) on motor map characteristics. Results: Twenty-four right-handed participants (median age 15.5 years, 52% female) completed the study with no serious adverse events or dropouts. Quality maps could not be obtained in two participants. No effect of time or group were observed on map area or volume. LFDI COG (mm) differed in the medial-lateral plane (x-axis) between tDCS and Sham (p = 0.038) from pre-to-post mapping sessions. Shifts in map COG were also observed for secondary left-hand muscles. Map metrics did not correlate with behavioural changes. Conclusion: Robotic TMS mapping can safely assess motor cortex neurophysiology in children undergoing motor learning and neuromodulation interventions. Large effects on map area and volume were not observed while changes in COG may occur. Larger controlled studies are required to understand the role of motor maps in interventional neuroplasticity in children.

Perinatal stroke: mapping and modulating developmental plasticity

Most cases of hemiparetic cerebral palsy are caused by perinatal stroke, resulting in lifelong disability for millions of people. However, our understanding of how the motor system develops following such early unilateral brain injury is increasing. Tools such as neuroimaging and brain stimulation are generating informed maps of the unique motor networks that emerge following perinatal stroke. As a focal injury of defined timing in an otherwise healthy brain, perinatal stroke represents an ideal human model of developmental plasticity. Here, we provide an introduction to perinatal stroke epidemiology and outcomes, before reviewing models of developmental plasticity after perinatal stroke. We then examine existing therapeutic approaches, including constraint, bimanual and other occupational therapies, and their potential synergy with non-invasive neurostimulation. We end by discussing the promise of exciting new therapies, including novel neurostimulation, brain-computer interfaces and robotics, all focused on improving outcomes after perinatal stroke.

Robotic transcranial magnetic stimulation motor maps and hand function in adolescents

Introduction

Transcranial magnetic stimulation (TMS) motor mapping can characterize the neurophysiology of the motor system. Limitations including human error and the challenges of pediatric populations may be overcome by emerging robotic systems. We aimed to show that neuronavigated robotic motor mapping in adolescents could efficiently produce discrete maps of individual upper extremity muscles, the characteristics of which would correlate with motor behavior.

Methods

Typically developing adolescents (TDA) underwent neuronavigated robotic TMS mapping of bilateral motor cortex. Representative maps of first dorsal interosseous (FDI), abductor pollicis brevis (APB), and abductor digiti minimi (ADM) muscles in each hand were created. Map features including area (primary), volume, and center of gravity were analyzed across different excitability regions (R100%, R75%, R50%, R25%). Correlations between map metrics and validated tests of hand motor function (Purdue Pegboard Test as primary) were explored.

Results

Twenty‐four right‐handed participants (range 12–18 years, median 15.5 years, 52% female) completed bilateral mapping and motor assessments with no serious adverse events or dropouts. Gender and age were associated with hand function and motor map characteristics. Full motor maps (R100%) for FDI did not correlate with motor function in either hand. Smaller excitability subset regions demonstrated reduced variance and dose‐dependent correlations between primary map variables and motor function in the dominant hemisphere.

Conclusions

Hand function in TDA correlates with smaller subset excitability regions of robotic TMS motor map outcomes. Refined motor maps may have less variance and greater potential to quantify interventional neuroplasticity. Robotic TMS mapping is safe and feasible in adolescents.

From adults to pediatrics: A review noninvasive brain stimulation (NIBS) to facilitate recovery from brain injury

Stroke is a major problem worldwide that impacts over 100 million adults and children annually. Rehabilitation therapy is the current standard of care to restore functional impairments post-stroke, however its effects are limited and many patients suffer persisting functional impairments and life-long disability. Noninvasive Brain Stimulation (NIBS) has emerged as a potential rehabilitation treatment option in both adults and children with brain injury. In the last decade, Transcranial Magnetic Stimulation (TMS), Transcranial Direct Current Stimulation (tDCS) and Transcutaneous Auricular Vagus Nerve Stimulation (taVNS) have been investigated to improve motor recovery in adults post-stroke. These promising adult findings using NIBS, however, have yet to be widely translated to the area of pediatrics. The limited studies exploring NIBS in children have demonstrated safety, feasibility, and utility of stimulation-augmented rehabilitation. This chapter will describe the mechanism of NIBS therapy (cortical excitability, neuroplasticity) that underlies its use in stroke and motor function and how TMS, tDCS, and taVNS are applied in adult stroke treatment paradigms. We will then discuss the current state of NIBS in early pediatric brain injury and will provide insight regarding practical considerations and future applications of NIBS in pediatrics to make this promising treatment option a viable therapy in children.

Reliability of robotic transcranial magnetic stimulation motor mapping

Robotic transcranial magnetic stimulation (TMS) is a noninvasive and safe tool that produces cortical motor maps using neuronavigational and neuroanatomical images. Motor maps are individualized representations of the primary motor cortex (M1) topography that may reflect developmental and interventional plasticity. Results of TMS motor map reliability testing have been variable, and robotic measures are undefined. We aimed to determine the short- and long-term reliability of robotic TMS motor maps. Twenty healthy participants underwent motor mapping at baseline, 24 h, and 4 wk. A 12 × 12 grid (7-mm spacing) was placed over the left M1, centered over the hand knob area. Four suprathreshold stimulations were delivered at each grid point. First dorsal interosseous (FDI) motor-evoked potentials (MEPs) were analyzed offline to generate map characteristics of area, volume, center of gravity (COG), and hotspot magnitude. Subsets of each outcome corresponding to 75%, 50%, and 25% of each map were determined. Reliability measures including intraclass correlation coefficient (ICC), minimal detectable change (MDC), and standard error of measure (SEM) were calculated. Map volume, COG, and hotspot magnitude were the most reliable measures (good-to-excellent) over both short- and long-term sessions. Map area reliability was poor-to-moderate for short- and long-term sessions. Smaller map percentile subsets showed decreased variability but only minimal improvements in reliability. MDC for most outcomes was >50%. Procedures were well tolerated with no serious adverse events. Robotic TMS motor mapping is relatively reliable over time, but careful consideration of specific outcomes is required for this method to interrogate plasticity in the human motor system.NEW & NOTEWORTHY Robotic transcranial magnetic stimulation (TMS) is a noninvasive and safe tool that produces cortical motor maps-individualized representations of the primary motor cortex (M1) topography-that may reflect developmental and interventional plasticity. This study is the first to evaluate short- and long-term relative and absolute reliability of TMS mapping outcomes at various M1 excitability levels using novel robotic neuronavigated TMS.

Imaging Developmental and Interventional Plasticity Following Perinatal Stroke

Perinatal stroke occurs around the time of birth and leads to lifelong neurological disabilities including hemiparetic cerebral palsy. Magnetic resonance imaging (MRI) has revolutionized our understanding of developmental neuroplasticity following early injury, quantifying volumetric, structural, functional, and metabolic compensatory changes after perinatal stroke. Such techniques can also be used to investigate how the brain responds to treatment (interventional neuroplasticity). Here, we review the current state of knowledge of how established and emerging neuroimaging modalities are informing neuroplasticity models in children with perinatal stroke. Specifically, we review structural imaging characterizing lesion characteristics and volumetrics, diffusion tensor imaging investigating white matter tracts and networks, task-based functional MRI for localizing function, resting state functional imaging for characterizing functional connectomes, and spectroscopy examining neurometabolic changes. Key challenges and exciting avenues for future investigations are also considered.

Transcranial Static Magnetic Field Stimulation of the Motor Cortex in Children

BACKGROUND

Non-invasive neuromodulation is an emerging therapy for children with early brain injury but is difficult to apply to preschoolers when windows of developmental plasticity are optimal. Transcranial static magnetic field stimulation (tSMS) decreases primary motor cortex (M1) excitability in adults but effects on the developing brain are unstudied.

OBJECTIVE/HYPOTHESIS

We aimed to determine the effects of tSMS on cortical excitability and motor learning in healthy children. We hypothesized that tSMS over right M1 would reduce cortical excitability and inhibit contralateral motor learning.

METHODS

This randomized, sham-controlled, double-blinded, three-arm, cross-over trial enrolled 24 healthy children aged 10-18 years. Transcranial Magnetic Stimulation (TMS) assessed cortical excitability via motor-evoked potential (MEP) amplitude and paired pulse measures. Motor learning was assessed via the Purdue Pegboard Test (PPT). A tSMS magnet (677 Newtons) or sham was held over left or right M1 for 30 min while participants trained the non-dominant hand. A linear mixed effect model was used to examine intervention effects.

RESULTS

All 72 tSMS sessions were well tolerated without serious adverse effects. Neither cortical excitability as measured by MEPs nor paired-pulse intracortical neurophysiology was altered by tSMS. Possible behavioral effects included contralateral tSMS inhibiting early motor learning (p < 0.01) and ipsilateral tSMS facilitating later stages of motor learning (p < 0.01) in the trained non-dominant hand.

CONCLUSION

tSMS is feasible in pediatric populations. Unlike adults, tSMS did not produce measurable changes in MEP amplitude. Possible effects of M1 tSMS on motor learning require further study. Our findings support further exploration of tSMS neuromodulation in young children with cerebral palsy.

Concordance Between Transcranial Magnetic Stimulation and Functional Magnetic Resonance Imaging (MRI) Derived Localization of Language in a Clinical Cohort

Transcranial magnetic stimulation (TMS) is a newer noninvasive language mapping tool that is safe and well-tolerated by children. We examined the accuracy of TMS-derived language maps in a clinical cohort by comparing it against functional magnetic resonance imaging (MRI)-derived language map. The number of TMS-induced speech disruptions and the volume of activation during functional MRI tasks were localized to Brodmann areas for each modality in 40 patients with epilepsy or brain tumor. We examined the concordance between TMS- and functional MRI-derived language maps by deriving statistical performance metrics for TMS including sensitivity, specificity, accuracy, and diagnostic odds ratio. Brodmann areas 6, 44, and 9 in the frontal lobe and 22 and 40 in the temporal lobe were the most commonly identified language areas by both modalities. Overall accuracy of TMS compared to functional MRI in localizing language cortex was 71%, with a diagnostic odds ratio of 1.27 and higher sensitivity when identifying left hemisphere regions. TMS was more accurate in determining the dominant hemisphere for language with a diagnostic odds ratio of 6. This study is the first to examine the accuracy of the whole brain language map derived by TMS in the largest cohort examined to date. While this comparison against functional MRI confirmed that TMS reliably localizes cortical areas that are not essential for speech function, it demonstrated only slight concordance between TMS- and functional MRI-derived language areas. That the localization of specific language cortices by TMS demonstrated low accuracy reveals a potential need to use concordant tasks between the modalities and other avenues for further optimization of TMS parameters.

Continuous Theta-Burst Stimulation in Children With High-Functioning Autism Spectrum Disorder and Typically Developing Children

Objectives: A neurophysiologic biomarker for autism spectrum disorder (ASD) is highly desirable and can improve diagnosis, monitoring, and assessment of therapeutic response among children with ASD. We investigated the utility of continuous theta-burst stimulation (cTBS) applied to the motor cortex (M1) as a biomarker for children and adolescents with high-functioning (HF) ASD compared to their age- and gender-matched typically developing (TD) controls. We also compared the developmental trajectory of long-term depression- (LTD-) like plasticity in the two groups. Finally, we explored the influence of a common brain-derived neurotrophic factor (BDNF) polymorphism on cTBS aftereffects in a subset of the ASD group. Methods: Twenty-nine children and adolescents (age range 10-16) in ASD (n = 11) and TD (n = 18) groups underwent M1 cTBS. Changes in MEP amplitude at 5-60 min post-cTBS and their cumulative measures in each group were calculated. We also assessed the relationship between age and maximum cTBS-induced MEP suppression (ΔMEPMax) in each group. Finally, we compared cTBS aftereffects in BDNF Val/Val (n = 4) and Val/Met (n = 4) ASD participants. Results: Cumulative cTBS aftereffects were significantly more facilitatory in the ASD group than in the TD group (P FDR's < 0.03). ΔMEPMax was negatively correlated with age in the ASD group (r = -0.67, P = 0.025), but not in the TD group (r = -0.12, P = 0.65). Cumulative cTBS aftereffects were not significantly different between the two BDNF subgroups (P-values > 0.18). Conclusions: The results support the utility of cTBS measures of cortical plasticity as a biomarker for children and adolescents with HF-ASD and an aberrant developmental trajectory of LTD-like plasticity in ASD.

Safety and tolerability of transcranial magnetic and direct current stimulation in children: Prospective single center evidence from 3.5 million stimulations

BACKGROUND

Non-invasive brain stimulation is being increasingly used to interrogate neurophysiology and modulate brain function. Despite the high scientific and therapeutic potential of non-invasive brain stimulation, experience in the developing brain has been limited.

OBJECTIVE

To determine the safety and tolerability of non-invasive neurostimulation in children across diverse modalities of stimulation and pediatric populations.

METHODS

A non-invasive brain stimulation program was established in 2008 at our pediatric, academic institution. Multi-disciplinary neurophysiological studies included single- and paired-pulse Transcranial Magnetic Stimulation (TMS) methods. Motor mapping employed robotic TMS. Interventional trials included repetitive TMS (rTMS) and transcranial direct current stimulation (tDCS). Standardized safety and tolerability measures were completed prospectively by all participants.

RESULTS

Over 10 years, 384 children underwent brain stimulation (median 13 years, range 0.8-18.0). Populations included typical development (n = 118), perinatal stroke/cerebral palsy (n = 101), mild traumatic brain injury (n = 121) neuropsychiatric disorders (n = 37), and other (n = 7). No serious adverse events occurred. Drop-outs were rare (<1%). No seizures were reported despite >100 participants having brain injuries and/or epilepsy. Tolerability between single and paired-pulse TMS (542340 stimulations) and rTMS (3.0 million stimulations) was comparable and favourable. TMS-related headache was more common in perinatal stroke (40%) than healthy participants (13%) but was mild and self-limiting. Tolerability improved over time with side-effect frequency decreasing by >50%. Robotic TMS motor mapping was well-tolerated though neck pain was more common than with manual TMS (33% vs 3%). Across 612 tDCS sessions including 92 children, tolerability was favourable with mild itching/tingling reported in 37%.

CONCLUSIONS

Standard non-invasive brain stimulation paradigms are safe and well-tolerated in children and should be considered minimal risk. Advancement of applications in the developing brain are warranted. A new and improved pediatric NIBS safety and tolerability form is included.

Intraoperative Neuromonitoring of Motor-Evoked Potentials in Infants Undergoing Surgery of the Spine and Spinal Cord

PURPOSE

The aim of this single-center prospective cohort study is to record reliable transcranial motor-evoked potentials (TcMEPs) and to determine their thresholds under inhalational anesthesia in infants undergoing spine and spinal cord surgery.

METHODS

A total of 15 infants (age <12 months) with mean (SD) months: 5.82 ± 3.45 were included. The entry criteria were that the child should be no older than 1 year of age and undergoing a surgical procedure at the conus-cauda region. The patients were monitored with motor-evoked potentials (TcMEPs) and bulbocavernosus reflex.

RESULTS

Transcranial motor-evoked potentials were recorded in all the patients in both upper and lower extremities in one muscle at least. All patients were monitored with a mean TcMEP threshold of 488.46 ± 99.76 V (range 310-740 V). The lowest threshold of TcMEPs was used to record the musculus abductor pollicis brevis mean of 315.15 ± 126.95 V (range 140-690 V) and the highest for musculus sphincter ani mean of 444.17 ± 138.54 V (range 206-700 V).

CONCLUSIONS

Intraoperative neuromonitoring for spine and spinal cord procedures of the infant population requires higher TcMEP thresholds and train count. Most patients aged older than 6 months require significantly lower TcMEPs.

Exploratory Study of rTMS Neuromodulation Effects on Electrocortical Functional Measures of Performance in an Oddball Test and Behavioral Symptoms in Autism

There is no accepted pathology to autism spectrum disorders (ASD) but research suggests the presence of an altered excitatory/inhibitory (E/I) bias in the cerebral cortex. Repetitive transcranial magnetic stimulation (rTMS) offers a non-invasive means of modulating the E/I cortical bias with little in terms of side effects. In this study, 124 high functioning ASD children (IQ > 80, <18 years of age) were recruited and assigned using randomization to either a waitlist group or one of three different number of weekly rTMS sessions (i.e., 6, 12, and 18). TMS consisted of trains of 1.0 Hz frequency pulses applied over the dorsolateral prefrontal cortex (DLPFC). The experimental task was a visual oddball with illusory Kanizsa figures. Behavioral response variables included reaction time and error rate along with such neurophysiological indices such as stimulus and response-locked event-related potentials (ERP). One hundred and twelve patients completed the assigned number of TMS sessions. Results showed significant changes from baseline to posttest period in the following measures: motor responses accuracy [lower percentage of committed errors, slower latency of commission errors and restored normative post-error reaction time slowing in both early and later-stage ERP indices, enhanced magnitude of error-related negativity (ERN), improved error monitoring and post-error correction functions]. In addition, screening surveys showed significant reductions in aberrant behavior ratings and in both repetitive and stereotypic behaviors. These differences increased with the total number of treatment sessions. Our results suggest that rTMS, particularly after 18 sessions, facilitates cognitive control, attention and target stimuli recognition by improving discrimination between task-relevant and task-irrelevant illusory figures in an oddball test. The noted improvement in executive functions of behavioral performance monitoring further suggests that TMS has the potential to target core features of ASD.

Non-Invasive Brain Stimulation in Children With Unilateral Cerebral Palsy: A Protocol and Risk Mitigation Guide

Non-invasive brain stimulation has been increasingly investigated, mainly in adults, with the aims of influencing motor recovery after stroke. However, a consensus on safety and optimal study design has not been established in pediatrics. The low incidence of reported major adverse events in adults with and without clinical conditions has expedited the exploration of NIBS in children with paralleled purposes to influence motor skill development after neurological injury. Considering developmental variability in children, with or without a neurologic diagnosis, adult dosing and protocols may not be appropriate. The purpose of this paper is to present recommendations and tools for the prevention and mitigation of adverse events (AEs) during NIBS in children with unilateral cerebral palsy (UCP). Our recommendations provide a framework for pediatric NIBS study design. The key components of this report on NIBS AEs are (a) a summary of related literature to provide the background evidence and (b) tools for anticipating and managing AEs from four international pediatric laboratories. These recommendations provide a preliminary guide for the assessment of safety and risk mitigation of NIBS in children with UCP. Consistent reporting of safety, feasibility, and tolerability will refine NIBS practice guidelines contributing to future clinical translations of NIBS.

Transcranial Magnetic and Direct Current Stimulation in Children

Promising results in adult neurologic and psychiatric disorders are driving active research into transcranial brain stimulation techniques, particularly transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), in childhood and adolescent syndromes. TMS has realistic utility as an experimental tool tested in a range of pediatric neuropathologies such as perinatal stroke, depression, Tourette syndrome, and autism spectrum disorder (ASD). tDCS has also been tested as a treatment for a number of pediatric neurologic conditions, including ASD, attention-deficit/hyperactivity disorder, epilepsy, and cerebral palsy. Here, we complement recent reviews with an update of published TMS and tDCS results in children, and discuss developmental neuroscience considerations that should inform pediatric transcranial stimulation.

Advancing non-invasive neuromodulation clinical trials in children: Lessons from perinatal stroke

Applications of non-invasive brain stimulation including therapeutic neuromodulation are expanding at an alarming rate. Increasingly established scientific principles, including directional modulation of well-informed cortical targets, are advancing clinical trial development. However, high levels of disease burden coupled with zealous enthusiasm may be getting ahead of rational research and evidence. Experience is limited in the developing brain where additional issues must be considered. Properly designed and meticulously executed clinical trials are essential and required to advance and optimize the potential of non-invasive neuromodulation without risking the well-being of children and families. Perinatal stroke causes most hemiplegic cerebral palsy and, as a focal injury of defined timing in an otherwise healthy brain, is an ideal human model of developmental plasticity. Advanced models of how the motor systems of young brains develop following early stroke are affording novel windows of opportunity for neuromodulation clinical trials, possibly directing neuroplasticity toward better outcomes. Reviewing the principles of clinical trial design relevant to neuromodulation and using perinatal stroke as a model, this article reviews the current and future issues of advancing such trials in children.

Cerebral plasticity: Windows of opportunity in the developing brain

BACKGROUND

Neuroplasticity refers to the inherently dynamic biological capacity of the central nervous system (CNS) to undergo maturation, change structurally and functionally in response to experience and to adapt following injury. This malleability is achieved by modulating subsets of genetic, molecular and cellular mechanisms that influence the dynamics of synaptic connections and neural circuitry formation culminating in gain or loss of behavior or function. Neuroplasticity in the healthy developing brain exhibits a heterochronus cortex-specific developmental profile and is heightened during "critical and sensitive periods" of pre and postnatal brain development that enable the construction and consolidation of experience-dependent structural and functional brain connections.

PURPOSE

In this review, our primary goal is to highlight the essential role of neuroplasticity in brain development, and to draw attention to the complex relationship between different levels of the developing nervous system that are subjected to plasticity in health and disease. Another goal of this review is to explore the relationship between plasticity responses of the developing brain and how they are influenced by critical and sensitive periods of brain development. Finally, we aim to motivate researchers in the pediatric neuromodulation field to build on the current knowledge of normal and abnormal neuroplasticity, especially synaptic plasticity, and their dependence on "critical or sensitive periods" of neural development to inform the design, timing and sequencing of neuromodulatory interventions in order to enhance and optimize their translational applications in childhood disorders of the brain.

METHODS

literature review.

RESULTS

We discuss in details five patterns of neuroplasticity expressed by the developing brain: 1) developmental plasticity which is further classified into normal and impaired developmental plasticity as seen in syndromic autism spectrum disorders, 2) adaptive (experience-dependent) plasticity following intense motor skill training, 3) reactive plasticity to pre and post natal CNS injury or sensory deprivation, 4) excessive plasticity (loss of homeostatic regulation) as seen in dystonia and refractory epilepsy, 6) and finally, plasticity as the brain's "Achilles tendon" which induces brain vulnerability under certain conditions such as hypoxic ischemic encephalopathy and epileptic encephalopathy syndromes. We then explore the unique feature of "time-sensitive heightened plasticity responses" in the developing brain in the in the context of neuromodulation.

CONCLUSION

The different patterns of neuroplasticity and the unique feature of heightened plasticity during critical and sensitive periods are important concepts for researchers and clinicians in the field of pediatric neurology and neurodevelopmental disabilities. These concepts need to be examined systematically in the context of pediatric neuromodulation. We propose that critical and sensitive periods of brain development in health and disease can create "windows of opportunity" for neuromodulatory interventions that are not commonly seen in adult brain and probably augment plasticity responses and improve clinical outcomes.

Transcranial direct current stimulation for children with perinatal stroke and hemiparesis

Objective:

To determine whether the addition of transcranial direct current stimulation (tDCS) to intensive therapy increases motor function in children with perinatal stroke and hemiparetic cerebral palsy.

Methods:

This was a randomized, controlled, double-blind clinical trial. Participants were recruited from a population-based cohort with MRI-classified unilateral perinatal stroke, age of 6 to 18 years, and disabling hemiparesis. All completed a goal-directed, peer-supported, 2-week after-school motor learning camp (32 hours of therapy). Participants were randomized 1:1 to 1 mA cathodal tDCS over the contralesional primary motor cortex (M1) for the initial 20 minutes of daily therapy or sham. Primary subjective (Canadian Occupational Performance Measure [COPM]), objective (Assisting Hand Assessment [AHA]), safety, and secondary outcomes were measured at 1 week and 2 months after intervention. Analysis was by intention to treat.

Results:

Twenty-four participants were randomized (median age 11.8 ± 2.7 years, range 6.7–17.8). COPM performance and satisfaction scores doubled at 1 week with sustained gains at 2 months (p < 0.001). COPM scores increased more with tDCS compared to sham control (p = 0.004). AHA scores demonstrated only mild increases at both time points with no tDCS effects. Procedures were safe and well tolerated with no decrease in either arm function or serious adverse events.

Conclusion:

tDCS trials appear feasible and safe in hemiparetic children. Lack of change in objective motor function may reflect underdosing of therapy. Marked gains in subjective function with tDCS warrant further study.

ClinicalTrials.gov identifier:

NCT02170285.

Classification of evidence:

This study provides Class II evidence that for children with perinatal stroke and hemiparetic cerebral palsy, the addition of tDCS to moderate-dose motor learning therapy does not significantly improve motor function as measured by the AHA.

Noninvasive Brain Stimulation in Pediatric Attention-Deficit Hyperactivity Disorder (ADHD): A Review

Attention-deficit hyperactivity disorder (ADHD) is one of the most prevalent neurodevelopmental disorders in the pediatric population. The clinical management of ADHD is currently limited by a lack of reliable diagnostic biomarkers and inadequate therapy for a minority of patients who do not respond to standard pharmacotherapy. There is optimism that noninvasive brain stimulation may help to address these limitations. Transcranial magnetic stimulation and transcranial direct current stimulation are 2 methods of noninvasive brain stimulation that modulate cortical excitability and brain network activity. Transcranial magnetic stimulation can be used diagnostically to probe cortical neurophysiology, whereas daily use of repetitive transcranial magnetic stimulation or transcranial direct current stimulation can induce long-lasting and potentially therapeutic changes in targeted networks. In this review, we highlight research showing the potential diagnostic and therapeutic applications of transcranial magnetic stimulation and transcranial direct current stimulation in pediatric ADHD. We also discuss the safety and ethics of using these tools in the pediatric population.

Brain stimulation and constraint for perinatal stroke hemiparesis: The PLASTIC CHAMPS Trial

OBJECTIVE

To determine whether the addition of repetitive transcranial magnetic stimulation (rTMS) and/or constraint-induced movement therapy (CIMT) to intensive therapy increases motor function in children with perinatal stroke and hemiparesis.

METHODS

A factorial-design, blinded, randomized controlled trial (clinicaltrials.gov/NCT01189058) assessed rTMS and CIMT effects in hemiparetic children (aged 6-19 years) with MRI-confirmed perinatal stroke. All completed a 2-week, goal-directed, peer-supported motor learning camp randomized to daily rTMS, CIMT, both, or neither. Primary outcomes were the Assisting Hand Assessment and the Canadian Occupational Performance Measure at baseline, and 1 week, 2 and 6 months postintervention. Outcome assessors were blinded to treatment. Interim safety analyses occurred after 12 and 24 participants. Intention-to-treat analysis examined treatment effects over time (linear mixed effects model).

RESULTS

All 45 participants completed the trial. Addition of rTMS, CIMT, or both doubled the chances of clinically significant improvement. Assisting Hand Assessment gains at 6 months were additive and largest with rTMS + CIMT (β coefficient = 5.54 [2.57-8.51], p = 0.0004). The camp alone produced large improvements in Canadian Occupational Performance Measure scores, maximal at 6 months (Cohen d = 1.6, p = 0.002). Quality-of-life scores improved. Interventions were well tolerated and safe with no decrease in function of either hand.

CONCLUSIONS

Hemiparetic children participating in intensive, psychosocial rehabilitation programs can achieve sustained functional gains. Addition of CIMT and rTMS increases the chances of improvement.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that combined rTMS and CIMT enhance therapy-induced functional motor gains in children with stroke-induced hemiparetic cerebral palsy.

Transcranial magnetic stimulation in autism spectrum disorder: Challenges, promise, and roadmap for future research

Autism Spectrum Disorder (ASD) is a behaviorally defined complex neurodevelopmental syndrome characterized by impairments in social communication, by the presence of restricted and repetitive behaviors, interests and activities, and by abnormalities in sensory reactivity. Transcranial magnetic stimulation (TMS) is a promising, emerging tool for the study and potential treatment of ASD. Recent studies suggest that TMS measures provide rapid and noninvasive pathophysiological ASD biomarkers. Furthermore, repetitive TMS (rTMS) may represent a novel treatment strategy for reducing some of the core and associated ASD symptoms. However, the available literature on the TMS use in ASD is preliminary, composed of studies with methodological limitations. Thus, off-label clinical rTMS use for therapeutic interventions in ASD without an investigational device exemption and outside of an IRB approved research trial is premature pending further, adequately powered and controlled trials. Leaders in this field have gathered annually for a two-day conference (prior to the 2014 and 2015 International Meeting for Autism Research, IMFAR) to share recent progress, promote collaboration across laboratories, and establish consensus on protocols. Here we review the literature in the use of TMS in ASD in the context of the unique challenges required for the study and exploration of treatment strategies in this population. We also suggest future directions for this field of investigations. While its true potential in ASD has yet to be delineated, TMS represents an innovative research tool and a novel, possibly transformative approach to the treatment of neurodevelopmental disorders.

Transcranial magnetic stimulation facilitates neurorehabilitation after pediatric traumatic brain injury

Traumatic brain injury (TBI) is the leading cause of death and disability among children in the United States. Affected children will often suffer from emotional, cognitive and neurological impairments throughout life. In the controlled cortical impact (CCI) animal model of pediatric TBI (postnatal day 16-17) it was demonstrated that injury results in abnormal neuronal hypoactivity in the non-injured primary somatosensory cortex (S1). It materializes that reshaping the abnormal post-injury neuronal activity may provide a suitable strategy to augment rehabilitation. We tested whether high-frequency, non-invasive transcranial magnetic stimulation (TMS) delivered twice a week over a four-week period can rescue the neuronal activity and improve the long-term functional neurophysiological and behavioral outcome in the pediatric CCI model. The results show that TBI rats subjected to TMS therapy showed significant increases in the evoked-fMRI cortical responses (189%), evoked synaptic activity (46%), evoked neuronal firing (200%) and increases expression of cellular markers of neuroplasticity in the non-injured S1 compared to TBI rats that did not receive therapy. Notably, these rats showed less hyperactivity in behavioral tests. These results implicate TMS as a promising approach for reversing the adverse neuronal mechanisms activated post-TBI. Importantly, this intervention could readily be translated to human studies.

Clinical Applications of Transcranial Magnetic Stimulation in Pediatric Neurology

Noninvasive brain stimulation is now an accepted technique that is used as a diagnostic aid and in the treatment of neuropsychiatric disorders in adults, and is being increasingly used in children. In this review, we will discuss the basic principles and safety of one noninvasive brain stimulation method, transcranial magnetic stimulation. Improvements in the spatial accuracy of transcranial magnetic stimulation are described in the context of image-guided transcranial magnetic stimulation. The article describes and provides examples of the current clinical applications of transcranial magnetic stimulation in children as an aid in the diagnosis and treatment of neuropsychiatric disorders and discusses future potential applications. Transcranial magnetic stimulation is a noninvasive tool that is safe for use in children and adolescents for functional mapping and treatment, and for many children it aids in the preoperative evaluation and the risk-benefit decision making.

Efficient and reliable characterization of the corticospinal system using transcranial magnetic stimulation

PURPOSE

The purpose of this study is to develop a method to reliably characterize multiple features of the corticospinal system in a more efficient manner than typically done in transcranial magnetic stimulation studies.

METHODS

Forty transcranial magnetic stimulation pulses of varying intensity were given over the first dorsal interosseous motor hot spot in 10 healthy adults. The first dorsal interosseous motor-evoked potential size was recorded during rest and activation to create recruitment curves. The Boltzmann sigmoidal function was fit to the data, and parameters relating to maximal motor-evoked potential size, curve slope, and stimulus intensity leading to half-maximal motor-evoked potential size were computed from the curve fit.

RESULTS

Good to excellent test-retest reliability was found for all corticospinal parameters at rest and during activation with 40 transcranial magnetic stimulation pulses.

CONCLUSIONS

Through the use of curve fitting, important features of the corticospinal system can be determined with fewer stimuli than typically used for the same information. Determining the recruitment curve provides a basis to understand the state of the corticospinal system and select subject-specific parameters for transcranial magnetic stimulation testing quickly and without unnecessary exposure to magnetic stimulation. This method can be useful in individuals who have difficulty in maintaining stillness, including children and patients with motor disorders.

The Corticospinal Tract: A Biomarker to Categorize Upper Limb Functional Potential in Unilateral Cerebral Palsy

Children with unilateral cerebral palsy (CP) typically present with largely divergent upper limb sensorimotor deficits and individual differences in response to upper limb rehabilitation. This review summarizes how early brain damage can cause dramatic deviations from the normal anatomy of sensory and motor tracts, resulting in unique "wiring patterns" of the sensorimotor system in CP. Based on the existing literature, we suggest that corticospinal tract (CST) anatomy and integrity constrains sensorimotor function of the upper limb and potentially also the response to treatment. However, it is not possible to infer CST (re)organization from clinical presentation alone and conventional biomarkers, such as time of insult, location, and lesion extent seem to have limited clinical utility. Here, we propose a theoretical framework based on a detailed examination of the motor system using behavioral, neurophysiological, and magnetic resonance imaging measures, akin to those used to predict potential for upper limb recovery of adults after stroke. This theoretical framework might prove useful because it provides testable hypotheses for future research with the goal to develop and validate a clinical assessment flowchart to categorize children with unilateral CP.

Developmental aspects of cortical excitability and inhibition in depressed and healthy youth: an exploratory study

Objectives: The objective of this post-hoc exploratory analysis was to examine the relationship between age and measures of cortical excitability and inhibition.

Methods: Forty-six participants (24 with major depressive disorder and 22 healthy controls) completed MT, SICI, ICF, and CSP testing in a cross-sectional protocol. Of these 46 participants, 33 completed LICI testing. Multiple linear robust regression and Spearman partial correlation coefficient were used to examine the relationship between age and the TMS measures.

Results: In the overall sample of 46 participants, age had a significant negative relationship with motor threshold (MT) in both the right (r_s = −0.49, adjusted p = 0.007; β = −0.08, adjusted p = 0.001) and left (r_s = −0.42, adjusted p = 0.029; β = −0.05, adjusted p = 0.004) hemispheres. This significant negative relationship of age with MT was also observed in the sample of depressed youth in both the right (r_s = −0.70, adjusted p = 0.002; β = −0.09, adjusted p = 0.001) and left (r_s = −0.54, adjusted p = 0.034; β = −0.05, adjusted p = 0.017) hemispheres, but not in healthy controls. In the sample of the 33 participants who completed LICI testing, age had a significant negative relationship with LICI (200 ms interval) in both the right (r_s = −0.48, adjusted p = 0.05; β = −0.24, adjusted p = 0.007) and left (r_s = −0.64, adjusted p = 0.002; β = −0.23, adjusted p = 0.001) hemispheres. This negative relationship between age and LICI (200 ms interval) was also observed in depressed youth in both the right (r_s = −0.76, adjusted p = 0.034; β = −0.35, adjusted p = 0.004) and left (r_s = −0.92, adjusted p = 0.002; β = −0.25, adjusted p = 0.001) hemispheres.

Conclusion: These findings suggest that younger children have higher MTs. This is more pronounced in depressed youth than healthy controls. LICI inhibition may also increase with age in youth.

Modulation of corticospinal excitability by transcranial magnetic stimulation in children and adolescents with autism spectrum disorder

The developmental pathophysiology of autism spectrum disorders (ASD) is currently not fully understood. However, multiple lines of evidence suggest that the behavioral phenotype may result from dysfunctional inhibitory control over excitatory synaptic plasticity. Consistent with this claim, previous studies indicate that adults with Asperger’s Syndrome show an abnormally extended modulation of corticospinal excitability following a train of repetitive transcranial magnetic stimulation (rTMS). As ASD is a developmental disorder, the current study aimed to explore the effect of development on the duration of modulation of corticospinal excitability in children and adolescents with ASD. Additionally, as the application of rTMS to the understanding and treatment of pediatric neurological and psychiatric disorders is an emerging field, this study further sought to provide evidence for the safety and tolerability of rTMS in children and adolescents with ASD. Corticospinal excitability was measured by applying single pulses of TMS to the primary motor cortex both before and following a 40 s train of continuous theta burst stimulation. 19 high-functioning males ages 9–18 with ASD participated in this study. Results from this study reveal a positive linear relationship between age and duration of modulation of rTMS after-effects. Specifically we found that the older participants had a longer lasting response. Furthermore, though the specific protocol employed typically suppresses corticospinal excitability in adults, more than one third of our sample had a paradoxical facilitatory response to the stimulation. Results support the safety and tolerability of rTMS in pediatric clinical populations. Data also support published theories implicating aberrant plasticity and GABAergic dysfunction in this population.

Can noninvasive brain stimulation measure and modulate developmental plasticity to improve function in stroke-induced cerebral palsy?

The permanent nature of motor deficits is a consistent cornerstone of cerebral palsy definitions. Such pessimism is disheartening to children, families, and researchers alike and may no longer be appropriate for it ignores the fantastic plastic potential of the developing brain. Perinatal stroke is presented as the ideal human model of developmental neuroplasticity following distinct, well-defined, focal perinatal brain injury. Elegant animal models are merging with human applied technology methods, including noninvasive brain stimulation for increasingly sophisticated models of plastic motor development following perinatal stroke. In this article, how potential central therapeutic targets are identified and potentially modulated to enhance motor function within these models is discussed. Also, future directions and emerging clinical trials are reviewed.

Modeling developmental plasticity after perinatal stroke: defining central therapeutic targets in cerebral palsy

Perinatal stroke is presented as the ideal human model of developmental neuroplasticity. The precise timing, mechanisms, and locations of specific perinatal stroke diseases provide common examples of well defined, focal, perinatal brain injuries. Motor disability (hemiparetic cerebral palsy) constitutes the primary adverse outcome and the focus of models explaining how motor systems develop in health and after early injury. Combining basic science animal work with human applied technology (functional magnetic resonance imaging, diffusion tensor imaging, and transcranial magnetic stimulation), a model of plastic motor development after perinatal stroke is presented. Potential central therapeutic targets are revealed. The means to measure and modulate these targets, including evidence-based rehabilitation therapies and noninvasive brain stimulation, are suggested. Implications for clinical trials and future directions are discussed.

NON-INVASIVE BRAIN STIMULATION IN CHILDREN: APPLICATIONS AND FUTURE DIRECTIONS

Transcranial magnetic stimulation (TMS) is a neurostimulation and neuromodulation technique that has provided over two decades of data in focal, non-invasive brain stimulation based on the principles of electromagnetic induction. Its minimal risk, excellent tolerability and increasingly sophisticated ability to interrogate neurophysiology and plasticity make it an enviable technology for use in pediatric research with future extension into therapeutic trials. While adult trials show promise in using TMS as a novel, non-invasive, non-pharmacologic diagnostic and therapeutic tool in a variety of nervous system disorders, its use in children is only just emerging. TMS represents an exciting advancement to better understand and improve outcomes from disorders of the developing brain.

Reduced corticomotor excitability and motor skills development in children born preterm

The mechanisms underlying the altered neurodevelopment commonly experienced by children born preterm, but without brain lesions, remain unknown. While individuals born the earliest are at most risk, late preterm children also experience significant motor, cognitive and behavioural dysfunction from school age, and reduced income and educational attainment in adulthood. We used transcranial magnetic stimulation and functional assessments to examine corticomotor development in 151 children without cerebral palsy, aged 10-13 years and born after gestations of 25-41 completed weeks. We hypothesized that motor cortex and corticospinal development are altered in preterm children, which underpins at least some of their motor dysfunction. We report for the first time that every week of reduced gestation is associated with a reduction in corticomotor excitability that remains evident in late childhood. This reduced excitability was associated with poorer motor skill development, particularly manual dexterity. However, child adiposity, sex and socio-economic factors regarding the child's home environment soon after birth were also powerful influences on development of motor skills. Preterm birth was also associated with reduced left hemisphere lateralization, but without increasing the likelihood of being left handed per se. These corticomotor findings have implications for normal motor development, but also raise questions regarding possible longer term consequences of preterm birth on motor function.

GABAB-ergic motor cortex dysfunction in SSADH deficiency

OBJECTIVE

Succinic semialdehyde dehydrogenase (SSADH) deficiency is a rare autosomal recessive disorder of GABA degradation leading to elevations in brain GABA and γ-hydroxybutyric acid (GHB). The effect of chronically elevated GABA and GHB on cortical excitability is unknown. We hypothesized that use-dependent downregulation of GABA receptor expression would promote cortical disinhibition rather than inhibition, predominantly via presynaptic GABAergic mechanisms.

METHODS

We quantified the magnitude of excitation and inhibition in primary motor cortex (M1) in patients with SSADH deficiency, their parents (obligate heterozygotes), age-matched healthy young controls, and healthy adults using single and paired pulse transcranial magnetic stimulation (TMS).

RESULTS

Long interval intracortical inhibition was significantly reduced and the cortical silent period was significantly shortened in patients with SSADH deficiency compared to heterozygous parents and control groups.

CONCLUSIONS

Since long interval intracortical inhibition and cortical silent period are thought to reflect GABA(B) receptor-mediated inhibitory circuits, our results point to a particularly GABA(B)-ergic motor cortex dysfunction in patients with SSADH deficiency. This human phenotype is consistent with the proposed mechanism of use-dependent downregulation of postsynaptic GABA(B) receptors in SSADH deficiency animal models. Additionally, the results suggest autoinhibition of GABAergic neurons. This first demonstration of altered GABA(B)-ergic function in patients with SSADH deficiency may help to explain clinical features of the disease, and suggest pathophysiologic mechanisms in other neurotransmitter-related disorders.

Cortical inhibition in attention deficit hyperactivity disorder: new insights from the electroencephalographic response to transcranial magnetic stimulation

Attention deficit hyperactivity disorder is one of the most frequent neuropsychiatric disorders in childhood. Transcranial magnetic stimulation studies based on muscle responses (motor-evoked potentials) suggested that reduced motor inhibition contributes to hyperactivity, a core symptom of the disease. Here we employed the N100 component of the electroencephalographic response to transcranial magnetic stimulation as a novel marker for a direct assessment of cortical inhibitory processes, which has not been examined in attention deficit hyperactivity disorder so far. We further investigated to what extent affected children were able to regulate motor cortical inhibition, and whether effects of age on the electroencephalographic response to transcranial magnetic stimulation were compatible with either a delay in brain maturation or a qualitatively different development. N100 amplitude evoked by transcranial magnetic stimulation and its age-dependent development were assessed in 20 children with attention deficit hyperactivity disorder and 19 healthy control children (8-14 years) by 64-channel electroencephalography. Amplitude and latency of the N100 component were compared at rest, during response preparation in a forewarned motor reaction time task and during movement execution. The amplitude of the N100 component at rest was significantly lower and its latency tended to be shorter in children with attention deficit hyperactivity disorder. Only in controls, N100 amplitude to transcranial magnetic stimulation was reduced by response preparation. During movement execution, N100 amplitude decreased while motor evoked potential amplitudes showed facilitation, indicating that the electroencephalographic response to transcranial magnetic stimulation provides further information on cortical excitability independent of motor evoked potential amplitudes and spinal influences. Children with attention deficit hyperactivity disorder showed a smaller N100 amplitude reduction during movement execution compared with control children. The N100 amplitude evoked by transcranial magnetic stimulation decreased with increasing age in both groups. The N100 reduction in children with attention deficit hyperactivity disorder at all ages suggests a qualitative difference rather than delayed development of cortical inhibition in this disease. Findings further suggest that top-down control of motor cortical inhibition is reduced in children with attention deficit hyperactivity disorder. We conclude that evoked potentials in response to transcranial magnetic stimulation are a promising new marker of cortical inhibition in attention deficit hyperactivity disorder during childhood.

A practical guide to diagnostic transcranial magnetic stimulation: report of an IFCN committee

Transcranial magnetic stimulation (TMS) is an established neurophysiological tool to examine the integrity of the fast-conducting corticomotor pathways in a wide range of diseases associated with motor dysfunction. This includes but is not limited to patients with multiple sclerosis, amyotrophic lateral sclerosis, stroke, movement disorders, disorders affecting the spinal cord, facial and other cranial nerves. These guidelines cover practical aspects of TMS in a clinical setting. We first discuss the technical and physiological aspects of TMS that are relevant for the diagnostic use of TMS. We then lay out the general principles that apply to a standardized clinical examination of the fast-conducting corticomotor pathways with single-pulse TMS. This is followed by a detailed description of how to examine corticomotor conduction to the hand, leg, trunk and facial muscles in patients. Additional sections cover safety issues, the triple stimulation technique, and neuropediatric aspects of TMS.

Applications of transcranial magnetic stimulation (TMS) in child and adolescent psychiatry

Transcranial magnetic stimulation (TMS) is emerging as a new treatment and neurophysiological research tool for psychiatric disorders. Recent publications suggest that this modality will also serve as a treatment and research tool in child and adolescent psychiatry. Current reports on therapeutic trials of repetitive transcranial magnetic stimulation (rTMS) in adolescents have primarily focused on depression. However, other pilot work involves the treatment of attention-deficit/hyperactivity disorder (ADHD), autism and schizophrenia. Neurophysiological studies typically utilize single and paired-pulse TMS paradigms which index cortical excitability and inhibition. Initial studies have focused on ADHD, autism, and depression. General knowledge regarding TMS among child and adolescent psychiatrists is lacking. The aim of this review is to provide an overview of TMS in the context of child and adolescent psychiatry, discuss recent therapeutic and neurophysiological studies, and examine relevant ethical considerations.

[The significance of functional psychophysiological methods in child and adolescent psychiatry]

Psychophysiological research focusing on child development and on child and adolescent psychiatric disorders has provided many important insights. The use of cognitive neuroscience methods along with the assessment of peripheral psychophysiological measures - particularly functional magnetic resonance imaging and electroencephalography reflecting brain activity - have advanced our understanding of the physiological basis of many cognitive processes such as attention, memory, learning, and language in the context of child development and psychiatric disorders. These insights are proving increasingly helpful when evaluating and advancing treatment. The following review introduces the reader to psychophysiological and particularly electrophysiological methods widely used in child and adolescent psychiatry research.

Lateralization of motor innervation in children with intractable focal epilepsy--a TMS and fMRI study

PURPOSE

To correlate hand function with lateralization of motor innervation, as studied with transcranial magnetic stimulation (TMS) and functional magnetic imaging (fMRI), in children with intractable epilepsy and lesions in the vicinity of the motor cortex.

METHODS

In 34 children hand motor function was examined and motor evoked potentials (MEPs) were recorded after TMS of both hemispheres, establishing lateralization of corticospinal innervation. When feasible, patients underwent fMRI using a manual motor task.

RESULTS

Good function of the contralesional hand was associated with early lesions (p=0.02). Lateralization of motor innervation to the contralesional hand correlated with quality of motor function (p=0.001); 83% of children with poor hand function had ipsi- or bilateral innervation, whereas all children with good hand function had pure contralateral control. Mirror movements during movement of the unaffected hand predicted ipsilateral contribution to motor innervation (p=0.006). Fourteen children who had no TMS responses were younger than those with elicitable MEPs (p<0.001). TMS led to a temporary increase of seizure frequency in four children. fMRI results were concordant with TMS.

CONCLUSIONS

Poor function of the contralesional hand is strongly associated with ipsilateral motor innervation. Reorganization in the lesioned hemisphere mainly occurs in early developmental lesions and seems efficient in maintaining good hand function. Clinical examination of hand function has predictive value for the pattern of motor innervation prior to epilepsy surgery, which in older children can further be established by TMS and fMRI.

Neuromagnetic imaging of movement-related cortical oscillations in children and adults: age predicts post-movement beta rebound

We measured visually-cued motor responses in two developmentally separate groups of children and compared these responses to a group of adults. We hypothesized that if post-movement beta rebound (PMBR) depends on developmentally sensitive processes, PMBR will be greatest in adults and progressively decrease in children performing a basic motor task as a function of age. Twenty children (10 young children 4-6 years; 10 adolescent children 11-13 years) and 10 adults all had MEG recorded during separate recordings of right and left index finger movements. Beta band (15-30 Hz) event-related desynchronization (ERD) of bi-lateral sensorimotor areas was observed to increase significantly from both contralateral and ipsilateral MI with age. Movement-related gamma synchrony (60-90 Hz) was also observed from contralateral MI for each age group. However, PMBR was significantly reduced in the 4-6 year group and, while more prominent, remained significantly diminished in the adolescent (11-13 year) age group as compared to adults. PMBR measures were weak or absent in the youngest children tested and appear maximally from bilateral MI in adults. Thus PMBR may reflect an age-dependent inhibitory process of the primary motor cortex which comes on-line with normal development. Previous studies have shown PMBR may be observed from MI following a variety of movement-related tasks in adult participants - however, the origin and purpose of the PMBR is unclear. The current study shows that the expected PMBR from MI observed from adults is increasingly diminished in adolescent and young children respectively. A reduction in PMBR from children may reflect reduced motor cortical inhibition. Relatively less motor inhibition may facilitate neuronal plasticity and promote motor learning in children.

Neurocardiogenic syncope complicating pediatric transcranial magnetic stimulation

Pediatric applications of transcranial magnetic stimulation are rapidly expanding, but lack the safety data established for adults. Transcranial magnetic stimulation-induced neurocardiogenic syncope may represent an age-dependent adverse event that is essentially undescribed in the transcranial magnetic stimulation literature. We report on 2 adolescents (of 10 children studied) with transcranial magnetic stimulation-related neurocardiogenic syncope, identify modifiable risk factors, and suggest measures to improve the safety of future pediatric transcranial magnetic stimulation studies.