Tolerability of transcranial magnetic stimulation language mapping in children

OBJECTIVE

Transcranial Magnetic Stimulation (TMS) has emerged as a viable non-invasive method for mapping language networks. Little is known about the tolerability of transcranial magnetic stimulation language mapping in children.

METHODS

Children aged 5-18 years underwent bilateral language mapping using repetitive transcranial magnetic stimulation (rTMS) to target 33 sites/hemisphere. Stimulation was delivered at 5 Hz, in 1-2 second bursts, during visual naming and auditory verb generation. Pain unpleasantness and pain intensity were assessed using an unpleasantness visual analog scale (VAS).

RESULTS

49 participants tolerated motor mapping and had repetitive transcranial magnetic stimulation. 35/49 (71%) completed visual naming and 26/49 (53%) completed both visual naming and verb generation. Mean electrical field per participant was 115 V/m. Young age and lower language ability were associated with lower completion. Visual analogue scale scores were significantly higher (6.1 vs. 2.8) in participants who withdrew early compared to those who completed at least visual naming.

CONCLUSIONS

Pain measured by VAS was a major contributor to early withdrawal. However, a complete bilateral map was obtained with one paradigm in 71% of participants. Future studies designed to reduce pain during repetitive transcranial magnetic stimulation over language cortex will boost viability.

SIGNIFICANCE

This study represents the first attempt to characterize tolerability of bilateral repetitive transcranial magnetic stimulation language mapping in healthy children.

Transcranial Magnetic Stimulation as Treatment in Multiple Neurologic Conditions

PURPOSE OF REVIEW

Transcranial magnetic stimulation (TMS) is a method of Non-Invasive Brain Stimulation that is based on electro-physical principles discovered by Michael Faraday. A TMS device is made of one or two copper coils, positioned superficially to a site of interest in the brain, to non-invasively produce a brief magnetic pulse to an estimated depth from the surface of the scalp with the following axonal depolarization. This axonal depolarization activates cortical and subcortical networks with multiple effects. There are different methods of TMS used, all with different mechanisms of action. TMS is well tolerated with very few side effects.

RECENT FINDINGS

TMS is now approved for major depression disorder and obsessive-compulsive disorder. There is significant data to consider approval of TMS for many neurological disorders. This is a review of the uses of TMS in diverse neurological conditions, including stroke and spasticity, migraine, and dementia. TMS is a device that utilizes non-invasive brain stimulation, and it has shown promising results with objective clinical and basic science data. Its ability to trigger neuronal plasticity and potentiating synaptic transmission gives it incredible therapeutic potential. There are diverse mechanisms of action, and this could be troublesome in elaborating clinical trials and standardization of therapy.

Transcranial Magnetic Stimulation for the Treatment of Pediatric Neurological Disorders

PURPOSE OF REVIEW

Repetitive transcranial magnetic stimulation (rTMS) is a form of noninvasive brain stimulation that is used for the treatment of migraine and major depression in adults and is now being evaluated for use in other disorders. The purpose of this review is to summarize the physiology underlying TMS, the safety and tolerability in pediatric patients, and the evidence for TMS efficacy in the treatment of pediatric neurologic disorders.

RECENT FINDINGS

Studies investigating rTMS for adolescent depression, hemiparesis due to pediatric stroke, autism, and tics/Tourette syndrome have demonstrated some therapeutic benefit. rTMS has been insufficiently studied for migraine in children despite benefits demonstrated for adult migraine. Evidence for rTMS in childhood epilepsy and ADHD remains mixed. Repetitive transcranial magnetic stimulation is emerging as a safe, tolerable, and potentially effective therapeutic strategy in a number of pediatric neurological disorders, though high-quality, randomized controlled trials are needed. Ongoing studies should focus on optimization of treatment protocols, development of biomarkers to identify children who will benefit from the technique, and identification of the most appropriate indicators of response.

Brainstem reflex excitability after high-frequency repetitive transcranial magnetic stimulation in healthy and spinal cord injury subjects

BACKGROUND

The excitability of brainstem interneuronal circuits is partly under control from descending inputs. Since high frequency repetitive transcranial magnetic stimulation (rTMS) modulates cortical output, we hypothesized that it will also modulate brainstem functions. Such modulation may be different in healthy subjects than in subjects with spinal cord injury (SCI), submitted to an altered integration of body afferent inputs.

METHODS

In this randomized, double-blind, sham-controlled trial, we recruited 22 subjects with SCI assigned to either real (n = 11) or sham (n = 11) rTMS and nine healthy subjects, who served as control group, receiving both real (at 20 Hz, with double cone coil over vertex) and sham rTMS separated by at least one week. We recorded the blink reflex (BR) to supraorbital nerve (SON) electrical stimulation and its modification by another conditioning SON, to study the BR excitability recovery (BRER), or a prepulse electrical stimulus to the right index finger, to study the BR inhibition by prepulse (BRIP). Subjects were examined immediately before and after either sham or real rTMS.

RESULTS

Real but not sham rTMS significantly reduced the area of the BR R2 response in both SCI and healthy subjects. There were no changes in BRER and BRIP.

CONCLUSION

rTMS over the vertex modulates brainstem reflexes with no significant differences between SCI and healthy subjects.

Intervention Effect of Repetitive TMS on Behavioral Adjustment After Error Commission in Long-Term Methamphetamine Addicts: Evidence From a Two-Choice Oddball Task

Behavioral adjustment plays an important role in the treatment and relapse of drug addiction. Nonetheless, few studies have examined behavioral adjustment and its plasticity following error commission in methamphetamine (METH) dependence, which is detrimental to human health. Thus, we investigated the behavioral adjustment performance following error commission in long-term METH addicts and how it varied with the application of repetitive transcranial magnetic stimulation (rTMS) of the left dorsolateral prefrontal cortex (DLPFC). Twenty-nine male long-term METH addicts (for > 3 years) were randomly assigned to high-frequency (10 Hz, n = 15) or sham (n = 14) rTMS of the left DLPFC during a two-choice oddball task. Twenty-six age-matched, healthy male adults participated in the two-choice oddball task pretest to establish normal performance for comparison. The results showed that 10 Hz rTMS over the left DLPFC significantly decreased the post-error slowing effect in response times of METH addicts. In addition, the 10 Hz rTMS intervention remarkably reduced the reaction times during post-error trials but not post-correct trials. While the 10 Hz rTMS group showed a more pronounced post-error slowing effect than the healthy participants during the pretest, the post-error slowing effect in the posttest of this sample was similar to that in the healthy participants. These results suggest that high-frequency rTMS over the left DLPFC is a useful protocol for the improvement of behavioral adjustment after error commission in long-term METH addicts.

Causal role of the posterior parietal cortex for two-digit mental subtraction and addition: A repetitive TMS study

Although parietal areas of the left hemisphere are known to be involved in simple mental calculation, the possible role of the homologue areas of the right hemisphere in mental complex calculation remains debated. In the present study, we tested the causal role of the posterior parietal cortex of both hemispheres in two-digit mental addition and subtraction by means of neuronavigated repetitive TMS (rTMS), investigating possible hemispheric asymmetries in specific parietal areas. In particular, we performed two rTMS experiments, which differed only for the target sites stimulated, on independent samples of participants. rTMS was delivered over the horizontal and ventral portions of the intraparietal sulcus (HIPS and VIPS, respectively) of each hemisphere in Experiment 1, and over the angular and supramarginal gyri (ANG and SMG, respectively) of each hemisphere in Experiment 2. First, we found that each cerebral area of the posterior parietal cortex is involved to some degree in the two-digit addition and subtraction. Second, in Experiment 1, we found a stronger pattern of hemispheric asymmetry for the involvement of HIPS in addition compared to subtraction. In particular, results showed a greater involvement of the right HIPS than the left one for addition. Moreover, we found less asymmetry for the VIPS. Taken together, these results suggest that two-digit mental addition is more strongly associated with the use of a spatial mapping compared to subtraction. In support of this view, in Experiment 2, a greater role of left and right ANG was found for addition needed in verbal processing of numbers and in visuospatial attention processes, respectively. We also revealed a greater involvement of the bilateral SMG in two-digit mental subtraction, in response to greater working memory load required to solve this latter operation compared to addition.

Agonist contraction during intermittent theta burst stimulation enhances motor cortical plasticity of the wrist flexors

Differences in cortical control across the different muscles of the upper limb may mitigate the efficacy of TMS interventions targeting a specific muscle. The current study sought to determine whether weak concurrent contraction during TMS could enhance the efficacy of intermittent theta burst stimulation (iTBS) in the forearm flexors. Motor evoked potentials (MEP) were elicited from the flexor (FCR) and extensor carpi radialis (ECR) motor cortical hotspots before and after iTBS over the FCR cortical hotspot. During iTBS the FCR was either relaxed (iTBS-Relax) or tonically contracted to 10% of maximum voluntary force (iTBS-Contract). iTBS-Relax failed to produce consistent potentiation of MEPFCR amplitude. Individuals with a relatively lower RMTFCR compared RMTECR demonstrated MEPFCR facilitation post-iTBS-Relax. Individuals with relatively higher RMTFCR demonstrated less facilitation and even suppression of MEPFCR amplitude. iTBS-Contract facilitated MEPFCR amplitude but only for MEPFCR evoked from the ECR hotspot. Interactions between overlapping cortical representations determine the efficacy of iTBS. Tonic contraction increases the efficacy of iTBS by enhancing the volume of the cortical representation. However, metaplastic effects may attenuate the enhancement of MEP gain at the motor cortical hotspot. The use of TMS as an adjunct to physical therapy should account for inter-muscle interactions when targeting muscles of the forearm.

Cognitive and neural foundations of discrete sequence skill: a TMS study

Executing discrete movement sequences typically involves a shift with practice from a relatively slow, stimulus-based mode to a fast mode in which performance is based on retrieving and executing entire motor chunks. The dual processor model explains the performance of (skilled) discrete key-press sequences in terms of an interplay between a cognitive processor and a motor system. In the present study, we tested and confirmed the core assumptions of this model at the behavioral level. In addition, we explored the involvement of the pre-supplementary motor area (pre-SMA) in discrete sequence skill by applying inhibitory 20 min 1-Hz off-line repetitive transcranial magnetic stimulation (rTMS). Based on previous work, we predicted pre-SMA involvement in the selection/initiation of motor chunks, and this was confirmed by our results. The pre-SMA was further observed to be more involved in more complex than in simpler sequences, while no evidence was found for pre-SMA involvement in direct stimulus-response translations or associative learning processes. In conclusion, support is provided for the dual processor model, and for pre-SMA involvement in the initiation of motor chunks.

Clinical application of TMS to epilepsy

The role of transcranial magnetic stimulation in epileptology is discussed in this article. Usefulness of TMS are discussed as a diagnostic tool in testing altered cortical excitability in patients with epilepsy and the modes of action of antiepileptic drugs, which are helpful to evaluate the pathophysiology of epilepsy. Also potential therapeutic tool in epilepsy with repetitive transcranial magnetic stimulation would be mentioned.