Stimulation intensities of transcranial direct current stimulation have to be adjusted in children and adolescents

OBJECTIVE

The aim of the present study was to investigate the effect of the transcranial direct current stimulation (tDCS) on motor cortex excitability in healthy children and adolescents.

METHODS

We applied 1mA anodal or cathodal tDCS for 10min on the left primary motor cortex of 19 healthy children and adolescents (mean age 13.9±0.4years). In order to prove whether the effects of tDCS may be attributed to the stimulation intensity, 10 children and adolescents were studied again using 0.5mA anodal and cathodal tDCS. Sham stimulation was used as a control.

RESULTS

Compared with sham stimulation, both 1mA anodal and cathodal tDCS resulted in a significant increase of Motor evoked potentials (MEP) amplitudes which remained to be prominent even one hour after the end of stimulation. Interestingly, the 0.5mA cathodal tDCS decreased cortico-spinal excitability whereas the 0.5mA anodal stimulation did not result in any effect.

CONCLUSION

For the first time, the study demonstrates age-specific influences of tDCS on cortical excitability of the primary motor cortex.

SIGNIFICANCE

Thus, the stimulation protocols of the tDCS have to be optimized according to age by planning studies in pediatric population.

Poor Tolerance of Motor Cortex rTMS in Chronic Migraine

BACKGROUND

Two small studies had evaluated the efficacy of rTMS in migraine. One tested high frequency rTMS over the dorsolateral prefrontal cortex while the other evaluated 1 Hz rTMS over the vertex.

AIM

To test the feasibility of 10 Hz rTMS of motor cortex as an adjunctive therapy in patients with chronic migraine Materials and Methods: We randomized (2:1 ratio) chronic migraine patients on medical preventive treatment to receive either rTMS or sham therapy for 10 sessions. rTMS (80% resting motor threshold, 10Hz, 20 trains, 5 secs/train, inter-train interval 1 min, total 1000 stimuli/session) was applied over the right motor cortex.

RESULT

Nine patients were randomized. Six received rTMS and three had sham therapy. Three patients in the rTMS arm withdrew from the study due to increased headache frequency and discomfort from the treatment. The remaining six cases (3 rTMS, 3 sham) completed the study. The study was prematurely stopped due to the significant worsening of headache from rTMS. No significant differences in outcome measures were found between real and sham rTMS.

CONCLUSION

Although the study was terminated prematurely, the high dropout rate (50%) due to worsening headaches suggested that rTMS over the motor cortex is poorly tolerated in chronic migraine.

The neural control of coactivation during fatiguing contractions revisited

In addition to the role of muscle coactivation, a major question in the field is how antagonist activation is controlled to minimize its opposing effect on agonist muscle performance. Muscle fatigue is an interesting condition to analyze the neural adjustments in antagonist muscle activity and to gain more insights into the control mechanisms of coactivation. In that context, previous studies have reported that although the EMG activity of agonists and antagonists increase in parallel, the ratio between EMG activities in the two sets of muscles during a fatiguing submaximal contraction decreased progressively and contributed to a reduction in the time to task failure. In contrast, more recent studies using a novel normalization procedure indicated that the agonist/antagonist ratio remained relatively constant, suggesting that the fatigue-related increase in coactivation does not impede performance. Current knowledge also indicates that peripheral mechanisms cannot by themselves mediate the intensity of antagonist coactivation during fatiguing contractions, implying that supraspinal mechanisms are involved. The unique modulation of the synaptic input from Ia afferents to the antagonist motor neurones during a fatiguing contraction of the agonist muscles further suggests a separate control of the two sets of muscles.

Does the region of epileptogenicity influence the pattern of change in cortical excitability?

OBJECTIVE

To investigate whether cortical excitability measures on transcranial magnetic stimulation (TMS) differed between groups of patients with different focal epilepsy syndromes.

METHODS

85 Patients with focal epilepsy syndromes divided into temporal and extra-temporal lobe epilepsy were studied. The cohorts were further divided into drug naïve-new onset, refractory and seizure free groups. Motor threshold (MT) and paired pulse TMS at short (2, 5, 10, 15 ms) and long (100-300 ms) interstimulus intervals (ISIs) were measured. Results were compared to those of 20 controls.

RESULTS

Cortical excitability was higher at 2 & 5 ms and 250, 300 ms ISIs (p<0.01) in focal epilepsy syndromes compared to controls however significant inter-hemispheric differences in MT and the same ISIs were only seen in the drug naïve state early at onset and were much more prominent in temporal lobe epilepsy.

CONCLUSION

Disturbances in cortical excitability are more confined to the affected hemisphere in temporal lobe epilepsy but only early at onset in the drug naïve state.

SIGNIFICANCE

Group TMS studies show that cortical excitability measures are different in temporal lobe epilepsy and can be distinguished from other focal epilepsies early at onset in the drug naïve state. Further studies are needed to determine whether these results can be applied clinically as the utility of TMS in distinguishing between epilepsy syndromes at an individual level remains to be determined.

Age-related changes in intracortical inhibition are mental-cognitive state-dependent

INTRODUCTION

This study aimed to assess the impact of aging and 'state-dependency' on cortical excitability. Two studies investigated these factors using a motor task and found that the age-related differences observed at rest disappeared in the task condition. However, as both their tasks and excitability measurements involved the motor cortex, their results could be specific only to the motor system. To overcome this problem, the present study used a cognitive task to control mental state.

METHOD

Intracortical inhibition/facilitation (ICI/ICF) were assessed in young and older adults at rest and during the cognitive task. The cortical silent period (CSP) was also evaluated.

RESULTS

ICI and CSP were reduced with aging. However, ICI differences between young and old people disappeared when they performed the cognitive task.

CONCLUSION

Age and mental state modify cortical excitability. Taking these factors into consideration is crucial to clinical research using cortical excitability as a possible biomarker of pathology.

Distinctive patterns of cortical excitability to transcranial magnetic stimulation in obstructive sleep apnea syndrome, restless legs syndrome, insomnia, and sleep deprivation

Altered responses to transcranial magnetic stimulation (TMS) in obstructive sleep apnea syndrome (OSAS), restless legs syndrome (RLS), insomnia, and sleep-deprived healthy subjects have been reported. We have reviewed the relevant literature in order to identify eventual distinctive electrocortical profiles based on single and paired-pulse TMS, sensorimotor modulation, plasticity-related and repetitive TMS measures. Although obtained from heterogeneous studies, the detected changes might be the result of the different pathophysiological substrates underlying OSAS, RLS, insomnia and sleep deprivation rather than reflect the general effect of non-specific sleep loss and instability. OSAS tends to exhibit an increased motor cortex inhibition, which is reduced in RLS; intracortical excitability seems to be in favor of an "activating" profile in chronic insomnia and in sleep-deprived healthy individuals. Abnormal plasticity-related TMS phenomena have been demonstrated in OSAS and RLS. This review provides a perspective of TMS techniques by further understanding the role of neurotransmission pathways and plastic remodeling of neuronal networks involved in common sleep disorders. TMS might be considered a valuable tool in the assessment of sleep disorders, the evaluation of the effect of therapy and the design of non-pharmacological approaches.

The contribution of transcranial magnetic stimulation in the diagnosis and in the management of dementia

Transcranial magnetic stimulation (TMS) is emerging as a promising tool to non-invasively assess specific cortical circuits in neurological diseases. A number of studies have reported the abnormalities in TMS assays of cortical function in dementias. A PubMed-based literature review on TMS studies targeting primary and secondary dementia has been conducted using the key words "transcranial magnetic stimulation" or "motor cortex excitability" and "dementia" or "cognitive impairment" or "memory impairment" or "memory decline". Cortical excitability is increased in Alzheimer's disease (AD) and in vascular dementia (VaD), generally reduced in secondary dementias. Short-latency afferent inhibition (SAI), a measure of central cholinergic circuitry, is normal in VaD and in frontotemporal dementia (FTD), but suppressed in AD. In mild cognitive impairment, abnormal SAI may predict the progression to AD. No change in cortical excitability has been observed in FTD, in Parkinson's dementia and in dementia with Lewy bodies. Short-interval intracortical inhibition and controlateral silent period (cSP), two measures of gabaergic cortical inhibition, are abnormal in most dementias associated with parkinsonian symptoms. Ipsilateral silent period (iSP), which is dependent on integrity of the corpus callosum is abnormal in AD. While single TMS measure owns low specificity, a panel of measures can support the clinical diagnosis, predict progression and possibly identify earlier the "brain at risk". In dementias, TMS can be also exploited to select and evaluate the responders to specific drugs and, it might become a rehabilitative tool, in the attempt to restore impaired brain plasticity.

Combination of transcranial direct current stimulation and methylphenidate in subacute stroke

Noninvasive transcranial direct current stimulation (tDCS) and methylphenidate (MP) are associated with motor recovery after stroke. Based on the potentially complementary mechanisms of these interventions, we examined whether there is an interactive effect between MP and tDCS. In this preliminary study, we randomized subacute stroke subjects to receive tDCS alone, MP alone or combination of tDCS and MP. A blinded rater measured safety, hand function, and cortical excitability before and after treatment. None of the treatments caused any major or severe adverse effects or induced significant differences in cortical excitability. Analysis of variance of gain score, as measured by Purdue pegboard test, showed a significant between-group difference (F(2,6)=12.167, p=0.008). Post hoc analysis showed that the combination treatment effected greater Purdue pegboard gain scores than tDCS alone (p=0.017) or MP alone (p=0.01). Our preliminary data with nine subjects shows an interesting dissociation between motor function improvement and lack of motor corticospinal plasticity changes as indexed by transcranial magnetic stimulation in subacute stroke subjects.

Motor cortical excitability assessed by transcranial magnetic stimulation in psychiatric disorders: a systematic review

BACKGROUND

Transcranial magnetic stimulation (TMS) is a popular neurostimulation technique suitable for the investigation of inhibitory and facilitatory networks in the human motor system. In the last 20 years, several studies have used TMS to investigate cortical excitability in various psychiatric disorders, leading to a consequent improvement in pathophysiological understanding. However, little is known about the overlap and specificity of these findings across these conditions.

OBJECTIVE

To provide a systematic review of TMS studies (1985-2013) focusing on motor cortical excitability in dementia, schizophrenia, affective disorders (major depression and bipolar), attention deficit hyperactivity disorder (ADHD), obsessive compulsive disorder (OCD), Tourette Syndrome (TS), substance abuse (alcohol, cocaine, cannabis, nicotine) and other disorders (borderline personality disorder, posttraumatic stress disorder (PTSD)).

METHODS

Systematic literature-based review.

RESULTS

Across disorders, patients displayed a general pattern of cortical disinhibition, while the most consistent results of reduced short-interval intracortical inhibition could be found in schizophrenia, OCD and Tourette Syndrome. In dementia, the most frequently reported finding was reduced short-latency afferent inhibition as a marker of cholinergic dysfunction.

CONCLUSIONS

The results of this systematic review indicate a general alteration in motor cortical inhibition in mental illness, rather than disease-specific changes. Changes in motor cortical excitability provide insight that can advance understanding of the pathophysiology underlying various psychiatric disorders. Further investigations are needed to improve the diagnostic application of these parameters.

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.

Effect of Stimulation Polarity of Transcranial Direct Current Stimulation on Non-dominant Hand Function

Objective

To evaluate motor excitability and hand function on the non-dominant side according to the polarity of transcranial direct current stimulation (tDCS) on the motor cortex in a healthy person.

Method

tDCS was applied to the hand motor cortex for 15 minutes at an intensity of 1 mA in 28 healthy right-handed adults. Subjects were divided randomly into four groups: an anodal tDCS of the non-dominant hemisphere group, a cathodal tDCS of the non-dominant hemisphere group, an anodal tDCS of the dominant hemisphere group, and a sham group. We measured the motor evoked potential (MEP) in the abductor pollicis brevis and Jabsen-Taylor hand function test (JTT) in the non-dominant hand prior to and following tDCS. All study procedures were done under double-blind design.

Results

There was a significant increase in the MEP amplitude and a significant improvement in the JTT in the non-dominant hand following anodal tDCS of the non-dominant hemisphere (p<0.05). But there was no change in JTT and a significant decrease in the MEP amplitude in the non-dominant hand following cathodal tDCS on the non-dominant hemisphere and anodal tDCS of the dominant hemisphere.

Conclusion

Non-dominant hand function is improved by increased excitability of the motor cortex. Although motor cortex excitability is decreased in a healthy person, non-dominant hand function is maintained. A homeostatic mechanism in the brain might therefore be involved in preserving this function. Further studies are warranted to examine brain functions to clarify this mechanism.

Focal and bi-directional modulation of lower limb motor cortex using anodal transcranial direct current stimulation

BACKGROUND

Because we are interested in non-invasive transcranial brain stimulation as an adjuvant to post-stroke walking therapy, we applied direct current stimulation (tDCS) preferentially to either the left or right lower limb motor cortex (M1) in two separate sessions and assessed the resulting modulation in both cortices.

OBJECTIVE/HYPOTHESIS

We hypothesized that tDCS applied preferentially to one lower limb M1 of healthy subjects would induce between-hemisphere opposite sign modulation.

METHODS

Transcranial magnetic stimulation (TMS) with the coil offset 2 cm either side of vertex was used to assess the percent change in rectified motor evoked potential (MEP) area recorded bilaterally from vastus lateralis (VL) and tibialis anterior (TA) of 10 subjects during weak tonic contraction.

RESULTS

ANOVA revealed an up-regulation of the target cortex and a down-regulation of the non-target cortex (p = 0.001) and no effects of hemisphere (left, right) or muscle (TA, VL). Significant modulation was evident in 78% of VL and TA muscles (all p < 0.05). Excitability increased in 60%, but decreased in 18%. For 43% when excitability increased, a simultaneous decrease in excitability was evident in homologous muscle responses providing support for our hypothesis.

CONCLUSIONS

The results indicate a modest effectiveness and focality of anodal tDCS when applied to lower limb M1, suggesting in a human model that the strength and depth of polarizing cortical currents induced by tDCS likely depend on inter-individual differences in the electrical properties of superficial brain structures.