Methylphenidate facilitates and disinhibits the motor cortex in intact humans

Novel approaches to assessing upper motor neuron dysfunction in motor neuron disease/amyotrophic lateral sclerosis: IFCN handbook chapter

Identifying upper motor neuron (UMN) dysfunction is fundamental to the diagnosis and understanding of disease pathogenesis in motor neuron disease (MND). The clinical assessment of UMN dysfunction may be difficult, particularly in the setting of severe muscle weakness. From a physiological perspective, transcranial magnetic stimulation (TMS) techniques provide objective biomarkers of UMN dysfunction in MND and may also be useful to interrogate cortical and network function. Single, paired- and triple pulse TMS techniques have yielded novel diagnostic and prognostic biomarkers in MND, and have provided important pathogenic insights, particularly pertaining to site of disease onset. Cortical hyperexcitability, as heralded by reduced short interval intracortical inhibition (SICI) and increased short interval intracortical facilitation, has been associated with the onset of lower motor neuron degeneration, along with patterns of disease spread, development of specific clinical features such as the split hand phenomenon, and may provide an indication about the rate of disease progression. Additionally, reduction of SICI has emerged as a potential diagnostic aid in MND. The triple stimulation technique (TST) was shown to enhance the diagnostic utility of conventional TMS measures in detecting UMN dysfunction in MND. Separately, sophisticated brain imaging techniques have uncovered novel biomarkers of neurodegeneration that have bene associated with progression. The present review will discuss the utility of TMS and brain neuroimaging derived biomarkers of UMN dysfunction in MND, focusing on recently developed TMS techniques and advanced neuroimaging modalities that interrogate structural and functional integrity of the corticomotoneuronal system, with an emphasis on pathogenic, diagnostic, and prognostic utility.

Serotonergic and noradrenergic contributions to motor cortical and spinal motoneuronal excitability in humans

Animal models indicate that motor behaviour is shaped by monoamine neuromodulators released diffusely throughout the brain and spinal cord. As an alternative to conducting a single study to explore the effects of neuromodulators on the human motor system, we have identified and collated human experiments investigating motor effects of well-characterised drugs that act on serotonergic and noradrenergic networks. In doing so, we present strong neuropharmacology evidence that human motor pathways are affected by neuromodulators across both healthy and clinical populations, insight that cannot be determined from a single reductionist experiment. We have focused our review on the effects that monoaminergic drugs have on muscle responses to non-invasive stimulation of the motor cortex and peripheral nerves, and other closely related tests of motoneuron excitability, and discuss how these measurement techniques elucidate the effects of neuromodulators at motor cortical and spinal motoneuronal levels. Although there is some heterogeneity in study methods, we find drugs acting to enhance extracellular concentrations of serotonin tend to reduce the excitability of the human motor cortex, and enhanced extracellular concentrations of noradrenaline increases motor cortical excitability by enhancing intracortical facilitation and reducing inhibition. Both monoamines tend to enhance the excitability of spinal motoneurons. Overall, this review details the importance of neuromodulators for the output of human motor pathways and suggests that commonly prescribed monoaminergic drugs target the motor system in addition to their typical psychiatric/neurological indications.

Managing substance use in patients receiving therapeutic repetitive transcranial magnetic stimulation: A scoping review

Repetitive Transcranial Magnetic Stimulation (rTMS) is an invaluable treatment option for neuropsychiatric disorders. Co-occurring recreational and nonmedical substance use can be common in those presenting for rTMS treatment, and it is unknown how it may affect the safety and efficacy of rTMS for the treatment of currently approved neuropsychiatric indications. This scoping review aimed to map the literature on humans receiving rTMS and had a history of any type of substance use. The search identified 274 articles providing information on inclusion/exclusion criteria, withdrawal criteria, safety protocols, type of rTMS and treatment parameters, adverse events and effect on primary outcomes that related to substance use. There are neurophysiological effects of substance use on cortical excitability, although the relevance to clinical rTMS practice is unknown. The current literature supports the safety and feasibility of delivering rTMS to those who have co-occurring neuropsychiatric disorder and substance use. However, specific details on how varying degrees of substance use alters the safety, efficacy, and mechanisms of rTMS remains poorly described.

Clinical diagnostic utility of transcranial magnetic stimulation in neurological disorders. Updated report of an IFCN committee

The review provides a comprehensive update (previous report: Chen R, Cros D, Curra A, Di Lazzaro V, Lefaucheur JP, Magistris MR, et al. The clinical diagnostic utility of transcranial magnetic stimulation: report of an IFCN committee. Clin Neurophysiol 2008;119(3):504-32) on clinical diagnostic utility of transcranial magnetic stimulation (TMS) in neurological diseases. Most TMS measures rely on stimulation of motor cortex and recording of motor evoked potentials. Paired-pulse TMS techniques, incorporating conventional amplitude-based and threshold tracking, have established clinical utility in neurodegenerative, movement, episodic (epilepsy, migraines), chronic pain and functional diseases. Cortical hyperexcitability has emerged as a diagnostic aid in amyotrophic lateral sclerosis. Single-pulse TMS measures are of utility in stroke, and myelopathy even in the absence of radiological changes. Short-latency afferent inhibition, related to central cholinergic transmission, is reduced in Alzheimer's disease. The triple stimulation technique (TST) may enhance diagnostic utility of conventional TMS measures to detect upper motor neuron involvement. The recording of motor evoked potentials can be used to perform functional mapping of the motor cortex or in preoperative assessment of eloquent brain regions before surgical resection of brain tumors. TMS exhibits utility in assessing lumbosacral/cervical nerve root function, especially in demyelinating neuropathies, and may be of utility in localizing the site of facial nerve palsies. TMS measures also have high sensitivity in detecting subclinical corticospinal lesions in multiple sclerosis. Abnormalities in central motor conduction time or TST correlate with motor impairment and disability in MS. Cerebellar stimulation may detect lesions in the cerebellum or cerebello-dentato-thalamo-motor cortical pathways. Combining TMS with electroencephalography, provides a novel method to measure parameters altered in neurological disorders, including cortical excitability, effective connectivity, and response complexity.

Corticospinal and peripheral responses to heat-induced hypo-hydration: potential physiological mechanisms and implications for neuromuscular function

Heat-induced hypo-hydration (hyperosmotic hypovolemia) can reduce prolonged skeletal muscle performance; however, the mechanisms are less well understood and the reported effects on all aspects of neuromuscular function and brief maximal contractions are inconsistent. Historically, a 4–6% reduction of body mass has not been considered to impair muscle function in humans, as determined by muscle torque, membrane excitability and peak power production. With the development of magnetic resonance imaging and neurophysiological techniques, such as electromyography, peripheral nerve, and transcranial magnetic stimulation (TMS), the integrity of the brain-to-muscle pathway can be further investigated. The findings of this review demonstrate that heat-induced hypo-hydration impairs neuromuscular function, particularly during repeated and sustained contractions. Additionally, the mechanisms are separate to those of hyperthermia-induced fatigue and are likely a result of modulations to corticospinal inhibition, increased fibre conduction velocity, pain perception and impaired contractile function. This review also sheds light on the view that hypo-hydration has ‘no effect’ on neuromuscular function during brief maximal voluntary contractions. It is hypothesised that irrespective of unchanged force, compensatory reductions in cortical inhibition are likely to occur, in the attempt of achieving adequate force production. Studies using single-pulse TMS have shown that hypo-hydration can reduce maximal isometric and eccentric force, despite a reduction in cortical inhibition, but the cause of this is currently unclear. Future work should investigate the intracortical inhibitory and excitatory pathways within the brain, to elucidate the role of the central nervous system in force output, following heat-induced hypo-hydration.

A systematic review of TMS and neurophysiological biometrics in patients with schizophrenia

BACKGROUND

Transcranial magnetic stimulation can be combined with electromyography (TMS-EMG) and electroencephalography (TMS-EEG) to evaluate the excitatory and inhibitory functions of the cerebral cortex in a standardized manner. It has been postulated that schizophrenia is a disorder of functional neural connectivity underpinned by a relative imbalance of excitation and inhibition. The aim of this review was to provide a comprehensive overview of TMS-EMG and TMS-EEG research in schizophrenia, focused on excitation or inhibition, connectivity, motor cortical plasticity and the effect of antipsychotic medications, symptom severity and illness duration on TMS-EMG and TMS-EEG indices.

METHODS

We searched PsycINFO, Embase and Medline, from database inception to April 2020, for studies that included TMS outcomes in patients with schizophrenia. We used the following combination of search terms: transcranial magnetic stimulation OR tms AND interneurons OR glutamic acid OR gamma aminobutyric acid OR neural inhibition OR pyramidal neurons OR excita* OR inhibit* OR GABA* OR glutam* OR E-I balance OR excitation-inhibition balance AND schizoaffective disorder* OR Schizophrenia OR schizophreni*.

RESULTS

TMS-EMG and TMS-EEG measurements revealed deficits in excitation or inhibition, functional connectivity and motor cortical plasticity in patients with schizophrenia. Increased duration of the cortical silent period (a TMS-EMG marker of γ-aminobutyric acid B receptor activity) with clozapine was a relatively consistent finding.

LIMITATIONS

Most of the studies used patients with chronic schizophrenia and medicated patients, employed cross-sectional group comparisons and had small sample sizes.

CONCLUSION

TMS-EMG and TMS-EEG offer an opportunity to develop a novel and improved understanding of the physiologic processes that underlie schizophrenia and to assess the therapeutic effect of antipsychotic medications. In the future, these techniques may also help predict disease progression and further our understanding of the excitatory/inhibitory balance and its implications for mechanisms that underlie treatment-resistant schizophrenia.

Cortical hyperexcitability: Diagnostic and pathogenic biomarker of ALS

Cortical hyperexcitability is an early and intrinsic feature of both sporadic and familial forms of amyotrophic lateral sclerosis (ALS).. Importantly, cortical hyperexcitability appears to be associated with motor neuron degeneration, possibly via an anterograde glutamate-mediated excitotoxic process, thereby forming a pathogenic basis for ALS. The presence of cortical hyperexcitability in ALS patients may be readily determined by transcranial magnetic stimulation (TMS), a neurophysiological tool that provides a non-invasive and painless method for assessing cortical function. Utilising the threshold tracking TMS technique, cortical hyperexcitability has been established as a robust diagnostic biomarker that distinguished ALS from mimicking disorders at early stages of the disease process. The present review discusses the pathophysiological and diagnostic utility of cortical hyperexcitability in ALS.

Transcranial Magnetic Stimulation to Assess Exercise-Induced Neuroplasticity

Aerobic exercise facilitates neuroplasticity and has been linked to improvements in cognitive and motor function. Transcranial magnetic stimulation (TMS) is a non-invasive technique that can be used to quantify changes in neurophysiology induced by exercise. The present review summarizes the single- and paired-pulse TMS paradigms that can be used to probe exercise-induced neuroplasticity, the optimal stimulation parameters and the current understanding of the neurophysiology underlying each paradigm. Further, this review amalgamates previous research exploring the modulation of these paradigms with exercise-induced neuroplasticity in healthy and clinical populations and highlights important considerations for future TMS-exercise research.

Association of Cortical Hyperexcitability and Cognitive Impairment in Patients With Amyotrophic Lateral Sclerosis

OBJECTIVE

To determine whether cortical hyperexcitability was more prominent in cognitively impaired patients with amyotrophic lateral sclerosis (ALS).

METHODS

Threshold tracking transcranial magnetic stimulation (TMS) was used to assess cortical excitability and cognitive function was determined by the Edinburgh Cognitive and Behavioural ALS Screen (ECAS). Cognitive impairment was defined by ECAS < 105. Patients with ALS, defined by the Awaji criteria, were prospectively recruited. Patients unable to undergo TMS, or in whom TMS indices were compromised by coexistent medical conditions, were excluded. Cortical hyperexcitability was defined by reduced short interval intracortical inhibition (SICI) and increased short interval intracortical facilitation (SICF), index of excitability (IE), and motor evoked potential (MEP) amplitude. Student t test determined differences between groups and multivariable regression modeling was used to assess association among cognitive, clinical, and TMS measures. TMS results were compared with those of 42 controls.

RESULTS

Cognitive impairment was evident in 36% of the 40 patients with ALS (23 male, mean age 62.1 years). Cortical hyperexcitability was more prominent in cognitively impaired patients as indicated by an increase in SICF (ECAS_≥105 -15.3 ± 1.7%, ECAS_<105 -20.6 ± 1.2%; p < 0.01), IE (ECAS _≥105 80.9 ± 7.8, ECAS _<105 95.0 ± 4.5; p < 0.01), and MEP amplitude (ECAS_≥105 28.7 ± 3.3%, ECAS_<105 43.1 ± 5.9%; p < 0.05). SICF was independently associated with the ECAS score (β = 2.410; p < 0.05). Reduced SICI was evident in ALS, being more prominent in patients with reduced executive score (ECAS_{executive score>33} 6.2 ± 1.3%, ECAS_{executive score<33} 1.5 ± 2.1%; p < 0.01).

CONCLUSION

Cortical hyperexcitability was more prominent in cognitively impaired patients with ALS than in controls. Given that ECAS is a valid predictor of TDP-43 pathology, the increase in cortical hyperexcitability may be associated with TDP-43 accumulation.

Acute Low-Intensity Aerobic Exercise Modulates Intracortical Inhibitory and Excitatory Circuits in an Exercised and a Non-exercised Muscle in the Primary Motor Cortex

Recent studies have reported that acute aerobic exercise modulates intracortical excitability in the primary motor cortex (M1). However, whether acute low-intensity aerobic exercise can also modulate M1 intracortical excitability, particularly intracortical excitatory circuits, remains unclear. In addition, no previous studies have investigated the effect of acute aerobic exercise on short-latency afferent inhibition (SAI). The aim of this study was to investigate whether acute low-intensity aerobic exercise modulates intracortical circuits in the M1 hand and leg areas. Intracortical excitability of M1 (Experiments 1, 2) and spinal excitability (Experiment 3) were measured before and after acute low-intensity aerobic exercise. In Experiment 3, skin temperature was also measured throughout the experiment. Transcranial magnetic stimulation was applied over the M1 non-exercised hand and exercised leg areas in Experiments 1, 2, respectively. Participants performed 30 min of low-intensity pedaling exercise or rested while sitting on the ergometer. Short- and long-interval intracortical inhibition (SICI and LICI), and SAI were measured to assess M1 inhibitory circuits. Intracortical facilitation (ICF) and short-interval intracortical facilitation (SICF) were measured to assess M1 excitatory circuits. We found that acute low-intensity aerobic exercise decreased SICI and SAI in the M1 hand and leg areas. After exercise, ICF in the M1 hand area was lower than in the control experiment, but was not significantly different to baseline. The single motor-evoked potential, resting motor threshold, LICI, SICF, and spinal excitability did not change following exercise. In conclusion, acute low-intensity pedaling modulates M1 intracortical circuits of both exercised and non-exercised areas, without affecting corticospinal and spinal excitability.

Modulation of inhibitory function in the primary somatosensory cortex and temporal discrimination threshold induced by acute aerobic exercise

Acute aerobic exercise beneficially affects brain function. The effect of acute aerobic exercise on the inhibitory mechanism of the primary somatosensory cortex (S1) and somatosensory function remains unclear. We investigated whether acute aerobic exercise modulates S1 inhibitory function and somatosensory function. In Experiment 1, we measured somatosensory evoked potentials (SEP) and paired-pulse inhibition (PPI) in 15 healthy right-handed participants. The right median nerve underwent electrical stimulation (ES). Interstimulus intervals were 5 ms, 30 ms, and 100 ms. In Experiment 2, we assessed the somatosensory function by using a somatosensory temporal discrimination task. Single or paired ES was applied to the distal phalanx of the right index finger. Both the experiments involved three sessions: 20 min of moderate-intensity exercise, 30 min of low-intensity exercise, and 30 min of seated rest. Before and after each session, PPI and somatosensory temporal discrimination task performance were measured. The N20 latency was significantly shortened immediately after moderate exercise. The SEP amplitude was not modulated in any session. The PPI at 30 ms (PPI_30ms) significantly decreased 20 min after moderate exercise, whereas the PPI at 5 ms (PPI_5ms) and PPI at 100 ms (PPI_100ms) did not change. The 50% and 75% thresholds and reaction time did not improve in any session. We found negative relationships between the change in PPI_5ms and the change in the 75% threshold under low-intensity exercise condition. Thus, acute aerobic exercise modulated S1 inhibitory function depending on exercise intensity. The exercise-induced change in PPI was associated with the change in temporal discrimination.

Methylphenidate promotes the interaction between motor cortex facilitation and attention in healthy adults: A combined study using event-related potentials and transcranial magnetic stimulation

OBJECTIVE

This study investigated simultaneously the impact of methylphenidate (MPH) on the interaction of inhibitory and facilitative pathways in regions processing motor and cognitive functions.

METHOD

Neural markers of attention and response control (event-related potentials) and motor cortical excitability (transcranial magnetic stimulation) and their pharmacological modulation by MPH were measured simultaneously in a sample of healthy adults (n = 31) performing a cued choice reaction test.

RESULTS

Methylphenidate modulated attentional gating and response preparation processes (increased contingent negative variation) and response inhibition (increased nogo P3). N1, cue- and go-P3 were not affected by MPH. Motor cortex facilitation, measured with long-interval cortical facilitation, was increased under MPH in the nogo condition and was positively correlated with the P3 amplitude.

CONCLUSION

Methylphenidate seems particularly to enhance response preparation processes. The MPH-induced increased motor cortex facilitation during inhibitory task demands was accompanied by increased terminal response inhibition control, probably as a compensatory process.

Utility of threshold tracking transcranial magnetic stimulation in ALS

Upper motor neuron [UMN] and lower motor neuron [LMN] dysfunction, in the absence of sensory features, is a pathognomonic feature of amyotrophic lateral sclerosis [ALS]. Although the precise mechanisms have yet to be elucidated, one leading hypothesis is that UMN precede LMN dysfunction, which is induced by anterograde glutamatergic excitotoxicity. Transcranial magnetic stimulation (TMS) is a neurophysiological tool that provides a non-invasive and painless assessment of cortical function. Threshold tracking methodologies have been recently adopted for TMS, whereby changes in threshold rather than motor evoked potential (MEP) amplitude serve as outcome measures. This technique is reliable and provides a rapid assessment of cortical function in ALS. Utilisng the threshold tracking TMS technique, cortical hyperexcitability was demonstrated as an early feature in sporadic ALS preceding the onset of LMN dysfunction and possibly contributing to disease spread. Separately, cortical hyperexcitability was reported to precede the clinical onset of familial ALS. Of further relevance, the threshold tracking TMS technique was proven to reliably distinguish ALS from mimicking disorders, even in the presence of a comparable degree of LMN dysfunction, suggesting a diagnostic utility of TMS. Taken in total, threshold tracking TMS has provided support for a cortical involvement at the earliest detectable stages of ALS, underscoring the utility of the technique for probing the underlying pathophysiology. The present review will discuss the physiological processes underlying TMS parameters, while further evaluating the pathophysiological and diagnostic utility of threshold tracking TMS in ALS.

Imbalance of cortical facilitatory and inhibitory circuits underlies hyperexcitability in ALS

Objective

To determine the relative contribution of inhibitory and facilitatory circuits in the development of cortical hyperexcitability in amyotrophic lateral sclerosis (ALS).

Methods

In this cross-sectional study, cortical excitability was assessed in 27 patients with ALS, and results compared to 25 healthy controls. In addition, a novel neurophysiologic measure of cortical function, short-interval intracortical facilitation (SICF), was assessed reflecting activity of the facilitatory circuits.

Results

There was a significant increase in SICF (ALS −18.51 ± 1.56%, controls −8.52 ± 1.21%, p < 0.001) in patients with ALS that was accompanied by a reduction of short-interval intracortical inhibition (ALS 3.94 ± 1.29%, controls 14.23 ± 1.18%, p < 0.001) and cortical silent period duration (p = 0.034). The index of excitation, a biomarker reflecting the contribution of inhibitory and facilitatory circuit activity, was significantly increased in patients with ALS (82.79 ± 6.01%) compared to controls (36.15 ± 3.44, p < 0.001), suggesting a shift toward cortical excitation. Increased excitation correlated with upper motor neuron signs (R2 = 0.235, p = 0.016) and greater functional disability as reflected by a correlation with the Amyotrophic Lateral Sclerosis Functional Rating Scale–Revised score (R2 = 0.335, p = 0.002).

Conclusions

The present study established that cortical hyperexcitability is a key contributor to ALS pathophysiology, mediated through dysfunction of inhibitory and facilitatory intracortical circuits. Therapies aimed at restoring the cortical inhibitory imbalance provide novel avenues for future therapeutic targets.

Modulating Neural Circuits with Transcranial Magnetic Stimulation: Implications for Addiction Treatment Development

Although the last 50 years of clinical and preclinical research have demonstrated that addiction is a brain disease, we still have no neural circuit-based treatments for substance dependence or cue reactivity at large. Now, for the first time, it appears that a noninvasive brain stimulation technique known as transcranial magnetic stimulation (TMS), which is Food and Drug Administration approved to treat depression, may be the first tool available to fill this critical void in addiction treatment development. The goals of this review are to 1) introduce TMS as a tool to induce causal change in behavior, cortical excitability, and frontal-striatal activity; 2) describe repetitive TMS (rTMS) as an interventional tool; 3) provide an overview of the studies that have evaluated rTMS as a therapeutic tool for alcohol and drug use disorders; and 4) outline a conceptual framework for target selection when designing future rTMS clinical trials in substance use disorders. The manuscript concludes with some suggestions for methodological innovation, specifically with regard to combining rTMS with pharmacotherapy as well as cognitive behavioral training paradigms. We have attempted to create a comprehensive manuscript that provides the reader with a basic set of knowledge and an introduction to the primary experimental questions that will likely drive the field of TMS treatment development forward for the next several years.

Physiological Processes Underlying Short Interval Intracortical Facilitation in the Human Motor Cortex

Short interval intracortical facilitation (SICF) may be elicited by a paired pulse transcranial magnetic stimulation (TMS) paradigm, whereby a suprathreshold first stimulus (S1) precedes a perithreshold second stimulus (S2). Other facilitatory circuits can be probed by TMS such as intracranial facilitation, however the cortical contributions to these circuits may lie partially outside of M1. SICF as such represents a unique analog to M1 inhibitory circuits such as short interveal intracortical circuits. The aim of the present study was to provide insight into the physiological processes underlying the development of SICF using the threshold tracking TMS technique which was recently demonstrated to have significant reliability. TMS studies were undertaken on 35 healthy controls, using either a 90 mm circular and 70 mm figure of eight coil, and one of two targets (0.2 and 1.0 mV) tracked. The motor evoked potential (MEP) responses were recorded from the abductor pollicis brevis. SICF was consistently evident between interstimulus intervals (ISI) of 1–5 ms (P < 0.001), with two peaks occurring ISIs 1.5 and 3 ms when using the circular coil. A significant SICF reduction (F = 5.631, P < 0.05) was evident with the higher tracking target, while SICF increased when stimulating with the figure of eight coil. While there was a correlation between SICF and CSP duration, there was no relationship between SICF and SICI or ICF. Age appeared to have no influence on SICF, SICI, or ICF. Findings from the present work suggest that SICF appears to be mediated by I-wave facilitation.

Effects of monoaminergic drugs on training-induced motor cortex plasticity in older adults

Primary motor cortex (M1) plasticity is involved in motor learning and stroke motor recovery, and enhanced by increasing monoaminergic transmission. Age impacts these processes but there is a paucity of systematic studies on the effects of monoaminergic drugs in older adults. Here, in ten older adults (age 61+4years, 4 males), we determine the effects of a single oral dose of carbidopa/levodopa (DOPA), d-amphetamine (AMPH), methylphenidate (MEPH) and placebo (PLAC) on M1 excitability and motor training-induced M1 plasticity. M1 plasticity is defined as training related long lasting changes in M1 excitability and kinematics of the trained movement. At peak plasma level of the drugs, subjects trained wrist extension movements for 30min. Outcome measures were motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation at increasing intensity (stimulus response curve, SRC) and peak acceleration of the trained wrist extension movements. Measures were obtained before and after completion of training. The curve parameters plateau (MEPmax), inflection point, and slope were extracted from SRC. At baseline drugs had a differential effect on curve parameters, while kinematics remained unchanged. Training alone (PLAC) increased MEPmax but did not improve kinematics. Drugs affected training-related changes of the curve parameters differently, but did not enhance them or kinematics when compared to PLAC. The results demonstrate that in the older adults, MEPH, DOPA, or AMPH have differential effects on baseline M1 excitability and training-related M1 plasticity but fail to enhance them above the naïve level.

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.

The Effects of Methylphenidate on Resting-State Functional Connectivity of the Basal Nucleus of Meynert, Locus Coeruleus, and Ventral Tegmental Area in Healthy Adults

Background: Methylphenidate (MPH) influences catecholaminergic signaling. Extant work examined the effects of MPH on the neural circuits of attention and cognitive control, but few studies have investigated the effect of MPH on the brain's resting-state functional connectivity (rsFC).

Methods: In this observational study, we compared rsFC of a group of 24 healthy adults who were administered an oral 45 mg dose of MPH with a group of 24 age and gender matched controls who did not receive MPH. We focused on three seed regions: basal nucleus of Meynert (BNM), locus coeruleus (LC), and ventral tegmental area/substantia nigra, pars compacta (VTA/SNc), each providing cholinergic, noradrenergic and dopaminergic inputs to the cerebral cortex. Images were pre-processed and analyzed as in our recent work (Li et al., 2014; Zhang et al., 2015). We used one-sample t-test to characterize group-specific rsFC of each seed region and two-sample t-test to compare rsFC between groups.

Results: MPH reversed negative connectivity between BNM and precentral gyri. MPH reduced positive connectivity between LC and cerebellum, and induced positive connectivity between LC and right hippocampus. MPH decreased positive VTA/SNc connectivity to the cerebellum and putamen, and reduced negative connectivity to left middle occipital gyrus.

Conclusion: MPH had distinct effects on the rsFC of BNM, LC, and VTA/SNc in healthy adults. These new findings may further our understanding of the role of catecholaminergic signaling in Attention Deficit Hyperactivity Disorder (ADHD) and Parkinson's disease and provide insights into the therapeutic mechanisms of MPH in the treatment of clinical conditions that implicate catecholaminergic dysfunction.

TMS and drugs revisited 2014

The combination of pharmacology and transcranial magnetic stimulation to study the effects of drugs on TMS-evoked EMG responses (pharmaco-TMS-EMG) has considerably improved our understanding of the effects of TMS on the human brain. Ten years have elapsed since an influential review on this topic has been published in this journal (Ziemann, 2004). Since then, several major developments have taken place: TMS has been combined with EEG to measure TMS evoked responses directly from brain activity rather than by motor evoked potentials in a muscle, and pharmacological characterization of the TMS-evoked EEG potentials, although still in its infancy, has started (pharmaco-TMS-EEG). Furthermore, the knowledge from pharmaco-TMS-EMG that has been primarily obtained in healthy subjects is now applied to clinical settings, for instance, to monitor or even predict clinical drug responses in neurological or psychiatric patients. Finally, pharmaco-TMS-EMG has been applied to understand the effects of CNS active drugs on non-invasive brain stimulation induced long-term potentiation-like and long-term depression-like plasticity. This is a new field that may help to develop rationales of pharmacological treatment for enhancement of recovery and re-learning after CNS lesions. This up-dated review will highlight important knowledge and recent advances in the contribution of pharmaco-TMS-EMG and pharmaco-TMS-EEG to our understanding of normal and dysfunctional excitability, connectivity and plasticity of the human brain.

A combined therapeutic approach in stroke rehabilitation: A review on non-invasive brain stimulation plus pharmacotherapy

Stroke is a leading cause of disability in the United States. Available treatments for stroke have only a modest effect on motor rehabilitation and about 50-60% of stroke patients remain with some degree of motor impairment after standard treatment. Non-invasive brain stimulation (NIBS) techniques have been proposed as adjuvant treatments to physical therapy for motor recovery after stroke. High frequency rTMS and anodal tDCS can be delivered over the affected motor cortex in order to increase cortical excitability and induce brain plasticity with the intention to enhance motor learning and achieve functional goals in stroke patients. Similarly, low frequency rTMS and cathodal tDCS can be delivered to the unaffected motor cortex to reduce interhemispheric inhibition and hinder maladaptive plasticity. The use of several drugs such as amphetamines, selective serotonin reuptake inhibitors (SSRIs), levodopa and cholinergic agents have been also proposed to enhance the motor function. Given that both NIBS and pharmacotherapy might provide some treatment effect independently for motor rehabilitation in stroke and with the rationale that they could work in a synergistic fashion, we believe that a combined therapy- NIBS plus pharmacotherapy- canlead to better outcomes than one or the other alone. In this paper we review the literature that support the potential use of a combined approach in stroke recovery and present the studies that have already investigated this idea.

[Transcranial magnetic stimulation (TMS), inhibition processes and attention deficit/hyperactivity disorder (ADHD) - an overview]

Motor system excitability can be tested by transcranial magnetic stimulation CFMS). In this article, an overview of recent methodological developments and research findings related to attention deficit/hyperactivity disorder (ADHD) is provided. Different TMS parameters that reflect the function of interneurons in the motor cortex may represent neurophysiological markers of inhibition in ADHD, particularly the so-called intracortical inhibition. In children with a high level of hyperactivity and impulsivity, intracortical inhibition was comparably low at rest as shortly before the execution of a movement. TMS-evoked potentials can also be measured in the EEG so that investigating processes of excitability is not restricted to motor areas in future studies. The effects of methylphenidate on motor system excitability may be interpreted in the sense of a 'fine-tuning' with these mainly dopaminergic effects also depending on genetic parameters (DAT1 transporter). A differentiated view on the organization of motor control can be achieved by a combined analysis of TMS parameters and event-related potentials. Applying this bimodal approach, strong evidence for a deviant implementation of motor control in children with ADHD and probably compensatory mechanisms (with involvement of the prefrontal cortex) was obtained. These findings, which contribute to a better understanding of hyperactivity/impulsivity, inhibitory processes and motor control in ADHD as well as the mechanisms of medication, underline the relevance of TMS as a neurophysiological method in ADHD research.

Antipsychotic treatment with quetiapine increases the cortical silent period

RATIONALE

Measurement of motor cortex excitability with single and paired pulse transcranial magnetic stimulation has become an established method for in vivo characterization of the effects of central-acting drugs. The comparison of drug-free and medicated patients with schizophrenia suggests an association of neuroleptics intake and prolongation of the cortical silent period (CSP). However all available data come from cross-sectional non-randomized studies. Thus it is not clear whether the observed difference is an effect of medication or reflects differences in disease severity or both.

OBJECTIVES

We aimed to investigate whether the CSP or other parameters of cortical excitability change, when cortical excitability is measured in drug-free patients with acute psychosis before and after 3week intake of the atypical neuroleptic quetiapine.

METHODS

Different parameters of cortical excitability were studied in 24 drug-free patients with acute psychosis before and after 3weeks of treatment with a mean dose of 352±199mg quetiapine.

RESULTS

We observed a significant prolongation of the cortical silent period (CSP) after three week treatment with quetiapine. Other parameters of cortical excitability such as motor threshold (MT), short intracortical inhibition (SICI) and intracortical facilitation (ICF) remained unaffected. There was a significant improvement in clinical parameters (PANS, GAF) but no significant correlation between clinical improvement and changes in cortical excitability.

CONCLUSIONS

These longitudinal data are in line with previous reports from cross-sectional studies. The excitability changes induced by three-week intake of quetiapine in acute psychotic patients confirm the notion that neuroleptic treatment is associated with an increase in CSP.

Motor cortical disinhibition with baroreceptor unloading induced by orthostatic stress

Unloading of the baroreceptors due to orthostatic stress increases corticospinal excitability. The purpose of this study was to examine the effects of baroreceptor unloading due to orthostatic stress on intracortical excitatory and inhibitory pathways in the motor cortex. With transcranial magnetic stimulation, measures of intracortical excitability for a hand muscle were tested on 2 days in healthy young adults. Lower body negative pressure (LBNP) of 40 mmHg was applied during one of the days and not during the Control day. During application of LBNP heart rate and the low-frequency component of heart rate variability increased, while mean arterial blood pressure was maintained. In the resting state, LBNP decreased short-interval intracortical inhibition (SICI) and had no effect on intracortical facilitation (ICF) or short-interval intracortical facilitation (SICF) compared with the Control day. During isometric contraction, no effects of LBNP were observed on tested measures of intracortical excitability including SICI, SICF, and cortical silent period. It was concluded that baroreceptor unloading due to orthostatic stress results in diminished intracortical inhibition, at least in the resting muscle.

Enhanced corticospinal excitability with physiologically heightened sympathetic nerve activity

Corticospinal excitability is modulated differently with norepinephrine and dopamine agonists, although both monoamines are released with heightened sympathetic nerve activity. The purpose of this study was to investigate the influence of physiological heightening of sympathetic nerve activity on corticospinal excitability in healthy humans. Subjects were divided into control and experimental groups. In each participant, motor-evoked potentials (MEPs) were measured from the resting first dorsal interosseous muscle of the right hand with transcranial magnetic stimulation (TMS) in two trials separated by 1 h. In the experimental group, sympathetic nerve activity was physiologically heightened during the second trial by applying lower body negative pressure (LBNP). In the control group, sympathetic nerve activity was not altered between the two trials. MEP peak-to-peak amplitude increased from trial 1 to trial 2 in the experimental group only. This increase was evident at a TMS intensity of 130% resting motor threshold and higher. It was concluded that physiological heightening of sympathetic nerve activity with LBNP enhances corticospinal excitability.

Pharmaco-transcranial magnetic stimulation studies of motor excitability

Application of a single dose of a central nervous system (CNS) active drug with a defined single mode of action has been proven useful to explore and characterize the pharmacophysiological properties of transcranial magnetic stimulation (TMS) measures of motor cortical and corticospinal excitability in humans. With this pharmaco-TMS approach, it was demonstrated that different TMS measures reflect axon excitability (motor threshold), or inhibitory (cortical silent period, short-interval intracortical inhibition, long-interval intracortical inhibition, short-latency afferent inhibition) or excitatory synaptic excitability (motor evoked potential amplitude, intracortical facilitation, short-interval intracortical facilitation) of distinct neuronal elements in the CNS. Pharmaco-TMS has opened an exciting window into human cortical physiology. The array of pharmacophysiologically well defined TMS measures is now used by neurologists, psychiatrists, and clinical neurophysiologists for diagnosis or treatment monitoring in neuropsychiatric disease. This chapter reviews systematically the TMS measures of motor cortical and corticospinal excitability from the perspective of pharmacophysiological characterization. For example, it is demonstrated that blockers of voltage-gated sodium channels specifically increase motor threshold but do not alter other TMS measures of excitability, whereas positive modulators at γ-butyric acid (GABA) type A receptors, such as benzodiazepines, enhance short-interval intracortical inhibition and depress motor evoked potential amplitude but have no effect on motor threshold.

Utility of transcranial magnetic stimulation in delineating amyotrophic lateral sclerosis pathophysiology

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disorder of the motor neurons in the motor cortex, brainstem, and spinal cord. The clinical phenotype of ALS is underscored by a combination of upper and lower motor neuron dysfunction. Although this phenotype was observed over 100 years ago, the site of ALS onset and the pathophysiological mechanisms underlying the development of motor neuron degeneration remain to be elucidated. Transcranial magnetic stimulation (TMS) enables noninvasive assessment of the functional integrity of the motor cortex and its corticomotoneuronal projections. To date, TMS studies have established cortical dysfunction in ALS, with cortical hyperexcitability being an early feature in sporadic forms of ALS and preceding the clinical onset of familial ALS. Taken together, a central origin of ALS is supported by TMS studies, with an anterograde dying-forward mechanism implicated in ALS pathogenesis. Of further relevance, TMS techniques reliably distinguish ALS from mimic disorders, despite a compatible peripheral disease burden, thereby suggesting a potential diagnostic utility of TMS in ALS. This chapter reviews the mechanisms underlying the generation of TMS parameters utilized in assessment of cortical excitability, the contribution of TMS in enhancing the understanding of ALS pathophysiology, and the potential diagnostic utility of TMS techniques in ALS.

Effects of long-acting methylphenidate in adults with attention deficit hyperactivity disorder: a study with paired-pulse transcranial magnetic stimulation

BACKGROUND

Methylphenidate improves attention deficits, hyperactivity and impulsivity in attention deficit hyperactivity disorder (ADHD). Recent investigations into motor cortex excitability with paired-pulse transcranial magnetic stimulation (ppTMS) technique have shown inhibition deficits in ADHD which correlate with clinical symptomatology. Therefore, we investigated the neurophysiological effects of long-acting methylphenidate (LA-Mph) with the ppTMS technique in adult patients with ADHD.

METHODS

Thirteen right-handed adult ADHD patients who were first diagnosed with ADHD were included in this ppTMS study. Measurements took place before and during treatment with LA-Mph (30-54 mg/day). Statistical analyses were performed to investigate treatment effects and correlations with clinical symptomatology.

RESULTS

LA-Mph significantly decreased the relative short intracortical motor inhibition (SICI) magnetically evoked potential (MEP) amplitude at 3-ms interstimulus interval (conditioned/unconditioned MEP amplitude: 0.83 ± 0.76 drug-free vs. 0.29 ± 0.19 with LA-Mph; p=0.020). The relative intracortical facilitation MEP amplitude at 11 ms interstimulus interval (conditioned/unconditioned MEP amplitude: 1.51 ± 0.92 drug-free vs. 1.79 ± 0.95 with LA-Mph) was not significantly increased. The reduced relative SICI MEP amplitude with LA-Mph correlated significantly with the improvement of the psychopathological ADHD self-rating total scores (p=0.046).

CONCLUSION

These results show that in adult patients with ADHD, LA-Mph significantly improves motor disinhibition and might have differential stabilizing effects on motor hyperexcitability.

Neuromodulatory neurotransmitters influence LTP-like plasticity in human cortex: a pharmaco-TMS study

Long-term potentiation (LTP) of synaptic efficacy is considered a fundamental mechanism of learning and memory. At the cellular level a large body of evidence demonstrated that the major neuromodulatory neurotransmitters dopamine (DA), norepinephrine (NE), and acetylcholine (ACh) influence LTP magnitude. Noninvasive brain stimulation protocols provide the opportunity to study LTP-like plasticity at the systems level of human cortex. Here we applied paired associative stimulation (PAS) to induce LTP-like plasticity in the primary motor cortex of eight healthy subjects. In a double-blind, randomized, placebo-controlled, crossover design, the acute effects of a single oral dose of the neuromodulatory drugs cabergoline (DA agonist), haloperidol (DA antagonist), methylphenidate (indirect NE agonist), prazosine (NE antagonist), tacrine (ACh agonist), and biperiden (ACh antagonist) on PAS-induced LTP-like plasticity were examined. The antagonists haloperidol, prazosine, and biperiden depressed significantly the PAS-induced LTP-like plasticity observed under placebo, whereas the agonists cabergoline, methylphenidate, and tacrine had no effect. Findings demonstrate that antagonists in major neuromodulatory neurotransmitter systems suppress LTP-like plasticity at the systems level of human cortex, in accord with evidence of their modulating action of LTP at the cellular level. This provides further supportive evidence for the known detrimental effects of these drugs on LTP-dependent mechanisms such as learning and memory.

Transcranial magnetic stimulation in disorders of consciousness

We have reviewed the literature on transcranial magnetic stimulation studies in patients with brain death, coma, vegetative, minimally conscious, and locked-in states. Transcranial magnetic stimulation permits non-invasive study of brain excitability and may extend our understanding of the underlying mechanisms of these disorders. However, use of this technique in severe brain damage remains methodologically ill-defined and must be further validated prior to clinical application in these challenging patients.

Modulation of motorcortical excitability by methylphenidate in adult voluntary test persons performing a go/nogo task

This study investigated the interaction between motorcortical excitability (short interval cortical inhibition, intracortical facilitation and long interval cortical inhibition), different requirement conditions [choice reaction test (CRT), attention/go/nogo], and their pharmacological modulation by methylphenidate (MPH) in normal healthy adults (n = 31) using a transcranial magnetic stimulation paradigm. MPH was administered in a dosage of 1 mg/kg body weight, maximum 60 mg. Additionally, serum level and clearance of MPH were controlled. The statistical analysis of variance revealed a significant three-way interaction of 2 (MPH) x 3 (CRT) x 6 (ISI) predicting motor evoked potential amplitudes (P = 0.032, MPH none and full dose, n = 31). In order to compare effects of dosage an additional between-subjects factor (half vs. full MPH dose) was introduced. None of the interactions involving this between-subject factor reached statistical significance. Exploring interactions with MPH only, a 3 (MPH none, half and full dose) x 3 (CRT) x 6 (ISI) analysis of variance revealed significant two-way interactions for MPH x ISI (P = 0.040) and condition x ISI (P < 0.001, n = 18). Effects observed for MPH were strongest on facilitatory processes, weaker for intracortical inhibition. In sum, MPH seems to interact via striato-thalamo-cortical pathways with original motorcortical processes (ISI), to a lesser extent with task-dependent or behavioral parameters (CRT).

Effects of methylphenidate on motor system excitability in a response inhibition task

BACKGROUND

Motor system excitability is based on a complex interaction of excitatory and inhibitory processes, which in turn are modulated by internal (e.g., volitional inhibition) and external (e.g., drugs) factors. A well proven tool to investigate motor system excitability in vivo is the transcranial magnetic stimulation (TMS). In this study, we used TMS to investigate the effects of methylphenidate (MPH) on the temporal dynamics of motor system excitability during a go/nogo task.

METHODS

Using a double-blind, placebo-controlled, crossover design, 14 healthy adults (8 male, 6 female; aged 20-40 yrs) performed a spatial go/nogo task (S1-S2 paradigm) either under dl-methylphenidate (MPH, 20 mg) or placebo. TMS single and double-pulses (interstimulus interval: 3 ms) were delivered either at 120, 230 or 350 ms after the S2 stimulus (control, go and nogo trials).

RESULTS

At the performance level, faster reaction times and a trend towards less impulsivity errors under MPH vs. placebo were observed.In nogo trials, i.e., when a prepared response had to be inhibited, motor evoked potentials (MEPs) had a smaller amplitude at an interval of 230 ms compared to 120 and 350 ms. The short-interval intracortical inhibition (SICI) increased over time.Under MPH, SICI in nogo trials was larger compared to placebo. With the interval between S2 and the TMS-pulse increasing, MEP amplitudes increased under MPH in nogo trials but an early inhibitory effect (at 120 ms) could also be observed.

CONCLUSION

Our results show a distinct pattern of excitatory and inhibitory phenomena in a go/nogo task. MPH appears to significantly alter the dynamics of motor system excitability. Our findings suggest that a single dose of 20 mg MPH provides some fine-tuning of the motor system in healthy adults.

State of the art: Pharmacologic effects on cortical excitability measures tested by transcranial magnetic stimulation

The combination of brain stimulation techniques like transcranial magnetic stimulation (TMS) with CNS active drugs in humans now offers a unique opportunity to explore the physiologic effects of these substances in vivo in the human brain. Motor threshold, motor evoked potential size, motor evoked potential intensity curves, cortical silent period, short-interval intracortical inhibition, intracortical facilitation, short-interval intracortical facilitation, long-interval intracortical inhibition and short latency afferent inhibition represent the repertoire for investigating drug effects on motor cortical excitability by TMS. Here we present an updated overview on the pharmacophysiologic mechanisms with special emphasis on methodologic pitfalls and possible future developments or requirements.

Effects of methylphenidate on the catecholaminergic system in attention-deficit/hyperactivity disorder

Stimulants are part of the standard-of-care treatment for attention-deficit/hyperactivity disorder (ADHD). Methylphenidate, with a history of use spanning approximately 5 decades, is a first-line stimulant treatment for ADHD. Methylphenidate chiefly affects the prefrontal cortex and striatum, the mechanism of action being modulation of catecholaminergic tone. Methylphenidate treatment produces an increase in dopamine (DA) signaling through multiple actions, including blockade of the DA reuptake transporter and amplification of DA response duration, disinhibition of DA D2 autoreceptors and amplification of DA tone, and activation of D1 receptors on the postsynaptic neuron. The actions of methylphenidate may also be mediated by stimulation of the noradrenergic alpha2 receptor and DA D1 receptor in the cortex. The role of other neurotransmitters such as histamine, acetylcholine, serotonin, and alpha-agonists in modulating catecholamine pathophysiology in ADHD and ADHD treatment needs to be elucidated. Overall, the changes in catecholaminergic tone clinically manifest as improvements in attention deficit, distractibility, and motor hyperactivity in patients with ADHD.

Restoration of disturbed intracortical motor inhibition and facilitation in attention deficit hyperactivity disorder children by methylphenidate

BACKGROUND

Previous investigations using transcranial magnetic stimulation (TMS) have shown that neural inhibitory motor circuits are disturbed in ADHD children. We sought to investigate the influence of methylphenidate (MPH) on inhibitory and facilitatory motor circuits of ADHD children with TMS paired pulse protocols using surplus long interval inter-stimulus intervals (ISI) not investigated so far.

METHODS

Motorcortical modulation was tested with TMS paired pulse protocols employing ISI of 3, 13, 50, 100, 200, and 300 msec in 18 ADHD children before and on treatment with MPH. Clinical improvement by MPH was measured by the Conners score.

RESULTS

Analysis of variance (ANOVA) revealed a significant three-way interaction "Group x Amplitude x ISI," p = .001. Subsequent two-factorial ANOVAs and t-tests showed group specific differences of motor evoked potential (MEP) amplitudes for inhibitory ISIs of 3 and 100 msec, and for facilitatory ISIs of 13 and 50 msec. Compared to controls, an adjustment of these parameters by MPH could be shown. On MPH, a significant bivariate correlation was found between the Conners score reduction and averaged MEP amplitude changes only for inhibitory ISIs (3 and 100 msec).

CONCLUSIONS

In ADHD children, MPH modulates disturbed facilitatory and inhibitory motor circuits, which for the latter is associated with clinical improvement.

Atomoxetine treatment of ADHD in Tourette syndrome: reduction in motor cortex inhibition correlates with clinical improvement

OBJECTIVE

In children with attention deficit hyperactivity disorder (ADHD), clinical responses to the selective norepinephrine reuptake inhibitor atomoxetine (ATX) vary. We sought to determine in children with Tourette Syndrome (TS) whether clinical responses correlate with changes in short interval cortical inhibition (SICI).

METHODS

Fourteen children, ages 8-16, with ADHD and TS were treated open-label with ATX for one month. ADHD rating scale scores and SICI, measured with paired-pulse transcranial magnetic stimulation (pTMS), were assessed blindly and independently at treatment onset and one month later.

RESULTS

Eleven children, mean ADHD rating scale scores 31.8 (SD 8.2) at onset, completed the study. After one month, ADHDRS changes ranged from an increase of 4 points to a decrease (improvement) of 24 points (mean change -9.6, SD 9.1). The changes in ADHDRS scores correlated with reduction in SICI (r=.74, p=.010).

CONCLUSIONS

In children with TS, one month of atomoxetine treatment appears to induce correlated improvements in ADHD and, paradoxically, further reductions in cortical inhibition.

SIGNIFICANCE

PTMS-evoked SICI in ADHD with TS may be a biomarker of both deficiency and compensatory changes within cortical interneuronal systems. Effective atomoxetine treatment may augment compensatory processes and thereby reduce SICI.

Functional evaluation of cerebral cortex in dementia with Lewy bodies

Neurochemical investigations have demonstrated central cholinergic dysfunction in patients with dementia with Lewy bodies (DLB). Central cholinergic circuits of the human brain can be tested non-invasively by coupling peripheral nerve stimulation with transcranial magnetic stimulation of the contralateral motor cortex. This test, named short latency afferent inhibition has been shown in healthy subjects to be sensitive to the blockage of muscarinic acetylcholine receptors and it is impaired in patients with Alzheimer disease (AD), a cholinergic form of dementia, while it is normal in non-cholinergic forms of dementia such as fronto-temporal dementia. We evaluated short latency afferent inhibition in a group of patients with DLB and compared the data with that from a group of AD patients and a control group of age-matched healthy individuals. Short latency afferent inhibition was significantly reduced in DLB and AD patients. The findings suggest that this method can be used as a non-invasive test for the assessment of cholinergic pathways in patients with dementia and may represent a useful additional tool for discriminating between cholinergic and non-cholinergic forms of dementia.

Lack of differences of motorcortical excitability in the morning as compared to the evening in juvenile myoclonic epilepsy—A study using transcranial magnetic stimulation

We used transcranial magnetic stimulation (TMS) in patients with juvenile myoclonic epilepsy (JME) and healthy controls to characterise motorcortical excitability in the morning as compared to the evening. Intra- and interindividual comparisons in JME-patients and controls showed no significant differences of any TMS parameter. The expected rise of the resting motor thresholds (RMT) in JME-patients taking anticonvulsants could not be detected which may indicate a decreased RMT in JME-patients.

Methylphenidate modulates cerebral post-stroke reorganization

OBJECTIVE

We hypothesized that a single dose of methylphenidate (MP) would modulate cerebral motor activation and behavior in patients having suffered a subcortical stroke.

METHODS

Eight men with a single stroke on the corticospinal tract resulting in a pure motor hemiparesia were included in a randomized, cross-over, double-blind, placebo-controlled study. Patients were first evaluated 17 days after stroke onset by validated neurological scales, motor tests and fMRI (flexion/extension of the digits) after 20 mg MP or placebo. Seven days later, the patients underwent the same protocol and received the drug they had not taken at the first evaluation. Each patient was his own control.

RESULTS

Placebo intake did not change performance. MP compared to placebo elicited a significant improvement in motor performance of the affected hand at the finger tapping test. MP induced: (1) a hyperactivation of the ipsilesional primary sensorimotor cortex including the motor hand and face areas and of the contralesional premotor cortex; (2) a hypoactivation of the ipsilesional anterior cingulum. Hyperactivation in the face motor area correlated positively with the improvement in performance.

CONCLUSION

We demonstrated that the reorganized network may efficiently be targeted by the drug and that the effect of MP might partly rely on an improvement in attention/effort through cingulum modulation.

Effects of single-dose methylphenidate on cognitive performance in patients with traumatic brain injury: a double-blind placebo-controlled study

OBJECTIVES

To determine the effect of a single dose of methylphenidate on the cognitive performance of patients with traumatic brain injury (TBI), and particularly on working memory and visuospatial attention.

DESIGN

A double-blind placebo-controlled study. The subjects were randomly divided into an experimental group taking methylphenidate and a control group taking a placebo.

SETTING

The Department of Rehabilitation Medicine of a university hospital.

SUBJECTS

Eighteen subjects with TBI (16 male and two female) were enrolled.

INTERVENTIONS

The patients were given 20 mg methylphenidate or a placebo. Cognitive assessments were performed at three times: before the medication as a baseline, 2 h after medication and at follow-up (48 h later).

MAIN MEASURES

Cognitive assessments consisted of working memory tasks and endogenous visuospatial attention tasks designed using SuperLabPro 2.0 software. Response accuracy and reaction time were measured.

RESULTS

There were significant improvements in response accuracy in the methylphenidate group compared with the placebo group for both the working memory and visuospatial attention tasks. A significant decrease in the reaction time was also observed in the methylphenidate group only for the working memory task.

CONCLUSIONS

The administration of single-dose methylphenidate has an effect in improving cognitive functioning following a TBI. The effects were most prominent regarding the reaction time of the working memory.

The effect of methylphenidate on the sleep-wake cycle of brain-injured patients undergoing rehabilitation

BACKGROUND AND PURPOSE

A number of neuro-stimulants are routinely used as part of post-acute care of hospitalized brain-injured patients. To our knowledge, the effect of these stimulants on the sleep-wake cycles of brain-injured patients undergoing rehabilitation has not been addressed. We examined the effect of one of the most commonly used neuro-stimulants, methylphenidate, on the sleep-wake behavior of brain-injured patients undergoing rehabilitation at a dedicated brain injury clinic.

PATIENTS AND METHOD

For this study, records of patients admitted between January and December 1999 were scrutinized retrospectively for the data on observationally defined sleep-wake distribution. A total of 30 patients diagnosed with traumatic brain injury were identified as having been observed for a full 24h a day for at least 10 days. Some of these patients (n=17) were administered methylphenidate on clinical grounds. They served as the experimental group, while the unmedicated patients (n=13) served as controls. For the present analysis, the sleep-wake cycles were arbitrarily designated as nighttime and daytime, respectively. A cumulative sleep-wake quantity in a 24-h period was also observed.

RESULT

The average number of hours of sleep during a 24-h period was not significantly different for the two cohorts. Similar trends emerged for the nighttime and daytime observations. On the whole, methylphenidate appears not to have unfavorable effects on sleep-wake cycles, presently defined as nighttime, daytime and 24-h, in the traumatic brain injury population.

CONCLUSION

This study sought to gain better understanding of the effect of methylphenidate on daytime sleepiness and nighttime sleep, and the data suggest that administration of methylphenidate does not appear to have an adverse effect on sleep-wake quantity.

Comparison of the inhibitory and excitatory effects of ADHD medications methylphenidate and atomoxetine on motor cortex

Stimulant and norepinephrine (NE) reuptake inhibitor medications have different effects at the neuronal level, but both reduce symptoms of attention deficit hyperactivity disorder (ADHD). To understand their common physiologic effects and thereby gain insight into the neurobiology of ADHD treatment, we compared the effects of the stimulant methylphenidate (MPH) and NE uptake inhibitor atomoxetine (ATX) on inhibitory and excitatory processes in human cortex. Nine healthy, right-handed adults were given a single, oral dose of 30 mg MPH and 60 mg ATX at visits separated by 1 week in a randomized, double-blind crossover trial. We used paired and single transcranial magnetic stimulation (TMS) of motor cortex to measure conditioned and unconditioned motor-evoked potential amplitudes at inhibitory (3 ms) and facilitatory (10 ms) interstimulus intervals (ISI) before and after drug administration. Data were analyzed with repeated measures, mixed model regression. We also analyzed our findings and the published literature with meta-analysis software to estimate treatment effects of stimulants and NE reuptake inhibitors on these TMS measures. There were no significant pretreatment differences or effects of treatment order. Both agents produced a significant increase in facilitation and a decrease in inhibition. Effects of ATX and MPH did not differ significantly. Pooled estimates from published studies show similar results for stimulants and NE reuptake inhibitors. In conclusion, in healthy adults, both stimulant and nonstimulant medications for ADHD decrease cortical inhibition and increase cortical facilitation. Cortical inhibition, shown previously to be abnormal in ADHD, may play a key role producing behavioral pathology.

Modification of Practice-dependent Plasticity in Human Motor Cortex by Neuromodulators

Practice-dependent plasticity underlies motor learning in everyday life and motor relearning after lesions of the nervous system. Previous studies showed that practice-dependent plasticity is modifiable by neuromodulating transmitters such as norepinephrine (NE), dopamine (DA) or acetylcholine (ACh). Here we explored, for the first time comprehensively and systematically, the modifying effects of an agonist versus antagonist in each of these neuromodulating transmitter systems on practice-dependent plasticity in healthy subjects in a placebo-controlled, randomized, double-blind crossover design. We found that the agonists in all three neuromodulating transmitter systems (NE: methylphenidate; DA: cabergoline; ACh: tacrine) enhanced practice-dependent plasticity, whereas the antagonists decreased it (NE: prazosin; DA: haloperidol; ACh: biperiden). Enhancement of plasticity under methylphenidate and tacrine was associated with an increase in corticomotoneuronal excitability of the prime mover of the practice, as measured by the motor evoked potential amplitude, but with a decrease under cabergoline. Our findings demonstrate that agonists and antagonists in various neuromodulating transmitter systems produce significant and oppositely directed modifications of practice-dependent plasticity in human motor cortex. Enhancement of plasticity occurred through different strategies that either favoured extrinsic (NE, ACh) or intrinsic (DA) modulating influence on the motor cortical output network.