TMS and drugs revisited 2014

Clinical and electrophysiological impact of repetitive low-frequency transcranial magnetic stimulation on the sensory-motor network in patients with restless legs syndrome

BACKGROUND

Based on the hyperexcitability and disinhibition observed in patients with restless legs syndrome (RLS) following transcranial magnetic stimulation (TMS), we conducted a study with low-frequency repetitive TMS (rTMS) over the primary motor (M1) and somatosensory cortical areas (S1) in patients with RLS.

METHODS

A total of 13 right-handed patients and 10 age-matched controls were studied using clinical scales and TMS. Measurements included resting motor threshold (rMT), motor-evoked potentials (MEPs), cortical silent period (CSP), and central motor conduction time (CMCT). A single evening session of rTMS (1 Hz, 20 trains, 50 stimuli each) was administered over the left M1, left S1, and sham stimulation over M1 in a random order. Clinical and TMS measures were repeated after each stimulation modality.

RESULTS

Baseline CSP was shorter in patients than in controls and remained shorter in patients for both motor and somatosensory stimulation. The patients reported a subjective improvement of both initiating and maintaining sleep the night after the rTMS over S1. Patients exhibited a decrease in rMT after rTMS of S1 only, although the effect was smaller than in controls. MEP latency and CMCT changed only in controls after stimulation. Sham stimulation was without effect on the observed variables.

CONCLUSIONS

rTMS on S1-M1 connectivity alleviated the sensory-motor complaints of RLS patients. The TMS indexes of excitation and inhibition indicate an intracortical and corticospinal imbalance, mainly involving gamma-aminobutyric acid (GABA)ergic and glutamatergic circuitries, as well as an impairment of the short-term mechanisms of cortical plasticity. The rTMS-induced activation of the dorsal striatum with the consequent increase of dopamine release may have contributed to the clinical and neurophysiological outcome.

GABA concentration in sensorimotor cortex following high-intensity exercise and relationship to lactate levels

KEY POINTS

Magnetic resonance spectroscopy was conducted before and after high-intensity interval exercise. Sensorimotor cortex GABA concentration increased by 20%. The increase was positively correlated with the increase in blood lactate. There was no change in dorsolateral prefrontal cortex. There were no changes in the glutamate-glutamine-glutathione peak.

ABSTRACT

High-intensity exercise increases the concentration of circulating lactate. Cortical uptake of blood borne lactate increases during and after exercise; however, the potential relationship with changes in the concentration of neurometabolites remains unclear. Although changes in neurometabolite concentration have previously been demonstrated in primary visual cortex after exercise, it remains unknown whether these changes extend to regions such as the sensorimotor cortex (SM) or executive regions such as the dorsolateral prefrontal cortex (DLPFC). In the present study, we explored the acute after-effects of high-intensity interval training (HIIT) on the concentration of gamma-Aminobutyric acid (GABA) and the combined glutamate-glutamine-glutathione (Glx) spectral peak in the SM and DLPFC, as well as the relationship with blood lactate levels. Following HIIT, there was a robust increase in GABA concentration in the SM, as evident across the majority of participants. This change was not observed in the DLPFC. Furthermore, the increase in SM GABA was positively correlated with an increase in blood lactate. There were no changes in Glx concentration in either region. The observed increase in SM GABA concentration implies functional relevance, whereas the correlation with lactate levels may relate to the metabolic fate of exercise-derived lactate that crosses the blood-brain barrier.

Towards a neurodynamical understanding of the prodrome in schizophrenia

The identification of biomarkers for the early diagnosis of schizophrenia that could inform novel treatment developments is an important objective of current research. This paper will summarize recent work that has investigated changes in oscillatory activity and event-related potentials with Electro/Magnetoencephalography (EEG/MEG) in participants at high-risk for the development of schizophrenia, highlighting disruptions in sensory and cognitive operations prior to the onset of the syndrome. Changes in EEG/MEG-data are consistent with evidence for alterations in Glutamatergic and GABAergic neurotransmission as disclosed by Magnetic Resonance Spectroscopy and brain stimulation, indicating changes in Excitation/Inhibition balance parameters prior to the onset of psychosis. Together these data emphasize the importance of research into neuronal dynamics as a crucial approach to establish functional relationships between impairments in neural circuits and emerging psychopathology that together could be fundamental for early intervention and the identification of novel treatments for emerging psychosis.

Motor cortex excitability in seizure-free STX1B mutation carriers with a history of epilepsy and febrile seizures

OBJECTIVE

Mutations in STX1B encoding the presynaptic protein syntaxin-1B are associated with febrile seizures with or without epilepsy. It is unclear to what extent these mutations are linked to abnormalities of cortical glutamatergic or GABAergic neurotransmission. We explored this question using single- and paired-pulse transcranial magnetic stimulation (TMS) excitability markers.

METHODS

We studied nine currently asymptomatic adult STX1B mutation carriers with history of epilepsy and febrile seizures, who had been seizure-free for at least eight years without antiepileptic drug treatment, and ten healthy age-matched controls. Resting motor threshold (RMT), and input-output curves of motor evoked potential (MEP) amplitude, short-interval intracortical inhibition (SICI, marker of GABA_Aergic excitability) and intracortical facilitation (ICF, marker of glutamatergic excitability) were tested.

RESULTS

RMT, and input-output curves of MEP amplitude, SICI and ICF revealed no significant differences between STX1B mutation carriers and healthy controls.

CONCLUSIONS

Findings suggest normal motor cortical GABA_Aergic and glutamatergic excitability in currently asymptomatic STX1B mutation carriers.

SIGNIFICANCE

TMS measures of motor cortical excitability show utility in demonstrating normal excitability in adult STX1B mutation carriers with history of seizures.

GABA-from Inhibition to Cognition: Emerging Concepts

Neural functioning and plasticity can be studied on different levels of organization and complexity ranging from the molecular and synaptic level to neural circuitry of whole brain networks. Across neuroscience different methods are being applied to better understand the role of various neurotransmitter systems in the evolution of perception and cognition. GABA is the main inhibitory neurotransmitter in the adult mammalian brain and, depending on the brain region, up to 25% of the total number of cortical neurons are GABAergic interneurons. At the one end of the spectrum, GABAergic neurons have been accurately described with regard to cell morphological, molecular, and electrophysiological properties; at the other end researchers try to link GABA concentrations in specific brain regions to human behavior using magnetic resonance spectroscopy. One of the main challenges of modern neuroscience currently is to integrate knowledge from highly specialized subfields at distinct biological scales into a coherent picture that bridges the gap between molecules and behavior. In the current review, recent findings from different fields of GABA research are summarized delineating a potential strategy to develop a more holistic picture of the function and role of GABA.

Rehabilitating the addicted brain with transcranial magnetic stimulation

Substance use disorders (SUDs) are one of the leading causes of morbidity and mortality worldwide. In spite of considerable advances in understanding the neural underpinnings of SUDs, therapeutic options remain limited. Recent studies have highlighted the potential of transcranial magnetic stimulation (TMS) as an innovative, safe and cost-effective treatment for some SUDs. Repetitive TMS (rTMS) influences neural activity in the short and long term by mechanisms involving neuroplasticity both locally, under the stimulating coil, and at the network level, throughout the brain. The long-term neurophysiological changes induced by rTMS have the potential to affect behaviours relating to drug craving, intake and relapse. Here, we review TMS mechanisms and evidence that rTMS is opening new avenues in addiction treatments.

Neurophysiology of the "Celiac Brain": Disentangling Gut-Brain Connections

Celiac disease (CD) can be considered a complex multi-organ disorder with highly variable extra-intestinal, including neurological, involvement. Cerebellar ataxia, peripheral neuropathy, seizures, headache, cognitive impairment, and neuropsychiatric diseases are complications frequently reported. These manifestations may be present at the onset of the typical disease or become clinically evident during its course. However, CD subjects with subclinical neurological involvement have also been described, as well as patients with clear central and/or peripheral nervous system and intestinal histopathological disease features in the absence of typical CD manifestations. Based on these considerations, a sensitive and specific diagnostic method that is able to detect early disease process, progression, and complications is desirable. In this context, neurophysiological techniques play a crucial role in the non-invasive assessment of central nervous system (CNS) excitability and conductivity. Moreover, some of these tools are known for their valuable role in early diagnosis and follow-up of several neurological diseases or systemic disorders, such as CD with nervous system involvement, even at the subclinical level. This review provides an up-to-date summary of the neurophysiological basis of CD using electroencephalography (EEG), multimodal evoked potentials, and transcranial magnetic stimulation (TMS). The evidence examined here seems to converge on an overall profile of "hyperexcitable celiac brain," which partially recovers after institution of a gluten-free diet (GFD). The main translational correlate is that in case of subclinical neurological involvement or overt unexplained symptoms, neurophysiology could contribute to the diagnosis, assessment, and monitoring of a potentially underlying CD.

Exploring genetic influences underlying acute aerobic exercise effects on motor learning

The objective of the current work was to evaluate whether the effects of acute aerobic exercise on motor learning were dependent on genetic variants impacting brain-derived neurotrophic factor (BDNF val66met polymorphism) and the dopamine D2 receptor (DRD2/ANKK1 glu713lys polymorphism) in humans. A retrospective analysis was performed to determine whether these polymorphisms influence data from our two previous studies, which both demonstrated that a single bout of aerobic exercise prior to motor practice enhanced implicit motor learning. Here, our main finding was that the effect of acute aerobic exercise on motor learning was dependent on DRD2/ANKK1 genotype. Motor learning was enhanced when aerobic exercise was performed prior to skill practice in glu/glu homozygotes, but not lys allele carriers. In contrast, the BDNF val66met polymorphism did not impact the exercise effect. The results suggest that the dopamine D2 receptor may be involved in acute aerobic exercise effects on motor learning. Such genetic information could inform the development of individualized aerobic exercise strategies to promote motor learning.

Neurophysiology of the "Celiac Brain": Disentangling Gut-Brain Connections

Celiac disease (CD) can be considered a complex multi-organ disorder with highly variable extra-intestinal, including neurological, involvement. Cerebellar ataxia, peripheral neuropathy, seizures, headache, cognitive impairment, and neuropsychiatric diseases are complications frequently reported. These manifestations may be present at the onset of the typical disease or become clinically evident during its course. However, CD subjects with subclinical neurological involvement have also been described, as well as patients with clear central and/or peripheral nervous system and intestinal histopathological disease features in the absence of typical CD manifestations. Based on these considerations, a sensitive and specific diagnostic method that is able to detect early disease process, progression, and complications is desirable. In this context, neurophysiological techniques play a crucial role in the non-invasive assessment of central nervous system (CNS) excitability and conductivity. Moreover, some of these tools are known for their valuable role in early diagnosis and follow-up of several neurological diseases or systemic disorders, such as CD with nervous system involvement, even at the subclinical level. This review provides an up-to-date summary of the neurophysiological basis of CD using electroencephalography (EEG), multimodal evoked potentials, and transcranial magnetic stimulation (TMS). The evidence examined here seems to converge on an overall profile of "hyperexcitable celiac brain," which partially recovers after institution of a gluten-free diet (GFD). The main translational correlate is that in case of subclinical neurological involvement or overt unexplained symptoms, neurophysiology could contribute to the diagnosis, assessment, and monitoring of a potentially underlying CD.

Effects of the Selective α5-GABAAR Antagonist S44819 on Excitability in the Human Brain: A TMS-EMG and TMS-EEG Phase I Study

Alpha-5 gamma-aminobutyric acid type A receptors (α5-GABAARs) are located extrasynaptically, regulate neuronal excitability through tonic inhibition, and are fundamentally important for processes such as plasticity and learning. For example, pharmacological blockade of α5-GABAAR in mice with ischemic stroke improved recovery of function by normalizing exaggerated perilesional α5-GABAAR-dependent tonic inhibition. S44819 is a novel competitive selective antagonist of the α5-GABAAR at the GABA-binding site. Pharmacological modulation of α5-GABAAR-mediated tonic inhibition has never been investigated in the human brain. Here, we used transcranial magnetic stimulation (TMS) to test the effects of a single oral dose of 50 and 100 mg of S44819 on electromyographic (EMG) and electroencephalographic (EEG) measures of cortical excitability in 18 healthy young adults in a randomized, double-blinded, placebo-controlled, crossover phase I study. A dose of 100 mg, but not 50 mg, of S44819 decreased active motor threshold, the intensity needed to produce a motor evoked potential of 0.5 mV, and the amplitude of the N45, a GABAAergic component of the TMS-evoked EEG response. The peak serum concentration of 100 mg S44819 correlated directly with the decrease in N45 amplitude. Short-interval intracortical inhibition, a TMS-EMG measure of synaptic GABAAergic inhibition, and other components of the TMS-evoked EEG response remained unaffected. These findings provide first time evidence that the specific α5-GABAAR antagonist S44819 reached human cortex to impose an increase in cortical excitability. These data warrant further development of S44819 in a human clinical trial to test its efficacy in enhancing recovery of function after ischemic stroke.

SIGNIFICANCE STATEMENT

The extrasynaptic α-5 gamma-aminobutyric acid type A receptor (α5-GABAAR) regulates neuronal excitability through tonic inhibition in the mammalian brain. Tonic inhibition is important for many fundamental processes such as plasticity and learning. Pharmacological modulation of α5-GABAAR-mediated tonic inhibition has never been investigated in the human brain. This study demonstrates that S44819, a selective α5-GABAAR antagonist, increases cortical excitability in healthy human subjects, as indicated by specific markers of transcranial magnetic stimulation-induced muscle and brain responses measured by electromyography and electroencephalography. Our findings imply that tonic inhibition in human cortex can be modified effectively and that this modification can be quantified with noninvasive brain stimulation methods. The actions of S44819 may be suitable to improve plasticity and learning.

Attention modulates specific motor cortical circuits recruited by transcranial magnetic stimulation

Skilled performance and acquisition is dependent upon afferent input to motor cortex. The present study used short-latency afferent inhibition (SAI) to probe how manipulation of sensory afference by attention affects different circuits projecting to pyramidal tract neurons in motor cortex. SAI was assessed in the first dorsal interosseous muscle while participants performed a low or high attention-demanding visual detection task. SAI was evoked by preceding a suprathreshold transcranial magnetic stimulus with electrical stimulation of the median nerve at the wrist. To isolate different afferent intracortical circuits in motor cortex SAI was evoked using either posterior-anterior (PA) or anterior-posterior (PA) monophasic current. In an independent sample, somatosensory processing during the same attention-demanding visual detection tasks was assessed using somatosensory-evoked potentials (SEP) elicited by median nerve stimulation. SAI elicited by AP TMS was reduced under high compared to low visual attention demands. SAI elicited by PA TMS was not affected by visual attention demands. SEPs revealed that the high visual attention load reduced the fronto-central P20-N30 but not the contralateral parietal N20-P25 SEP component. P20-N30 reduction confirmed that the visual attention task altered sensory afference. The current results offer further support that PA and AP TMS recruit different neuronal circuits. AP circuits may be one substrate by which cognitive strategies shape sensorimotor processing during skilled movement by altering sensory processing in premotor areas.

Combining Dopaminergic Facilitation with Robot-Assisted Upper Limb Therapy in Stroke Survivors: A Focused Review

Despite aggressive conventional therapy, lasting hemiplegia persists in a large percentage of stroke survivors. The aim of this article is to critically review the rationale behind targeting multiple sites along the motor learning network by combining robotic therapy with pharmacotherapy and virtual reality–based reward learning to alleviate upper extremity impairment in stroke survivors. Methods for personalizing pharmacologic facilitation to each individual’s unique biology are also reviewed. At the molecular level, treatment with levodopa was shown to induce long-term potentiation-like and practice-dependent plasticity. Clinically, trials combining conventional therapy with levodopa in stroke survivors yielded statistically significant but clinically unconvincing outcomes because of limited personalization, standardization, and reproducibility. Robotic therapy can induce neuroplasticity by delivering intensive, reproducible, and functionally meaningful interventions that are objective enough for the rigors of research. Robotic therapy also provides an apt platform for virtual reality, which boosts learning by engaging reward circuits. The future of stroke rehabilitation should target distinct molecular, synaptic, and cortical sites through personalized multimodal treatments to maximize motor recovery.

Cortical Plasticity in Depression

Neural plasticity is considered the neurophysiological correlate of learning and memory, although several studies have also noted that it plays crucial roles in a number of neurological and psychiatric diseases. Indeed, impaired brain plasticity may be one of the pathophysiological mechanisms that underlies both cognitive decline and major depression. Moreover, a degree of cognitive impairment is frequently observed throughout the clinical spectrum of mood disorders, and the relationship between depression and cognition is often bidirectional. However, most evidence for dysfunctional neural plasticity in depression has been indirect. Transcranial magnetic stimulation has emerged as a noninvasive tool for investigating several parameters of cortical excitability with the aim of exploring the functions of different neurotransmission pathways and for probing in vivo plasticity in both healthy humans and those with pathological conditions. In particular, depressed patients exhibit a significant interhemispheric difference in motor cortex excitability, an imbalanced inhibitory or excitatory intracortical neurochemical circuitry, reduced postexercise facilitation, and an impaired long-term potentiation-like response to paired-associative transcranial magnetic stimulation, and these symptoms may indicate disrupted plasticity. Research aimed at disentangling the mechanism by which neuroplasticity plays a role in the pathological processes that lead to depression and evaluating the effects of modulating neuroplasticity are needed for the field to facilitate more powerful translational research studies and identify novel therapeutic targets.

Disruption of GABA(A)-mediated intracortical inhibition in patients with chorea-acanthocytosis

Chorea-acanthocytosis (Ch-Ac) is an autosomal recessive neurodegenerative disorder characterized by adult-onset chorea, acanthocytes in the peripheral blood, and Huntington's disease-like neuropsychiatric symptoms. Animal studies have shown mutation-related dysregulated cortical gamma-aminobutyric acid (GABA)ergic inhibitory networks in its pathophysiology. Herein we found that in patients with Ch-Ac there is a striking alteration of intracortical inhibitory circuits detected by using paired pulse transcranial magnetic stimulation protocols. Our findings show in vivo the functional disruption of GABA(A)-mediated networks in humans with Ch-Ac supporting the existing data in mice models with this condition.

Abnormal EEG Responses to TMS During the Cortical Silent Period Are Associated With Hand Function in Chronic Stroke

BACKGROUND

Abnormal brain excitability influences recovery after stroke at which time a prolonged transcranial magnetic stimulation (TMS)-induced electromyographic silent period is thought to reflect abnormal inhibitory interneuron excitability. Cortical excitability can be probed directly during the silent period using concurrent electroencephalography (EEG) of TMS-evoked responses.

OBJECTIVE

The primary study objectives were to characterize TMS-evoked cortical potentials (TEPs) using EEG and to investigate associations with persistent hand and arm motor dysfunction in individuals with chronic stroke.

METHODS

Thirteen participants with chronic stroke-related mild-moderate arm motor impairment and 12 matched controls completed a single TMS-EEG cortical excitability assessment. TEPs recorded from the vertex during cortical silent period (CSP) assessment and while at rest were used to evaluate differences in cortical excitability between stroke and control participants. Associations between TEPs and CSP duration with measures of upper extremity motor behavior were investigated.

RESULTS

Significantly increased TEP component peak amplitudes and delayed latencies were observed for stroke participants compared with controls during CSP assessment and while at rest. Delayed early TEP component (P30) peak latencies during CSP assessment were associated with less manual dexterity. CSP duration was prolonged in stroke participants, and correlated with P30 peak latency and paretic arm dysfunction.

CONCLUSIONS

Abnormal cortical excitability directly measured by early TMS-evoked EEG responses during CSP assessment suggests abnormal cortical inhibition is associated with hand dysfunction in chronic stroke. Further investigation of abnormal cortical inhibition in specific brain networks is necessary to characterize the salient neurophysiologic mechanisms contributing to persistent motor dysfunction after stroke.

Changes in transcranial magnetic stimulation outcome measures in response to upper-limb physical training in stroke: A systematic review of randomized controlled trials

BACKGROUND

Physical training is known to be an effective intervention to improve sensorimotor impairments after stroke. However, the link between brain plastic changes, assessed by transcranial magnetic stimulation (TMS), and sensorimotor recovery in response to physical training is still misunderstood. We systematically reviewed reports of randomized controlled trials (RCTs) involving the use of TMS over the primary motor cortex (M1) to probe brain plasticity after upper-limb physical training interventions in people with stroke.

METHODS

We searched 5 databases for articles published up to October 2016, with additional studies identified by hand-searching. RCTs had to investigate pre/post-intervention changes in at least one TMS outcome measure. Two independent raters assessed the eligibility of potential studies and reviewed the selected articles' quality by using 2 critical appraisal scales.

RESULTS

In total, 14 reports of RCTs (pooled participants=358; mean 26±12 per study) met the selection criteria. Overall, 11 studies detected plastic changes with TMS in the presence of clinical improvements after training, and these changes were more often detected in the affected hemisphere by using map area and motor evoked potential (MEP) latency outcome measures. Plastic changes mostly pointed to increased M1/corticospinal excitability and potential interhemispheric rebalancing of M1 excitability, despite sometimes controversial results among studies. Also, the strength of the review observations was affected by heterogeneous TMS methods and upper-limb interventions across studies as well as several sources of bias within the selected studies.

CONCLUSIONS

The current evidence encourages the use of TMS outcome measures, especially MEP latency and map area to investigate plastic changes in the brain after upper-limb physical training post-stroke. However, more studies involving rigorous and standardized TMS procedures are needed to validate these observations.

Influences of glutamine administration on response selection and sequence learning: a randomized-controlled trial

Precursors of neurotransmitters are increasingly often investigated as potential, easily-accessible methods of neuromodulation. However, the amino-acid glutamine, precursor to the brain’s main excitatory and inhibitory neurotransmitters glutamate and GABA, remains notably little investigated. The current double-blind, randomized, placebo-controlled study provides first evidence 2.0 g glutamine administration in healthy adults affects response selection but not motor sequence learning in a serial reaction time task. Specifically, glutamine increased response selection errors when the current target response required a different hand than the directly preceding target response, which might indicate enhanced cortical excitability via a presumed increase in glutamate levels. These results suggest glutamine can alter cortical excitability but, despite the critical roles of glutamate and GABA in motor learning, at its current dose glutamine does not affect sequence learning.

Cortical involvement in celiac disease before and after long-term gluten-free diet: A Transcranial Magnetic Stimulation study

OBJECTIVE

Transcranial Magnetic Stimulation in de novo patients with Celiac Disease previously revealed an imbalance in the excitability of cortical facilitatory and inhibitory circuits. After a median period of 16 months of gluten-free diet, a global increase of cortical excitability was reported, suggesting a glutamate-mediated compensation for disease progression. We have now evaluated cross-sectionally the changes of cortical excitability to TMS after a much longer gluten-free diet.

METHODS

Twenty patients on adequate gluten-free diet for a mean period of 8.35 years were enrolled and compared with 20 de novo patients and 20 healthy controls. Transcranial Magnetic Stimulation measures, recorded from the first dorsal interosseous muscle of the dominant hand, consisted of: resting motor threshold, cortical silent period, motor evoked potentials, central motor conduction time, mean short-latency intracortical inhibition and intracortical facilitation.

RESULTS

The cortical silent period was shorter in de novo patients, whereas in gluten-free diet participants it was similar to controls. The amplitude of motor responses was significantly smaller in all patients than in controls, regardless of the dietary regimen. Notwithstanding the diet, all patients exhibited a statistically significant decrease of mean short-latency intracortical inhibition and enhancement of intracortical facilitation with respect to controls; more intracortical facilitation in gluten-restricted compared to non-restricted patients was also observed. Neurological examination and celiac disease-related antibodies were negative.

CONCLUSIONS

In this new investigation, the length of dietary regimen was able to modulate the electrocortical changes in celiac disease. Nevertheless, an intracortical synaptic dysfunction, mostly involving excitatory and inhibitory interneurons within the motor cortex, may persist. The clinical significance of subtle neurophysiological changes in celiac disease needs to be further investigated.

Cortical Plasticity in Depression

Neural plasticity is considered the neurophysiological correlate of learning and memory, although several studies have also noted that it plays crucial roles in a number of neurological and psychiatric diseases. Indeed, impaired brain plasticity may be one of the pathophysiological mechanisms that underlies both cognitive decline and major depression. Moreover, a degree of cognitive impairment is frequently observed throughout the clinical spectrum of mood disorders, and the relationship between depression and cognition is often bidirectional. However, most evidence for dysfunctional neural plasticity in depression has been indirect. Transcranial magnetic stimulation has emerged as a noninvasive tool for investigating several parameters of cortical excitability with the aim of exploring the functions of different neurotransmission pathways and for probing in vivo plasticity in both healthy humans and those with pathological conditions. In particular, depressed patients exhibit a significant interhemispheric difference in motor cortex excitability, an imbalanced inhibitory or excitatory intracortical neurochemical circuitry, reduced postexercise facilitation, and an impaired long-term potentiation-like response to paired-associative transcranial magnetic stimulation, and these symptoms may indicate disrupted plasticity. Research aimed at disentangling the mechanism by which neuroplasticity plays a role in the pathological processes that lead to depression and evaluating the effects of modulating neuroplasticity are needed for the field to facilitate more powerful translational research studies and identify novel therapeutic targets.

Neuromuscular fatigue during exercise: Methodological considerations, etiology and potential role in chronic fatigue

The term fatigue is used to describe a distressing and persistent symptom of physical and/or mental tiredness in certain clinical populations, with distinct but ultimately complex, multifactorial and heterogenous pathophysiology. Chronic fatigue impacts on quality of life, reduces the capacity to perform activities of daily living, and is typically measured using subjective self-report tools. Fatigue also refers to an acute reduction in the ability to produce maximal force or power due to exercise. The classical measurement of exercise-induced fatigue involves neuromuscular assessments before and after a fatiguing task. The limitations and alternatives to this approach are reviewed in this paper in relation to the lower limb and whole-body exercise, given the functional relevance to locomotion, rehabilitation and activities of daily living. It is suggested that under some circumstances, alterations in the central and/or peripheral mechanisms of fatigue during exercise may be related to the sensations of chronic fatigue. As such, the neurophysiological correlates of exercise-induced fatigue are briefly examined in two clinical examples where chronic fatigue is common: cancer survivors and people with multiple sclerosis. This review highlights the relationship between objective measures of fatigability with whole-body exercise and perceptions of fatigue as a priority for future research, given the importance of exercise in relieving symptoms of chronic fatigue and/or overall disease management. As chronic fatigue is likely to be specific to the individual and unlikely to be due to a simple biological or psychosocial explanation, tailored exercise programmes are a potential target for therapeutic intervention.

Comparison between adaptive and fixed stimulus paired-pulse transcranial magnetic stimulation (ppTMS) in normal subjects

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Excitability indices from adaptive paired-pulse TMS correlated to those of fixed-stimulus ppTMS.

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Floor/ceiling effects in fixed-stimulus ppTMS excitability data did not occur with adaptive ppTMS.

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Adaptive ppTMS seems to be more sensitive in detecting changes in cortical inhibition.

Objectives

Paired-pulse TMS (ppTMS) examines cortical excitability but may require lengthy test procedures and fine tuning of stimulus parameters due to the inherent variability of the elicited motor evoked potentials (MEPs) and their tendency to exhibit a ‘ceiling/floor effects’ in inhibition trials. Aiming to overcome some of these limitations, we implemented an ‘adaptive’ ppTMS protocol and compared the obtained excitability indices with those from ‘conventional’ fixed-stimulus ppTMS.

Methods

Short- and long interval intracortical inhibition (SICI and LICI) as well as intracortical facilitation (ICF) were examined in 20 healthy subjects by adaptive ppTMS and fixed-stimulus ppTMS. The test stimulus intensity was either adapted to produce 500 μV MEPs (by a maximum likelihood strategy in combination with parameter estimation by sequential testing) or fixed to 120% of resting motor threshold (rMT). The conditioning stimulus was 80% rMT for SICI and ICF and 120% MT for LICI in both tests.

Results

There were significant (p < 0.05) intraindividual correlations between the two methods for all excitability measures. There was a clustering of SICI and LICI indices near maximal inhibition (‘ceiling effect’) in fixed-stimulus ppTMS which was not observed for adaptive SICI and LICI.

Conclusions

Adaptive ppTMS excitability data correlates to those acquired from fixed-stimulus ppTMS.

Significance

Adaptive ppTMS is easy to implement and may serve as a more sensitive method to detect changes in cortical inhibition than fixed stimulus ppTMS. Whether equally confident data are produced by less stimuli with our adaptive approach (as already confirmed for motor threshold estimation) remains to be explored.

High-intensity Interval Exercise Promotes Motor Cortex Disinhibition and Early Motor Skill Consolidation

Gamma-aminobutyric acid (GABA) inhibition shapes motor cortex output, gates synaptic plasticity in the form of long-term potentiation, and plays an important role in motor learning. Remarkably, recent studies have shown that acute cardiovascular exercise can improve motor memory, but the cortical mechanisms are not completely understood. We investigated whether an acute bout of lower-limb high-intensity interval (HIT) exercise could promote motor memory formation in humans through changes in cortical inhibition within the hand region of the primary motor cortex. We used TMS to assess the input–output relationship, along with inhibition involving GABAA and GABAB receptors. Measures were obtained before and after a 20-min session of HIT cycling (exercise group) or rest (control group). We then had the same participants learn a new visuomotor skill and perform a retention test 5 hr later in the absence of sleep. No differences were found in corticomotor excitability or GABAB inhibition; however, synaptic GABAA inhibition was significantly reduced for the exercise group but not the control group. HIT exercise was found to enhance motor skill consolidation. These findings link modification of GABA to improved motor memory consolidation after HIT exercise and suggest that the beneficial effects of exercise on consolidation might not be dependent on sleep.

Vascular Cognitive Impairment through the Looking Glass of Transcranial Magnetic Stimulation

In the last years, there has been a significant growth in the literature exploiting transcranial magnetic stimulation (TMS) with the aim at gaining further insights into the electrophysiological and neurochemical basis underlying vascular cognitive impairment (VCI). Overall, TMS points at enhanced brain cortical excitability and synaptic plasticity in VCI, especially in patients with overt dementia, and neurophysiological changes seem to correlate with disease process and progress. These findings have been interpreted as part of a glutamate-mediated compensatory effect in response to vascular lesions. Although a single TMS parameter owns low specificity, a panel of measures can support the VCI diagnosis, predict progression, and possibly identify early markers of "brain at risk" for future dementia, thus making VCI a potentially preventable cause of both vascular and degenerative dementia in late life. Moreover, TMS can be also exploited to select and evaluate the responders to specific drugs, as well as to become an innovative rehabilitative tool in the attempt to restore impaired neural plasticity. The present review provides a perspective of the different TMS techniques by further understanding the cortical electrophysiology and the role of distinctive neurotransmission pathways and networks involved in the pathogenesis and pathophysiology of VCI and its subtypes.

Physical activity levels determine exercise-induced changes in brain excitability

Emerging evidence suggests that regular physical activity can impact cortical function and facilitate plasticity. In the present study, we examined how physical activity levels influence corticospinal excitability and intracortical circuitry in motor cortex following a single session of moderate intensity aerobic exercise. We aimed to determine whether exercise-induced short-term plasticity differed between high versus low physically active individuals. Participants included twenty-eight young, healthy adults divided into two equal groups based on physical activity level determined by the International Physical Activity Questionnaire: low-to-moderate (LOW) and high (HIGH) physical activity. Transcranial magnetic stimulation was used to assess motor cortex excitability via motor evoked potential (MEP) recruitment curves for the first dorsal interosseous (FDI) muscle at rest (MEP_REST) and during tonic contraction (MEP_ACTIVE), short-interval intracortical inhibition (SICI) and facilitation (SICF), and intracortical facilitation (ICF). All dependent measures were obtained in the resting FDI muscle, with the exception of AMT and MEP_ACTIVE recruitment curves that were obtained during tonic FDI contraction. Dependent measures were acquired before and following moderate intensity aerobic exercise (20 mins, ~60% of the age-predicted maximal heart rate) performed on a recumbent cycle ergometer. Results indicate that MEP_REST recruitment curve amplitudes and area under the recruitment curve (AURC) were increased following exercise in the HIGH group only (p = 0.002 and p = 0.044, respectively). SICI and ICF were reduced following exercise irrespective of physical activity level (p = 0.007 and p = 0.04, respectively). MEP_ACTIVE recruitment curves and SICF were unaltered by exercise. These findings indicate that the propensity for exercise-induced plasticity is different in high versus low physically active individuals. Additionally, these data highlight that a single session of aerobic exercise can transiently reduce inhibition in the motor cortex regardless of physical activity level, potentially priming the system for plasticity induction.

Comparing GABA-dependent physiological measures of inhibition with proton magnetic resonance spectroscopy measurement of GABA using ultra-high-field MRI

Imbalances in glutamatergic (excitatory) and GABA (inhibitory) signalling within key brain networks are thought to underlie many brain and mental health disorders, and for this reason there is considerable interest in investigating how individual variability in localised concentrations of these molecules relate to brain disorders. Magnetic resonance spectroscopy (MRS) provides a reliable means of measuring, in vivo, concentrations of neurometabolites such as GABA, glutamate and glutamine that can be correlated with brain function and dysfunction. However, an issue of much debate is whether the GABA observed and measured using MRS represents the entire pool of GABA available for measurement (i.e., metabolic, intracellular, and extracellular) or is instead limited to only some portion of it. GABA function can also be investigated indirectly in humans through the use of non-invasive transcranial magnetic stimulation (TMS) techniques that can be used to measure cortical excitability and GABA-mediated physiological inhibition. To investigate this issue further we collected in a single session both types of measurement, i.e., TMS measures of cortical excitability and physiological inhibition and ultra-high-field (7 T) MRS measures of GABA, glutamate and glutamine, from the left sensorimotor cortex of the same group of right-handed individuals. We found that TMS and MRS measures were largely uncorrelated with one another, save for the plateau of the TMS IO curve that was negatively correlated with MRS-Glutamate (Glu) and intra-cortical facilitation (10ms ISI) that was positively associated with MRS-Glutamate concentration. These findings are consistent with the view that the GABA concentrations measured using the MRS largely represent pools of GABA that are linked to tonic rather than phasic inhibition and thus contribute to the inhibitory tone of a brain area rather than GABAergic synaptic transmission.

Cortical excitability correlates with seizure control and epilepsy duration in chronic epilepsy

Objective

Cortical excitability differs between treatment responders and nonresponders in new‐onset epilepsy. Moreover, during the first 3 years of epilepsy, cortical excitability becomes more abnormal in nonresponders but normalizes in responders. Here, we study chronic active epilepsy, to examine whether cortical excitability continues to evolve over time, in association with epilepsy duration and treatment response.

Methods

We studied 28 normal subjects, 28 patients with moderately controlled epilepsy (≤4 seizures per year) and 40 patients with poorly controlled epilepsy (≥20 or more seizures per year). Resting motor threshold (RMT), active motor threshold (AMT), short‐interval intracortical inhibition (SICI), intracortical facilitation (ICF) and cortical silent period (CSP) were measured, using transcranial magnetic stimulation (TMS). Disease and treatment covariates were collected (age at onset of epilepsy, epilepsy duration, number of drugs prescribed, total drug load, sodium channel drug load).

Results

RMT and AMT were higher in patients than in normal subjects; RMT and AMT were higher in poorly controlled than moderately controlled patients. ICF at 12 msec and 15 msec were lower in poorly controlled patients than in normal subjects. Long‐interval intracortical inhibition (LICI) at 50 msec was higher in poorly controlled compared to moderately controlled patients. These differences were not explained by antiepileptic drug (AED) treatment or duration of epilepsy. RMT and AMT increased with duration in the poorly controlled group, but did not increase with duration in the moderately controlled group.

Interpretation

Cortical excitability differs markedly between moderately controlled and poorly controlled patients with chronic epilepsy, not explained by disease or treatment variables. Moreover, the evolution of cortical excitability over time differs, becoming more abnormal in the poorly controlled group.

Preliminary Results on Long-Term Potentiation-Like Cortical Plasticity and Cholinergic Dysfunction After Miglustat Treatment in Niemann-Pick Disease Type C

Niemann-Pick disease type C (NPC) is a rare autosomal recessive lysosomal storage disorder, which manifests clinically with a wide range of neurological signs and symptoms. We assessed multiple neurological, neuropsychological and neurophysiological biomarkers using a transcranial magnetic stimulation (TMS) multi-paradigm approach in two patients with NPC carrying a homozygous mutation in the NPC1 gene, and in two heterozygous family members.We assessed short-interval intracortical inhibition (SICI), intracortical facilitation (ICF), long-interval intracortical inhibition (LICI), short-latency afferent inhibition (SAI) and long-term potentiation (LTP)-like cortical plasticity with a paired associative stimulation (PAS) protocol.Baseline SAI and LTP-like plasticity were impaired in both patients with NPC and in the symptomatic heterozygous NPC1 gene mutation carrier. Only a limited decrease in SICI and ICF was observed, while LICI was within normal range in all subjects at baseline. After 12 months of treatment with miglustat, a considerable improvement in SAI and LTP-like plasticity was observed in both patients with NPC. In conclusion, these biomarkers could help to confirm the diagnosis of NPC, and may give an indication of prognostic outcomes in pharmacological trials.

Changes in Cortical Plasticity in Relation to a History of Concussion during Adolescence

Adolescence and early adulthood is a critical period for neurophysiological development potentially characterized by an increased susceptibility to the long-term effects of traumatic brain injury. The current study investigated differences in motor cortical physiology and neuroplastic potential across a cohort of young adults with adolescent concussion history and those without. Transcranial magnetic stimulation (TMS) was used to assess motor evoked potential (MEP) amplitude, short-interval cortical inhibition (SICI) and intracortical facilitation (ICF) before and after intermittent theta burst stimulation (iTBS). Pre-iTBS, MEP amplitude, but not SICI or ICF, was greater in the concussion history group. Post-iTBS, the expected increase in MEP amplitude and ICF was tempered in the concussion history group. Change in SICI was variable within the concussion history group. Post hoc assessment revealed that SICI was significantly lower in individuals whose concussion was not diagnosed at the time of injury compared to both those without a concussion history or whose concussion was medically diagnosed. Concussive impacts during adolescence appear to result in a persistent reduction of the ability to modulate facilitatory motor networks. Failure to report/identify concussive impacts close to injury during adolescence also appears to produce persistent change in inhibitory networks. These findings highlight the potential long-term impact of adolescent concussion upon motor cortical physiology.

Parameter-Based Evaluation of Attentional Impairments in Schizophrenia and Their Modulation by Prefrontal Transcranial Direct Current Stimulation

BACKGROUND

Attentional dysfunctions constitute core cognitive symptoms in schizophrenia, but the precise underlying neurocognitive mechanisms remain to be elucidated.

METHODS

In this randomized, double-blind, sham-controlled study, we applied, for the first time, a theoretically grounded modeling approach based on Bundesen's Theory of Visual Attention (TVA) to (i) identify specific visual attentional parameters affected in schizophrenia and (ii) assess, as a proof of concept, the potential of single-dose anodal transcranial direct current stimulation (tDCS; 20 min, 2 mA) to the left dorsolateral prefrontal cortex to modulate these attentional parameters. To that end, attentional parameters were measured before (baseline), immediately after, and 24 h after the tDCS intervention in 20 schizophrenia patients and 20 healthy controls.

RESULTS

At baseline, analyses revealed significantly reduced visual processing speed and visual short-term memory storage capacity in schizophrenia. A significant stimulation condition × time point interaction in the schizophrenia patient group indicated improved processing speed at the follow-up session only in the sham condition (a practice effect), whereas performance remained stable across the three time points in patients receiving verum stimulation. In healthy controls, anodal tDCS did not result in a significant change in attentional performance.

CONCLUSION

With regard to question (i) above, these findings are indicative of a processing speed and short-term memory deficit as primary sources of attentional deficits in schizophrenia. With regard to question (ii), the efficacy of single-dose anodal tDCS for improving (speed aspects of visual) cognition, it appears that prefrontal tDCS (at the settings used in the present study), rather than ameliorating the processing speed deficit in schizophrenia, actually may interfere with practice-dependent improvements in the rate of visual information uptake. Such potentially unexpected effects of tDCS ought to be taken into consideration when discussing its applicability in psychiatric populations. The study was registered at http://apps.who.int/trialsearch/Trial2.aspx?TrialID=DRKS00011665.

Vascular Cognitive Impairment through the Looking Glass of Transcranial Magnetic Stimulation

In the last years, there has been a significant growth in the literature exploiting transcranial magnetic stimulation (TMS) with the aim at gaining further insights into the electrophysiological and neurochemical basis underlying vascular cognitive impairment (VCI). Overall, TMS points at enhanced brain cortical excitability and synaptic plasticity in VCI, especially in patients with overt dementia, and neurophysiological changes seem to correlate with disease process and progress. These findings have been interpreted as part of a glutamate-mediated compensatory effect in response to vascular lesions. Although a single TMS parameter owns low specificity, a panel of measures can support the VCI diagnosis, predict progression, and possibly identify early markers of "brain at risk" for future dementia, thus making VCI a potentially preventable cause of both vascular and degenerative dementia in late life. Moreover, TMS can be also exploited to select and evaluate the responders to specific drugs, as well as to become an innovative rehabilitative tool in the attempt to restore impaired neural plasticity. The present review provides a perspective of the different TMS techniques by further understanding the cortical electrophysiology and the role of distinctive neurotransmission pathways and networks involved in the pathogenesis and pathophysiology of VCI and its subtypes.

Cortical involvement in celiac disease before and after long-term gluten-free diet: A Transcranial Magnetic Stimulation study

OBJECTIVE

Transcranial Magnetic Stimulation in de novo patients with Celiac Disease previously revealed an imbalance in the excitability of cortical facilitatory and inhibitory circuits. After a median period of 16 months of gluten-free diet, a global increase of cortical excitability was reported, suggesting a glutamate-mediated compensation for disease progression. We have now evaluated cross-sectionally the changes of cortical excitability to TMS after a much longer gluten-free diet.

METHODS

Twenty patients on adequate gluten-free diet for a mean period of 8.35 years were enrolled and compared with 20 de novo patients and 20 healthy controls. Transcranial Magnetic Stimulation measures, recorded from the first dorsal interosseous muscle of the dominant hand, consisted of: resting motor threshold, cortical silent period, motor evoked potentials, central motor conduction time, mean short-latency intracortical inhibition and intracortical facilitation.

RESULTS

The cortical silent period was shorter in de novo patients, whereas in gluten-free diet participants it was similar to controls. The amplitude of motor responses was significantly smaller in all patients than in controls, regardless of the dietary regimen. Notwithstanding the diet, all patients exhibited a statistically significant decrease of mean short-latency intracortical inhibition and enhancement of intracortical facilitation with respect to controls; more intracortical facilitation in gluten-restricted compared to non-restricted patients was also observed. Neurological examination and celiac disease-related antibodies were negative.

CONCLUSIONS

In this new investigation, the length of dietary regimen was able to modulate the electrocortical changes in celiac disease. Nevertheless, an intracortical synaptic dysfunction, mostly involving excitatory and inhibitory interneurons within the motor cortex, may persist. The clinical significance of subtle neurophysiological changes in celiac disease needs to be further investigated.

Cortical excitability in tramadol dependent patients: A transcranial magnetic stimulation study

BACKGROUND

Addiction to tramadol, a widely used analgesic, is becoming increasingly common. Tramadol can also induce seizures even after a single clinical dose. We tested whether the epileptogenicity of tramadol was associated with any changes in cortical excitability and inhibitory transmission using transcranial magnetic stimulation (TMS).

METHODS

The study included 16 tramadol dependent patients and 15 age and sex matched healthy volunteers. Clinical evaluation was conducted using an addiction severity index. TMS assessment of excitability was conducted on the motor cortex since the response to each TMS pulse at that site is easily measured in terms of the amplitude of the twitches it evokes in contralateral muscles. Measures included resting and active motor threshold (RMT and AMT respectively), motor evoked potential (MEP) amplitude, cortical silent period (CSP) duration, transcallosal inhibition (TCI), and short interval intracortical inhibition and facilitation (SICI and ICF respectively). Urinary level of tramadol was measured immediately before assessing cortical excitability in each patient.

RESULTS

RMT and AMT were significantly lower, the duration of the CSP was shorter and SICI was reduced in patients compared with the control group. These findings are suggestive of increased neural excitability and reduced GABAergic inhibition following exposure to tramadol. Also there were negative correlations between the severity of tramadol dependence and a number of cortical excitability parameters (AMT, RMT, and CSP with P=0.002, 0.005, and 0.04 respectively).

CONCLUSIONS

The results provide evidence for hyperexcitability of the motor cortex coupled with inhibitory deficits in tramadol dependent patients.

An Exploratory Study of Spectroscopic Glutamatergic Correlates of Cortical Excitability in Depressed Adolescents

Introduction: Transcranial magnetic stimulation (TMS) research has suggested dysfunction in cortical glutamatergic systems in adolescent depression, while proton magnetic resonance spectroscopy (¹H-MRS) studies have demonstrated deficits in concentrations of glutamatergic metabolites in depressed individuals in several cortical regions, including the anterior cingulate cortex (ACC). However, few studies have combined TMS and MRS methods to examine relationships between glutamatergic neurochemistry and excitatory and inhibitory neural functions, and none have utilized TMS-MRS methodology in clinical populations or in youth. This exploratory study aimed to examine relationships between TMS measures of cortical excitability and inhibition and concentrations of glutamatergic metabolites as measured by ¹H-MRS in depressed adolescents. Methods: Twenty-four adolescents (aged 11-18 years) with depressive symptoms underwent TMS testing, which included measures of the resting motor threshold (RMT), cortical silent period (CSP), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF). Fourteen participants from the same sample also completed ¹H-MRS in a 3 T MRI scanner after TMS testing. Glutamate + glutamine (Glx) concentrations were measured in medial ACC and left primary motor cortex voxels with a TE-optimized PRESS sequence. Metabolite concentrations were corrected for cerebrospinal fluid (CSF) after tissue segmentation. Pearson product-moment and Spearman rank-order correlations were calculated to assess relationships between TMS measures and [Glx]. Results: In the left primary motor cortex voxel, [Glx] had a significant positive correlation with the RMT. In the medial ACC voxel, [Glx] had significant positive correlations with ICF at the 10-ms and 20-ms interstimulus intervals (ISIs). Conclusion: These preliminary data implicate glutamate in cortical excitatory processes measured by TMS. Limitations included small sample size, lack of healthy control comparators, possible age- and sex-related effects, and observational nature of the study. Further research aimed at examining the relationship between glutamatergic metabolite concentrations measured through MRS and the excitatory and inhibitory physiology measured through TMS is warranted. Combined TMS-MRS methods show promise for future investigations of the pathophysiology of depression in adults as well as in children and adolescents.

The side of chronic low back pain matters: evidence from the primary motor cortex excitability and the postural adjustments of multifidi muscles

Hemispheric lateralization of pain processing was reported with overactivation of the right frontal lobe. Specifically in chronic low back pain (CLBP), functional changes in the left primary motor cortex (M1) with impaired anticipatory postural activation (APA) of trunk muscles have been observed. Given the connections between frontal and M1 areas for motor planning, it is hypothesized that the pain side could differently influence M1 function and APA of paravertebral multifidus (MF) muscles. This study aimed at testing whether people with right- versus left-sided CLBP showed different M1 excitability and APA. Thirty-five individuals with lateralized CLBP (19 right-sided and 16 left-sided) and 13 pain-free subjects (normative values) were tested for the excitability of MF M1 area (active motor threshold-AMT) with transcranial magnetic stimulation and for the latency of MF APA during bilateral shoulder flexion and during unilateral hip extension in prone lying. In the right-sided CLBP group, the AMT of both M1 areas was lower than in the left-sided group and the pain-free subjects; the latency of MF APA was shorter in bilateral shoulder flexion and in the left hip extension tasks as compared to the left-sided group. In CLBP, an earlier MF APA was correlated with lower AMT in both tasks. People with right-sided CLBP presented with increased M1 excitability in both hemispheres and earlier MF APA. These results likely rely on cortical motor adaptation related to the tasks and axial muscles tested. Future studies should investigate whether CLBP side-related differences have a clinical impact, e.g. in diagnosis and intervention.

The role of white matter microstructure in inhibitory deficits in patients with schizophrenia

BACKGROUND

Inhibitory-excitatory (I-E) imbalance has increasingly been proposed as a fundamental mechanism giving rise to many schizophrenia-related pathophysiology. The integrity of I-E functions should require precise and rapid electrical signal transmission.

OBJECTIVE/HYPOTHESIS

We hypothesized that part of the I-E abnormality in schizophrenia may originate from their known abnormal white matter connectivity that may interfere the I-E functions.

METHODS

We test this using short-interval intracortical inhibition (SICI) vs. intracortical facilitation (ICF) which is a non-invasive measurement of I-E signaling. SICI-ICF from left motor cortex and white matter microstructure were assessed in schizophrenia patients and healthy controls.

RESULTS

Schizophrenia patients showed significantly reduced SICI but not ICF. White matter microstructure as measured by fraction anisotropy (FA) in diffusion tensor imaging had a significant effect on SICI in patients, such that weaker SICI was associated with lower FA in several white matter tracts, most strongly with left corona radiata (r = -0.68, p = 0.0002) that contains the fibers connecting with left motor cortex. Left corticospinal tract, which carries the motor fibers to peripheral muscular output, also showed significant correlation with SICI (r = -0.54, p = 0.005). Mediation analysis revealed that much of the schizophrenia disease effect on SICI can be accounted for by mediation through left corona radiata. SICI was also significantly associated with the performance of processing speed in patients.

CONCLUSION

This study demonstrated the importance of structural circuitry integrity in inhibitory signaling in schizophrenia, and encouraged modeling the I-E dysfunction in schizophrenia from a circuitry perspective.

Clinical Factors Underlying the Inter-individual Variability of the Resting Motor Threshold in Navigated Transcranial Magnetic Stimulation Motor Mapping

Correctly determining individual's resting motor threshold (rMT) is crucial for accurate and reliable mapping by navigated transcranial magnetic stimulation (nTMS), which is especially true for preoperative motor mapping in brain tumor patients. However, systematic data analysis on clinical factors underlying inter-individual rMT variability in neurosurgical motor mapping is sparse. The present study examined 14 preselected clinical factors that may underlie inter-individual rMT variability by performing multiple regression analysis (backward, followed by forward model comparisons) on the nTMS motor mapping data of 100 brain tumor patients. Data were collected from preoperative motor mapping of abductor pollicis brevis (APB), abductor digiti minimi (ADM), and flexor carpi radialis (FCR) muscle representations among these patients. While edema and age at exam in the ADM model only jointly reduced the unexplained variance significantly, the other factors kept in the ADM model (gender, antiepileptic drug intake, and motor deficit) and each of the factors kept in the APB and FCR models independently significantly reduced the unexplained variance. Hence, several clinical parameters contribute to inter-individual rMT variability and should be taken into account during initial and follow-up motor mappings. Thus, the present study adds basic evidence on inter-individual rMT variability, whereby some of the parameters are specific to brain tumor patients.

Fish Oil Prevents Lipopolysaccharide-Induced Depressive-Like Behavior by Inhibiting Neuroinflammation

Depression is associated with somatic immune changes, and neuroinflammation is now recognized as hallmark for depressive disorders. N-3 (or omega-3) polyunsaturated fatty acids (PUFAs) are well known to suppress neuroinflammation, reduce oxidative stress, and protect neuron from injury. We pretreated animals with fish oil and induced acute depression-like behaviors with systemic lipopolysaccharide (LPS) injection. The levels of cytokines and stress hormones were determined from plasma and different brain areas. The results showed that fish oil treatment prevent LPS-induce depressive behavior by suppression of neuroinflammation. LPS induced acute neuroinflammation in different brain regions, which were prevented in fish oil fed mice. However, neither LPS administration nor fish oil treatment has strong effect on stress hormone secretion in the hypothalamus and adrenal. Fish oil might provide a useful therapy against inflammation-associated depression.

Lamotrigine and levetiracetam exert a similar modulation of TMS-evoked EEG potentials

Objective

Antiepileptic drug (AED) treatment failures may occur because there is insufficient drug in the brain or because of a lack of relevant therapeutic response. Until now it has not been possible to measure these factors. It has been recently shown that the combination of transcranial magnetic stimulation and electroencephalography (TMS‐EEG) can measure the effects of drugs in healthy volunteers. TMS‐evoked EEG potentials (TEPs) comprise a series of positive and negative deflections that can be specifically modulated by drugs with a well‐known mode of action targeting inhibitory neurotransmission. Therefore, we hypothesized that TMS‐EEG can detect effects of two widely used AEDs, lamotrigine and levetiracetam, in healthy volunteers.

Methods

Fifteen healthy subjects participated in a pseudo‐randomized, placebo‐controlled, double‐blind, crossover design, using a single oral dose of lamotrigine (300 mg) and levetiracetam (3,000 mg). TEPs were recorded before and 120 min after drug intake, and the effects of drugs on the amplitudes of TEP components were statistically evaluated.

Results

A nonparametric cluster‐based permutation analysis of TEP amplitudes showed that AEDs both increased the amplitude of the negative potential at 45 msec after stimulation (N45) and suppressed the positive peak at 180 msec (P180). This is the first demonstration of AED‐induced modulation of TMS‐EEG measures.

Significance

Despite the different mechanism of action that lamotrigine and levetiracetam exert at the molecular level, both AEDs impact the TMS‐EEG response in a similar way. These TMS‐EEG fingerprints observed in healthy subjects are candidate predictive markers of treatment response in patients on monotherapy with lamotrigine and levetiracetam.

Cathodal transcranial direct-current stimulation for treatment of drug-resistant temporal lobe epilepsy: A pilot randomized controlled trial

Objective

To investigate the effect of cathodal transcranial direct‐current stimulation (c‐tDCS) on seizure frequency in patients with drug‐resistant temporal lobe epilepsy (TLE).

Method

Twenty‐nine patients with drug‐resistant TLE participated in this study. They were randomized to experimental or sham group. Twenty participants (experimental group) received within‐session repeated c‐tDCS intervention over the affected temporal lobe, and nine (sham group) received sham tDCS. Paired‐pulse transcranial magnetic stimulation was used to assess short interval intracortical inhibition (SICI) in primary motor cortex ipsilateral to the affected temporal lobe. SICI was measured from motor evoked potentials recorded from the contralateral first dorsal interosseous muscle. Adverse effects were monitored during and after each intervention in both groups. A seizure diary was given to each participant to complete for 4 weeks following the tDCS intervention. The mean response ratio was calculated from their seizure rates before and after the tDCS intervention.

Results

The experimental group showed a significant increase in SICI compared to the sham group (F = 10.3, p = 0.005). None of the participants reported side effects of moderate or severe degree. The mean response ratio in seizure frequency was −42.14% (standard deviation [SD] 35.93) for the experimental group and −16.98% (SD 52.41) for the sham group.

Significance

Results from this pilot study suggest that tDCS may be a safe and efficacious nonpharmacologic intervention for patients with drug‐resistant TLE. Further evaluation in larger double‐blind randomized controlled trials is warranted.

Pre-stimulus Alpha Oscillations and Inter-subject Variability of Motor Evoked Potentials in Single- and Paired-Pulse TMS Paradigms

Inter- and intra-subject variability of the motor evoked potentials (MEPs) to TMS is a well-known phenomenon. Although a possible link between this variability and ongoing brain oscillations was demonstrated, the results of the studies are not consistent with each other. Exploring this topic further is important since the modulation of MEPs provides unique possibility to relate oscillatory cortical phenomena to the state of the motor cortex probed with TMS. Given that alpha oscillations were shown to reflect cortical excitability, we hypothesized that their power and variability might explain the modulation of subject-specific MEPs to single- and paired-pulse TMS (spTMS, ppTMS, respectively). Neuronal activity was recorded with multichannel electroencephalogram. We used spTMS and two ppTMS conditions: intracortical facilitation (ICF) and short-interval intracortical inhibition (SICI). Spearman correlations were calculated within and across subjects between MEPs and the pre-stimulus power of alpha oscillations in low (8-10 Hz) and high (10-12 Hz) frequency bands. Coefficient of quartile variation was used to measure variability. Across-subject analysis revealed no difference in the pre-stimulus alpha power among the TMS conditions. However, the variability of high-alpha power in spTMS condition was larger than in the SICI condition. In ICF condition pre-stimulus high-alpha power variability correlated positively with MEP amplitude variability. No correlation has been observed between the pre-stimulus alpha power and MEP responses in any of the conditions. Our results show that the variability of the alpha oscillations can be more predictive of TMS effects than the commonly used power of oscillations and we provide further support for the dissociation of high and low-alpha bands in predicting responses produced by the stimulation of the motor cortex.

Differences in Motor Evoked Potentials Induced in Rats by Transcranial Magnetic Stimulation under Two Separate Anesthetics: Implications for Plasticity Studies

Repetitive transcranial magnetic stimulation (rTMS) is primarily used in humans to change the state of corticospinal excitability. To assess the efficacy of different rTMS stimulation protocols, motor evoked potentials (MEPs) are used as a readout due to their non-invasive nature. Stimulation of the motor cortex produces a response in a targeted muscle, and the amplitude of this twitch provides an indirect measure of the current state of the cortex. When applied to the motor cortex, rTMS can alter MEP amplitude, however, results are variable between participants and across studies. In addition, the mechanisms underlying any change and its locus are poorly understood. In order to better understand these effects, MEPs have been investigated in vivo in animal models, primarily in rats. One major difference in protocols between rats and humans is the use of general anesthesia in animal experiments. Anesthetics are known to affect plasticity-like mechanisms and so may contaminate the effects of an rTMS protocol. In the present study, we explored the effect of anesthetic on MEP amplitude, recorded before and after intermittent theta burst stimulation (iTBS), a patterned rTMS protocol with reported facilitatory effects. MEPs were assessed in the brachioradialis muscle of the upper forelimb under two anesthetics: a xylazine/zoletil combination and urethane. We found MEPs could be induced under both anesthetics, with no differences in the resting motor threshold or the average baseline amplitudes. However, MEPs were highly variable between animals under both anesthetics, with the xylazine/zoletil combination showing higher variability and most prominently a rise in amplitude across the baseline recording period. Interestingly, application of iTBS did not facilitate MEP amplitude under either anesthetic condition. Although it is important to underpin human application of TMS with mechanistic examination of effects in animals, caution must be taken when selecting an anesthetic and in interpreting results during prolonged TMS recording.

The neurophysiological effects of single-dose theophylline in patients with chronic stroke: A double-blind, placebo-controlled, randomized cross-over study

BACKGROUND

Reducing inhibitory neurotransmission with pharmacological agents is a potential approach for augmenting plasticity after stroke. Previous work in healthy subjects showed diminished intracortical inhibition after administration of theophylline.

OBJECTIVE

We assessed the effect of single-dose theophylline on intracortical and interhemispheric inhibition in patients with chronic stroke, in a double-blind, placebo-controlled, cross-over study.

METHODS

Eighteen subjects were randomly administered 300 mg of extended-release theophylline or placebo. Immediately and 5 hours following administration, transcranial magnetic stimulation was used to assess bihemispheric resting motor threshold, short-interval intracortical inhibition, long-interval intracortical inhibition, and interhemispheric inhibition. Adverse effects on cardiovascular, neurological, and motor performance outcomes were also surveilled. Change between morning and afternoon sessions were compared across conditions. One week later, patients underwent the same assessments after crossing over to the opposite experimental condition. Subjects and investigators were blinded to the experimental condition during data acquisition and analysis.

RESULTS

For both hemispheres, changes in intracortical or interhemispheric neurophysiology were comparable under theophylline and placebo conditions. Theophylline induced no adverse neurological, cardiovascular, or motor performance effects. For both conditions and hemipsheres, the baseline level of inhibition inversely correlated with its change between sessions: less baseline inhibition (i.e. disinhibition) was associated with a strengthening in inhibition over the day, and vice versa.

CONCLUSION

A single dose of theophylline is well-tolerated by patients with chronic stroke, but does not alter cortical excitability. The inverse relationship between baseline inhibition and its change suggests the existence of a homeostatic process. The lack of effect on cortical inhibition may be related to an insufficiently long exposure to theophylline, or to differential responsiveness of disinhibited neural circuitry in patients with stroke.

Oral supplementation with L-homoarginine in young volunteers

AIMS

Low blood concentrations of the naturally occurring amino acid L-homoarginine (L-hArg) are related to impaired cardiovascular outcome and mortality in humans and animals. L-hArg is a weak substrate of nitric oxide synthase and an inhibitor of arginases in vitro. The aim of our study was to obtain kinetic and dynamic data after oral L-hArg supplementation.

METHODS

In a double-blind, randomized, placebo-controlled crossover study, 20 young volunteers received 125 mg L-hArg once daily for 4 weeks. Kinetic parameters (C_max , T_max and AUC_0-24h ) were calculated after ingestion of single and multiple doses of oral supplementation as primary endpoint. Secondary endpoints that were evaluated were routine laboratory, L-arginine, asymmetric dimethylarginine (ADMA), pulse wave velocity (PWV), augmentation index (AIx), flow-mediated vasodilatation (FMD), corticospinal excitability, i.e. motor threshold (MT), and cortical excitability, i.e. intracortical inhibition (ICI) and facilitation (ICF).

RESULTS

One hour after ingestion (T_max ), L-hArg increased the baseline L-hArg plasma concentration (2.87 ± 0.91 μmol l^-1 , mean ± SD) by 8.74 ± 4.46 [95% confidence intervals 6.65; 10.9] and 17.3 ± 4.97 [14.9; 19.6] μmol l^-1 (C_max ), after single and multiple doses, respectively. Once-only and 4 weeks of supplementation resulted in AUCs_0-24h of 63.5 ± 28.8 [50.0; 76.9] and 225 ± 78.5 [188; 2624] μmol l^-1 *h, for single and multiple doses, respectively. Routine laboratory parameters, L-arginine, ADMA, PWV, AIx, FMD, MT, ICI and ICF did not change by L-hArg supplementation compared to baseline.

CONCLUSION

Once daily orally applied 125 mg L-hArg raises plasma L-hArg four- and sevenfold after single dose and 4 weeks of supplementation, respectively, and is safe and well tolerated in young volunteers.