EEG Artifact Removal in TMS Studies of Cortical Speech Areas

The combination of transcranial magnetic stimulation (TMS) and electroencephalography (EEG) is commonly applied for studying the effective connectivity of neuronal circuits. The stimulation excites neurons, and the resulting TMS-evoked potentials (TEPs) are recorded with EEG. A serious obstacle in this method is the generation of large muscle artifacts from scalp muscles, especially when frontolateral and temporoparietal, such as speech, areas are stimulated. Here, TMS–EEG data were processed with the signal-space projection and source-informed reconstruction (SSP–SIR) artifact-removal methods to suppress these artifacts. SSP–SIR suppressed muscle artifacts according to the difference in frequency contents of neuronal signals and muscle activity. The effectiveness of SSP–SIR in rejecting muscle artifacts and the degree of excessive attenuation of brain EEG signals were investigated by comparing the processed versions of the recorded TMS–EEG data with simulated data. The calculated individual lead-field matrix describing how the brain signals spread on the cortex were used as simulated data. We conclude that SSP–SIR was effective in suppressing artifacts also when frontolateral and temporoparietal cortical sites were stimulated, but it may have suppressed also the brain signals near the stimulation site. Effective connectivity originating from the speech-related areas may be studied even when speech areas are stimulated at least on the contralateral hemisphere where the signals were not suppressed that much.Peer reviewe

Coherent neural oscillations predict future motor and language improvement after stroke

See Ward (doi:10.1093/brain/awv265) for a scientific commentary on this article. Disrupted network interactions are associated with neurological deficits after stroke, but the significance of these interactions for post-stroke plasticity is less clear. Nicolo et al. show that language and motor improvement is associated with synchronisation of oscillations. Specific frequencies are preferred for recovery-related interactions, dependent on hemisphere and post-stroke interva

A Multimodal Imaging- and Stimulation-based Method of Evaluating Connectivity-related Brain Excitability in Patients with Epilepsy

Resting-state functional connectivity MRI (rs-fcMRI) is a technique that identifies connectivity between different brain regions based on correlations over time in the blood-oxygenation level dependent signal. rs-fcMRI has been applied extensively to identify abnormalities in brain connectivity in different neurologic and psychiatric diseases. However, the relationship among rs-fcMRI connectivity abnormalities, brain electrophysiology and disease state is unknown, in part because the causal significance of alterations in functional connectivity in disease pathophysiology has not been established. Transcranial Magnetic Stimulation (TMS) is a technique that uses electromagnetic induction to noninvasively produce focal changes in cortical activity. When combined with electroencephalography (EEG), TMS can be used to assess the brain's response to external perturbations. Here we provide a protocol for combining rs-fcMRI, TMS and EEG to assess the physiologic significance of alterations in functional connectivity in patients with neuropsychiatric disease. We provide representative results from a previously published study in which rs-fcMRI was used to identify regions with abnormal connectivity in patients with epilepsy due to a malformation of cortical development, periventricular nodular heterotopia (PNH). Stimulation in patients with epilepsy resulted in abnormal TMS-evoked EEG activity relative to stimulation of the same sites in matched healthy control patients, with an abnormal increase in the late component of the TMS-evoked potential, consistent with cortical hyperexcitability. This abnormality was specific to regions with abnormal resting-state functional connectivity. Electrical source analysis in a subject with previously recorded seizures demonstrated that the origin of the abnormal TMS-evoked activity co-localized with the seizure-onset zone, suggesting the presence of an epileptogenic circuit. These results demonstrate how rs-fcMRI, TMS and EEG can be utilized together to identify and understand the physiological significance of abnormal brain connectivity in human diseases

Unravelling the effect of experimental pain on the corticomotor system using transcranial magnetic stimulation and electroencephalography.

Abstract : The interaction between pain and the motor system is well-known, with past studies showing that pain can alter corticomotor excitability and have deleterious effects on motor learning. The aim of this study was to better understand the cortical mechanisms underlying the interaction between pain and the motor system. Experimental pain was induced on 19 young and healthy participants using capsaicin cream, applied on the middle volar part of the left forearm. The effect of pain on brain activity and on the corticomotor system was assessed with electroencephalography (EEG) and transcranial magnetic stimulation (TMS), respectively. Compared to baseline, resting state brain activity significantly increased after capsaicin application in the central cuneus (theta frequency), left dorsolateral prefrontal cortex (alpha frequency), and left cuneus and right insula (beta frequency). A pain-evoked increase in the right primary motor cortex (M1) activity was also observed (beta frequency), but only among participants who showed a reduction in corticospinal output (as depicted by TMS recruitment curves). These participants further showed greater beta M1-cuneus connectivity than the other participants. These findings indicate that pain-evoked increases in M1 beta power are intimately tied to changes in the corticospinal system, and provide evidence that beta M1-cuneus connectivity is related to the corticomotor alterations induced by pain. The differential pattern of response observed in our participants suggest that the effect of pain on the motor system is variable from on individual to another; an observation that could have important clinical implications for rehabilitation professionals working with pain patients

TMS- EEG Signatures of GABAergic Neurotransmission in the Human Cortex

Combining transcranial magnetic stimulation (TMS) and electroencephalography (EEG) constitutes a powerful tool to directly assess human cortical excitability and connectivity. TMS of the primary motor cortex elicits a sequence of TMS-evoked EEG potentials (TEPs). It is thought that inhibitory neurotransmission through GABA-A receptors (GABAAR) modulates early TEPs (<50 ms after TMS), whereas GABA-B receptors (GABABR) play a role for later TEPs (at ∼100 ms after TMS). However, the physiological underpinnings of TEPs have not been clearly elucidated yet. Here, we studied the role of GABAA/B-ergic neurotransmission for TEPs in healthy subjects using a pharmaco-TMS-EEG approach. In Experiment 1, we tested the effects of a single oral dose of alprazolam (a classical benzodiazepine acting as allosteric-positive modulator at α1, α2, α3, and α5 subunit-containing GABAARs) and zolpidem (a positive modulator mainly at the α1 GABAAR) in a double-blind, placebo-controlled, crossover study. In Experiment 2, we tested the influence of baclofen (a GABABR agonist) and diazepam (a classical benzodiazepine) versus placebo on TEPs. Alprazolam and diazepam increased the amplitude of the negative potential at 45 ms after stimulation (N45) and decreased the negative component at 100 ms (N100), whereas zolpidem increased the N45 only. In contrast, baclofen specifically increased the N100 amplitude. These results provide strong evidence that the N45 represents activity of α1-subunit-containing GABAARs, whereas the N100 represents activity of GABABRs. Findings open a novel window of opportunity to study alteration of GABAA-/GABAB-related inhibition in disorders, such as epilepsy or schizophrenia

Mechanisms and therapeutic applications of electromagnetic therapy in Parkinson's disease

© 2015 Vadalà et al. Electromagnetic therapy is a non-invasive and safe approach for the management of several pathological conditions including neurodegenerative diseases. Parkinson's disease is a neurodegenerative pathology caused by abnormal degeneration of dopaminergic neurons in the ventral tegmental area and substantia nigra pars compacta in the midbrain resulting in damage to the basal ganglia. Electromagnetic therapy has been extensively used in the clinical setting in the form of transcranial magnetic stimulation, repetitive transcranial magnetic stimulation, high-frequency transcranial magnetic stimulation and pulsed electromagnetic field therapy which can also be used in the domestic setting. In this review, we discuss the mechanisms and therapeutic applications of electromagnetic therapy to alleviate motor and non-motor deficits that characterize Parkinson's disease

motor cortical inhibition during concurrent action execution and action observation

Abstract Action Execution (AE) and Action Observation (AO) share an extended cortical network of activated areas. During coordinative action these processes also overlap in time, potentially giving rise to behavioral interference effects. The neurophysiological mechanisms subtending the interaction between concurrent AE and AO are substantially unknown. To assess the effect of AO on observer's corticomotor drive, we run one electromyography (EMG) and three Transcranial Magnetic Stimulation (TMS) studies. Participants were requested to maintain a steady hand opening or closing posture while observing the same or a different action (hand opening and closing in the main TMS study). By measuring Cortical Silent Periods (CSP), an index of GABAB-mediated corticospinal inhibitory strength, we show a selective reduction of inhibitory motor drive for mismatching AE-AO pairs. The last two TMS experiments, show that this mismatch is computed according to a muscle-level agonist-antagonist representation. Combined, our results suggest that corticospinal inhibition may be the central neurophysiological mechanism by which one's own motor execution is adapted to the contextual visual cues provided by other's actions

No hemispheric asymmetries in long-acting cortical inhibition in young adults using

It is well established that fine motor control is asymmetrical: this is known as handedness. Handedness is controlled by cortical motor processes, including long-acting inhibition. Long-acting cortical inhibition is asymmetric between the left and right hemispheres. Therefore, asymmetries of handedness may be attributable to asymmetries in long-acting inhibition. Asymmetries of long-acting inhibition have previously been tested using a measure of corticospinal excitability, but have not been previously investigated using combined transcranial magnetic stimulation (TMS) and electroencephalography (TMS-EEG), a measure of cortical inhibition not influenced by spinal excitability. This study aimed to determine if long-acting cortical inhibition is asymmetrical using TMS-EEG and to investigate any associations of asymmetrical inhibition with fine motor control. In young adults (n = 14) fine motor control was measured using the Purdue Pegboard task. EEG was used to record the cortical responses to paired-pulse, single-pulse and sham TMS. Results showed no asymmetry in fine motor control using the Purdue Pegboard task and no asymmetries of long-acting inhibition between the left and right hemispheres using TMS-EEG. There was no significant difference between the response to sham and single-pulse stimulation, suggesting that the cortical response to TMS was influenced by auditory or physiological artefacts. There were no associations between TEPs of long-acting inhibition and fine motor control. Overall, there were no conclusive results whether asymmetries of long-acting inhibition are replicable using TMS-EEG. Further investigation of the importance of LICI as a neural underpinning of handedness is important to better understanding the workings of handedness and fine motor control

THE ROLE OF PLASTICITY IN COGNITION: A TMS-EEG STUDY

This item is only available electronically.Past studies have implicated a relationship between the Dorsolateral Prefrontal Cortex (DLPFC), and working memory and cognitive flexibility performance as measured via the N back and Trail Making tasks. It stands to reason that inducing plastic change to increase excitability of the DLPFC should result in improved performance on these tasks. This study used a 2 x 2 within groups single-blinded design with fourteen healthy participants (19 to 29 years old) attending two sessions, receiving iTBS in one, and sham in the other, investigating whether intermittent theta burst stimulation (iTBS) increased excitability of the DLPFC, and improved task performance. Cortical excitability was measured with TMS-evoked potentials (TEPs). Wilcoxon tests were used to determine the effect of iTBS on TEPs and psychometric performance, and the relationships between dependent variables were investigated using correlational analyses. Results show nonsignificant mild increases in 2-Back and Trail Making A tasks following iTBS relative to sham, and moderate correlations between changes in task performance and iTBS induced TEP changes. These findings go against previous research that support the iTBS to modulate TEP amplitudes, but are consistent with literature only finding mild effects of rTMS on improving working memory and cognitive flexibility.Thesis (B.PsychSc(Hons)) -- University of Adelaide, School of Psychology, 201