Effects Of cTBS Research Articles

Motor network connectivity predicts neuroplastic response following theta burst stimulation in healthy adults.

A patterned repetitive transcranial magnetic stimulation protocol, known as continuous theta burst stimulation (cTBS), can suppress corticospinal excitability via mechanisms that appear similar to long-term depression synaptic plasticity. Despite much potential, this technique is currently limited by substantial response variability. The purpose of this study was to investigate whether baseline resting state functional connectivity is a determinant of response to cTBS. Eighteen healthy young adults participated in up to three experimental sessions. Single-pulse transcranial magnetic stimulation was used to quantify change in corticospinal excitability following cTBS. Three minutes of resting electroencephalographic activity was recorded, and functional connectivity was estimated using the debiased weighted phase lag index across different frequency bands. Partial least squares regression identified models of connectivity between a seed region (C3) and the whole scalp that maximally accounted for variance in cTBS responses. There was no group-level effect of a single cTBS train or spaced cTBS trains on corticospinal excitability (p = 0.092). A low beta frequency band model of connectivity accounted for the largest proportion of variance in spaced cTBS response (R2 = 0.50). Based on the low beta frequency model, a-priori regions of interest were identified and predicted 39% of variance in response to spaced cTBS at a subsequent session. Importantly, weaker connectivity between the seed electrode (C3) and a cluster approximating a frontocentral region was associated with greater spaced cTBS response (p = 0.02). It appears M1-frontocentral networks may have an important role in determining the effects of cTBS on corticospinal excitability.

The role of the posterior parietal cortex on cognition: An exploratory study

Theta burst stimulation (TBS) is a form of repetitive transcranial magnetic stimulation (rTMS) that can be used to increase (intermittent TBS) or reduce (continuous TBS) cortical excitability. The current study provides a preliminary report of the effects of iTBS and cTBS in healthy young adults, to investigate the causal role of the posterior parietal cortex (PPC) during the performance of four cognitive functions: attention, inhibition, sequence learning and working memory. A 2 × 2 repeated measures design was incorporated using hemisphere (left/right) and TBS type (iTBS/cTBS) as the independent variables. 20 participants performed the cognitive tasks both before and after TBS stimulation in 4 counterbalanced experimental sessions (left cTBS, right cTBS, left iTBS and right iTBS) spaced 1 week apart. No change in performance was identified for the attentional cueing task after TBS stimulation, however TBS applied to the left PPC decreased reaction time when inhibiting a reflexive response. The sequence learning task revealed differential effects for encoding of the sequence versus the learnt items. cTBS on the right hemisphere resulted in faster responses to learnt sequences, and iTBS on the right hemisphere reduced reaction times during the initial encoding of the sequence. The reaction times in the 2-back working memory task were increased when TBS stimulation was applied to the right hemisphere. Results reveal clear differential effects for tasks explored, and more specifically where TBS stimulation on right PPC could provide a potential for further investigation into improving oculomotor learning by inducing plasticity-like mechanisms in the brain.

Behavioral effects of continuous theta-burst stimulation in macaque parietal cortex

The neural mechanisms underlying the effects of continuous Theta-Burst Stimulation (cTBS) in humans are poorly understood. Animal studies can clarify the effects of cTBS on individual neurons, but behavioral evidence is necessary to demonstrate the validity of the animal model. We investigated the behavioral effect of cTBS applied over parietal cortex in rhesus monkeys performing a visually-guided grasping task with two differently sized objects, which required either a power grip or a pad-to-side grip. We used Fitts’ law, predicting shorter grasping times (GT) for large compared to small objects, to investigate cTBS effects on two different grip types. cTBS induced long-lasting object-specific and dose-dependent changes in GT that remained present for up to two hours. High-intensity cTBS increased GTs for a power grip, but shortened GTs for a pad-to-side grip. Thus, high-intensity stimulation strongly reduced the natural GT difference between objects (i.e. the Fitts’ law effect). In contrast, low-intensity cTBS induced the opposite effects on GT. Modifying the coil orientation from the standard 45-degree to a 30-degree angle induced opposite cTBS effects on GT. These findings represent behavioral evidence for the validity of the nonhuman primate model to study the neural underpinnings of non-invasive brain stimulation.

Evidence for a Window of Enhanced Plasticity in the Human Motor Cortex Following Ischemic Stroke

Background In preclinical models, behavioral training early after stroke produces larger gains compared with delayed training. The effects are thought to be mediated by increased and widespread reorganization of synaptic connections in the brain. It is viewed as a period of spontaneous biological recovery during which synaptic plasticity is increased. Objective To look for evidence of a similar change in synaptic plasticity in the human brain in the weeks and months after ischemic stroke. Methods We used continuous theta burst stimulation (cTBS) to activate synapses repeatedly in the motor cortex. This initiates early stages of synaptic plasticity that temporarily reduces cortical excitability and motor-evoked potential amplitude. Thus, the greater the effect of cTBS on the motor-evoked potential, the greater the inferred level of synaptic plasticity. Data were collected from separate cohorts (Australia and UK). In each cohort, serial measurements were made in the weeks to months following stroke. Data were obtained for the ipsilesional motor cortex in 31 stroke survivors (Australia, 66.6 ± 17.8 years) over 12 months and the contralesional motor cortex in 29 stroke survivors (UK, 68.2 ± 9.8 years) over 6 months. Results Depression of cortical excitability by cTBS was most prominent shortly after stroke in the contralesional hemisphere and diminished over subsequent sessions (P = .030). cTBS response did not differ across the 12-month follow-up period in the ipsilesional hemisphere (P = .903). Conclusions Our results provide the first neurophysiological evidence consistent with a period of enhanced synaptic plasticity in the human brain after stroke. Behavioral training given during this period may be especially effective in supporting poststroke recovery.

Effects of cTBS on the Frequency-Following Response and Other Auditory Evoked Potentials.

The frequency-following response (FFR) is an auditory evoked potential (AEP) that follows the periodic characteristics of a sound. Despite being a widely studied biosignal in auditory neuroscience, the neural underpinnings of the FFR are still unclear. Traditionally, FFR was associated with subcortical activity, but recent evidence suggested cortical contributions which may be dependent on the stimulus frequency. We combined electroencephalography (EEG) with an inhibitory transcranial magnetic stimulation protocol, the continuous theta burst stimulation (cTBS), to disentangle the cortical contribution to the FFR elicited to stimuli of high and low frequency. We recorded FFR to the syllable /ba/ at two fundamental frequencies (Low: 113 Hz; High: 317 Hz) in healthy participants. FFR, cortical potentials, and auditory brainstem response (ABR) were recorded before and after real and sham cTBS in the right primary auditory cortex. Results showed that cTBS did not produce a significant change in the FFR recorded, in any of the frequencies. No effect was observed in the ABR and cortical potentials, despite the latter known contributions from the auditory cortex. Possible reasons behind the negative results include compensatory mechanisms from the non-targeted areas, intraindividual variability of the cTBS effectiveness, and the particular location of our target area, the primary auditory cortex.

Time-course of pain threshold after continuous theta burst stimulation of primary somatosensory cortex in pain-free subjects

Primary somatosensory cortex (S1) is involved in pain processing and thus its suppression using neuromodulatory techniques such as continuous theta burst stimulation (cTBS) might be a potential pain management strategy in patients with neuropathic pain. cTBS over S1 is known to elevate pain threshold in young adults. However, the time course of this after-effect is unknown. Furthermore, the effect of cTBS over S1 on pain threshold might be confounded by changes in the excitability of primary motor cortex (M1), an area known to be involved in pain processing, due to spread of current. Therefore, whether S1 plays a role in pain processing independent of M1 also remains unknown. The corticospinal excitability (CSE) can provide a measure of M1 excitability because cTBS over M1 is known to reduce CSE. Here, we studied the time-course of the effects of MRI-guided cTBS over S1 on electrical pain threshold (EPT) and CSE. Ten healthy young adults received cTBS over S1 and sham stimulation in counterbalanced sessions at least 5 days apart. EPT and CSE were recorded before and following cTBS over S1. We assessed each measure once before stimulation and then every 10 min starting immediately after stimulation until 40 min. cTBS over S1 elevated EPT compared to sham stimulation with the after-effect lasting for 40 min. We observed no change in CSE following cTBS and sham stimulation. Our findings suggest that cTBS over S1 can elevate EPT for 40 min without altering M1 excitability.

Targeted Stimulation of Human Orbitofrontal Networks Disrupts Outcome-Guided Behavior.

Outcome-guided behavior requires knowledge about the current value of expected outcomes. Such behavior can be isolated in the reinforcer devaluation task, which assesses the ability to infer the current value of specific rewards after devaluation. Animal lesion studies demonstrate that orbitofrontal cortex (OFC) is necessary for normal behavior in this task, but a causal role for human OFC in outcome-guided behavior has not been established. Here, we used sham-controlled, non-invasive, continuous theta-burst stimulation (cTBS) to temporarily disrupt human OFC network activity by stimulating a site in the lateral prefrontal cortex that is strongly connected to OFC prior to devaluation of food odor rewards. Subjects in the sham group appropriately avoided Pavlovian cues associated with devalued food odors. However, subjects in the stimulation group persistently chose those cues, even though devaluation of food odors themselves was unaffected by cTBS. This behavioral impairment was mirrored in changes in resting-state functional magnetic resonance imaging (rs-fMRI) activity such that subjects in the stimulation group exhibited reduced OFC network connectivity after cTBS, and the magnitude of this reduction was correlated with choices after devaluation. These findings demonstrate the feasibility of indirectly targeting the human OFC with non-invasive cTBS and indicate that OFC is specifically required for inferring the value of expected outcomes.

Phasic GABA signaling mediates the protective effects of cTBS against cerebral ischemia in mice

Continuous theta burst stimulation (cTBS) has been widely recognized as a therapeutic treatment for ischemic stroke, but the underlying mechanism is still elusive. Here, we investigated the protective effects of cTBS in the posterior parietal cortex during the chronic phase of stroke in the photothrombotic ischemic model. Infarction volume and neuron excitability in the peri-infarct area were assessed using immunohistochemistry and whole-cell patch-clamp. Spatial cognitive function was measured using the Morris water maze. Gamma-Amino butyric acid (GABA) interneurons were responsive to cTBS, and cTBS induced elevated phasic inhibition rather than tonic inhibition. Given that GABA-A-mediated phasic inhibition was elevated during the chronic phase of ischemic stroke for 30 days and was beneficial for stroke recovery, we investigated the therapeutic potential of cTBS in promoting functional recovery and found that the elevated phasic inhibition by cTBS improved spatial cognitive function in the photothrombotic stroke mouse model with induction in the posterior parietal cortex. Our study indicates the mechanism by which cTBS may modify the excitability of the brain cortex and provides novel insight into the potential of cTBS to protect against neuronal dysfunction in ischemic stroke.

Continuous theta burst stimulation provides neuroprotection by accelerating local cerebral blood flow and inhibiting inflammation in a mouse model of acute ischemic stroke

Acute ischemic stroke is a leading cause of disability with limited therapeutic options. Continuous theta burst stimulation (cTBS) has recently been shown to be a promising noninvasive therapeutic strategy for neuroprotection in ischemic stroke patients. Here, we investigated the protective effects of cTBS following acute infarction using a photothrombotic stroke (PTS) model in the right posterior parietal cortex (PPC) of C57BL/6 mice. Treatment with cTBS resulted in a reduction in the volume of the infarct region and significantly increased vascular diameter and blood flow velocity in peri-infarct region, as well as decreased the numbers of calcium binding adapter molecule 1 (Iba-1)-positive microglia and glial fibrillary acidic protein (GFAP)-positive astrocytes. Moreover, the number of CD16/32 positive microglia was decreased, whereas the number of CD206 positive microglia was increased. In addition, performance in a water maze task was significantly improved. These results indicated that cTBS protected against PPC infarct region, leading to an improvement in spatial cognitive function, possibly as a result of changes to cerebral microvascular function and inflammatory responses.

A differential role for the posterior cerebellum in the adaptive control of convergence eye movements

IntroductionThe vergence oculomotor system possesses two robust adaptive mechanisms; a fast “dynamic” and a slow “tonic” system that are both vital for single, clear and comfortable binocular vision. The neural substrates underlying these vergence adaptive mechanisms in humans is unclear. MethodsWe investigated the role of the posterior cerebellum in convergence adaptation using inhibitory continuous theta-burst repetitive transcranial magnetic stimulation (cTBS) within a double-blind, sham controlled design while eye movements were recorded at 250hz via infrared oculography. ResultsIn a preliminary experiment we validated our stimulation protocols by reproducing results from previous work on saccadic adaptation during the classic double-step adaptive shortening paradigm. Following this, across a series of three separate experiments we observed a clear dissociation in the effect of cTBS on convergence adaptation. Dynamic adaptation was substantially reduced while tonic adaptation was unaffected. Baseline dynamic fusional vergence response were also unaffected by stimulation. ConclusionsThese results indicate a differential role for the posterior cerebellum in the adaptive control of convergence eye movements and provide initial evidence that repetitive transcranial magnetic stimulation is a viable tool to investigate the neurophysiology of vergence control. The results are discussed in the context of the current models of implicit motor adaptation of vergence and their application to clinical populations and technology design in virtual and augmented head mounted display architectures. Significance statementThe cerebellum plays a critical role in the adaptive control of motor systems. Vergence eye movements shift our gaze in depth allowing us to see in 3D and exhibit two distinct adaptive mechanisms that are engaged under a range of conditions including reading, wearing head-mounted displays and using a new spectacle prescription. It is unclear what role the cerebellum plays in these adaptive mechanisms. To answer this, we temporarily disrupted the function of the posterior cerebellum using non-invasive brain stimulation and report impairment of only one adaptive mechanism, providing evidence for neural compartmentalization. The results have implications for vergence control models and applications to comfort and experience studies in head-mounted displays and the rehabilitation of clinical populations exhibiting vergence dysfunctions.

Transcranial Magnetic Stimulation-Electroencephalography Measures of Cortical Neuroplasticity Are Altered after Mild Traumatic Brain Injury.

While the potential long-term side effects of mild traumatic brain injury (mTBI) are becoming increasingly recognized, the associated neurophysiological mechanisms remain poorly understood. However, changes in cortical inhibitory function and neuroplasticity have been suggested as possible contributing factors. The current study applied transcranial magnetic stimulation (TMS) in conjunction with electroencephalography (combined TMS-EEG) to investigate further the effects of mTBI on these processes. In 17 patients with a history of mTBI and 15 healthy control subjects with no mTBI history, paired-pulse TMS-EEG measures of short- (SICI) and long-interval intracortical inhibition (LICI) were used to assess intracortical inhibitory function. Single-pulse TMS-EEG was used to assess neuroplastic changes in cortical excitability after application of continuous theta burst stimulation (cTBS, a plasticity inducing TMS paradigm). Inhibition of the TMS-evoked EEG potential after application of SICI and LICI was not different between groups. In contrast, the inhibitory effects of cTBS on both P30 (p < 0.05) and N45 (p = 0.04) TEP components was significantly increased in patients, with the modulation of N45 in patients significantly related to the time since injury (p = 0.04). While these results provide further evidence that inhibitory circuits involving γ-aminobutyric acid (GABA) are modified after mTBI, they place greater emphasis on the plasticity of inhibitory networks involving the GABAA receptor subtype.

State-Dependent Effects of Ventromedial Prefrontal Cortex Continuous Thetaburst Stimulation on Cocaine Cue Reactivity in Chronic Cocaine Users.

Cue-induced craving is a significant barrier to obtaining abstinence from cocaine. Neuroimaging research has shown that cocaine cue exposure evokes elevated activity in a network of frontal-striatal brain regions involved in drug craving and drug seeking. Prior research from our laboratory has demonstrated that when targeted at the medial prefrontal cortex (mPFC), continuous theta burst stimulation (cTBS), an inhibitory form of non-invasive brain stimulation, can decrease drug cue-related activity in the striatum in cocaine users and alcohol users. However, it is known that there are individual differences in response to repetitive transcranial magnetic stimulation (rTMS), with some individuals being responders and others non-responders. There is some evidence that state-dependent effects influence response to rTMS, with baseline neural state predicting rTMS treatment outcomes. In this single-blind, active sham-controlled crossover study, we assess the striatum as a biomarker of treatment response by determining if baseline drug cue reactivity in the striatum influences striatal response to mPFC cTBS. The brain response to cocaine cues was measured in 19 cocaine-dependent individuals immediately before and after real and sham cTBS (110% resting motor threshold, 3600 total pulses). Group independent component analysis (ICA) revealed a prominent striatum network comprised of bilateral caudate, putamen, and nucleus accumbens, which was modulated by the cocaine cue reactivity task. Baseline drug cue reactivity in this striatal network was inversely related to change in striatum reactivity after real (vs. sham) cTBS treatment (ρ = -.79; p < .001; R 2 Adj = .58). Specifically, individuals with a high striatal response to cocaine cues at baseline had significantly attenuated striatal activity after real but not sham cTBS (t 9 = -3.76; p ≤ .005). These data demonstrate that the effects of mPFC cTBS on the neural circuitry of craving are not uniform and may depend on an individual’s baseline frontal-striatal reactivity to cues. This underscores the importance of assessing individual variability as we develop brain stimulation treatments for addiction.

Contextual cues as modifiers of cTBS effects on indulgent eating

BackgroundPrior studies have found that continuous theta burst stimulation (cTBS) targeting the left dlPFC results in reliable increases in consumption of calorie-dense food items. However, it is not known to what extent such effects are modified by cues in the immediate eating environment. Tempting environments (i.e., those saturated with appetitive eating cues) may lead to more reliance on cognitive control networks involving the dlPFC, thereby enhancing cTBS effects on indulgent eating. Objective/HypothesisThe objective was to examine the extent to which cTBS effects on indulgent eating would be modified by contextual cues. It was hypothesized that cTBS effects would be stronger in the presence of facilitating cues. MethodsUsing a single-blinded between-subjects factorial design, 107 TMS-naïve adults were randomly assigned to one of four conditions: 1) active cTBS + facilitating cues, 2) sham cTBS + facilitating cues, 3) active cTBS + inhibiting cues, 4) sham cTBS + inhibiting cues. Following stimulation participants completed a flanker paradigm and a taste test during which quantity consumed was assessed surreptitiously. ResultsFindings revealed a significant interaction between stimulation and cue type (F(1,102) = 6.235, p = .014), such that cTBS resulted in increased food consumption (compared to sham) in the presence of the facilitating cue but not in the presence of the inhibiting cue. Moderated mediational analyses showed selective mediation of cTBS effects on consumption through cTBS attenuation of flanker interference scores. ConclusionsThe effects of cTBS on indulgent eating are strengthened in the presence of facilitating cues. Methodologically speaking, facilitating cues may be a functional prerequisite for exploring cTBS effects on eating in the laboratory. Substantively, the findings also suggest that facilitating cues in the eating environment may amplify counter-intentional food indulgence in everyday life via cognitive control failure.

Continuous theta burst stimulation over right pars triangularis facilitates naming abilities in chronic post-stroke aphasia by enhancing phonological access

BackgroundRepetitive transcranial magnetic stimulation (rTMS) has been used experimentally to facilitate naming abilities in individuals with chronic post-stroke aphasia. However, little is known about how rTMS confers clinical improvement, hampering its therapeutic value. The present study investigated the characteristics of naming failure that improve following administration of continuous theta burst stimulation (cTBS)—an inhibitory form of rTMS—to the right pars triangularis (rPTr) in persons with chronic aphasia. MethodsEleven participants with chronic aphasia following left hemisphere stroke named pictures prior to and immediately following cTBS of the rPTr and a control site (vertex) in separate sessions. Prior to stimulation, we obtained two baseline measurements of picture naming ability to determine the extent and type (i.e., phonological vs. semantic) of naming impairment. Items presented for naming during stimulation were those that were named incorrectly in one or both of the baseline sessions (i.e., inconsistent vs. wrong items, respectively). Analyses assessed whether cTBS effects differed depending on the severity and/or type of naming impairment. ResultsRelative to vertex, cTBS of the rPTr improved naming of inconsistent, but not wrong, items for individuals with more severe baseline naming impairment. Critically, baseline phonological but not semantic naming impairment severity marginally correlated with improved accuracy overall, and significantly correlated with decreased phonological errors following rPTr stimulation. ConclusionCTBS of the rPTr enhances naming by facilitating phonological access during word retrieval, indicating that individuals whose naming impairment is localized to this stage of processing may be most likely to benefit from this rTMS approach.

Assessing cTBS virtual lesioning effects on parietal cortices and its ability to shift spatial attention

Theta burst stimulation (TBS) is being considered as a potential treatment for spatial neglect by restoring the normal balance of interhemispheric inhibition across right / left posterior parietal cortices (PPC). Recent studies suggest the observed hyperactivity of the left hemisphere may result from neuroplastic change, rather than a release of inhibition. The present study investigates attentional theories in healthy individuals by administering continuous-TBS to induce a virtual lesion and probing excitability connections of the PPC to the contralateral primary motor cortex (M1) bilaterally, using twin coil transcranial magnetic stimulation (TMS). Any behavioural changes from pre/post cTBS will be assessed by the landmark task and the bilateral perceptual decision making paradigm. Preliminary data suggests cTBS altered spatial attention in individuals with initial pseudoneglect, whilst any effect on PPC excitability levels is currently inconclusive. In conclusion, these results may have implications for cTBS effectiveness whilst also aiding further knowledge on the effects of cTBS on the contralateral unstimulated hemisphere. As cTBS was effective in altering spatial preference immediately, it is possible that spatial neglect arises due to a release of inhibition to the left PPC rather than due to neuroplasticity changes.

Forgiveness and cognitive control – Provoking revenge via theta-burst-stimulation of the DLPFC

In order to act in a socially acceptable way, the ability to forgive is indispensable. It has been suggested that forgiveness relies on cognitive control, more specifically inhibition. In this study, we combined an ultimatum game (UG) and a dictator game (DG) with inhibitory, continuous theta-burst stimulation (cTBS; verum vs. placebo, within-subjects design) of the right dorsolateral prefrontal cortex (DLPFC) to investigate the effect of reduced cognitive control on forgiveness. To this end, participants played an UG against fair and unfair opponents, where they had to accept or reject (fair and unfair) monetary offers, and then received a cTBS prior to playing a DG against the same opponents with reversed roles. The participants now had the possibility to forgive the unfair opponents (allocation of a fair amount of money) or to take revenge whereby the cTBS effects were assessed with functional near-infrared spectroscopy. Following verum cTBS, participants allocated significantly less money to their unfair opponents than in the placebo cTBS condition. Also, reaction times (RTs) differed significantly between verum and placebo cTBS for unfair opponents (higher RTs following verum stimulation) but not for fair opponents. These results strongly indicate that cognitive control is a fundamental requirement for overcoming unwanted emotional responses.

Behavioural effect of continuous Theta Burst Stimulation in macaque parietal cortex

Event Abstract Back to Event Behavioural effect of continuous Theta Burst Stimulation in macaque parietal cortex Lara Merken1, Maria C. Romero1, 2*, Peter Janssen1 and Marco Davare2 1 Laboratory for Neuro- and Psychophysiology, Doctoral School of Biomedical Sciences, KU Leuven, Belgium 2 Movement Control and Neuroplasticity Research Group, Department of Kinesiology, Biomedical Sciences Group, KU Leuven, Belgium Theta-burst stimulation (TBS), a well-known type of repetitive Transcranial Magnetic Stimulation (TMS), is a powerful neuromodulation tool due to its ability to induce long-term changes in brain activity. However, behavioural results in human volunteers are still highly variable. Recently, Romero et al. (FENS Forum of Neuroscience Berlin, 2018; Abstract No. D037) showed that continuous TBS (cTBS; triplets of pulses at 50 Hz, applied every 200 ms, during 20 sec) induces a robust reduction in neuronal excitability of parietal neurons in rhesus monkeys. Here, we studied the effect of cTBS on the macaque parietal cortex, by measuring the grasping times (GT) during a visually-guided grasping (VGG) task. Monkeys were trained to perform the VGG under six different conditions, combining the grasping of two objects (large and small cylinder, i.e. power grip and precision grip, respectively) under three different stimulation conditions: no stimulation (NS), low stimulation (LS) - 40% of the resting motor threshold (rMT) -, and high stimulation (HS) - 80% of the rMT -. Data were obtained from two rhesus monkeys (3 sessions per condition, average of 797 trials/session in monkey 1 and 862 trials/session in monkey 2). cTBS induced significant changes (p < 0.05 two-tailed) in GT in both monkeys. In the power grip sessions of monkey 1, high stimulation cTBS significantly increased the GT from 20 min to at least 120 min post-cTBS by up to 20% compared to NS (p < 0.001, two-tailed). In contrast, for precision grip, cTBS caused a significant reduction in the GT after 100 min to at least 120 min post-cTBS (5% reduction compared to NS, p < 0.001, two-tailed). For monkey 2, we also observed opposite effects for both objects. For power grip, the GT was significantly reduced from 20 min to at least 120 min post cTBS (max of 12% reduction compared to NS, p < 0.05 two-tailed), while for precision grip cTBS significantly increased the GT from 80 min post cTBS to at least 120 min (up to 11% increase compared to NS, p < 0.05, two-tailed). Interestingly, in each condition and in each monkey, low stimulation cTBS increased or decreased the GT in the opposite direction compared to the effect of high stimulation. A two-way ANOVA for grip type (power/precision grip) and stimulation type (high/low/no) as factors, showed significant interactions for all tested time intervals in both monkeys (p < 0.01). These findings demonstrate long-lasting changes of cTBS on behaviour, which are strongly dependent on the applied stimulation intensity. Keywords: TMS, transcranial magnetic stimulation, Theta-burst stimulation (TBS), Visually-guided grasping, Power grip, macaque, Precision Grip Conference: 13th National Congress of the Belgian Society for Neuroscience , Brussels, Belgium, 24 May - 24 May, 2019. Presentation Type: Poster presentation Topic: Behavioral/Systems Neuroscience Citation: Merken L, Romero MC, Janssen P and Davare M (2019). Behavioural effect of continuous Theta Burst Stimulation in macaque parietal cortex. Front. Neurosci. Conference Abstract: 13th National Congress of the Belgian Society for Neuroscience . doi: 10.3389/conf.fnins.2019.96.00075 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 23 Apr 2019; Published Online: 27 Sep 2019. * Correspondence: PhD. Maria C Romero, Laboratory for Neuro- and Psychophysiology, Doctoral School of Biomedical Sciences, KU Leuven, Leuven, Belgium, mela.romero@kuleuven.be Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Lara Merken Maria C Romero Peter Janssen Marco Davare Google Lara Merken Maria C Romero Peter Janssen Marco Davare Google Scholar Lara Merken Maria C Romero Peter Janssen Marco Davare PubMed Lara Merken Maria C Romero Peter Janssen Marco Davare Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Does TMS Disruption of the Left Primary Motor Cortex Affect Verb Retrieval Following Exposure to Pantomimed Gestures?

Previous research suggests that meaning-laden gestures, even when produced in the absence of language (i.e., pantomimed gestures), influence lexical retrieval. Yet, little is known about the neural mechanisms that underlie this process. Based on embodied cognition theories, many studies have demonstrated motor cortex involvement in the representation of action verbs and in the understanding of actions. The present study aimed to investigate whether the motor system plays a critical role in the behavioral influence of pantomimed gestures on action naming. Continuous theta burst stimulation (cTBS) was applied over the hand area of the left primary motor cortex and to a control site (occipital cortex). An action-picture naming task followed cTBS. In the naming task, participants named action pictures that were preceded by videos of congruent pantomimed gestures, unrelated pantomimed gestures or a control video with no movement (as a neutral, non-gestural condition). In addition to behavioral measures of performance, cTBS-induced changes in corticospinal activity were assessed. We replicated previous finding that exposure to congruent pantomimed gestures facilitates word production, compared to unrelated or neutral primes. However, we found no evidence that the left primary motor area is crucially involved in the mechanism underlying behavioral facilitation effects of gesture on verb production. Although, at the group level, cTBS induced motor cortex suppression, at the individual level we found remarkable variability of cTBS effects on the motor cortex. We found cTBS induction of both inhibition of corticospinal activity (with slower behavioral of responses) and enhancement (with faster behavioral responses). Our findings cast doubt on assumptions that the motor cortex is causally involved in the impact of gestures on action-word processing. Our results also highlight the importance of careful consideration of interindividual variability for the interpretation of cTBS effects.

Continuous theta-burst stimulation over the dorsolateral prefrontal cortex inhibits improvement on a working memory task

Theta-burst stimulation (TBS) over the dorsolateral prefrontal cortex (DLPFC) may be more effective for modulating cortical excitability compared to standard repetitive transcranial magnetic stimulation. However, the impact of intermittent (iTBS) and continuous TBS (cTBS) on working memory (WM) is poorly studied. The aim of our study was to compare the effects of iTBS and cTBS on WM over the left and right DLPFC. iTBS, cTBS or sham stimulation was administered over the right and left hemisphere of fifty-one healthy human subjects. WM was assessed before and after TBS using the 1-back, 2-back, and 3-back tasks. We found classical practice effects in the iTBS and the sham group: WM performance improved following stimulation as measured by the discriminability index. However, this effect could not be observed in the cTBS group. We did not find any hemisphere-dependent effects, suggesting that the practice effect is not lateralized, and TBS affects WM performance in a comparable manner if administered either over the left or the right hemisphere. We propose that our findings represent a useful addition to the literature of TBS-induced effects on WM. Moreover, these results indicate the possibility of clarifying processes underlying WM performance changes by using non-invasive brain stimulation.

Reproducibility and sources of interindividual variability in the responsiveness to prefrontal continuous theta burst stimulation (cTBS)

Despite the increasing use of continuous theta burst (cTBS) protocols targeting the prefrontal cortex in clinical and research settings, very little is known regarding the interindividual factors that influence the magnitude and duration of cTBS aftereffects. The few existing studies have predominantly focussed on motor and corticospinal excitability, and the applicability of such findings to prefrontal modulation remains unclear. The current investigation aggregated published data from our laboratory to (1) assess the reproducibility of the effects of cTBS targeting the left dorsolateral prefrontal cortex (dlPFC) on executive function task performance, and (2) determine which factors are associated with individual differences in cTBS responsivity. Data from 76 healthy young adult female participants aged 19–26 (M = 20.6; SD = 1.6) were included in the analyses. Significant attenuations in executive function task performance from baseline were observed following active cTBS. However, these effects were not totally universal in that cTBS-induced attenuation of executive functions was observed in 61.8% of participants (i.e., responders). In addition, baseline task performance was a significant predictor of the magnitude of the cTBS-induced change in task performance in that cTBS effect was larger for individuals with higher baseline executive control abilities than those with lower abilities. Together, these data provide a quantitative estimate of the degree to which healthy participants may vary in the responsiveness to prefrontal cTBS, and potential moderating factors.