Changes In Interhemispheric Connectivity Research Articles

Brain Connectivity: A Journal of Clinical Neurology, Neuroscience, & Neuroimaging Advancing the Field of Neurology

Brain Connectivity: A Journal of Clinical Neurology, Neuroscience, & Neuroimaging Advancing the Field of Neurology

Disrupted voxel-mirrored homotopic connectivity in congenital nystagmus using resting-state fMRI.

Idiopathic congenital nystagmus (CN) is a rare eye disease that can cause early blindness (EB). CN deficits are observed most frequently with oculomotor dysfunction; however, it is still unclear what neuromechanics underly CN with EB. Based on that visual experience requires the functional integration of both hemispheres, we hypothesized that CN adolescents with EB might exhibit impaired interhemispheric synchrony. Our study aimed to investigate the interhemispheric functional connectivity alterations using voxel-mirrored homotopic connectivity (VMHC) and their relationships with clinical features in CN patients. This study included 21 patients with CN and EB, and 21 sighted controls (SC), who were matched for sex, age and educational level. The 3.0 T MRI scan and ocular examination were performed. The VMHC differences were examined between the two groups, and the relationships between mean VMHC values in altered brain regions and clinical variables in the CN group were evaluated by Pearson correlation analysis. Compared with the SC group, the CN had increased VMHC values in the bilateral cerebellum posterior and anterior lobes/cerebellar tonsil/declive/pyramis/culmen/pons, middle frontal gyri (BA 10) and frontal eye field/superior frontal gyri (BA 6 and BA 8). No particular areas of the brain had lower VMHC values. Furthermore, no correlation with the duration of disease or blindness could be demonstrated in CN. Our results suggest the existence of interhemispheric connectivity changes and provide further evidence for the neurological basis of CN with EB.

Dissociation in Neural Correlates of Hyperactive/Impulsive vs. Inattentive Symptoms in Attention-Deficit/Hyperactivity Disorder.

Attention-deficit/hyperactivity disorder (ADHD) is one of the most common neurodevelopmental disorders characterized in current diagnostic criteria by two dominant symptoms, inattention and hyperactivity/impulsivity. Here, we show that task-related alpha (8–12 Hz) interhemispheric connectivity changes, as assessed during a unimanual finger-tapping task, is correlated with inattentive symptom severity (r = 0.55, p = 0.01) but not with severity of hyperactive/impulsive symptoms. Prior published analyses of the same dataset have already show that alpha event-related desynchronization (ERD) in the hemisphere contralateral to unimanual tapping is related to hyperactive/impulsive symptom severity (r = 0.43, p = 0.04) but not to inattentive symptom severity. Our findings demonstrate a neurobiological dissociation in ADHD symptom severity, with implications for understanding the structure of endophenotypes in the disorder as well as for biomarker development.

Improved Interhemispheric Functional Connectivity in Postpartum Depression Disorder: Associations With Individual Target-Transcranial Magnetic Stimulation Treatment Effects.

Postpartum depression (PPD) is a depressive condition that is associated with a high risk of stressful life events, poor marital relationships, and even suicide. Neuroimaging techniques have enriched our understanding of cerebral mechanisms underlying PPD; namely, abnormalities in the amygdala-insula-frontal circuit might contribute to the pathogenesis of PPD. Stanford Accelerated Intelligent Neuromodulation Therapy (SAINT) is a recently validated neuroscience-informed accelerated intermittent theta-burst stimulation repetitive transcranial magnetic stimulation (rTMS) protocol. It has been shown to be effective, safe, tolerable, and rapid acting for treating treatment-resistant depression, and may be a valuable tool in the treatment of PPD. The purpose of the current study was to detect inter-hemispheric connectivity changes and their relationship with the clinical treatment effects of rTMS. Resting-state fMRI data from 32 patients with PPD treated with SAINT were collected and compared with findings from 32 age matched healthy controls. Voxel-mirrored homotopic connectivity (VMHC) was used to analyze the patterns of interhemispheric intrinsic functional connectivity in patients with PPD. Scores on the 17-item Hamilton Depression Rating Scale, Edinburgh Postnatal Depression Scale (EPDS) scores, and the relationships between these clinical characteristics and VMHC were the primary outcomes. Patients with PPD at baseline showed reduced VMHC in the amygdala, insula, and medial frontal gyrus compared with the HCs. These properties showed a renormalization after individualized rTMS treatment. Furthermore, increased connectivity between the left and right insula after SAINT was significantly correlated with the improvement of EPDS scores. Our results reveal the disruptions in the intrinsic functional architecture of interhemispheric communication in patients with PPD, and provide evidence for the pathophysiological mechanisms and the effects of rTMS.

Brain-Computer Interface Training With Functional Electrical Stimulation: Facilitating Changes in Interhemispheric Functional Connectivity and Motor Outcomes Post-stroke.

While most survivors of stroke experience some spontaneous recovery and receive treatment in the subacute setting, they are often left with persistent impairments in upper limb sensorimotor function which impact autonomy in daily life. Brain-Computer Interface (BCI) technology has shown promise as a form of rehabilitation that can facilitate motor recovery after stroke, however, we have a limited understanding of the changes in functional connectivity and behavioral outcomes associated with its use. Here, we investigate the effects of EEG-based BCI intervention with functional electrical stimulation (FES) on resting-state functional connectivity (rsFC) and motor outcomes in stroke recovery. 23 patients post-stroke with upper limb motor impairment completed BCI intervention with FES. Resting-state functional magnetic resonance imaging (rs-fMRI) scans and behavioral data were collected prior to intervention, post- and 1-month post-intervention. Changes in rsFC within the motor network and behavioral measures were investigated to identify brain-behavior correlations. At the group-level, there were significant increases in interhemispheric and network rsFC in the motor network after BCI intervention, and patients significantly improved on the Action Research Arm Test (ARAT) and SIS domains. Notably, changes in interhemispheric rsFC from pre- to both post- and 1 month post-intervention correlated with behavioral improvements across several motor-related domains. These findings suggest that BCI intervention with FES can facilitate interhemispheric connectivity changes and upper limb motor recovery in patients after stroke.

Brain connectivity alterations after additional sensorimotor or motor therapy for the upper limb in the early-phase post stroke: a randomized controlled trial.

Somatosensory function plays an important role for upper limb motor learning. However, knowledge about underlying mechanisms of sensorimotor therapy is lacking. We aim to investigate differences in therapy-induced resting-state functional connectivity changes between additional sensorimotor compared with motor therapy in the early-phase post stroke. Thirty first-stroke patients with a sensorimotor impairment were included for an assessor-blinded multi-centre randomized controlled trial within 8 weeks post stroke [13 (43%) females; mean age: 67 ± 13 years; mean time post stroke: 43 ± 13 days]. Patients were randomly assigned to additional sensorimotor (n = 18) or motor (n = 12) therapy, receiving 16 h of additional therapy within 4 weeks. Sensorimotor evaluations and resting-state functional magnetic resonance imaging were performed at baseline (T1), post-intervention (T2) and after 4 weeks follow-up (T3). Resting-state functional magnetic resonance imaging was also performed in an age-matched healthy control group (n = 19) to identify patterns of aberrant connectivity in stroke patients between hemispheres, or within ipsilesional and contralesional hemispheres. Mixed model analysis investigated session and treatment effects between stroke therapy groups. Non-parametric partial correlations were used to investigate brain−behaviour associations with age and frame-wise displacement as nuisance regressors. Connections within the contralesional hemisphere that showed hypo-connectivity in subacute stroke patients (compared with healthy controls) showed a trend towards a more pronounced pre-to-post normalization (less hypo-connectivity) in the motor therapy group, compared with the sensorimotor therapy group (mean estimated difference = −0.155 ± 0.061; P = 0.02). Further, the motor therapy group also tended to show a further pre-to-post increase in functional connectivity strength among connections that already showed hyper-connectivity in the stroke patients at baseline versus healthy controls (mean estimated difference = −0.144 ± 0.072; P = 0.06). Notably, these observed increases in hyper-connectivity of the contralesional hemisphere were positively associated with improvements in functional activity (r = 0.48), providing indications that these patterns of hyper-connectivity are compensatory in nature. The sensorimotor and motor therapy group showed no significant differences in terms of pre-to-post changes in inter-hemispheric connectivity or ipsilesional intrahemispheric connectivity. While effects are only tentative within this preliminary sample, results suggest a possible stronger normalization of hypo-connectivity and a stronger pre-to-post increase in compensatory hyper-connectivity of the contralesional hemisphere after motor therapy compared with sensorimotor therapy. Future studies with larger patient samples are however recommended to confirm these trend-based preliminary findings.

Myelination of Callosal Axons Is Hampered by Early and Late Forelimb Amputation in Rats.

Deafferentation is an important determinant of plastic changes in the CNS, which consists of a loss of inputs from the body periphery or from the CNS itself. Although cortical reorganization has been well documented, white matter plasticity was less explored. Our goal was to investigate microstructural interhemispheric connectivity changes in early and late amputated rats. For that purpose, we employed diffusion-weighted magnetic resonance imaging, as well as Western blotting, immunohistochemistry, and electron microscopy of sections of the white matter tracts to analyze the microstructural changes in the corticospinal tract and in the corpus callosum (CC) sector that contains somatosensory fibers integrating cortical areas representing the forelimbs and compare differences in rats undergoing forelimb amputation as neonates, with those amputated as adults. Results showed that early amputation induced decreased fractional anisotropy values and reduction of total myelin amount in the cerebral peduncle contralateral to the amputation. Both early and late forelimb amputations induced decreased myelination of callosal fibers. While early amputation affected myelination of thinner axons, late amputation disrupted axons of all calibers. Since the CC provides a modulation of inhibition and excitation between the hemispheres, we suggest that the demyelination observed among callosal fibers may misbalance this modulation.

Aberrant connectivity in auditory precision encoding in schizophrenia spectrum disorder and across the continuum of psychotic-like experiences

BackgroundThe ability to generate a precise internal model of statistical regularities is impaired in schizophrenia. Predictive coding accounts of schizophrenia suggest that psychotic symptoms may be explained by a failure to build precise beliefs or a model of the world. The precision of this model may vary with context. For example, in a noisy environment the model will be more imprecise compared to a model built in an environment with lower noise. However compelling, this idea has not yet been empirically studied in schizophrenia. Methods: In this study, 62 participants engaged in a stochastic mismatch negativity paradigm with high and low precision. We included inpatients with a schizophrenia spectrum disorder (N = 20), inpatients with a psychiatric disorder but without psychosis (N = 20), and healthy controls (N = 22), with comparable sex ratio and age distribution. Bayesian mapping and dynamic causal modelling were employed to investigate the underlying microcircuitry of precision encoding of auditory stimuli. Results: We found strong evidence (exceedance P > 0.99) for differences in the underlying connectivity associated with precision encoding between the three groups as well as on the continuum of psychotic-like experiences assessed across all participants. Critically, we show changes in interhemispheric connectivity between the two inpatient groups, with some connections further aligning on the continuum of psychotic-like experiences. Conclusions: While our results suggest continuity in backward connectivity alterations with psychotic-like experiences regardless of diagnosis, they also point to specificity for the schizophrenia spectrum disorder group in interhemispheric connectivity alterations.

MRI-based visualization of rTMS-induced cortical plasticity in the primary motor cortex.

Repetitive transcranial magnetic stimulation (rTMS) induces changes in cortical excitability for minutes to hours after the end of intervention. However, it has not been precisely determined to what extent cortical plasticity prevails spatially in the cortex. Recent studies have shown that rTMS induces changes in “interhemispheric” functional connectivity, the resting-state functional connectivity between the stimulated region and the symmetrically corresponding region in the contralateral hemisphere. In the present study, quadripulse stimulation (QPS) was applied to the index finger representation in the left primary motor cortex (M1), while the position of the stimulation coil was constantly monitored by an online navigator. After QPS application, resting-state functional magnetic resonance imaging was performed, and the interhemispheric functional connectivity was compared with that before QPS. A cluster of connectivity changes was observed in the stimulated region in the central sulcus. The cluster was spatially extended approximately 10 mm from the center [half width at half maximum (HWHM): approximately 3 mm] and was extended approximately 20 mm long in depth (HWHM: approximately 7 mm). A localizer scan of the index finger motion confirmed that the cluster of interhemispheric connectivity changes overlapped spatially with the activation related to the index finger motion. These results indicate that cortical plasticity in M1 induced by rTMS was relatively restricted in space and suggest that rTMS can reveal functional dissociation associated with adjacent small areas by inducing neural plasticity in restricted cortical regions.

Tracking perceptual decision mechanisms through changes in interhemispheric functional connectivity in human visual cortex

The role of long-range integration mechanisms underlying visual perceptual binding and their link to interhemispheric functional connectivity, as measured by fMRI, remains elusive. Only inferences on anatomical organization from resting state data paradigms not requiring coherent binding have been achieved. Here, we used a paradigm that allowed us to study such relation between perceptual interpretation and functional connectivity under bistable interhemispheric binding vs. non-binding of visual surfaces. Binding occurs by long-range perceptual integration of motion into a single object across hemifields and non-binding reflects opponent segregation of distinct moving surfaces into each hemifield. We hypothesized that perceptual integration vs. segregation of surface motion, which is achieved in visual area hMT+, is modulated by changes in interhemispheric connectivity in this region. Using 7T fMRI, we found that perceptual long-range integration of bistable motion can be tracked by changes in interhemispheric functional connectivity between left/right hMT+. Increased connectivity was tightly related with long-range perceptual integration. Our results indicate that hMT+ interhemispheric functional connectivity reflects perceptual decision, suggesting its pivotal role on long-range disambiguation of bistable physically constant surface motion. We reveal for the first time, at the scale of fMRI, a relation between interhemispheric functional connectivity and decision based perceptual binding.

Effects of HD-tDCS on Resting-State Functional Connectivity in the Prefrontal Cortex: An fNIRS Study

Functional connectivity is linked to several degenerative brain diseases prevalent in our aging society. Electrical stimulation is used for the clinical treatment and rehabilitation of patients with many cognitive disorders. In this study, the effects of high-definition transcranial direct current stimulation (HD-tDCS) on resting-state brain networks in the human prefrontal cortex were investigated by using functional near-infrared spectroscopy (fNIRS). The intrahemispheric as well as interhemispheric connectivity changes induced by 1 mA HD-tDCS were examined in 15 healthy subjects. Pearson correlation coefficient-based correlation matrices were generated from filtered time series oxyhemoglobin (ΔHbO) signals and converted into binary matrices. Common graph theory metrics were computed to evaluate the network changes. Systematic interhemispheric, intrahemispheric, and intraregional connectivity analyses demonstrated that the stimulation positively affected the resting-state connectivity in the prefrontal cortex. The poststimulation connectivity was increased throughout the prefrontal region, while focal HD-tDCS effects induced an increased rate of connectivity in the stimulated hemisphere. The graph theory metrics clearly distinguished the prestimulation and poststimulation networks for a range of thresholds. The results of this study suggest that HD-tDCS can be used to increase functional connectivity in the prefrontal cortex. The increase in functional connectivity can be explored clinically for neurorehabilitation of patients with degenerative brain diseases.

Extreme male developmental trajectories of homotopic brain connectivity in autism.

It has been proposed that autism spectrum disorder (ASD) may be characterized by an extreme male brain (EMB) pattern of brain development. Here, we performed the first investigation of how age-related changes in functional brain connectivity may be expressed differently in females and males with ASD. We analyzed resting-state functional magnetic resonance imaging data of 107 typically developing (TD) females, 114 TD males, 104 females, and 115 males with ASD (6-26 years) from the autism brain imaging data exchange repository. We explored how interhemispheric homotopic connectivity and its maturational curvatures change across groups. Differences between ASD and TD and between females and males with ASD were observed for the rate of changes in connectivity in the absence of overall differences in connectivity. The largest portion of variance in age-related changes in connectivity was described through similarities between TD males, ASD males, and ASD females, in contrast to TD females. We found that shape of developmental curvature is associated with symptomatology in both males and females with ASD. We demonstrated that females and males with ASD tended to follow the male pattern of developmental changes in interhemispheric connectivity, supporting the EMB theory of ASD.

Education, and the balance between dynamic and stationary functional connectivity jointly support executive functions in relapsing-remitting multiple sclerosis.

Graphical network characteristics and nonstationary functional connectivity features, both derived from resting-state functional magnetic resonance imaging (rsfMRI) data, have been associated with cognitive performance in healthy subjects. How these features jointly relate to cognition in diseased states has not been investigated. In this study, 46 relapsing-remitting multiple sclerosis subjects underwent rsfMRI scans and a focused cognitive battery. With a sliding window approach, we examined six dynamic network features that indicated how connectivity changed over time as well as six measures derived from graph theory to reflect static network characteristics. Multiset canonical correlation analysis (MCCA) was then carried out to investigate the relations between dynamic network features, stationary network characteristics, cognitive testing, demographic, disease severity, and mood. Multiple sclerosis (MS) subjects demonstrated weaker connectivity strength, decreased network density, reduced global changes, but increased changes in interhemispheric connectivity compared to controls. The MCCA model determined that executive functions and processing speed ability measured by Wechsler Adult Intelligence Scale IV (WAIS-IV) Working Memory Index, WAIS-IV Processing Speed Index, and the Verbal Fluency Test were positively correlated with education, dynamic connectivity, and static connectivity strength; while poor task switching was correlated with disease severity, psychiatric comorbidities such as depression, anxiety, and fatigue, and static network density. Taken together, our results suggest that better executive functioning in MS requires maintenance of a continued coordination between stationary and dynamic functional connectivity as well as the support of education, and dynamic functional connectivity may provide an additional cognitive biomarker of disease severity in the MS population.

Age-Dependent Modulations of Resting State Connectivity Following Motor Practice.

Recent work in young adults has demonstrated that motor learning can modulate resting state functional connectivity. However, evidence for older adults is scarce. Here, we investigated whether learning a bimanual tracking task modulates resting state functional connectivity of both inter- and intra-hemispheric regions differentially in young and older individuals, and whether this has behavioral relevance. Both age groups learned a set of complex bimanual tracking task variants over a 2-week training period. Resting-state and task-related functional magnetic resonance imaging scans were collected before and after training. Our analyses revealed that both young and older adults reached considerable performance gains. Older adults even obtained larger training-induced improvements relative to baseline, but their overall performance levels were lower than in young adults. Short-term practice resulted in a modulation of resting state functional connectivity, leading to connectivity increases in young adults, but connectivity decreases in older adults. This pattern of age differences occurred for both inter- and intra-hemispheric connections related to the motor network. Additionally, long-term training-induced increases were observed in intra-hemispheric connectivity in the right hemisphere across both age groups. Overall, at the individual level, the long-term changes in inter-hemispheric connectivity correlated with training-induced motor improvement. Our findings confirm that short-term task practice shapes spontaneous brain activity differentially in young and older individuals. Importantly, the association between changes in resting state functional connectivity and improvements in motor performance at the individual level may be indicative of how training shapes the short-term functional reorganization of the resting state motor network for improvement of behavioral performance.

O201 Interhemispheric processing in hyperkinetic movement disorders

Objectives changes in interhemispheric connectivity have been recently studied in Huntington’s Disease (HD), although their significance and temporal relation with clinical features are still debated. We studied interhemispheric connectivity in healthy volunteers, early HD and in patients with idiopathic dystonia. Methods ipsilateral Silent Period (onset latency, iSPOL, and duration, iSPD) and Transcallosal Conduction Time (TCT) from the abductor pollicis brevis (APB) muscle were evaluated. In HD, we correlated TMS data with clinical (UHDRS-I, Disease Burden Index), genetic (CAG-length) and cognitive (UHDRS-II) scores. Results iSPD decreased in HD, paralleled by a significant lengthening of iSPOL and TCT (p Discussion Our results could have implications for the disruption of both sensorimotor integration and voluntary motor control in HD. Before voluntary movements, interhemispheric interactions are responsible for the temporary inhibition of ipsilateral primary motor cortex (M1) and the increased excitability of contralateral one. Concurrently, especially during non-dominant hand movements, enhanced interhemispheric inhibition from the ipsilateral hemisphere suppresses superfluous activation arising from the contralateral cortex. These mutual interactions may be lost in symptomatic HD, thus contributing to hyperkinesias. Significance This is the first study using TMS to assess interhemispheric connectivity in hyperkinetic movement disorders, possibly leading to a better knowledge of disease mechanisms.

EP 137. The influence of age on hemispheric connectivity, a combined TMS and DTI study

Background Age effects both functional and structural brain function. Here, we combine two different methods to assess the impact of age on the neurophysiological and structural measurements of interhemispheric motor connectivity. We expect to find a clear association between both connectivity parameters and age. Methods 15 participants between 22 and 72 years (median 36 years) participated in this study. Ipsilateral silent period (ISP) was collected from both dominant and non-dominant first dorsal interosseus (FDI) muscle. Structural M1-M1 connectivity was calculated using probabilistic tractography (fMRI software library, FSL). Interhemispheric M1-M1 tract volume and mean fractional anisotropy (FA) of the tract were calculated between dominant and non-dominant M1 and vice versa. We tested associations between ISP depth, tract volume and FA and age by calculating Pearson correlations. Results ISP of the dominant hand correlated negatively with age (r = −0.54; p Discussion As expected, we found an association of age on the interhemispheric connectivity in both neurophysiological and structural MRI measurements. Interestingly, the effect was only present from the non-dominant to the dominant hemisphere, and not in the other direction. In addition, interhemispheric inhibition was associated with tract volume, but not with averaged FA values of the tract, and again, only in the direction from the non-dominant to the dominant hemisphere. Our findings indicate that the age-related changes in interhemispheric connectivity are different between the dominant and non dominant primary motor cortex. Furthermore, the data suggest that the age-related interhemispheric tract volume loss may be the underlying cause of the age-related decrease of interhemispheric inhibition.

91. Impaired interhemispheric processing in early Huntington’s disease: A transcranial magnetic stimulation study

A growing number of papers have recently investigated changes in interhemispheric connectivity in HD, although little is known about their temporal relation with clinical features and electrophysiological parameters. In this study we evaluated for the first time interhemispheric connectivity in Huntington’s disease (HD) by using a transcranial magnetic stimulation (TMS) protocol. We evaluated ipsilateral silent period (onset latency, iSPOL, and duration, iSPD) and transcallosal conduction time (TCT) in early manifest HD patients compared with sex and age-matched healthy volunteers; then, in HD group, we correlated TMS data with cognitive (MMSE), genetic (CAG-length), and clinical (UHDRS-I) scores. Compared with healthy volunteers, patients showed a marked decrease of iSPD, paralleled by a significant lengthening of iSPOL and TCT ( p p

Puberty in the corpus callosum

Adolescence is an important period for brain development. White matter growth is influenced by sex hormones such as testosterone, and the corpus callosum—the largest white matter structure in the human brain—may change structurally during the hormone-laden period of adolescence. Little is known about puberty’s relationship to structural brain development, even though pubertal stage may better predict cognitive and behavioral maturity than chronological age. We therefore aimed to establish the presence and direction of pubertal effects on callosal anatomy. For this purpose, we applied advanced surface-based mesh-modeling to map correlations between callosal thickness and pubertal stage in a large and well-matched sample of 124 children and adolescents (62 female and 62 male) aged 5–18years from a normative database. When linking callosal anatomy to pubertal status, only positive correlations reached statistical significance, indicating that callosal growth advances with puberty. In tests of differences in callosal anatomy at different stages of puberty, callosal growth was concentrated in different locations depending on the pubertal stage. Changing levels of circulating sex hormones during different phases of puberty likely contributed to the observed effects, and further research is clearly needed. Direct quantification of sex hormone levels and regional fiber connectivity—ideally using fiber tractography—will reveal whether hormones are the main drivers of callosal change during puberty. These callosal findings may lead to hypotheses regarding cortical changes during puberty, which may promote or result from changes in inter-hemispheric connectivity.

Modulating functional connectivity patterns and topological functional organization of the human brain with transcranial direct current stimulation

Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique that alters cortical excitability and activity in a polarity-dependent way. Stimulation for few minutes has been shown to induce plastic alterations of cortical excitability and to improve cognitive performance. These effects might be caused by stimulation-induced alterations of functional cortical network connectivity. We aimed to investigate the impact of tDCS on cortical network function through functional connectivity and graph theoretical analysis. Single recordings in healthy volunteers with 62 electroencephalography channels were acquired before and after 10 min of facilitatory anodal tDCS over the primary motor cortex (M1), combined with inhibitory cathodal tDCS of the contralateral frontopolar cortex, in resting state and during voluntary hand movements. Correlation matrices containing all 62 pairwise electrode combinations were calculated with the synchronization likelihood (SL) method and thresholded to construct undirected graphs for the θ, α, β, low-γ and high-γ frequency bands. SL matrices and undirected graphs were compared before and after tDCS. Functional connectivity patterns significantly increased within premotor, motor, and sensorimotor areas of the stimulated hemisphere during motor activity in the 60-90 Hz frequency range. Additionally, tDCS-induced significant intrahemispheric and interhemispheric connectivity changes in all the studied frequency bands. In summary, we show for the first time evidence for tDCS-induced changes in brain synchronization and topological functional organization.