Self-paced Finger Movements Research Articles

EMG-projected MEG high-resolution source imaging of human motor execution: Brain-muscle coupling above movement frequencies.

Magnetoencephalography (MEG) is a non-invasive functional imaging technique for pre-surgical mapping. However, movement-related MEG functional mapping of primary motor cortex (M1) has been challenging in presurgical patients with brain lesions and sensorimotor dysfunction due to the large numbers of trials needed to obtain adequate signal to noise. Moreover, it is not fully understood how effective the brain communication is with the muscles at frequencies above the movement frequency and its harmonics. We developed a novel Electromyography (EMG)-projected MEG source imaging technique for localizing early-stage (-100 to 0 ms) M1 activity during ~l min recordings of left and right self-paced finger movements (~1 Hz). High-resolution MEG source images were obtained by projecting M1 activity towards the skin EMG signal without trial averaging. We studied delta (1-4 Hz), theta (4-7 Hz), alpha (8-12 Hz), beta (15-30 Hz), gamma (30-90 Hz), and upper-gamma (60-90 Hz) bands in 13 healthy participants (26 datasets) and three presurgical patients with sensorimotor dysfunction. In healthy participants, EMG-projected MEG accurately localized M1 with high accuracy in delta (100.0%), theta (100.0%), and beta (76.9%) bands, but not alpha (34.6%) or gamma/upper-gamma (0.0%) bands. Except for delta, all other frequency bands were above the movement frequency and its harmonics. In three presurgical patients, M1 activity in the affected hemisphere was also accurately localized, despite highly irregular EMG movement patterns in one patient. Altogether, our EMG-projected MEG imaging approach is highly accurate and feasible for M1 mapping in presurgical patients. The results also provide insight into movement-related brain-muscle coupling above the movement frequency and its harmonics.

Voluntary Motor Command Release Coincides with Restricted Sensorimotor Beta Rhythm Phases.

Sensory perception and memory are enhanced during restricted phases of ongoing brain rhythms, but whether voluntary movement is constrained by brain rhythm phase is not known. Voluntary movement requires motor commands to be released from motor cortex (M1) and transmitted to spinal motoneurons and effector muscles. Here, we tested the hypothesis that motor commands are preferentially released from M1 during circumscribed phases of ongoing sensorimotor rhythms. Healthy humans of both sexes performed a self-paced finger movement task during electroencephalography (EEG) and electromyography (EMG) recordings. We first estimated the time of motor command release preceding each finger movement by subtracting individually measured corticomuscular transmission latencies from EMG-determined movement onset times. Then, we determined the phase of ipsilateral and contralateral sensorimotor mu (8-12 Hz) and beta (13-35 Hz) rhythms during release of each motor command. We report that motor commands were most often released between 120 and 140° along the contralateral beta cycle but were released uniformly along the contralateral mu cycle. Motor commands were also released uniformly along ipsilateral mu and beta cycles. Results demonstrate that motor command release coincides with restricted phases of the contralateral sensorimotor beta rhythm, suggesting that sensorimotor beta rhythm phase may sculpt the timing of voluntary human movement.SIGNIFICANCE STATEMENT Perceptual and cognitive function is optimal during specific brain rhythm phases. Although brain rhythm phase influences motor cortical neuronal activity and communication between the motor cortex and spinal cord, its role in voluntary movement is poorly understood. Here, we show that the motor commands needed to produce voluntary movements are preferentially released from the motor cortex during contralateral sensorimotor beta rhythm phases. Our findings are consistent with the notion that sensorimotor rhythm phase influences the timing of voluntary human movement.

Neuromagnetic Cerebellar Activity Entrains to the Kinematics of Executed Finger Movements

This magnetoencephalography (MEG) study aims at characterizing the coupling between cerebellar activity and the kinematics of repetitive self-paced finger movements. Neuromagnetic signals were recorded in 11 right-handed healthy adults while they performed repetitive flexion-extensions of right-hand fingers at three different movement rates: slow (~ 1Hz), medium (~ 2Hz), and fast (~ 3Hz). Right index finger acceleration was monitored with an accelerometer. Coherence analysis was used to index the coupling between right index finger acceleration and neuromagnetic signals. Dynamic imaging of coherent sources was used to locate coherent sources. Coupling directionality between primary sensorimotor (SM1), cerebellar, and accelerometer signals was assessed with renormalized partial directed coherence. Permutation-based statistics coupled with maximum statistic over the entire brain volume or restricted to the cerebellum were used. At all movement rates, maximum coherence peaked at SM1 cortex contralateral to finger movements at movement frequency (F0) and its first harmonic (F1). Significant (statistics restricted to the cerebellum) coherence consistently peaked at the right posterior lobe of the cerebellum at F0 with no influence of movement rate. Coupling between Acc and cerebellar signals was significantly stronger in the afferent than in the efferent direction with no effective contribution of cortico-cerebellar or cerebello-cortical pathways. This study demonstrates the existence of significant coupling between finger movement kinematics and neuromagnetic activity at the posterior cerebellar lobe ipsilateral to finger movement at F0. This coupling is mainly driven by spinocerebellar, presumably proprioceptive, afferences.

Association between stimulus-evoked somatosensory inhibition and movement-related sensorimotor oscillation: A magnetoencephalographic study

The interaction between the somatosensory and motor cortices is understood; however, their functional relationship remains elusive. To elucidate the association between somatosensory and sensorimotor functions, this study investigated the correlation between somatosensory activities in response to paired-pulse stimulation and sensorimotor oscillations during self-paced finger movement in 18 healthy male subjects by using a magnetoencephalographic recording. The main finding was that stimulus-evoked somatosensory gating activities were significantly correlated with movement-related sensorimotor oscillatory responses. Specifically, the gating ratios of somatosensory N20m were related to the power changes of sensorimotor beta event-related desynchronization (ERD) (p=0.003) and event-related synchronization (ERS) (p=0.05). In conclusion, we confirmed that the inhibition of stimulus-evoked somatosensory responses is associated with the oscillatory characteristics of movement-related sensorimotor activities.

A Pilot Study on the Effects of Transcranial Direct Current Stimulation on Brain Rhythms and Entropy during Self-Paced Finger Movement using the Epoc Helmet.

Transcranial direct current stimulation (tDCS) of the cerebellum is emerging as a novel non-invasive tool to modulate the activity of the cerebellar circuitry. In a single blinded study, we applied anodal tDCS (atDCS) of the cerebellum to assess its effects on brain entropy and brain rhythms during self-paced sequential finger movements in a group of healthy volunteers. Although wearable electroencephalogram (EEG) systems cannot compete with traditional clinical/laboratory set-ups in terms of accuracy and channel density, they have now reached a sufficient maturity to envision daily life applications. Therefore, the EEG was recorded with a comfortable and easy to wear 14 channels wireless helmet (Epoc headset; electrode location was based on the 10–20 system). Cerebellar neurostimulation modified brain rhythmicity with a decrease in the delta band (electrode F3 and T8, p < 0.05). By contrast, our study did not show any significant change in entropy ratios and laterality coefficients (LC) after atDCS of the cerebellum in the 14 channels. The cerebellum is heavily connected with the cerebral cortex including the frontal lobes and parietal lobes via the cerebello-thalamo-cortical pathway. We propose that the effects of anodal stimulation of the cerebellar cortex upon cerebral cortical rhythms are mediated by this key-pathway. Additional studies using high-density EEG recordings and behavioral correlates are now required to confirm our findings, especially given the limited coverage of Epoc headset.

Timing of Cortical Events Preceding Voluntary Movement.

We studied magnetic signals from the human brain recorded during a second before a self-paced finger movement. Sharp triangular peaks were observed in the averaged signals about 0.7 second before the finger movement. The amplitude of the peaks varied considerably from trial to trial, which indicated that the peaks were concurrent with much longer oscillatory processes. One can cluster trials into distinct groups with characteristic sequences of events. Prominent short trains of pulses in the beta frequency band were identified in the premovement period. This observation suggests that during preparation of the intended movement, cortical activity is well organized in time but differs from trial to trial. Magnetoencephalography can capture these processes with high temporal resolution and allows their study in fine detail.

Action observation training to improve motor function recovery: a systematic review.

Following the discovery of Mirror Neuron System (MNS), Action Observation Training (AOT) has become an emerging rehabilitation tool to improve motor functions both in neurologic and orthopedic pathologies.The aim of this study is to present the state of the art on the use of AOT in experimental studies to improve motor function recovery in any disease.The research was performed in PubMed, PEDro, Embase, CINAHL and Cochrane Central Register of Controlled Trials (last search July 2015). Randomized controlled trials (RCTs) that analyse efficacy of AOT for recovery of motor functions, regardless of the kind of disease, were retrieved. The validity of the included studies was assessed using the Cochrane Collaboration tool for evaluating risk of bias.Twenty RCTs were eligible. Four studies showed AOT efficacy in improving upper limb functional recovery in participants with chronic stroke, two studies in sub-acute ones and one in acute ones. Six articles suggested its effectiveness on walking performance in chronic stroke individuals, and three of them also suggested an efficacy in improving balance. The use of AOT was also recommended in individuals with Parkinson’s disease to improve autonomy in activities of daily living, to improve spontaneous movement rate of self-paced finger movements and to reduce freezing of gait. Other two studies also indicated that AOT improves upper limb motor function in children with cerebral palsy. The last two studies, showed the efficacy of AOT in improving motor recovery in postsurgical orthopedic participants. Overall methodological quality of the considered studies was medium.The majority of analyzed studies suggest the efficacy of AOT, in addition to conventional physiotherapy, to improve motor function recovery in individuals with neurological and orthopedic diseases. However, the application of AOT is very heterogeneous in terms of diseases and outcome measures assessed, which makes it difficult to reach, to date, any conclusion that might influence clinical practice.Electronic supplementary materialThe online version of this article (doi:10.1186/s40945-015-0013-x) contains supplementary material, which is available to authorized users.

Individual trial-to-trial variability of different components of neuromagnetic signals associated with self-paced finger movements

We measured magnetic cortical responses to self-paced finger movements. Wide frequency band measurements revealed sharp elements of the response wave-shape, and allowed analysis of individual trials. The signal time course was decomposed into three components in the time window from 600ms before to 600ms after the movement. Each component had its own wave-shape and highly individual behavior. Two components displayed large trial-to-trial amplitude variations, whereas the amplitude of the third, high-frequency component remained stable. The frequency spectrum of the high-frequency component decayed exponentially, which indicates deterministic dynamics for the processes generating this magnetic signal. In spite of the large variations in the movement-related cortical signals, the movement itself, as measured by accelerometer attached to the finger tip, remained stable from trial to trial. The magnetic measurements are well-suited to reveal fine details of the process of movement initiation.

140. Effects of transcranial alternating current stimulation (tACS) on spontaneous motor tempo and sensorimotor synchronization: Preliminary data

We used transcranial alternating current stimulation (tACS) to modulate brain oscillations during spontaneous motor tempo and sensorimotor synchronization tasks to evaluate the effect of specific frequencies on motor performance. Six healthy subjects performed self-paced finger movements and auditory-paced finger tapping (synchronization–continuation task) with isochronous rhythmic sequences of 500 and 1500 ms interstimulus intervals (ISI). During each task, tACS was delivered to the left M1 (“reference” electrode on Pz) at an intensity of 1 mA in 5 randomized conditions: 5, 10, 20, 40 Hz, and sham. Baseline recordings (without tACS) were performed before and after each experimental session. In synchronization task with sequences of ISI 500 ms, 20 Hz tACS modified anticipatory mechanisms as revealed by a reduction of the negative mean asynchrony between the onset of the auditory cue and the motor response. However, this effect did not reach statistical significance due to the small sample. No effect emergent in the other conditions. We hypothesize that the reduction of the negative mean asynchrony may reflect a slowing of the motor output. These preliminary data are in line with previous studies in literature reporting specific effects of tACS at beta frequency on motor functions and cortical excitability.

Understanding cortical networks involved in the preparation of voluntary movement using simultaneous EEG-fMRI

Event Abstract Back to Event Understanding cortical networks involved in the preparation of voluntary movement using simultaneous EEG-fMRI Vinh T. Nguyen1*, Michael Breakspear2, 3, 4, 5 and Ross Cunnington1, 6 1 The University of Queensland, Queensland Brain Institute, Australia 2 Queensland Institute of Medical Research, Australia 3 University of New South Wales, School of Psychiatry, Australia 4 The Black Dog Institute, Australia 5 The Royal Brisbane and Womans Hospital, Australia 6 The University of Queensland, School of Psychology, Australia Background The cortical correlates of voluntary actions precede movement by at least 1-2 seconds. This sustained activity is reflected in the widely studied readiness potential (RP), which provides insight into the brain processes underlying the preparation of actions. Key contributing regions have been identified, including the middle cingulate cortex (MCC) and the supplementary motor area (SMA), but the relationship of activity within and between these regions to the RP is not understood. We sought to examine this relationship by integrating simultaneously acquired EEG and fMRI through computational modelling. Method We acquired simultaneous EEG and fMRI data from 20 healthy participants as they performed a simple task of voluntary, self-paced finger movements made every 10–15 seconds. We applied an EEG-informed fMRI analysis to examine trial-by-trial correlation between BOLD signals and neural responses reflected in the RP and global field power (GFP) activity preceding movements. We then used dynamic causal modelling (DCM) to examine interactions between the network of SMA and MCC during the preparation and performance of actions. DCM models were therefore informed by movement events as well as contextual modulators derived from EEG activity. The latter accounts for the correlation shown by the EEG-informed fMRI analysis. Bayesian model selection with a random-effects analysis was employed to select the most likely model of cortical interactions for our data. Results and Discussion The EEG-informed fMRI analysis revealed a positive correlation between GFP over the period from 750 ms to 400 ms prior to movement and BOLD responses in MCC. Specifically, trials in which neural activity in the GFP was greater over this premovement period also involved greater activation of the MCC. The best fitting model to infer the interactions between MCC and SMA comprised the GFP regulating the self-feedback connection of MCC to itself, and MCC activity regulating the self-feedback connection of SMA. This result suggests that the MCC modulates its own activity, and this modulation is strongest on trials with greater premovement GFP activity. Together, our study suggests that the internal modulation of MCC is essential to sustain premovement activity over time, and drives SMA activity in preparation for actions. Keywords: voluntary movements, simultaneous EEG-fMRI, multimodal neuroimaging, readiness potential, dynamic causal modeling, middle cingulate cortex Conference: ACNS-2013 Australasian Cognitive Neuroscience Society Conference, Clayton, Melbourne, Australia, 28 Nov - 1 Dec, 2013. Presentation Type: Oral Topic: Motor Citation: Nguyen VT, Breakspear M and Cunnington R (2013). Understanding cortical networks involved in the preparation of voluntary movement using simultaneous EEG-fMRI. Conference Abstract: ACNS-2013 Australasian Cognitive Neuroscience Society Conference. doi: 10.3389/conf.fnhum.2013.212.00183 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: 15 Oct 2013; Published Online: 25 Nov 2013. * Correspondence: Mr. Vinh T Nguyen, The University of Queensland, Queensland Brain Institute, Brisbane, QLD, Australia, vinh.nguyen@uq.edu.au 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 Vinh T Nguyen Michael Breakspear Ross Cunnington Google Vinh T Nguyen Michael Breakspear Ross Cunnington Google Scholar Vinh T Nguyen Michael Breakspear Ross Cunnington PubMed Vinh T Nguyen Michael Breakspear Ross Cunnington 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.

Paradoxical worsening of gait with levodopa in Parkinson disease

Despite many recent advances in the treatment of Parkinson disease (PD), levodopa is still the most effective medication for PD. While there are many “nondopaminergic” features of PD that do not improve with levodopa, PD motor symptoms generally improve with dopaminergic medications. However, not all the motor manifestations of PD are improved to the same extent and some may not respond at all to levodopa. Tremor is often less responsive to levodopa than bradykinesia. Different aspects of bradykinesia may even respond differently. For example, recent studies showed that with self-paced finger and hand movement tasks similar to those used in the Unified Parkinson's Disease Rating Scale, levodopa improved the speed of movement but had little effect on the amplitude of movement and on movement fatigue, although impairment of movement amplitude was more prevalent than impairment of speed in PD.1,2 In contrast, when finger tapping was paced to an external rhythm, patients with PD had a dramatic reduction in the amplitude of movement when the tapping rate was higher than 2 Hz and this reduction in amplitude did not improve with levodopa.3 Gait disturbance in …

Motor-Cortical Interaction in Gilles de la Tourette Syndrome

BackgroundIn Gilles de la Tourette syndrome (GTS) increased activation of the primary motor cortex (M1) before and during movement execution followed by increased inhibition after movement termination was reported. The present study aimed at investigating, whether this activation pattern is due to altered functional interaction between motor cortical areas.Methodology/Principal Findings10 GTS-patients and 10 control subjects performed a self-paced finger movement task while neuromagnetic brain activity was recorded using Magnetoencephalography (MEG). Cerebro-cerebral coherence as a measure of functional interaction was calculated. During movement preparation and execution coherence between contralateral M1 and supplementary motor area (SMA) was significantly increased at beta-frequency in GTS-patients. After movement termination no significant differences between groups were evident.Conclusions/SignificanceThe present data suggest that increased M1 activation in GTS-patients might be due to increased functional interaction between SMA and M1 most likely reflecting a pathophysiological marker of GTS. The data extend previous findings of motor-cortical alterations in GTS by showing that local activation changes are associated with alterations of functional networks between premotor and primary motor areas. Interestingly enough, alterations were evident during preparation and execution of voluntary movements, which implies a general theme of increased motor-cortical interaction in GTS.

Compensatory movement-related recruitment in amyotrophic lateral sclerosis patients with dominant upper motor neuron signs: An EEG source analysis study

Cortical reorganization to simple movement in patients with amyotrophic lateral sclerosis (ALS) has been investigated in neuroimaging studies, reporting recruitment of ipsilateral primary sensorimotor (iSMC) and premotor regions (PMd). In order to investigate the spatiotemporal pattern of such overactivation, EEG source analysis to brisk self-paced finger movements was performed in thirty-two ALS patients, able to initiate their movement as fast as controls and clustered according to their most affected motor neuron (upper or lower). Reduced activity within cortical sources in bilateral SMC and caudal mesial areas was found only in patients subgroup with extensive upper motor neuron (UMN) clinical signs and mild motor weakness (U>L). Its absence in patients with opposite clinical features (L>U) suggest that this reduction might represent a possible marker of UMN impairment, and that the lower motor neuron (LMN) degeneration in L>U patients did not exert a retrograde effect over their cortical motor neurons. An ipsilateral premotor recruitment was observed in U>L patients only and since its extent positively correlated with movement initiation speed and right hand Medical Research Council (MRC) score, it might represent a compensatory recruitment. The latter correlation might suggest that the slight motor weakness in those patients may at least partly depend from a UMN dysfunction that can be compensated by cortical recruitment.

Attention and the readiness for action

The initiation of voluntary action is preceded by up to 2s of preparatory neural activity, originating in premotor and supplementary motor regions of the brain. The function of this extended period of pre-movement activity is unclear. Although recent studies have suggested that pre-movement activity is influenced by attention to action, little is understood about the specific processes that are involved in this preparatory period prior to voluntary action. We recorded readiness potentials averaged from EEG activity as participants made voluntary self-paced finger movements. We manipulated the processing resources available for action preparation using concurrent perceptual load and cognitive working memory load tasks. Results showed that pre-movement activity was significantly reduced only under conditions of high working memory load, when resources for planning action were limited by the concurrent cognitive load task. In contrast, limiting attentional resources in the perceptual load task had no effect on pre-movement readiness activity. This suggests that movement preparatory processes involve mechanisms of cognitive control that are also required for working memory, and not more general engagement of selective attentional resources. We propose that the extended period of pre-movement neural activity preceding voluntary action reflects the engagement of cognitive control mechanisms for endogenously orienting attention in time, in readiness for the initiation of voluntary action.

Non-invasive simultaneous recording of neuronal and vascular signals in subacute ischemic stroke

In acute focal cerebral ischemia blood flow and neuronal activity change dramatically. A better understanding of the pathophysiological interactions of these two important parameters is limited owing to the lack of noninvasive techniques to simultaneously measure these parameters in humans. In this feasibility study, we used DC-magnetoencephalography and near-infrared spectroscopy to find out whether blood flow and neuronal activity as well as neurovascular coupling can be analyzed in patients suffering from subacute ischemic stroke. In a simple motor test condition, six patients with subacute ischemic stroke performed self-paced finger movements (30-s periods of movement, separated by 30-s periods of rest; for a total of 15 min). Combined DC-magnetoencephalography and near-infrared spectroscopy were recorded over the affected and unaffected hemispheres. As a control group, four healthy subjects were investigated. In four out of six patients, the time courses of both signals closely followed the motor task cycles revealing significant differences between movement and rest periods. The vascular signal reached a maximum 1-5 s later than the neuronal signals. This proof-of-principle study demonstrates that it has become feasible to simultaneously and noninvasively monitor neuronal and vascular signal changes in patients in the subacute state of ischemic stroke.

Altered pattern of motor cortical activation–inhibition during voluntary movements in Tourette syndrome

In patients with Gilles de la Tourette syndrome (GTS) alterations of motor cortex (M1) excitability at rest have been evidenced. In contrast, there has so far been little research into changes of motor cortical reactivity during the time course of voluntary movements in GTS patients. The present study investigates neuromagnetic event-related desynchronization (ERD) and event-related synchronization (ERS) of bilateral M1 in 11 GTS patients and 11 healthy control subjects. ERD represents motor cortical activation, whereas ERS most likely indicates its inhibition. Subjects performed a self-paced finger movement task while magnetoencephalography was used to record neuromagnetic activity. In GTS patients, ERD at beta frequency was significantly increased in the contralateral hemisphere before and during movements, whereas ERS following movement termination was increased in M1 ipsilateral. Ipsilateral ERS was inversely correlated with tic severity as determined by the Yale Global Tic Severity Rating Scale. The data of the present study support the hypothesis that during voluntary movements, motor cortical reactivity is pathologically altered in GTS patients. The observed pattern of increased activation (ERD) prior to and during movement execution followed by increased inhibition (ERS) after movement termination at beta frequency suggests abnormally increased motor cortical activation, possibly driving stronger inhibition. The stronger this inhibition is, the better symptoms appear to be controlled.

High-frequency transcutaneous electrical nerve stimulation (TENS) differentially modulates sensorimotor cortices: An MEG study

Transcutaneous electrical nerve stimulation (TENS) affects excitability of the central motor system as well as the somatosensory system. To determine whether TENS has influence on excitability in the sensorimotor cortices of TENS-treated finger muscle, we investigated magnetoencephalogram associated with voluntary, self-paced finger movement before and after TENS. High-frequency TENS was applied on the extensor digitorum muscle for 15 min. Subjects underwent alternate middle finger and thumb extension movements before and after the TENS. We recorded movement-related cortical magnetic field (MRCF) associated with TENS-treated middle finger movement and that from untreated thumb movement. The current source for motor field (MF) was located in the pre-central motor cortex and anteriorly-oriented, and that for motor evoked field one (MEF1) was found in the post-central somatosensory cortex and posteriorly-oriented. The amplitude of MF for TENS-treated middle finger movement decreased but unchanged for untreated thumb movement after TENS. The amplitude of MEF1 decreased for either finger movement after TENS. High-frequency TENS to the forearm muscle modulates excitability of the limited area of motor cortex but wider area of primary somatosensory cortex. High-frequency TENS to the forearm muscle modulates excitability of the primary somatosensory cortex and motor cortex in a different manner.

High gamma mapping using EEG

High gamma (HG) power changes during motor activity, especially at frequencies above 70 Hz, play an important role in functional cortical mapping and as control signals for BCI (brain–computer interface) applications. Most studies of HG activity have used ECoG (electrocorticography) which provides high-quality spatially localized signals, but is an invasive method. Recent studies have shown that non-invasive modalities such as EEG and MEG can also detect task-related HG power changes. We show here that a 27 channel EEG (electroencephalography) montage provides high-quality spatially localized signals non-invasively for HG frequencies ranging from 83 to 101 Hz. We used a generic head model, a weighted minimum norm least squares (MNLS) inverse method, and a self-paced finger movement paradigm. The use of an inverse method enables us to map the EEG onto a generic cortex model. We find the HG activity during the task to be well localized in the contralateral motor area. We find HG power increases prior to finger movement, with average latencies of 462 ms and 82 ms before EMG (electromyogram) onset. We also find significant phase-locking between contra- and ipsilateral motor areas over a similar HG frequency range; here the synchronization onset precedes the EMG by 400 ms. We also compare our results to ECoG data from a similar paradigm and find EEG mapping and ECoG in good agreement. Our findings demonstrate that mapped EEG provides information on two important parameters for functional mapping and BCI which are usually only found in HG of ECoG signals: spatially localized power increases and bihemispheric phase-locking.

A randomized comparison of thalamic stimulation and lesion on self-paced finger movement in essential tremor

Deep brain stimulation (DBS) and ablation (thalamotomy) of the motor thalamus reduce tremor and improve function of the contralateral hand in patients with essential tremor (ET). Neuroimaging and electrophysiological evidence suggest that unlike a focal lesion, high frequency stimulation affects widespread neural networks that include those involved in motor timing. The purpose of this pilot study was to compare the effects of thalamic stimulation and lesion on the timing of simple, self-paced finger movements in patients with ET. Twenty-one subjects with advanced ET were randomized to unilateral thalamotomy or DBS. Nine healthy controls were also enrolled. Index finger tapping was performed on both hands before and 6 months after surgery. Prior to surgery, timing of simple, repetitive index finger taps was abnormal in both TH and DBS subjects on the contralateral hand. After surgery, regularity was improved by both stimulation and thalamotomy with significantly more improvement in the TH group. On the ipsilateral (non-targeted) hand, timing of index finger taps was improved by stimulation. These results suggest that temporal processing is differentially affected by stimulating and lesioning thalamocortical fibers. That timing regularity is improved ipsilateral to the stimulated thalamus provides evidence that DBS influences a widespread neural network involved in timing of simple repetitive movements.

Stockwell Coherence Measures Resting-state Connectivity with Low Between-session Variability

Introduction Analyses of resting-state functional magnetic resonance imaging (fMRI) data typically use approaches that determine the similarity between the time courses of individual image voxels or target regions and reference time courses from seed regions. This can be accomplished either in the time domain (e.g., cross-correlation) or in the frequency domain (e.g., coherence). These approaches assume fMRI signals are stationary over time; however, during a resting-state scan, a subject’s rest may become intermittently disrupted due to changes in subject arousal, visual imagery, internal dialogue, etc. [1], which may impact results as well as reduce between-session reproducibility of resting-state connectivity. In this study, we introduce a time-frequency approach based on the Stockwell transform [2] to measure resting-state connectivity and to investigate the effect of imaging repetition time (TR) and scan duration in comparison to cross-correlation and coherence approaches [3]. Methods: Four healthy subjects participated in three sessions after providing informed consent. During each session, six 400-second resting-state T2*-weighted images (GRE-EPI: TE = 30 ms, 24-cm FOV; twenty 5-mm thick slices, 64x64 matrix size) were collected with differing TRs (2 each of 600, 900, 1200 ms) in random order. Additional images were collected during the performance of a bilateral finger movement task (five visually-cued epochs of 20 seconds of self-paced finger movements and 20 seconds of rest). T1-weighted anatomical images were also collected. For the fMRI data collected during finger movements, the location of the 300 most significant voxels within left (seed) and right (target) primary sensorimotor cortex was determined using the General Linear Model (FSL: http://www.fmrib.ox.ac.uk/fsl). These seed and target regions were then used to extract their average time courses during the resting-state scans. For each TR and for three scan durations (200, 300, and 400 seconds), resting-state connectivity between the seed and target regions was computed using cross-correlation and coherence [3] as well as using Stockwell coherence. To compute Stockwell coherence, first the Stockwell transforms (i.e., temporally resolved frequency spectra) of the seed and target time courses were computed. Similar to the computation of coherence, the Stockwell auto-spectra for the seed and target regions as well as their cross-spectrum were calculated, and the ratio of the square of the cross-spectrum to the product of the auto-spectra was defined as Stockwell coherence. The result is a time-frequency spectrum of coherence. To take full advantage of Stockwell coherence, we recorded the median coherence across time and across the frequency range of 0 to 0.1 Hz rather than the mean, as the median is less sensitive to intermittent disruptions of the resting-state. For each method separately, values of connectivity were entered into a repeated measures AONVA with session, TR and scan duration as within-subject factors. An alpha level of 0.01 was considered as significant. Also, the inter-session coefficient of variation was computed for all methods and entered into a repeated-measures ANOVA with method, TR, and scan duration as within-subject factors. An alpha level of 0.05 was considered as significant. Results: For cross-correlation, ANOVA revealed a significant session/TR interaction [F(4,12)=5.53; p=0.009]. Hence, there was a difference in crosscorrelation estimates of connectivity across sessions, which were dependent on the choice of TR. For coherence, ANOVA revealed a significant session/duration interaction [F(4,12)=58.93; p=0.001]. Hence, there was a difference in coherence estimates of connectivity across sessions, which were dependent on the choice of scan duration. For Stockwell Coherence, ANOVA revealed no significant effects. Hence, there were no differences in Stockwell coherence estimates of connectivity across any of the sessions, TRs, and scan durations. For the coefficients of variation, ANOVA revealed significant effects of method [F(3,9)=5.68; p=0.018] and scan duration [F(2,6)=8.64; p<0.017]. Follow-up t-tests analyses revealed that the coefficient of variation for Stockwell coherence was significantly lower than coherence (p=0.017; see Figure 1), and the coefficient of variation for a scan duration of 400 seconds was significantly lower than for 200 seconds (p=0.046) and 300 seconds (p=0.016). Conclusion: Estimates of resting-state connectivity using Stockwell coherence are not susceptible to changes in TR and scan duration and do not differ between sessions. Cross-correlation and coherence exhibit dependencies on TR and scan duration, respectively. Resting-state connectivity estimated by Stockwell coherence also exhibits a significantly lower coefficient of variation across imaging sessions. Hence, Stockwell coherence is a potentially useful tool for estimations of resting-state connectivity across repeated sessions even in the presence of intermittent disruptions of the resting state.