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People have a natural and intrinsic ability to coordinate body movements with rhythms surrounding them, known as sensorimotor synchronisation. This can be observed in daily environments, when dancing or singing along with music, or spontaneously walking, talking or applauding in synchrony with one another. However, the neurophysiological mechanisms underlying accurately synchronised movement with selected rhythms in the environment remain unclear. Here we studied real and imagined sensorimotor synchronisation with interleaved auditory and visual rhythms using cortico-muscular coherence (CMC) to better understand the processes underlying the preparation and execution of synchronised movement. Electroencephalography (EEG), electromyography (EMG) from the finger flexors, and continuous force signals were recorded in 20 participants during tapping and imagined tapping with discrete stimulus sequences consisting of alternating auditory beeps and visual flashes. The results show that the synchronisation between cortical and muscular activity in the beta (14-38 Hz) frequency band becomes time-locked to the taps executed in synchrony with the visual and auditory stimuli. Dynamic modulation in CMC also occurred when participants imagined tapping with the visual stimuli, but with lower amplitude and a different temporal profile compared to real tapping. These results suggest that CMC does not only reflect changes related to the production of the synchronised movement, but also to its preparation, which appears heightened under higher attentional demands imposed when synchronising with the visual stimuli. These findings highlight a critical role of beta band neural oscillations in the cortical-muscular coupling underlying sensorimotor synchronisation.

Synchronous correlation brain and muscle oscillations during motor task execution is termed as functional coupling. Functional coupling between two signals appears with a delay time which can be used to infer the directionality of information flow. Functional coupling of brain and muscle depends on the type of muscle contraction and motor task performance. Although there have been many studies of functional coupling with types of muscle contraction and force level, there has been a lack of investigation with various motor task performances. Motor task types play an essential role that can reflect the amount of functional interaction. Thus, we examined functional coupling under four different motor tasks: real movement, intention, motor imagery and movement observation tasks. We explored interaction of two signals with linear and nonlinear information flow. The aim of this study is to investigate the synchronization between brain and muscle signals in terms of functional coupling and delay time. The results proved that brain–muscle functional coupling and delay time change according to motor tasks. Quick synchronization of localized cortical activity and motor unit firing causes good functional coupling and this can lead to short delay time to oscillate between signals. Signals can flow with bidirectionality between efferent and afferent pathways.

Synchronization between oscillatory signals is considered to be one of the main mechanisms through which neuronal populations interact with each other. It is conventionally studied with mass-bivariate measures utilizing either sensor-to-sensor or voxel-to-voxel signals. However, none of these approaches aims at maximizing syn-chronization, especially when two multichannel datasets are present. Examples include cortico-muscular coherence (CMC), cortico-subcortical interactions or hyperscanning (where electroencephalographic EEG/magnetoencephalographic MEG activity is recorded simultaneously from two or more subjects). For all of these cases, a method which could find two spatial projections maximizing the strength of synchronization would be desirable. Here we present such method for the maximization of coherence between two sets of EEG/MEG/EMG(electromyographic)/LFP (localfield potential) recordings. We refer to it as canonical Coherence (caCOH). caCOH maximizes the absolute value of the coherence between the two multivariate spaces in the frequency domain. Thisallows very fast optimization for many frequency bins. Apart from presenting details of the caCOH algorithm, we test its efficacy with simulations using realistic head modelling and focus on the application of caCOH to the detection of cortico-muscular coherence. For this, we used diverse multichannel EEG and EMG recordings and demonstrate the ability of caCOH to extract complex patterns of CMC distributed across spatial and frequency domains. Finally, we indicate other scenarios where caCOH can be used for the extraction of neuronal interactions. C.V. was supported by the Spanish Ministry of Economy with Grant RyC 2014-15671. G.N. was partially funded by the German Research Foundation (DFG, SFB936 Z3 and TRR169, B4). K.-R.M. work was supported by the German Ministry for Education and Research (BMBF) under Grants 01IS14013A-E, 01GQ1115 and 01GQ0850; the German Research Foundation (DFG) under Grant Math+, EXC 2046/1, Project ID 390685689 and by the Institute for Information & Communications Technology Planning & Evaluation (IITP) grant funded by the Korea government (No. 2017-0-00451, No. 2017-0-01779). T.W.B. was supported by a Future Fellowship from the Australian Research Council (FT180100622). V.V.N. was partially supported by the Center for Bioelectric Interfaces NRU HSE, RF Government grant, ag. No. 14.641.31.0003. The authors thank Katherina von Carlowitz-Ghori for her support with rCMC code and results.

Changes in human gait resulting from ageing or neurodegenerative diseases are multifactorial. Here we assess the effects of age and Parkinson’s disease (PD) on corticospinal activity recorded during treadmill and overground walking. Electroencephalography (EEG) from 10 electrodes and electromyography (EMG) from bilateral tibialis anterior muscles were acquired from 22 healthy young, 24 healthy older and 20 adults with PD. Event-related power, corticomuscular coherence (CMC) and inter-trial coherence were assessed for EEG from bilateral sensorimotor cortices and EMG during the double-support phase of the gait cycle. CMC and EMG power at low beta frequencies (13–21 Hz) was significantly decreased in older and PD participants compared to young people, but there was no difference between older and PD groups. Older and PD participants spent shorter time in the swing phase than young individuals. These findings indicate age-related changes in the temporal coordination of gait. The decrease in low-beta CMC suggests reduced cortical input to spinal motor neurons in older people during the double-support phase. We also observed multiple changes in electrophysiological measures at low-gamma frequencies during treadmill compared to overground walking, indicating task-dependent differences in corticospinal locomotor control. These findings may be affected by artefacts and should be interpreted with caution.

The mapping of the sensorimotor cortex gives information about the cortical motor and sensory functions. Typical mapping methods are navigated transcranial magnetic stimulation (TMS) and magnetoencephalography (MEG). The differences between these mapping methods are, however, not fully known. TMS center of gravities (CoGs), MEG somatosensory evoked fields (SEFs), corticomuscular coherence (CMC), and corticokinematic coherence (CKC) were mapped in ten healthy adults. TMS mapping was performed for first dorsal interosseous (FDI) and extensor carpi radialis (ECR) muscles. SEFs were induced by tactile stimulation of the index finger. CMC and CKC were determined as the coherence between MEG signals and the electromyography or accelerometer signals, respectively, during voluntary muscle activity. CMC was mapped during the activation of FDI and ECR muscles separately, whereas CKC was measured during the waving of the index finger at a rate of 3–4 Hz. The maximum CMC was found at beta frequency range, whereas maximumCKC was found at the movement frequency. The mean Euclidean distances between different localizations were within 20 mm. The smallest distance was found between TMS FDI and TMS ECR CoGs and longest between CMC FDI and CMC ECR sites. TMS-inferred localizations (CoGs) were less variable across participants than MEG-inferred localizations (CMC, CKC). On average, SEF locations were 8 mm lateral to the TMS CoGs (p < 0.01). No differences between hemispheres were found. Based on the results, TMS appears to be more viable than MEG in locating motor cortical areas.

Tongue movements contribute to oral functions including swallowing, vocalizing, and breathing. Fine tongue movements are regulated through efferent and afferent connections between the cortex and tongue. It has been demonstrated that cortico-muscular coherence (CMC) is reflected at two frequency bands during isometric tongue protrusions: the beta (β) band at 15-35Hz and the low-frequency band at 2-10Hz. The CMC at the β band (β-CMC) reflects motor commands from the primary motor cortex (M1) to the tongue muscles through hypoglossal motoneuron pools. However, the generator mechanism of the CMC at the low-frequency band (low-CMC) remains unknown. Here, we evaluated the mechanism of low-CMC during isometric tongue protrusion using magnetoencephalography (MEG). Somatosensory evoked fields (SEFs) were also recorded following electrical tongue stimulation. Significant low-CMC and β-CMC were observed over both hemispheres for each side of the tongue. Time-domain analysis showed that the MEG signal followed the electromyography signal for low-CMC, which was contrary to the finding that the MEG signal preceded the electromyography signal for β-CMC. The mean conduction time from the tongue to the cortex was not significantly different between the low-CMC (mean, 80.9ms) and SEFs (mean, 71.1ms). The cortical sources of low-CMC were located significantly posterior (mean, 10.1mm) to the sources of β-CMC in M1, but were in the same area as tongue SEFs in the primary somatosensory cortex (S1). These results reveal that the low-CMC may be driven by proprioceptive afferents from the tongue muscles to S1, and that the oscillatory interaction was derived from each side of the tongue to both hemispheres. Oscillatory proprioceptive feedback from the tongue muscles may aid in the coordination of sophisticated tongue movements in humans.

Available online 9 September 2019 Electroencephalographic and magnetoencephalographic data have characterized two types of brain–body interactions observed during various types of motor actions, “corticokinematic” and “corticomuscular” coupling. Here, we review the literature on these interactions in healthy individuals, discuss several open debates, and outline current limitations and directions for future research. Corticokinematic coupling (commonly referred to as corticokinematic coherence) probes the relationship between activity of sensorimotor network nodes and various movement-related signals (e.g., speed, velocity, acceleration). It is mainly driven by movement rhythmicity during active, passive, and observed dynamic motor actions. It typically predominates at the primary sensorimotor cortex contralateral to the moving limb, occurs at movement frequency and its harmonics, and predominantly reflects the cortical processing of proprioceptive feedback driven by movement rhythmicity in a broad range of dynamic motor actions. Corticomuscular coupling (commonly referred to as corticomuscular coherence) probes the interaction between sensorimotor cortical rhythms and electromyographic (EMG) activity that mainly occurs during steady isometric muscle contraction. We will here focus on the ~20-Hz coupling that is observed during weak isometric contraction and is linked to the modulation of the descending motor command by the ~20-Hz sensorimotor rhythm. This review argues that corticokinematic and corticomuscular couplings have different neural bases. Corticokinematic coupling is mainly driven by afferent signals, while corticomuscular coupling is mainly (but not solely) driven by efferent signals. This distinction should be considered when investigating interactions between brain and body movements. Mathieu Bourguignon was supported by the program Attract of Innoviris (grant 2015-BB2B-10), by the Marie Skłodowska-Curie Action of the European Commission (grant 743562) and by the Spanish Ministry of Economy and Competitiveness (grant PSI2016-77175-P). Sarang S. Dalal was supported by the European Research Council (Starting Grant 640448). Karim Jerbi is supported by funding from the Canada Research Chairs program and a Discovery Grant (RGPIN-2015-04854) from the Natural Sciences and Engineering Research Council of Canada, a New Investigators Award from the Fonds de Recherche du Qu ebec - Nature et Technologies (2018-NC-206005) and an IVADO-Apog ee fundamental research project grant. Xavier De Ti ege is Post-doctorate Clinical Master Specialist at the FRS-FNRS. The MEG project at the CUB H^opital Erasme is financially supported by the Fonds Erasme (Research convention “Les Voies du Savoir”, Fonds Erasme, Brussels, Belgium). We would like to warmly thank Professor Riitta Hari for her helpful comments on the manuscript.

Background To explore the cortical network sustaining action myoclonus and to found markers of the resulting functional impairment, we evaluated the distribution of the cortico-muscular coherence (CMC) and the frequency of coherent cortical oscillations with magnetoencephalography (MEG). All patients had EPM1 (Unverricht-Lundborg) disease known to present with prominent and disabling movement-activated myoclonus. Methods Using autoregressive models, we evaluated CMC on MEG sensors grouped in regions of interests (ROIs) above the main cortical areas. The movement was a repeated sustained isometric extension of the right hand and right foot. We compared the data obtained in 10 EPM1 patients with those obtained in 10 age-matched controls. Results As expected, CMC in beta band was significantly higher in EPM1 patients compared to controls in the ROIs exploring the sensorimotor cortex, but, it was also significantly higher in adjacent ROIs ipsilateral and contralateral to the activated limb. Moreover, the beta-CMC peak occurred at frequencies significantly slower and more stable frequencies in EPM1 patients with respect to controls. The frequency of the beta-CMC peak inversely correlated with the severity of myoclonus. Conclusions the high and spatially extended beta-CMC peaking in a restricted range of low-beta frequencies in EPM1 patients, suggest that action myoclonus may result not only from an enhanced local synchronization but also from a specific oscillatory activity involving an expanded neuronal pool. The significant relationship between beta-CMC peak frequency and the severity of the motor impairment can represent a useful neurophysiological marker for the patients’ evaluation and follow-up.

To obtain a direct sensorimotor integration assessment in primary hand cortical areas (M1) of patients suffering from focal task-specific hand dystonia, magnetoencephalographic (MEG) and opponens pollicis electromyographic (EMG) activities were acquired during a motor task expressly chosen not to induce dystonic movements in our patients, to disentangle abnormalities indicating a possible substrate on which dystonia develops. A simple isometric contraction was performed either alone or in combination with median nerve stimulation, i.e. when a non-physiological sensory inflow was overlapping with the physiological feedback. As control condition, median nerve stimulation was also performed at rest. The task was performed bilaterally both in eight patients and in 16 healthy volunteers. In comparison with results in controls we found that in dystonic patients: i) MEG-EMG coherence was higher; ii) it reduced much less during galvanic stimulation in the hemisphere contralateral to the dystonic arm, simultaneously with iii) stronger inhibition of the sensory areas responsiveness due to movement; iv) the cortical component including contributions from sensory inhibitory and motor structures was reduced and v) much more inhibited during movement. It is documented that a simultaneous cortico-muscular coherence increase occurs in presence of a reduced M1 responsiveness to the inflow from the sensory regions. This could indicate an unbalance of the fronto-parietal functional impact on M1, with a weakening of the parietal components. Concurrently, signs of a less differentiated sensory hand representation--possibly due to impaired inhibitory mechanisms efficiency--and signs of a reduced repertoire of voluntary motor control strategies were found.

Movement control requires continuous and reciprocal exchange of information between activities of motor areas involved in the task program execution and those elaborating proprioceptive sensory information. Our aim was to investigate the sensorimotor interactions in the region dedicated to hand control in healthy humans, focusing onto primary sensory and motor cortices, by selecting the time window at very early latencies. Through magnetoencephalographic recordings, we obtained a simultaneous assessment of sensory cortex activity modulation due to movement and of motor cortex activity modulation due to sensory stimulation, by eliciting a galvanic stimulation to the nerve (the median nerve) innervating a muscle (the opponens pollicis), at rest or during voluntary contraction. The primary sensory and motor cortices activities were investigated respectively through excitability in response to sensory stimulation and the cortico-muscular coherence. The task was performed bilaterally. A clear reduction of the cortico-muscular coherence was found in the short time window following stimuli (between around 150-450 ms). In the same time period, the motor control of isometric contraction was preserved. This could suggest that cortical component of voluntary movement control was transiently mediated by neuronal firing rate tuning more than by cortico-muscular synchronization. In addition to the known primary sensory cortex inhibition due to movement, a more evident reduction was found for the component known to include a contribution from primary motor areas. Gating effects were lower in the dominant left hemisphere, suggesting that sensorimotor areas dominant for hand control benefit of narrowing down gating effects.

Background: Dystonia is often currently treated with botulinum toxin injections to spastic muscles, or deep brain stimulation to the basal ganglia. In addition to these pharmacological or neurosurgical measures, a new noninvasive treatment concept, functional modulation using a brain-computer interface, was tested for feasibility. We recorded electroencephalograms (EEGs) over the bilateral sensorimotor cortex from a patient suffering from chronic writer’s cramp. The patient was asked to suppress an exaggerated beta frequency component in the EEG during hand extension., Results: The patient completed biweekly one-hour training for 5 months without any adverse effects. Significant decrease of the beta frequency component during handwriting was confirmed, and was associated with clear functional improvement., Conclusion: The current pilot study suggests that a brain-computer Interface can give explicit feedback of ongoing cortical excitability to patients with dystonia and allow them to suppress exaggerated neural activity, resulting in functional recovery., This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.