Movement-related magnetic fields to tongue protrusion

Neurophysiological Basis of Deep Brain Stimulation and Botulinum Neurotoxin Injection for Treating Oromandibular Dystonia

Oromandibular dystonia (OMD) induces severe motor impairments, such as masticatory disturbances, dysphagia, and dysarthria, resulting in a serious decline in quality of life. Non-invasive brain-imaging techniques such as electroencephalography (EEG) and magnetoencephalography (MEG) are powerful approaches that can elucidate human cortical activity with high temporal resolution. Previous studies with EEG and MEG have revealed that movements in the stomatognathic system are regulated by the bilateral central cortex. Recently, in addition to the standard therapy of botulinum neurotoxin (BoNT) injection into the affected muscles, bilateral deep brain stimulation (DBS) has been applied for the treatment of OMD. However, some patients' OMD symptoms do not improve sufficiently after DBS, and they require additional BoNT therapy. In this review, we provide an overview of the unique central spatiotemporal processing mechanisms in these regions in the bilateral cortex using EEG and MEG, as they relate to the sensorimotor functions of the stomatognathic system. Increased knowledge regarding the neurophysiological underpinnings of the stomatognathic system will improve our understanding of OMD and other movement disorders, as well as aid the development of potential novel approaches such as combination treatment with BoNT injection and DBS or non-invasive cortical current stimulation therapies.

Beyond language: The unspoken sensory-motor representation of the tongue in non-primates, non-human and human primates

The English idiom "on the tip of my tongue" commonly acknowledges that something is known, but it cannot be immediately brought to mind. This phrase accurately describes sensorimotor functions of the tongue, which are fundamental for many tongue-related behaviors (e.g., speech), but often neglected by scientific research. Here, we review a wide range of studies conducted on non-primates, non-human and human primates with the aim of providing a comprehensive description of the cortical representation of the tongue's somatosensory inputs and motor outputs across different phylogenetic domains. First, we summarize how the properties of passive non-noxious mechanical stimuli are encoded in the putative somatosensory tongue area, which has a conserved location in the ventral portion of the somatosensory cortex across mammals. Second, we review how complex self-generated actions involving the tongue are represented in more anterior regions of the putative somato-motor tongue area. Finally, we describe multisensory response properties of the primate and non-primate tongue area by also defining how the cytoarchitecture of this area is affected by experience and deafferentation.

Feasibility and Challenges of Performing Magnetoencephalography Experiments in Children With Arthrogryposis Multiplex Congenita

Arthrogryposis multiplex congenita (AMC) has recently drawn substantial attention from researchers and clinicians. New effective surgical and physiotherapeutic methods have been developed to improve the quality of life of patients with AMC. While it is clear that all these interventions should strongly rely on the plastic reorganization of the central nervous system, almost no studies have investigated this topic. The present study demonstrates the feasibility of using magnetoencephalography (MEG) to investigate brain activity in young AMC patients. We also outlined the general challenges and limitations of electrophysiological investigations on patients with arthrogryposis. We conducted MEG recordings using a 306-channel Elekta Neuromag VectorView system during a cued motor task performance in four patients with arthrogryposis, five normally developed children, and five control adults. Following the voice command of the experimenter, each subject was asked to bring their hand toward their mouth to imitate the self-feeding process. Two patients had latissimus dorsi transferred to the biceps brachii position, one patient had a pectoralis major transferred to the biceps brachii position, and one patient had no elbow flexion restoration surgery before the MEG investigation. Three patients who had undergone autotransplantation prior to the MEG investigation demonstrated activation in the sensorimotor area contralateral to the elbow flexion movement similar to the healthy controls. One patient who was recorded before the surgery demonstrated subjectively weak distributed bilateral activation during both left and right elbow flexion. Visual inspection of MEG data suggested that neural activity associated with motor performance was less pronounced and more widely distributed across the cortical areas of patients than of healthy control subjects. In general, our results could serve as a proof of principle in terms of the application of MEG in studies on cortical activity in patients with AMC. Reported trends might be consistent with the idea that prolonged motor deficits are associated with more difficult neuronal recruitment and the spatial heterogeneity of neuronal sources, most likely reflecting compensatory neuronal mechanisms. On the practical side, MEG could be a valuable technique for investigating the neurodynamics of patients with AMC as a function of postoperative abilitation.

Cortical Mechanisms of Tongue Sensorimotor Functions in Humans: A Review of the Magnetoencephalography Approach

The tongue plays important roles in a variety of critical human oral functions, including speech production, swallowing, mastication and respiration. These sophisticated tongue movements are in part finely regulated by cortical entrainment. Many studies have examined sensorimotor processing in the limbs using magnetoencephalography (MEG), which has high spatiotemporal resolution. Such studies have employed multiple methods of analysis, including somatosensory evoked fields (SEFs), movement-related cortical fields (MRCFs), event-related desynchronization/synchronization (ERD/ERS) associated with somatosensory stimulation or movement and cortico-muscular coherence (CMC) during sustained movement. However, the cortical mechanisms underlying the sensorimotor functions of the tongue remain unclear, as contamination artifacts induced by stimulation and/or muscle activity within the orofacial region complicates MEG analysis in the oral region. Recently, several studies have obtained MEG recordings from the tongue region using improved stimulation methods and movement tasks. In the present review, we provide a detailed overview of tongue sensorimotor processing in humans, based on the findings of recent MEG studies. In addition, we review the clinical applications of MEG for sensory disturbances of the tongue caused by damage to the lingual nerve. Increased knowledge of the physiological and pathophysiological mechanisms underlying tongue sensorimotor processing may improve our understanding of the cortical entrainment of human oral functions.

Movement-related cortical magnetic fields associated with self-paced tongue protrusion in humans

Sophisticated tongue movements are coordinated finely via cortical control. We elucidated the cortical processes associated with voluntary tongue movement. Movement-related cortical fields were investigated during self-paced repetitive tongue protrusion. Surface tongue electromyograms were recorded to determine movement onset. To identify the location of the primary somatosensory cortex (S1), tongue somatosensory evoked fields were measured. The readiness fields (RFs) over both hemispheres began prior to movement onset and culminated in the motor fields (MFs) around movement onset. These signals were followed by transient movement evoked fields (MEFs) after movement onset. The MF and MEF peak latencies and magnitudes were not different between the hemispheres. The MF current sources were located in the precentral gyrus, suggesting they were located in the primary motor cortex (M1); this was contrary to the MEF sources, which were located in S1. We conclude that the RFs and MFs mainly reflect the cortical processes for the preparation and execution of tongue movement in the bilateral M1, without hemispheric dominance. Moreover, the MEFs may represent proprioceptive feedback from the tongue to bilateral S1. Such cortical processing related to the efferent and afferent information may aid in the coordination of sophisticated tongue movements.

Mu rhythm desynchronization by tongue thrust observation

We aimed to investigate the mu rhythm in the sensorimotor area during tongue thrust observation and to obtain an answer to the question as to how subtle non-verbal orofacial movement observation activates the sensorimotor area. Ten healthy volunteers performed finger tap execution, tongue thrust execution, and tongue thrust observation. The electroencephalogram (EEG) was recorded from 128 electrodes placed on the scalp, and regions of interest were set at sensorimotor areas. The event-related desynchronization (ERD) and event-related synchronization (ERS) for the mu rhythm (8-13 Hz) and beta (13-25 Hz) bands were measured. Tongue thrust observation induced mu rhythm ERD, and the ERD was detected at the left hemisphere regardless whether the observed tongue thrust was toward the left or right. Mu rhythm ERD was also recorded during tongue thrust execution. However, temporal analysis revealed that the ERD associated with tongue thrust observation preceded that associated with execution by approximately 2 s. Tongue thrust observation induces mu rhythm ERD in sensorimotor cortex with left hemispheric dominance.

Corticomotor plasticity induced by tongue-task training in humans: a longitudinal fMRI study

Corticomotor pathways may undergo neuroplastic changes in response to acquisition of new motor skills. Little is known about the motor control strategies for learning new tongue tasks. The aim of this study was to investigate the longitudinal effect of novel tongue-task training on corticomotor neuroplasticity. Thirteen healthy, right-handed men, aged 24-35 years (mean age ± SD: 27.3 ± 0.3 years), performed a training task consisting of standardized tongue protrusion onto a force transducer. The tongue task consisted of a relax-protrude-hold-relax cycle with 1.0 N as the target at the hold phase lasting for 1.5 s. Subjects repeated this task for 1 h. Functional magnetic resonance imaging was carried out before the tongue-task training (baseline), 1-h after the training, and one-day and one-week follow-up. During scanning, the subjects performed tongue protrusion in blocks interspersed with rest. A region-of-interest (ROI) approach and an explorative search were implemented for the analysis of corticomotor activity across conditions. All subjects completed the tongue-task training (mean success rate 43.0 ± 13.2%). In the baseline condition, tongue protrusion resulted in bilateral activity in regions most typically associated with a motor task including medial frontal gyrus (supplementary motor area [SMA]), precentral gyrus (tongue motor cortex), putamen, thalamus, and cerebellum. The ROI analysis revealed increased activity in the precentral gyrus already 1 h post-training. One day after the training, increased activity was observed in the precentral gyrus, SMA, putamen, and cerebellum. No increase was found 1 week after training. Correlation analyses between changes in success rates and changes in the numbers of voxels showed robust associations for left Area 4a in primary motor cortex 1 h, 1 day, and 1 week after the tongue-task training and for the left Area 4p in primary motor cortex and the left lateral premotor cortex 1 day after the training. In the unrestricted analysis, increased activity was found in the parahippocampal gyrus 1 h after the tongue-task training and remained for a week. Decreased activity was found in right post-central and middle frontal gyri 1 h and 1 week post-training. The results verified the involvement of specific corticomotor areas in response to tongue protrusion. Short-term tongue-task training was associated with longer-lasting (up to 1 week) changes in motor-related brain activity. The results suggested that primary motor areas are involved in the early and late stages, while other motor areas mainly are engaged in the later stage of corticomotor neuroplasticity of the tongue.

Somatotopic distribution of peri-rolandic spikes may predict prognosis in pediatric-onset epilepsy with sensorimotor seizures

OBJECTIVE

Peri-rolandic spikes are typically seen in benign childhood epilepsy with centro-temporal spikes. However, some cases of epilepsy with peri-rolandic spikes manifest with medical intractability or cognitive dysfunction. The present study evaluated whether spike source localization is predictive of different prognosis of epilepsy and/or cognitive function.

METHODS

The localization of peri-rolandic spikes was compared between 6 patients whose seizure remitted under age of 15 years with no cognitive impairment (benign group) and 6 patients with either intractable epilepsy or cognitive dysfunction (non-benign group). The sources of epileptic spikes were approximated by the single equivalent current dipole (ECD) model using whole-head magnetoencephalography.

RESULTS

The spike locations in the benign group were significantly lateral (14.8±5.3 versus 5.3±3.3 mm, p<0.05), anterior (11.6±2.1 versus 3.7±4.8 mm, p<0.01), and inferior (27.7±3.6 versus 12.0±10.0 mm, p<0.01) to those in the non-benign group. Seizures tended to involve the laryngo-pharyngo-oro-facial area in the benign group and the facial-hand-foot area in the non-benign group.

CONCLUSION

The clear difference in spike dipole location between benign group and non-benign groups.

SIGNIFICANCE

Spike localization may be useful for predicting prognosis in epilepsy with sensorimotor seizures and spikes along with central sulcus.

Primary face motor area as the motor representation of articulation

No clinical data have yet been presented to show that a lesion localized to the primary motor area (M1) can cause severe transient impairment of articulation, although a motor representation for articulation has been suggested to exist within M1. Here we describe three cases of patients who developed severe dysarthria, temporarily mimicking speech arrest or aphemia, due to a localized brain lesion near the left face representation of the human primary motor cortex (face-M1). Speech was slow, effortful, lacking normal prosody, and more affected than expected from the degree of facial or tongue palsy. There was a mild deficit in tongue movements in the sagittal plane that impaired palatolingual contact and rapid tongue movements. The speech disturbance was limited to verbal output, without aphasia or orofacial apraxia. Overlay of magnetic resonance images revealed a localized cortical region near face-M1, which displayed high intensity on diffusion weighted images, while the main portion of the corticobulbar fibers arising from the lower third of the motor cortex was preserved. The cases suggest the existence of a localized brain region specialized for articulation near face-M1. Cortico-cortical fibers connecting face-M1 with the lower premotor areas including Broca's area may also be important for articulatory control.

Rhythmic brain activities related to singing in humans

To investigate the motor control related to sound production, we studied cortical rhythmic changes during continuous vocalization such as singing. Magnetoencephalographic (MEG) responses were recorded while subjects spoke in the usual way (speaking), sang (singing), hummed (humming) and imagined (imagining) a popular song. The power of alpha (8-15 Hz), beta (15-30 Hz) and low-gamma (30-60 Hz) frequency bands was changed during and after vocalization (singing, speaking and humming). In the alpha band, the oscillatory changes for singing were most pronounced in the right premotor, bilateral sensorimotor, right secondary somatosensory and bilateral superior parietal areas. The beta oscillation for the singing was also confirmed in the premotor, primary and secondary sensorimotor and superior parietal areas in the left and right hemispheres where were partly activated even for imagined a song (imaging). These regions have been traditionally described as vocalization-related sites. The cortical rhythmic changes were distinct in the singing condition compared with the other vocalizing conditions (speaking and humming) and thus we considered that more concentrated control of the vocal tract, diaphragm and abdominal muscles is responsible. Furthermore, characteristic oscillation in the high-gamma (60-200 Hz) frequency band was found in Broca's area only in the imaging condition and might occur singing rehearsal and storage process in Broca's area.

One hour of tongue-task training is associated with plasticity in corticomotor control of the human tongue musculature

Corticomotor control of the human tongue has been reported to undergo neuroplastic changes following several days of training in a tongue-protrusion task. The aims of the present study were to determine if a 1 h tongue-task training is sufficient to induce signs of neuroplastic changes in the corticomotor pathways, and to obtain preliminary information on the time course of such changes. Corticomotor excitability was assessed by changes in electromyographic activity evoked by transcortical magnetic stimulation (TMS) in 11 healthy subjects. Motor evoked potentials (MEPs) recorded in the tongue musculature and the first dorsal interosseous (FDI) muscle were assessed at four sessions: at baseline before training, 30 min after training, and 1 and 7 days after training. All subjects performed successfully the task (success rate: 38+/-4%). Thresholds for evoking MEPs by TMS in the tongue were decreased at 30 min, 1 and 7 days after training compared with baseline (ANOVA: P<0.001). Tongue MEP amplitudes were significantly increased at 1 day follow-up and had returned to baseline values at 7 days follow-up (ANOVA: P<0.001). No significant effect of tongue-task training on FDI MEPs was observed (ANOVA: P=0.160). Corticomotor topographic maps revealed increases (ANOVA: P<0.001) in area at the 1 day follow-up. The success rate was significantly correlated to the net increases in tongue MEPs at 1 day follow-up (Spearman: 0.615; P=0.0039). The present findings confirm that tongue task training is associated with plasticity of corticomotor excitability specifically related to the tongue musculature and further document that plasticity is evident within 30 min post-training and may last up to at least 7 days.

Prediction on affected upper extremity function in hemiplegic patients after thalamic hemorrhage using somatosensory evoked magnetic fields

The aim of the present study was to investigate the prognostic value of somatosensory evoked magnetic fields (SEFs) at an acute stage on recovery of an affected upper extremity (UE) function as practicality in hemiplegic patients after thalamic hemorrhage. Nine hemiplegic patients after thalamic hemorrhage were enrolled in this study. Median nerve SEFs, evoked by electrical stimulation at the wrist of the affected UE, were measured using a 204 channel whole-head magnetoencephalography system within 72 hours after the onset of thalamic hemorrhage (acute stage). Assessments on the affected UE, which included the motor palsies of the UE and fingers (Brunnstrom's motor recovery stage: BS), sensory disturbance (the thumb localizing test) and UE function (the UE ability test), were performed at both the acute stage and 3 months after the onset of thalamic hemorrhage (chronic stage). Almost all the patients showing any median nerve SEF components that originated from the somatosensory cortex in the affected hemisphere and occurred between about 20 ms and 100 ms post-stimulus at the acute stage demonstrated good outcomes in the motor palsies (BSV), sensory disturbance (normal) and affected UE function (practical hand) at the chronic stage. In contrast, majority of patients not showing them at all demonstrated poor outcomes in the motor palsies (BSIII or less), sensory disturbance (severely impaired) and affected UE function (disabled hand) at the chronic stage. These results suggest that the findings of the median nerve SEFs at the acute stage would contribute to the early outcome prediction on the affected UE function in hemiplegic patients after thalamic hemorrhage.

Dissociating the spatio-temporal characteristics of cortical neuronal activity associated with human volitional swallowing in the healthy adult brain

Human swallowing represents a complex highly coordinated sensorimotor function whose functional neuroanatomy remains incompletely understood. Specifically, previous studies have failed to delineate the temporo-spatial sequence of those cerebral loci active during the differing phases of swallowing. We therefore sought to define the temporal characteristics of cortical activity associated with human swallowing behaviour using a novel application of magnetoencephalography (MEG). In healthy volunteers (n = 8, aged 28-45), 151-channel whole cortex MEG was recorded during the conditions of oral water infusion, volitional wet swallowing (5 ml bolus), tongue thrust or rest. Each condition lasted for 5 s and was repeated 20 times. Synthetic aperture magnetometry (SAM) analysis was performed on each active epoch and compared to rest. Temporal sequencing of brain activations utilised time-frequency wavelet plots of regions selected using virtual electrodes. Following SAM analysis, water infusion preferentially activated the caudolateral sensorimotor cortex, whereas during volitional swallowing and tongue movement, the superior sensorimotor cortex was more strongly active. Time-frequency wavelet analysis indicated that sensory input from the tongue simultaneously activated caudolateral sensorimotor and primary gustatory cortex, which appeared to prime the superior sensory and motor cortical areas, involved in the volitional phase of swallowing. Our data support the existence of a temporal synchrony across the whole cortical swallowing network, with sensory input from the tongue being critical. Thus, the ability to non-invasively image this network, with intra-individual and high temporal resolution, provides new insights into the brain processing of human swallowing.