BrainWave: A Matlab Toolbox for Beamformer Source Analysis of MEG Data

Artificial embodiment displaces cortical neuromagnetic somatosensory responses

Integrating artificial limbs as part of one's body involves complex neuroplastic changes resulting from various sensory inputs. While somatosensory feedback is crucial, plastic processes that enable embodiment remain unknown. We investigated this using somatosensory evoked fields (SEFs) in the primary somatosensory cortex (S1) following the Rubber Hand Illusion (RHI), known to quickly induce artificial limb embodiment. During electrical stimulation of the little finger and thumb, 19 adults underwent neuromagnetic recordings before and after the RHI. We found early SEF displacement, including an illusion-brain correlation between extent of embodiment and specific changes to the first cortical response at 20 ms in Area 3b, within S1. Furthermore, we observed a posteriorly directed displacement at 35 ms towards Area 1, known to be important for visual integration during touch perception. That this second displacement was unrelated to extent of embodiment implies a functional distinction between neuroplastic changes of these components and areas. The earlier shift in Area 3b may shape extent of limb ownership, while subsequent displacement into Area 1 may relate to early visual-tactile integration that initiates embodiment. Here we provide evidence for multiple neuroplastic processes in S1-lasting beyond the illusion-supporting integration of artificial limbs like prostheses within the body representation.

Decoding kinematic information from beta-band motor rhythms of speech motor cortex: a methodological/analytic approach using concurrent speech movement tracking and magnetoencephalography

Introduction

Articulography and functional neuroimaging are two major tools for studying the neurobiology of speech production. Until now, however, it has generally not been feasible to use both in the same experimental setup because of technical incompatibilities between the two methodologies.

Methods

Here we describe results from a novel articulography system dubbed Magneto-articulography for the Assessment of Speech Kinematics (MASK), which is technically compatible with magnetoencephalography (MEG) brain scanning systems. In the present paper we describe our methodological and analytic approach for extracting brain motor activities related to key kinematic and coordination event parameters derived from time-registered MASK tracking measurements. Data were collected from 10 healthy adults with tracking coils on the tongue, lips, and jaw. Analyses targeted the gestural landmarks of reiterated utterances/ipa/ and /api/, produced at normal and faster rates.

Results

The results show that (1) Speech sensorimotor cortex can be reliably located in peri-rolandic regions of the left hemisphere; (2) mu (8-12 Hz) and beta band (13-30 Hz) neuromotor oscillations are present in the speech signals and contain information structures that are independent of those present in higher-frequency bands; and (3) hypotheses concerning the information content of speech motor rhythms can be systematically evaluated with multivariate pattern analytic techniques.

Discussion

These results show that MASK provides the capability, for deriving subject-specific articulatory parameters, based on well-established and robust motor control parameters, in the same experimental setup as the MEG brain recordings and in temporal and spatial co-register with the brain data. The analytic approach described here provides new capabilities for testing hypotheses concerning the types of kinematic information that are encoded and processed within specific components of the speech neuromotor system.

Parietofrontal oscillations show hand-specific interactions with top-down movement plans

To generate a hand-specific reach plan, the brain must integrate hand-specific signals with the desired movement strategy. Although various neurophysiology/imaging studies have investigated hand-target interactions in simple reach-to-target tasks, the whole brain timing and distribution of this process remain unclear, especially for more complex, instruction-dependent motor strategies. Previously, we showed that a pro/anti pointing instruction influences magnetoencephalographic (MEG) signals in frontal cortex that then propagate recurrently through parietal cortex (Blohm G, Alikhanian H, Gaetz W, Goltz HC, DeSouza JF, Cheyne DO, Crawford JD. NeuroImage 197: 306-319, 2019). Here, we contrasted left versus right hand pointing in the same task to investigate 1) which cortical regions of interest show hand specificity and 2) which of those areas interact with the instructed motor plan. Eight bilateral areas, the parietooccipital junction (POJ), superior parietooccipital cortex (SPOC), supramarginal gyrus (SMG), medial/anterior interparietal sulcus (mIPS/aIPS), primary somatosensory/motor cortex (S1/M1), and dorsal premotor cortex (PMd), showed hand-specific changes in beta band power, with four of these (M1, S1, SMG, aIPS) showing robust activation before movement onset. M1, SMG, SPOC, and aIPS showed significant interactions between contralateral hand specificity and the instructed motor plan but not with bottom-up target signals. Separate hand/motor signals emerged relatively early and lasted through execution, whereas hand-motor interactions only occurred close to movement onset. Taken together with our previous results, these findings show that instruction-dependent motor plans emerge in frontal cortex and interact recurrently with hand-specific parietofrontal signals before movement onset to produce hand-specific motor behaviors.NEW & NOTEWORTHY The brain must generate different motor signals depending on which hand is used. The distribution and timing of hand use/instructed motor plan integration are not understood at the whole brain level. Using MEG we show that different action planning subnetworks code for hand usage and integrating hand use into a hand-specific motor plan. The timing indicates that frontal cortex first creates a general motor plan and then integrates hand specificity to produce a hand-specific motor plan.

Inhibitory Control in the Absence of Awareness: Interactions Between Frontal and Motor Cortex Oscillations Mediate Implicitly Learned Responses

Cognitive control of action is associated with conscious effort and is hypothesised to be reflected by increased frontal theta activity. However, the functional role of these increases in theta power, and how they contribute to cognitive control remains unknown. We conducted an MEG study to test the hypothesis that frontal theta oscillations interact with sensorimotor signals in order to produce controlled behaviour, and that the strength of these interactions will vary with the amount of control required. We measured neuromagnetic activity in 16 healthy adults performing a response inhibition (Go/Switch) task, known from previous work to modulate cognitive control requirements using hidden patterns of Go and Switch cues. Learning was confirmed by reduced reaction times (RT) to patterned compared to random Switch cues. Concurrent measures of pupil diameter revealed changes in subjective cognitive effort with stimulus probability, even in the absence of measurable behavioural differences, revealing instances of covert variations in cognitive effort. Significant theta oscillations were found in five frontal brain regions, with theta power in the right middle frontal and right premotor cortices parametrically increasing with cognitive effort. Similar increases in oscillatory power were also observed in motor cortical gamma, suggesting an interaction. Right middle frontal and right precentral theta activity predicted changes in pupil diameter across all experimental conditions, demonstrating a close relationship between frontal theta increases and cognitive control. Although no theta-gamma cross-frequency coupling was found, long-range theta phase coherence among the five significant sources between bilateral middle frontal, right inferior frontal, and bilateral premotor areas was found, thus providing a mechanism for the relay of cognitive control between frontal and motor areas via theta signalling. Furthermore, this provides the first evidence for the sensitivity of frontal theta oscillations to implicit motor learning and its effects on cognitive load. More generally these results present a possible a mechanism for this frontal theta network to coordinate response preparation, inhibition and execution.

Somatosensory Plasticity in Hemiplegic Cerebral Palsy Following Constraint Induced Movement Therapy

BACKGROUND

Children with hemiplegic cerebral palsy (HCP) experience upper limb somatosensory and motor deficits. Although constraint-induced movement therapy (CIMT) improves motor function, its impact on somatosensory function remains underinvestigated.

OBJECTIVE

The objective of this study was to evaluate somatosensory perception and related brain responses in children with HCP, before and after a somatosensory enhanced CIMT protocol, as measured using clinical sensory and motor assessments and magnetoencephalography.

METHODS

Children with HCP attended a somatosensory enhanced CIMT camp. Clinical somatosensory (tactile registration, 2-point discrimination, stereognosis, proprioception, kinesthesia) and motor outcomes (Quality of Upper Extremity Skills [QUEST] Total/Grasp, Jebsen-Taylor Hand Function Test, grip strength, Assisting Hand Assessment), as well as latency and amplitude of magnetoencephalography somatosensory evoked fields (SEF), were assessed before and after the CIMT camp with paired sample t-tests or Wilcoxon signed-rank tests.

RESULTS

Twelve children with HCP (mean age: 7.5 years, standard deviation: 2.4) participated. Significant improvements in tactile registration for the affected (hemiplegic) hand (Z = 2.39, P = 0.02) were observed in addition to statistically and clinically significant improvements in QUEST total (t = 3.24, P = 0.007), QUEST grasp (t = 3.24, P = 0.007), Assisting Hand Assessment (Z = 2.25, P = 0.03), and Jebsen-Taylor Hand Function Test (t = -2.62, P = 0.03). A significant increase in the SEF peak amplitude was also found in the affected hand 100 ms after stimulus onset (t = -2.22, P = 0.04).

CONCLUSIONS

Improvements in somatosensory clinical function and neural processing in the affected primary somatosensory cortex in children with HCP were observed after a somatosensory enhanced CIMT program. Further investigation is warranted to continue to evaluate the effectiveness of a sensory enhanced CIMT program in larger samples and controlled study designs.

Complexity-Dependent Modulations of Beta Oscillations for Verbal and Nonverbal Movements

Purpose The planning and execution of motor behaviors require coordination of neurons that are established through synchronization of neural activity. Movements are typically preceded by event-related desynchronization (ERD) in the beta range (15-30 Hz) primarily localized in the motor cortex, while movement onset is associated with event-related synchronization (ERS). It is hypothesized that ERD is important for movement preparation and execution, and ERS serves to inhibit movement and update the motor plan. The primary objective of this study was to determine to what extent movement-related oscillatory brain patterns (ERD and ERS) during verbal and nonverbal tasks may be affected differentially by variations in task complexity. Method Seventeen right-handed adult participants (nine women, eight men; M _age = 25.8 years, SD = 5.13) completed a sequential button press and verbal task. The final analyses included data for 15 participants for the nonverbal task and 13 for the verbal task. Both tasks consisted of two complexity levels: simple and complex sequences. Magnetoencephalography was used to record modulations in beta band brain oscillations during task performance. Results Both the verbal and button press tasks were characterized by significant premovement ERD and postmovement ERS. However, only simple sequences showed a distinct transient synchronization during the premovement phase of the task. Differences between the two tasks were reflected in both latency and peak amplitude of ERD and ERS, as well as in lateralization of oscillations. Conclusions Both verbal and nonverbal movements showed a significant desynchronization of beta oscillations during the movement preparation and holding phase and a resynchronization upon movement termination. Importantly, the premovement phase for simple but not complex tasks was characterized by a transient partial synchronization. In addition, the data revealed significant differences between the two tasks in terms of lateralization of oscillatory modulations. Our findings suggest that, while data from the general motor control research can inform our understanding of speech motor control, significant differences exist between the two motor systems that caution against overgeneralization of underlying neural control processes.

White matter microstructural differences underlying beta oscillations during speech in adults who stutter

The basal ganglia-thalamocortical (BGTC) loop may underlie speech deficits in developmental stuttering. In this study, we investigated the relationship between abnormal cortical neural oscillations and structural integrity alterations in adults who stutter (AWS) using a novel magnetoencephalography (MEG) guided tractography approach. Beta oscillations were analyzed using sensorimotor speech MEG, and white matter pathways were examined using tract-based spatial statistics (TBSS) and probabilistic tractography in 11 AWS and 11 fluent speakers. TBSS analysis revealed overlap between cortical regions of increased beta suppression localized to the mouth motor area and a reduced fractional anisotropy (FA) in the AWS group. MEG-guided tractography showed reduced FA within the BGTC loop from left putamen to subject-specific MEG peak. This is the first study to provide evidence that structural abnormalities may be associated with functional deficits in stuttering and reflect a network deficit within the BGTC loop that includes areas of the left ventral premotor cortex and putamen.

A Polarity Alignment Method for Group-Averaging of Event-Related Neural Signals at Source Level in MEG Beamforming Applications

Brain waveforms reconstructed at source level, like in beamforming, suffer polarity indeterminacy, which precludes direct group averaging of associated waveforms. We describe a polarity alignment method as an alternative of averaging rectified (i.e. absolute value) waveforms. Using MEG from an auditory localisation task, we compare the ability of the two approaches to enable signal detection in the primary auditory cortex over increasing sample size. The two methods are comparable in signal detection sensitivity, but the alignment method preserves group-average polarity alternation.

Theta oscillations support the interface between language and memory

Recent evidence shows that hippocampal theta oscillations, usually linked to memory and navigation, are also observed during online language processing, suggesting a shared neurophysiological mechanism between language and memory. However, it remains to be established what specific roles hippocampal theta oscillations may play in language, and whether and how theta mediates the communication between the hippocampus and the perisylvian cortical areas, generally thought to support language processing. With whole-head magnetoencephalographic (MEG) recordings, the present study investigated these questions with two experiments. Using a violation paradigm, extensively used for studying neural underpinnings of different aspects of linguistic processing, we found increased theta power (4-8 ​Hz) in the hippocampal formation, when participants read a semantically incorrect vs. correct sentence ending. Such a pattern of results was replicated using different sentence stimuli in another cohort of participants. Importantly, no significant hippocampal theta power increase was found when participants read a semantically correct but syntactically incorrect sentence ending vs. a correct sentence ending. These findings may suggest that hippocampal theta oscillations are specifically linked to lexical-semantic related processing, and not general information processing in sentence reading. Furthermore, we found significantly transient theta phase coupling between the hippocampus and the left superior temporal gyrus, a hub area of the cortical network for language comprehension. This transient theta phase coupling may provide an important channel that links the memory and language systems for the generation of sentence meaning. Overall, these findings help specify the role of hippocampal theta in language, and provide a novel neurophysiological mechanism at the network level that may support the interface between memory and language.

Mapping neural dynamics underlying saccade preparation and execution and their relation to reaction time and direction errors

Our ability to control and inhibit automatic behaviors is crucial for negotiating complex environments, all of which require rapid communication between sensory, motor, and cognitive networks. Here, we measured neuromagnetic brain activity to investigate the neural timing of cortical areas needed for inhibitory control, while 14 healthy young adults performed an interleaved prosaccade (look at a peripheral visual stimulus) and antisaccade (look away from stimulus) task. Analysis of how neural activity relates to saccade reaction time (SRT) and occurrence of direction errors (look at stimulus on antisaccade trials) provides insight into inhibitory control. Neuromagnetic source activity was used to extract stimulus‐aligned and saccade‐aligned activity to examine temporal differences between prosaccade and antisaccade trials in brain regions associated with saccade control. For stimulus‐aligned antisaccade trials, a longer SRT was associated with delayed onset of neural activity within the ipsilateral parietal eye field (PEF) and bilateral frontal eye field (FEF). Saccade‐aligned activity demonstrated peak activation 10ms before saccade‐onset within the contralateral PEF for prosaccade trials and within the bilateral FEF for antisaccade trials. In addition, failure to inhibit prosaccades on anti‐saccade trials was associated with increased activity prior to saccade onset within the FEF contralateral to the peripheral stimulus. This work on dynamic activity adds to our knowledge that direction errors were due, at least in part, to a failure to inhibit automatic prosaccades. These findings provide novel evidence in humans regarding the temporal dynamics within oculomotor areas needed for saccade programming and the role frontal brain regions have on top‐down inhibitory control.

Individual differences in motor development during early childhood: An MEG study

In a previous study, we reported the first measurements of pre-movement and sensorimotor cortex activity in preschool age children (ages 3-5 years) using a customized pediatric magnetoencephalographic system. Movement-related activity in the sensorimotor cortex differed from that typically observed in adults, suggesting that maturation of cortical motor networks was still incomplete by late preschool age. Here we compare these earlier results to a group of school age children (ages 6-8 years) including seven children from the original study measured again two years later, and a group of adults (mean age 31.1 years) performing the same task. Differences in movement-related brain activity were observed both longitudinally within children in which repeated measurements were made, and cross-sectionally between preschool age children, school age children, and adults. Movement-related mu (8-12 Hz) and beta (15-30 Hz) oscillations demonstrated linear increases in amplitude and mean frequency with age. In contrast, movement-evoked gamma synchronization demonstrated a step-like transition from low (30-50 Hz) to high (70-90 Hz) narrow-band oscillations, and this occurred at different ages in different children. Notably, pre-movement activity ('readiness fields') observed in adults was absent in even the oldest children. These are the first direct observations of brain activity accompanying motor responses throughout early childhood, confirming that maturation of this activity is still incomplete by mid-childhood. In addition, individual children demonstrated markedly different developmental trajectories in movement-related brain activity, suggesting that individual differences need to be taken into account when studying motor development across age groups.

White matter plasticity and maturation in human cognition

White matter plasticity likely plays a critical role in supporting cognitive development. However, few studies have used the imaging methods specific to white matter tissue structure or experimental designs sensitive to change in white matter necessary to elucidate these relations. Here we briefly review novel imaging approaches that provide more specific information regarding white matter microstructure. Furthermore, we highlight recent studies that provide greater clarity regarding the relations between changes in white matter and cognition maturation in both healthy children and adolescents and those with white matter insult. Finally, we examine the hypothesis that white matter is linked to cognitive function via its impact on neural synchronization. We test this hypothesis in a population of children and adolescents with recurrent demyelinating syndromes. Specifically, we evaluate group differences in white matter microstructure within the optic radiation; and neural phase synchrony in visual cortex during a visual task between 25 patients and 28 typically developing age-matched controls. Children and adolescents with demyelinating syndromes show evidence of myelin and axonal compromise and this compromise predicts reduced phase synchrony during a visual task compared to typically developing controls. We investigate one plausible mechanism at play in this relationship using a computational model of gamma generation in early visual cortical areas. Overall, our findings show a fundamental connection between white matter microstructure and neural synchronization that may be critical for cognitive processing. In the future, longitudinal or interventional studies can build upon our knowledge of these exciting relations between white matter, neural communication, and cognition.