Structural correlates of atypical visual and motor cortical oscillations in pediatric-onset multiple sclerosis.

We have previously demonstrated that pediatric-onset multiple sclerosis (POMS) negatively impacts the visual pathway as well as motor processing speed. Relationships between MS-related diffuse structural damage of gray and white matter (WM) tissue and cortical responses to visual and motor stimuli remain poorly understood. We used magnetoencephalography in 14 POMS patients and 15 age- and sex-matched healthy controls to assess visual gamma (30-80 Hz), motor gamma (60-90 Hz), and motor beta (15-30 Hz) cortical oscillatory responses to a visual-motor task. Then, 3T MRI was used to: (a) calculate fractional anisotropy (FA) of the posterior visual and corticospinal motor WM pathways and (b) quantify volume and thickness of the cuneus and primary motor cortex. Visual gamma band power was reduced in POMS and was associated with reduced FA of the optic radiations but not with loss of cuneus volume or thickness. Activity in the primary motor cortex, as measured by postmovement beta rebound amplitude associated with peak latency, was decreased in POMS, although this reduction was not predicted by structural metrics. Our findings implicate loss of WM integrity as a contributor to reduced electrical responses in the visual cortex in POMS. Future work in larger cohorts will inform on the cognitive implications of this finding in terms of visual processing function and will determine whether the progressive loss of brain volume known to occur in POMS ultimately contributes to both progressive dysfunction in such tasks as well as progressive reduction in cortical electrical responses in the visual cortex.

Transient Alpha and Beta Synchrony Underlies Preparatory Recruitment of Directional Motor Networks.

Modulations in motor cortical beta and alpha activity have been implicated in the preparation, execution, and termination of voluntary movements. The functional role of motor cortex beta activity is yet to be defined, though two opposing theories prevail. The idling cortex theory suggests that large-scale motor networks, in the absence of input, revert to an intrinsic oscillatory state. The alternative theory proposes that beta activity promotes postural tone at the expense of voluntary movement. These theories are primarily based on observations of event-related desynchronization associated with movement onset. Here, we explore the changes in alpha and beta oscillatory activity associated with the specific behavioral patterns during an established directional uncertainty paradigm. We demonstrate that, consistent with current proposals, alpha and beta desynchronization reflects a process of disengagement from existing networks to enable the creation of functional assemblies. We demonstrate that, following desynchronization, a novel signature of transient alpha synchrony underlies the recruitment of functional assemblies required for directional control. Although alpha and beta desynchronization are dependent upon the number of cues presented, they are not predictive of movement preparation. However, the transient alpha synchrony occurs only when participants have sufficient information to prepare for movement and shows a direct relationship with behavioral performance measures.

Magnetoencephalography.

Although magnetoencephalography (MEG) may not be familiar to many pediatric radiologists, it is an increasingly available neuroimaging technique both for evaluating normal and abnormal intracranial neural activity and for functional mapping. By providing spatial, temporal, and time-frequency spectral information, MEG affords patients with epilepsy, intracranial neoplasia, and vascular malformations an opportunity for a sensitive and accurate non-invasive preoperative evaluation. This technique can optimize selection of surgical candidates as well as increase confidence in preoperative counseling and prognosis. Research applications that appear promising for near-future clinical translation include the evaluation of children with autism spectrum disorder, traumatic brain injury, and schizophrenia.

Spatiotemporal patterns of oscillatory brain activity during auditory word recognition in children: a synthetic aperture magnetometry study.

OBJECTIVE: We studied the task-induced spatiotemporal evolution and characteristics of cortical neural oscillations in children during an auditory word recognition task. METHODS: We presented abstract nouns binaurally and recorded the MEG response in eight healthy right-handed children (6-12 years). We calculated the event-related changes in cortical oscillations using a beamformer spatial filter analysis technique (SAM), then transformed each subject's statistical maps into standard space and used these to make group statistical inferences. RESULTS: Across subjects, the cortical response to words could be divided into at least two phases: an initial event-related synchronization in both the right temporal (100-300 ms, 15-25 Hz; 200-400 ms, 5-15 Hz) and left frontal regions (200-400 ms; 15-25 Hz); followed by a strong left-lateralized event-related desynchronization in the left temporal region (500-700 ms; 5-15 Hz). CONCLUSIONS: We found bilateral event-related synchronization followed by later left lateralized event-related desynchronization in language-related cortical areas. These data demonstrate the spatiotemporal time course of neural activation during an auditory word recognition task in a group of children. As well, this demonstrates the utility of SAM analyses to detect subtle sequential task-related neural activations.

Cortical reorganization after modified constraint-induced movement therapy in pediatric hemiplegic cerebral palsy.

Constraint-induced movement therapy improves motor function in the affected hand of children with hemiplegic cerebral palsy and results in cortical changes in adults with stroke. This study measured clinical improvement and cortical reorganization in a child with hemiplegia who underwent modified constraint-induced movement therapy for 3 weeks. Clinical, functional magnetic resonance imaging and magnetoencephalography measurements were done at baseline, after therapy, and 6 months after therapy. Modified constraint-induced movement therapy resulted in clinical improvement as measured by the Pediatric Motor Activity Log. Functional magnetic resonance imaging showed bilateral sensorimotor activation before and after therapy and a shift in the laterality index from ipsilateral to contralateral hemisphere after therapy. Magnetoencephalography showed increased cortical activation in the ipsilateral motor field and contralateral movement evoked field after therapy. Cortical reorganization was maintained at the 6-month follow-up. This is the first study to demonstrate cortical reorganization after any version of constraint-induced movement therapy in a child with hemiplegia.

Neural processing of observed oro-facial movements reflects multiple action encoding strategies in the human brain.

In this experiment, the oscillatory responses of the MEG were characterized during the observation of four viewing conditions: (a) observation of mouth movements, (b) observation of a non-biological motion stimulus (a mechanical aperture opening and shutting), (c) observation of object-directed mouth movements and (d) observation of speech-like mouth movements. Data were analyzed using synthetic aperture magnetometry (SAM) in three frequency bands, beta (15-35 Hz), gamma (35-70 Hz) and alpha/mu (8-15 Hz). Results showed that observations of biological motion resulted in beta desynchronization over lateral sensorimotor areas, while observations of non-biological motion resulted in a more medial desynchronization, an effect that may be related to the processing of a structured event sequence. Observation of linguistic movements resulted in less alpha/beta desynchronization in posterior brain regions in comparison to biological motion stimuli, suggesting that linguistically-relevant stimuli are processed with different neuronal systems than those recruited by normal action observation. We suggest that non-linguistic actions recruit dorsal systems while linguistic actions engage ventral processing systems. Object-directed movements showed the largest sensorimotor activations, suggesting that, as is the case for observations of hand movements, motoric processing is particularly sensitive to the viewing of goal-directed actions. Taken together, the results indicate that the brain utilizes multiple action encoding strategies, tailored to the function of the observed movement.

Spatiotemporal analysis of feedback processing during a card sorting task using spatially filtered MEG.

A card sorting paradigm was used to observe the neural correlates of feedback processing in adult participants. Visually presented feedback was used to indicate response accuracy and the requirement to shift response set in a 2-category card sorting task. Magnetoencephalography (MEG) responses to feedback cues were analysed using a beamformer-based spatial filtering algorithm (event-related Synthetic Aperture Magnetometry, erSAM). Analysis of source power revealed activity in rostral anterior cingulate cortex (ACC) only to negative feedback processing, which peaked at 260 ms after stimulus onset. The results are in agreement with both evidence from fMRI on spatial characteristics of negative feedback processing, and evidence from event-related potentials (ERPs) on the temporal profile of this ACC response. The superior temporal gyrus was activated only with positive feedback, reflecting integration of actions with successful outcomes. The present MEG erSAM findings are the first to provide both accurate spatial localization as well as temporal specificity for the neural correlates of feedback processing.

Localization of human somatosensory cortex using spatially filtered magnetoencephalography.

A spatial filter algorithm based on minimum-variance beamforming (synthetic aperture magnetometry (SAM)) was applied to single trial neuromagnetic recordings in order to localize primary somatosensory cortex. Magnetoencephalography (MEG) responses to electrical stimulation of the right and left median nerve were recorded using a whole-head MEG system and localized using both SAM spatial filtering and dipole analysis. Spatial filtering was applied to single trial neuromagnetic recordings to produce 3-dimensional difference images of source power between active (0-50 ms) and control states (-50-0 ms) in the range of 15-300 Hz. Average difference between N20m dipole location and location of maximal increase in power in the SAM images was 3.7 mm (1.5 mm SD) and localized to primary somatosensory cortex. Time-frequency analysis of spatially filtered output for the peak SAM locations showed a brief (10 ms) increase in the 60-100 Hz band coincident with the N20m response and a longer duration (approx. 80 ms) increase in power in the 10-40 Hz band following N20m onset. These results indicate that beamformer based spatial filter methods such as SAM can be used to localize temporally discrete cortical activity produced by median nerve stimulation.

Post-movement beta rebound is generated in motor cortex: evidence from neuromagnetic recordings.

Voluntary movements are accompanied by amplitude changes in cortical rhythms presumably as a result of functional activation of sensorimotor areas. Recently, the location of the neural generators involved in increasing power within the beta (15-30 Hz) frequency band following movement (post-movement beta rebound, PMBR) has come into question [Parkes, L.M, Bastiaansen, M.C.M, Norris, D.G., 2006. Combining EEG and fMRI to investigate the post-movement beta rebound. NeuroImage 29, 685-696.]. We used the synthetic aperture magnetometry (SAM) spatial filtering method to identify the time course and location of oscillatory changes within the beta and mu (8-14 Hz) frequency bands during the performance of voluntary movements. Neuromagnetic activity was recorded from 10 adult subjects during abduction of the right index finger. Changes in beta and mu source power were calculated for periods during and following movement, relative to pre-movement baseline activity. Decreases in beta band activity (event-related desynchronization, ERD) were observed during movement, with a strong increase (PMBR) beginning 230+/-170 ms following movement, lasting for 680+/-170 ms. Mu band ERD was observed both during and following movement, with little to no post-movement rebound. Beta and mu ERD were localized bilaterally to the hand region of postcentral gyrus whereas PMBR was localized bilaterally to the hand region of precentral gyrus (motor cortex). Both PMBR and beta ERD were strongest contralateral to the side of movement. These results provide further evidence that movement influences independent cortical rhythms in sensorimotor areas, and confirm previous reports of precentral generators of PMBR in the region of motor cortex, with postcentral generators of beta and mu ERD during movement.