Xiaolin Huo

Frequency and spatial characteristics of high-frequency neuromagnetic signals in childhood epilepsy

PURPOSEnInvasive intracranial recordings have suggested that high-frequency oscillation is involved in epileptogenesis and is highly localized to epileptogenic zones. The aim of the present study is to characterize the frequency and spatial patterns of high-frequency brain signals in childhood epilepsy using a non-invasive technology.nnnMETHODSnThirty children with clinically diagnosed epilepsy were studied using a whole head magnetoencephalography (MEG) system. MEG data were digitized at 4,000 Hz. The frequency and spatial characteristics of high-frequency neuromagnetic signals were analyzed using continuous wavelet transform and beamformer. Three-dimensional magnetic resonance imaging (MRI) was obtained for each patient to localize magnetic sources.nnnRESULTSnTwenty-six patients showed high-frequency (100-1,000 Hz) components (26/30, 86%). Nineteen patients showed more than one high-frequency component (19/30, 63%). The frequency range of high-frequency components varied across patients. The highest frequency band was identified around 910 Hz. The loci of high-frequency epileptic activities were concordant with the lesions identified by magnetic resonance imaging for 21 patients (21/30, 70%). The MEG source localizations of high-frequency components were found to be concordant with intracranial recordings for nine of the eleven patients who underwent epilepsy surgery (9/11, 82%).nnnCONCLUSIONnThe results have demonstrated that childhood epilepsy was associated with high-frequency epileptic activity in a wide frequency range. The concordance of MEG source localization, MRI and intracranial recordings suggests that measurement of high-frequency neuromagnetic signals might provide a novel approach for clinical management of childhood epilepsy.

Noninvasive localization of epileptogenic zones with ictal high-frequency neuromagnetic signals

OBJECTnRecent reports suggest that high-frequency epileptic activity is highly localized to epileptogenic zones. The goal of the present study was to investigate the potential usefulness of noninvasive localization of high-frequency epileptic activity for epilepsy surgery.nnnMETHODSnData obtained in 4 patients, who had seizures during routine magnetoencephalography (MEG) tests, were retrospectively studied. The MEG data were digitized at 4000 Hz, and 3D MR images were obtained. The magnetic sources were volumetrically localized with wavelet-based beamformer. The MEG results were subsequently compared with clinical data.nnnRESULTSnThe 4 patients had 1-4 high-frequency neuromagnetic components (110-910 Hz) in ictal and interictal activities. The loci of high-frequency activities were concordant with intracranial recordings therein 3 patients, who underwent presurgical evaluation. The loci of high-frequency ictal activities were in line with semiology and neuroimaging in all 4 of the patients. High-frequency epileptic activity was highly localized to the epileptogenic zones.nnnCONCLUSIONSnHigh-frequency epileptic activity can be volumetrically localized with MEG. Source analysis of high-frequency neuromagnetic signals has the potential to determine epileptogenic zones noninvasively and preoperatively for epilepsy surgery.

Gamma oscillations in the primary motor cortex studied with MEG

In recent years, there has been a growing interest on the role of gamma band (>30 Hz) neural oscillations in motor control, although the function of this activity in motor control is unknown clearly. With the goal of discussing the high frequency sources non-invasively and precisely during unilateral index finger movement, we investigated gamma band oscillations in 20 right-handed normal adults with magnetoencephalography (MEG). The results showed that gamma band activity appeared only during finger movement. Nineteen subjects displayed consistently contralateral event-related synchronization (C-ERS) within high gamma band (70-150 Hz) in primary motor cortex (M1) of both hemispheres. Interestingly, 15 subjects displayed ipsilateral event-related desynchronization (I-ERD) and C-ERS within broad gamma band (30-150 Hz). The locations of the broad gamma band I-ERD and C-ERS revealed hemispherical symmetry in M1. These findings demonstrate that there are consistent high gamma C-ERS and inconsistent low gamma I-ERD during a simple finger movement in the motor cortex. This study provides new evidence for the use of high gamma frequency oscillations as biomarkers in the analyses of functional brain activity and the localization of the motor cortex.

Time, frequency and volumetric differences of high-frequency neuromagnetic oscillation between left and right somatosensory cortices.

Hemispheric specialization or asymmetry in higher brain functions such as language is well accepted. This study was designed to quantitatively determine if the hemispheric asymmetry is measurable in the somatosensory system. Twenty-two participants were studied with magnetoencephalography (MEG) while their left and right index fingers were stimulated in randomized order. The finger representation in the cortex was volumetrically localized using a wavelet based beamformer. The strength of functional activity was estimated with an intensity volume while the waveforms of the virtual sensors were computed with a virtual sensor placed in the center of localized finger area. The results showed that the latency of the first identifiable response evoked by left finger stimulation was significantly shorter than that evoked by right finger stimulation (p<0.05). The left somatosensory cortex generated higher frequency neuromagnetic signals than did the right somatosensory cortex (p<0.05). Moreover, the volume of neuromagnetic activation elicited by right finger stimulation was significantly larger than that elicited by left finger stimulation in males (p<0.001). The neuromagnetic activation revealed by virtual sensors was more consistent than that revealed by physical sensors across participants. We conclude that neuromagnetic activities in the left and right somatosensory cortices have significant differences in terms of response latency, oscillation frequency and activation volume in high-frequency neuromagnetic signals. An investigation of the hemispheric specific features of neuromagnetic activation in the somatosensory cortex lays a foundation for the study of psychophysiologic asymmetries in the brain.

Neuromagnetic correlates of developmental changes in endogenous high-frequency brain oscillations in children: A wavelet-based beamformer study

Recent studies have found that the brain generates very fast oscillations. The objective of the present study was to investigate the spectral, spatial and coherent features of high-frequency brain oscillations in the developing brain. Sixty healthy children and 20 healthy adults were studied using a 275-channel magnetoencephalography (MEG) system. MEG data were digitized at 12,000 Hz. The frequency characteristics of neuromagnetic signals in 0.5-2000 Hz were quantitatively determined with Morlet wavelet transform. The magnetic sources were volumetrically estimated with wavelet-based beamformer at 2.5 mm resolution. The neural networks of endogenous brain oscillations were analyzed with coherent imaging. Neuromagnetic activities in 8-12 Hz and 800-900 Hz were found to be the most reliable frequency bands in healthy children. The neuromagnetic signals were localized in the occipital, temporal and frontal cortices. The activities in the occipital and temporal cortices were strongly correlated in 8-12 Hz but not in 800-900 Hz. In comparison to adults, children had brain oscillations in intermingled frequency bands. Developmental changes in children were identified for both low- and high-frequency brain activities. The results of the present study suggest that the development of the brain is associated with spatial and coherent changes of endogenous brain activities in both low- and high-frequency ranges. Analysis of high-frequency neuromagnetic oscillation may provide novel insights into cerebral mechanisms of brain function. The noninvasive measurement of neuromagnetic brain oscillations in the developing brain may open a new window for analysis of brain function.

Identification of Abnormal Neuromagnetic Signatures in the Motor Cortex of Adolescent Migraine

(Headache 2010;50:1005‐1016)

Aberrant high-gamma oscillations in the somatosensory cortex of children with cerebral palsy: a meg study.

OBJECTIVEnOur study is to investigate somatosensory dysfunction in children with spastic cerebral palsy (CP) using magnetoencephalography (MEG) and synthetic aperture magnetometry (SAM).nnnMETHODSnSix children with spastic CP and six age- and gender-matched typically developing children were studied using a 275-channel MEG system while their left and right index fingers were stimulated in random order. The latency and amplitude of somatosensory evoked magnetic fields were analyzed at sensor level. The patterns of high-gamma oscillations were investigated with SAM at source level.nnnRESULTSnIn comparison to the children with typical development, the latency of the first response of somatosensory evoked magnetic fields (SEFs) in the children with spastic CP was significantly delayed (p<0.05). High-gamma oscillations were identified in the somatosensory cortex in both children with CP and typical developing children. Interestingly, children with spastic CP had significantly higher incidence of ipsilateral activation in the somatosensory cortex following right and left finger stimulation, compared to typically developing children (p=0.05).nnnCONCLUSIONnThe results suggest that children with spastic CP have a measurable delay of SEFs and high-gamma oscillations. The high rates of ipsilateral cortical activation imply the impairments of functional lateralization in the developing brain. This is the first MEG study to demonstrate abnormal high-gamma oscillations of somatosensory cortices representing the finger in children with spastic CP.

Neuromagnetic measures of word processing in Bilinguals and Monolinguals

Objective: This study aimed to use magnetoencephalography (MEG) to examine the question of whether Mandarin-English bilingual speakers recruit the same cortical areas or develop distinct language-specific networks without overlaps for word processing. Methods: Eight healthy Mandarin-English bilingual adults and eight healthy English monolingual adults were scanned while single-word paradigms were audio-visually presented. Results: Our results showed significantly stronger beta-band power suppression in the right inferior parietal lobe (IPL) covering the supramarginal gyrus (BA 40) and angular gyrus (BA 39) for bilinguals when processing Mandarin versus English. Moreover, there were no significant differences between bilinguals and monolinguals in the left inferior frontal cortex (LIFC, BA 44/45) when both were processing their first