Resting state oscillatory brain dynamics in Parkinson's disease: an MEG study.

OBJECTIVE: The pathophysiological mechanisms of cognitive dysfunction and dementia in Parkinson's disease (PD) are still poorly understood. Altered resting state oscillatory brain activity may reflect underlying neuropathological changes. The present study using magneto encephalography (MEG) was set up to study differences in the pattern of resting state oscillatory brain activity in groups of demented and non-demented PD patients and healthy, elderly controls. METHODS: The pattern of MEG background oscillatory activity was studied in 13 demented PD patients, 13 non-demented PD patients and 13 healthy controls. Whole head MEG recordings were obtained in the morning in an eyes closed and an eyes open, resting state condition. Relative spectral power was calculated using Fast Fourier Transformation in delta, theta, alpha, beta and gamma frequency bands. RESULTS: In the non-demented PD patients, relative theta power was diffusely increased and beta power concomitantly decreased relative to controls. gamma Power was decreased in central and parietal channels. In the demented PD patients, a diffuse increase in relative delta and to lesser extent theta power and a decrease in relative alpha, beta and to lesser extent gamma power were found in comparison to the non-demented PD group. In addition, reactivity to eye opening was much reduced in the demented PD group. CONCLUSIONS: Parkinson's disease is characterized by a slowing of resting state brain activity involving theta, beta and gamma frequency bands. Dementia in PD is associated with a further slowing of resting state brain activity, additionally involving delta and alpha bands, as well as a reduction in reactivity to eye-opening. SIGNIFICANCE: The differential patterns of slowing of resting state brain activity in demented and non-demented PD patients suggests that, in conjunction with a progression of the pathological changes already present in non-demented patients, additional mechanisms are involved in the development of dementia in PD.     

Top-down control of MEG alpha-band activity in children performing Categorical N-Back Task

Top-down cognitive control has been associated in adults with the prefrontal-parietal network. In children the brain mechanisms of top-down control have rarely been studied. We examined developmental differences in top-down cognitive control by monitoring event-related desynchronization (ERD) and event-related synchronization (ERS) of alpha-band oscillatory activity (8-13 Hz) during anticipation, target detection and post-response stages of a visual working memory task. Magnetoencephalography (MEG) was used to record brain oscillatory activity from healthy 10-year-old children and young adults performing the Categorical N-Back Task (CNBT). Neuropsychological measures assessing frontal lobe networks were also acquired. Whereas adults showed a modulation of the ERD at the anticipatory stages of CNBT and ERS at the post-response stage, children displayed only some anticipatory modulation of ERD but no ERS at the post-response stage, with alpha-band remaining at a desynchronized state. Since neuropsychological and prior neuroimaging findings indicate that the prefrontal-parietal networks are not fully developed in 10-year olds, and since the children performed as well as the adults on CNBT and yet displayed different patterns of ERD/ERS, we suggest that children may be using different top-down cognitive strategies and, hence, different, developmentally apt neuronal networks.     

Characterizing hippocampal dynamics with MEG: A systematic review and evidence‐based guidelines

The hippocampus, a hub of activity for a variety of important cognitive processes, is a target of increasing interest for researchers and clinicians. Magnetoencephalography (MEG) is an attractive technique for imaging spectro‐temporal aspects of function, for example, neural oscillations and network timing, especially in shallow cortical structures. However, the decrease in MEG signal‐to‐noise ratio as a function of source depth implies that the utility of MEG for investigations of deeper brain structures, including the hippocampus, is less clear. To determine whether MEG can be used to detect and localize activity from the hippocampus, we executed a systematic review of the existing literature and found successful detection of oscillatory neural activity originating in the hippocampus with MEG. Prerequisites are the use of established experimental paradigms, adequate coregistration, forward modeling, analysis methods, optimization of signal‐to‐noise ratios, and protocol trial designs that maximize contrast for hippocampal activity while minimizing those from other brain regions. While localizing activity to specific sub‐structures within the hippocampus has not been achieved, we provide recommendations for improving the reliability of such endeavors.     

Somatomotor mu rhythm amplitude correlates with rigidity during deep brain stimulation in Parkinsonian patients

Objective

Parkinsonian patients have abnormal oscillatory activity within the basal ganglia-thalamocortical circuitry. Particularly, excessive beta band oscillations are thought to be associated with akinesia. We studied whether cortical spontaneous activity is modified by deep brain stimulation (DBS) in advanced Parkinson’s disease and if the modifications are related to the clinical symptoms.

Methods

We studied the effects of bilateral electrical stimulation of subthalamic nucleus (STN) on cortical spontaneous activity by magnetoencephalography (MEG) in 11 Parkinsonian patients. The artifacts produced by DBS were suppressed by tSSS algorithm.

Results

During DBS, UPDRS (Unified Parkinson’s Disease Rating Scale) rigidity scores correlated with 6-10 Hz and 12-20 Hz somatomotor source strengths when eyes were open. When DBS was off UPDRS action tremor scores correlated with pericentral 6-10 Hz and 21-30 Hz and occipital alpha source strengths when eyes open.Occipital alpha strength decreased during DBS when eyes closed. The peak frequency of occipital alpha rhythm correlated negatively with total UPDRS motor scores and with rigidity subscores, when eyes closed.

Conclusion

STN DBS modulates brain oscillations both in alpha and beta bands and these oscillations reflect the clinical condition during DBS.

Significance

MEG combined with an appropriate artifact rejection method enables studies of DBS effects in Parkinson’s disease and presumably also in the other emerging DBS indications.     

Atypical resting synchrony in autism spectrum disorder

Autism spectrum disorder (ASD) is increasingly understood to be associated with aberrant functional brain connectivity. Few studies, however, have described such atypical neural synchrony among specific brain regions. Here, we used magnetoencephalography (MEG) to characterize alterations in functional connectivity in adolescents with ASD through source space analysis of phase synchrony. Resting‐state MEG data were collected from 16 adolescents with ASD and 15 age‐ and sex‐matched typically developing (TD) adolescents. Atlas‐guided reconstruction of neural activity at various cortical and subcortical regions was performed and inter‐regional phase synchrony was calculated in physiologically relevant frequency bands. Using a multilevel approach, we characterized atypical resting‐state synchrony within specific anatomically defined networks as well as altered network topologies at both regional and whole‐network scales. Adolescents with ASD demonstrated frequency‐dependent alterations in inter‐regional functional connectivity. Hyperconnectivity was observed among the frontal, temporal, and subcortical regions in beta and gamma frequency ranges. In contrast, parietal and occipital regions were hypoconnected to widespread brain regions in theta and alpha bands in ASD. Furthermore, we isolated a hyperconnected network in the gamma band in adolescents with ASD which encompassed orbitofrontal, subcortical, and temporal regions implicated in social cognition. Results from graph analyses confirmed that frequency‐dependent alterations of network topologies exist at both global and local levels. We present the first source‐space investigation of oscillatory phase synchrony in resting‐state MEG in ASD. This work provides evidence of atypical connectivity at physiologically relevant time scales and indicates that alterations of functional connectivity in adolescents with ASD are frequency dependent and region dependent. Hum Brain Mapp 35:6049–6066, 2014. © 2014 Wiley Periodicals, Inc.     

Event-related power modulations of brain activity preceding visually guided saccades

To analyze the characteristics of the event-related desynchronization (ERD) and synchronization (ERS) of cortical rhythms during the preparation and execution of a lateralized eye movement, EEG was recorded in normal subjects during a visually guided task. Alpha and beta bands were investigated in three temporal intervals: a sensory period, a delay period and a saccade preparation period time locked with saccade onset. Modulations of ERD/ERS power, coupled with the task, reached the largest amplitudes over the frontal and parieto-occipital regions. Differences of oscillatory activity in the alpha bands revealed an intriguing pattern of asymmetry in parieto-occipital areas. Rightward saccades induced a larger desynchronization with respect to the leftward saccades in the left hemisphere, but not in the right. If representative, these findings are congruent to the established right-hemisphere dominance of the brain areas that direct attention. Moreover differences between the two alpha types emerged in the frontal areas before and during the saccade preparation periods, indicative of differential engagement of these areas depending on the task demands. In conclusion, the present approach shows that planning eye movements is linked with covert orienting of spatial attention and may supply a useful method for studying eye movements and selective attention-related processes.     

Temporo‐frontal functional connectivity during auditory change detection is altered in Alzheimer's disease

Cortico‐cortical connections might be disturbed in patients with Alzheimer's disease (AD). This study aimed to investigate the alterations of functional connectivity in AD during auditory change detection processing by measuring the local neuronal activation and functional connectivity between cortical regions. Magnetoencephalographic responses to deviant and standard sounds were recorded in 16 AD patients, 18 young controls and 16 elderly controls. Larger source amplitudes and shorter peak latencies were found in the right temporal magnetic mismatch responses of young controls compared with elderly controls and AD patients. During deviant stimuli, the right theta temporal‐frontal phase synchrony was significantly smaller in AD than in young controls and elderly controls. Moreover, the left temporal‐frontal synchronization at theta and alpha bands was reduced in AD and elderly controls compared with young controls. In conclusion, the loss in temporo‐frontal theta synchronization might be an electrophysiological hallmark of AD. Hum Brain Mapp 35:5565–5577, 2014. © 2014 Wiley Periodicals, Inc.     

Magnetoencephalographic analysis of cortical activity in Alzheimer's disease: a pilot study.

OBJECTIVES: In the present study, MEG was used to analyze spectral power and reference-free coherence in patients with probable Alzheimer's disease (AD).METHODS: Sixty-one channel MEG was recorded in 5 AD patients and 5 age-matched controls at rest with eyes open and eyes closed, as well as during the performance of two different mental tasks. Artefact-free epochs were selected for the analysis of power and coherence values in each of 5 4-Hz wide frequency bands ranging from 2 to 22 Hz.RESULTS: In AD patients, the absolute low frequency magnetic power was significantly and rather diffusely increased relative to controls with a fronto-central maximum. High frequency power values were significantly decreased over the occipital and temporal areas. Reactivity to eye-opening and mental tasks was reduced in the patient group. Relative to controls, a general decrease of MEG coherence values, including all frequencies analyzed, was found in AD patients.CONCLUSIONS: These observations confirm the pattern of changes in spectral power and reactivity known from EEG studies and suggest that coherence decreases in AD patients are widespread and include frequencies outside the alpha band.     

Spontaneous pre‐stimulus oscillatory activity shapes the way we look: A concurrent imaging and eye‐movement study

Previous behavioural studies have accrued evidence that response time plays a critical role in determining whether selection is influenced by stimulus saliency or target template. In the present work, we investigated to what extent the variations in timing and consequent oculomotor controls are influenced by spontaneous variations in pre‐stimulus alpha oscillations. We recorded simultaneously brain activity using magnetoencephalography (MEG) and eye movements while participants performed a visual search task. Our results show that slower saccadic reaction times were predicted by an overall stronger alpha power in the 500 ms time window preceding the stimulus onset, while weaker alpha power was a signature of faster responses. When looking separately at performance for fast and slow responses, we found evidence for two specific sources of alpha activity predicting correct versus incorrect responses. When saccades were quickly elicited, errors were predicted by stronger alpha activity in posterior areas, comprising the angular gyrus in the temporal‐parietal junction (TPJ) and possibly the lateral intraparietal area (LIP). Instead, when participants were slower in responding, an increase of alpha power in frontal eye fields (FEF), supplementary eye fields (SEF) and dorsolateral pre‐frontal cortex (DLPFC) predicted erroneous saccades. In other words, oculomotor accuracy in fast responses was predicted by alpha power differences in more posterior areas, while the accuracy in slow responses was predicted by alpha power differences in frontal areas, in line with the idea that these areas may be differentially related to stimulus‐driven and goal‐driven control of selection.     

Load effects on spatial working memory performance are linked to distributed alpha and beta oscillations

Increasing spatial working memory (SWM) load is generally associated with declines in behavioral performance, but the neural correlates of load‐related behavioral effects remain poorly understood. Herein, we examine the alterations in oscillatory activity that accompany such performance changes in 22 healthy adults who performed a two‐ and four‐load SWM task during magnetoencephalography (MEG). All MEG data were transformed into the time‐frequency domain and significant oscillatory responses were imaged separately per load using a beamformer. Whole‐brain correlation maps were computed using the load‐related beamformer difference images and load‐related accuracy effects on the SWM task. The results indicated that load‐related differences in left inferior frontal alpha activity during encoding and maintenance were negatively correlated with load‐related accuracy differences on the SWM task. That is, individuals who had more substantial decreases in prefrontal alpha during high‐relative to low‐load SWM trials tended to have smaller performance decrements on the high‐load condition (i.e., they performed more accurately). The same pattern of neurobehavioral correlations was observed during the maintenance period for right superior temporal alpha activity and right superior parietal beta activity. Importantly, this is the first study to employ a voxel‐wise whole‐brain approach to significantly link load‐related oscillatory differences and load‐related SWM performance differences.     

Cortical oscillatory changes in human middle temporal cortex underlying smooth pursuit eye movements

Extra‐striate regions are thought to receive non‐retinal signals from the pursuit system to maintain perceptual stability during eye movements. Here, we used magnetoencephalography (MEG) to study changes in oscillatory power related to smooth pursuit in extra‐striate visual areas under three conditions: ‘pursuit’ of a small target, ‘retinal motion’ of a large background and ‘pursuit + retinal motion’ combined. All stimuli moved sinusoidally. MEG source reconstruction was performed using synthetic aperture magnetometry. Broadband alpha–beta suppression (5–25 Hz) was observed over bilateral extra‐striate cortex (consistent with middle temporal cortex (MT+)) during all conditions. A functional magnetic resonance imaging study using the same experimental protocols confirmed an MT+ localisation of this extra‐striate response. The alpha–beta envelope power in the ‘pursuit’ condition showed a hemifield‐dependent eye‐position signal, such that the global minimum in the alpha–beta suppression recorded in extra‐striate cortex was greatest when the eyes were at maximum contralateral eccentricity. The ‘retinal motion’ condition produced sustained alpha–beta power decreases for the duration of stimulus motion, while the ‘pursuit + retinal motion’ condition revealed a double‐dip ‘W’ shaped alpha–beta envelope profile with the peak suppression contiguous with eye position when at opposing maximum eccentricity. These results suggest that MT+ receives retinal as well as extra‐retinal signals from the pursuit system as part of the process that enables the visual system to compensate for retinal motion during eye movement. We speculate that the suppression of the alpha–beta rhythm reflects either the integration of an eye position‐dependent signal or one that lags the peak velocity of the sinusoidally moving target. Hum Brain Mapp, 2013. © 2011 Wiley Periodicals, Inc.     

Magnetoencephalography in the study of children with autism spectrum disorder

Magnetoencephalography (MEG) is a non‐invasive neuroimaging technique that provides a measure of cortical neural activity on a millisecond timescale with high spatial resolution. MEG has been clinically applied to various neurological diseases, including epilepsy and cognitive dysfunction. In the past decade, MEG has also emerged as an important investigatory tool in neurodevelopmental studies. It is therefore an opportune time to review how MEG is able to contribute to the study of atypical brain development. We limit this review to autism spectrum disorder (ASD). The relevant published work for children was accessed using PubMed on 5 January 2015. Case reports, case series, and papers on epilepsy were excluded. Owing to their accurate separation of brain activity in the right and left hemispheres and the higher accuracy of source localization, MEG studies have added new information related to auditory‐evoked brain responses to findings from previous electroencephalography studies of children with ASD. In addition, evidence of atypical brain connectivity in children with ASD has accumulated over the past decade. MEG is well suited for the study of neural activity with high time resolution even in young children. Although further studies are still necessary, the detailed findings provided by neuroimaging methods may aid clinical diagnosis and even contribute to the refinement of diagnostic categories for neurodevelopmental disorders in the future.     

Influence of coherence between multiple cortical columns on alpha rhythm: A computational modeling study

In electroencephalographic (EEG) and magnetoencephalographic (MEG) signals, stimulus‐induced amplitude increase and decrease in the alpha rhythm, known as event‐related synchronization and desynchronization (ERS/ERD), emerge after a task onset. ERS/ERD is assumed to reflect neural processes relevant to cognitive tasks. Previous studies suggest that several sources of alpha rhythm, each of which can serve as an alpha rhythm generator, exist in the cortex. Since EEG/MEG signals represent spatially summed neural activities, ERS/ERD of the alpha rhythm may reflect the consequence of the interactions between multiple alpha rhythm generators. Two candidates modulate the magnitude of ERS/ERD: (1) coherence between the activities of the alpha rhythm generators and (2) mean amplitude of the activities of the alpha rhythm generators. In this study, we use a computational model of multiple alpha rhythm generators to determine the factor that dominantly causes ERS/ERD. Each alpha rhythm generator is modeled based on local column circuits in the primary visual cortex and made to interact with the neighboring generators through excitatory connections. We observe that the model consistently reproduces spontaneous alpha rhythms, event‐related potentials, phase‐locked alpha rhythms, and ERS/ERD in a specific range of connectivity coefficients. Independent analyses of the coherence and amplitude of multiple alpha rhythm generators reveal that the ERS/ERD in the simulated data is dominantly caused by stimulus‐induced changes in the coherence between multiple alpha rhythm generators. Nonlinear phenomena such as phase‐resetting and entrainment of the alpha rhythm are related to the neural mechanism underlying ERS/ERD. Hum Brain Mapp, 2010. © 2009 Wiley‐Liss, Inc.     

Magnetoencephalography: applications in psychiatry.

Magnetoencephalography (MEG) measures the extracranial magnetic fields produced by intraneuronal ionic current flow within appropriately oriented cortical pyramidal cells. Based upon superconducting quantum interference device technology operating at liquid helium temperatures (4 K), MEG offers excellent temporal and spatial resolution for selected sources, and complements information obtained from electroencephalograms and other functional imaging strategies. Current instrumentation permits recording up to several hundred channels simultaneously with head-shaped dewars, although the cost of such systems is high. The fact that magnetic fields fall off with the square of the distance from the source is both a benefit (when separating activity in the two hemispheres) and a limitation (when attempting to record deep sources). The lack of skin contact facilitates using MEG to record direct current and very high frequency (> 600 Hz) brain activity. The clinical utility of MEG includes presurgical mapping of sensory cortical areas and localization of epileptiform abnormalities, and localization of areas of brain hypoperfusion in stroke patients. MEG studies in psychiatric disorders have contributed materially to improved understanding of anomalous brain lateralization in the psychoses, have suggested that P50 abnormalities may reflect altered gamma band activity, and have provided evidence of hemisphere-specific abnormalities of short-term auditory memory function.     

Dynamic changes of ICA‐derived EEG functional connectivity in the resting state

An emerging issue in neuroscience is how to identify baseline state(s) and accompanying networks termed “resting state networks” (RSNs). Although independent component analysis (ICA) in fMRI studies has elucidated synchronous spatiotemporal patterns during cognitive tasks, less is known about the changes in EEG functional connectivity between eyes closed (EC) and eyes open (EO) states, two traditionally used baseline indices. Here we investigated healthy subjects (n = 27) in EC and EO employing a four‐step analytic approach to the EEG: (1) group ICA to extract independent components (ICs), (2) standardized low‐resolution tomography analysis (sLORETA) for cortical source localization of IC network nodes, followed by (3) graph theory for functional connectivity estimation of epochwise IC band‐power, and (4) circumscribing IC similarity measures via hierarchical cluster analysis and multidimensional scaling (MDS). Our proof‐of‐concept results on alpha‐band power demonstrate five statistically clustered groups with frontal, central, parietal, occipitotemporal, and occipital sources. Importantly, during EO compared with EC, graph analyses revealed two salient functional networks with frontoparietal connectivity: a more medial network with nodes in the mPFC/precuneus which overlaps with the “default‐mode network” (DMN), and a more lateralized network comprising the middle frontal gyrus and inferior parietal lobule, coinciding with the “dorsal attention network” (DAN). Furthermore, a separate MDS analysis of ICs supported the emergence of a pattern of increased proximity (shared information) between frontal and parietal clusters specifically for the EO state. We propose that the disclosed component groups and their source‐derived EEG functional connectivity maps may be a valuable method for elucidating direct neuronal (electrophysiological) RSNs in healthy people and those suffering from brain disorders. Hum Brain Mapp, 2013. © 2012 Wiley Periodicals, Inc.     

A systematic review of MEG‐based studies in Parkinson's disease: The motor system and beyond

Parkinson's disease (PD) is accompanied by functional changes throughout the brain, including changes in the electromagnetic activity recorded with magnetoencephalography (MEG). An integrated overview of these changes, its relationship with clinical symptoms, and the influence of treatment is currently missing. Therefore, we systematically reviewed the MEG studies that have examined oscillatory activity and functional connectivity in the PD‐affected brain. The available articles could be separated into motor network‐focused and whole‐brain focused studies. Motor network studies revealed PD‐related changes in beta band (13–30 Hz) neurophysiological activity within and between several of its components, although it remains elusive to what extent these changes underlie clinical motor symptoms. In whole‐brain studies PD‐related oscillatory slowing and decrease in functional connectivity correlated with cognitive decline and less strongly with other markers of disease progression. Both approaches offer a different perspective on PD‐specific disease mechanisms and could therefore complement each other. Combining the merits of both approaches will improve the setup and interpretation of future studies, which is essential for a better understanding of the disease process itself and the pathophysiological mechanisms underlying specific PD symptoms, as well as for the potential to use MEG in clinical care.     

Magnetoencephalographic analysis of cortical activity in adults with and without Down syndrome

Background This preliminary study served as a pilot for an ongoing analysis of spectral power in adults with Down syndrome (DS) using a 151 channel whole head magnetoencephalography (MEG). The present study is the first step for examining and comparing cortical responses during spontaneous and task related activity in DS. Method Cortical responses were recorded with a 151 channel whole head MEG system in three adults with DS and three age‐matched adults without DS. MEG data were obtained at rest with eyes open and during observation of point‐light displays of human motion and object motion. Data from both groups were evaluated by spectral analysis. Results The preliminary results showed greater alpha (8–14 Hz) power particularly in the occipital and parietal areas during the eyes open condition in the adults with DS in relation to a normal comparison group. The visual task had little effect on alpha power in the comparison group. Engaging in the visual task reduced power in alpha across all regions in the DS group to the level observed in comparisons. In the gamma band (30–50 Hz), power values were similar across both groups for the eyes open condition. In the comparison group, large reductions in gamma were observed in the occipital and bilateral temporal areas during the visual task. This change was not observed in the DS group. Conclusions The results from this pilot study suggest that MEG may be useful in characterizing task‐specific changes in cortical activity in individuals with DS. Future studies with a larger group of individuals will further contribute to our understanding of the neurophysiology of Down syndrome.     

Altered dynamics of brain segregation and integration in poststroke aphasia

Poststroke aphasia (PSA) results from direct effect of focal lesions and dysfunction of distributed language networks. However, how flexible the activity at specific nodes control global dynamics is currently unknown. In this study, we demonstrate that alterations in the regional activity may cause imbalances between segregation and integration in temporo‐spatial pattern, and the transient dynamics are disrupted in PSA patients. Specifically, we applied dynamic framework to eyes‐closed resting‐state functional MRI data from PSA patients (n = 17), and age‐, gender‐, and education‐matched healthy controls (HCs, n = 20). Subsequently, we calculated two basis brain organizational principles: “dynamic segregation,” obtained from dynamic amplitude of low‐frequency fluctuations (dALFF), which represent the specialized processing within interconnected brain regions; and “dynamic integration,” obtained from dynamic functional connectivity, which measures the efficient communication between interconnected brain regions. We found that both measures were decreased in the PSA patients within the left frontal and temporal subregions compared to the HCs. PSA patients displayed increased flexibility of interaction between left temporo‐frontal subregions and right temporo‐parieto‐frontal subnetworks. Furthermore, we found that dALFF in the pars triangularis of left inferior frontal gyrus was associated with aphasia quotient. These findings suggest that the reduced temporal flexibility of regional activity in language‐relevant cortical regions in PSA is related to the disrupted organization of intrahemispheric networks, leading to a loss of the corresponding functions. By using dynamic framework, our results offer valuable information about the alterations in segregation and integration of spatiotemporal information across networks and illuminate how dysfunction in flexible activity may underlie language deficits in PSA.     

Examining the effects of prenatal alcohol exposure on corticothalamic connectivity: A multimodal neuroimaging study in children

Children with a fetal alcohol spectrum disorder (FASD) experience a range of cognitive and behavioral effects. Prior studies have demonstrated white matter changes in children with FASD relative to typically developing controls (TDC) and these changes relate to behavior. Our prior MEG study (Candelaria-Cook et al. 2020) demonstrated reduced alpha oscillations during rest in FASD relative to TDC and alpha power is correlated with behavior. However, little is known about how brain structure influences brain function. We hypothesized that alpha power was related to corticothalamic connectivity. Children 8–13 years of age (TDC: N = 25, FASD: N = 24) underwent rest MEG with eyes open or closed and MRI to collect structural and diffusion tensor imaging data. MEG spectral analysis was performed for sensor and source data. We estimated mean fractional anisotropy in regions of interest (ROIs) that included the corticothalamic tracts. The FASD group had reduced mean FA in three of the corticothalamic ROIs. FA in these tracts was significantly correlated with alpha power at the sensor and source level. The results support the hypothesis that integrity of the corticothalamic tracts influences cortical alpha power. Further research is needed to understand how brain structure and function influence behavior.     

Cephalic aura after frontal lobe resection

A cephalic aura is a common sensory aura typically seen in frontal lobe epilepsy. The generation mechanism of cephalic aura is not fully understood. It is hypothesized that to generate a cephalic aura extensive cortical areas need to be excited. We report a patient who started to have cephalic aura after right frontal lobe resection. Magnetoencephalography (MEG) showed interictal spike and ictal change during cephalic aura, both of which were distributed in the right frontal region, and the latter involved much more widespread areas than the former on MEG sensors. The peculiar seizure onset pattern may indicate that surgical modification of the epileptic network was related to the appearance of cephalic aura. We hypothesize that generation of cephalic aura may be associated with more extensive cortical involvement of epileptic activity than that of interictal activity, in at least a subset of cases.