McDonald, C. R. et al. Distributed source modeling of language with magnetoencephalography: application to patients with intractable epilepsy. Epilepsia 50, 2256-2266

Department of Psychiatry, University of California, San Diego, California, USA.
Epilepsia (Impact Factor: 4.57). 07/2009; 50(10):2256-66. DOI: 10.1111/j.1528-1167.2009.02172.x
Source: PubMed


To examine distributed patterns of language processing in healthy controls and patients with epilepsy using magnetoencephalography (MEG), and to evaluate the concordance between laterality of distributed MEG sources and language laterality as determined by the intracarotid amobarbital procedure (IAP).
MEG was performed in 10 healthy controls using an anatomically constrained, noise-normalized distributed source solution (dynamic statistical parametric map, dSPM). Distributed source modeling of language was then applied to eight patients with intractable epilepsy. Average source strengths within temporoparietal and frontal lobe regions of interest (ROIs) were calculated, and the laterality of activity within ROIs during discrete time windows was compared to results from the IAP.
In healthy controls, dSPM revealed activity in visual cortex bilaterally from approximately 80 to 120 ms in response to novel words and sensory control stimuli (i.e., false fonts). Activity then spread to fusiform cortex approximately 160-200 ms, and was dominated by left hemisphere activity in response to novel words. From approximately 240 to 450 ms, novel words produced activity that was left-lateralized in frontal and temporal lobe regions, including anterior and inferior temporal, temporal pole, and pars opercularis, as well as bilaterally in posterior superior temporal cortex. Analysis of patient data with dSPM demonstrated that from 350 to 450 ms, laterality of temporoparietal sources agreed with the IAP 75% of the time, whereas laterality of frontal MEG sources agreed with the IAP in all eight patients.
Our results reveal that dSPM can unveil the timing and spatial extent of language processes in patients with epilepsy and may enhance knowledge of language lateralization and localization for use in preoperative planning.

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    • "In particular, the reliability with which this protocol has been used to establish hemispheric dominance for receptive language in children has been shown in several normative, as well as clinical, cohorts. Moreover, the suitability of MEG language mapping protocols as an alternative to the Wada procedure have been addressed over the course of several validation studies, with concordance rates ranging from 87% in the study with largest sample to date (Papanicolaou et al., 2004) to 100% agreement in the first sub-sample of patients of the same series (Breier et al., 1999), with the rest of the studies reporting uniformly, high agreement (Breier et al., 2001; Maestú et al., 2002; Hirata et al., 2004; Bowyer et al., 2005; Merrifield et al., 2007; Doss et al., 2009; McDonald et al., 2009; Hirata et al., 2010; Findlay et al., 2012; Tanaka et al., 2013). "
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    Frontiers in Human Neuroscience 08/2014; 8:657. DOI:10.3389/fnhum.2014.00657 · 3.63 Impact Factor
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    • "Following the procedure of Tanaka et al., (2013), we used anatomically defined ROIs that consisted of the supramarginal gyrus (SMG), superior temporal gyrus (STG) and the inferior frontal gyrus (IFG). We chose these areas in line with the core language network presented in Tanaka et al. (2013), that were based on previous language lateralization MEG studies (Bowyer et al., 2005; McDonald et al., 2009). Furthermore, these areas are the key areas in which previous functional imaging studies (e.g., De Nil and Beal, 2008) have shown there to be laterality anomalies in stuttering subjects. "
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    ABSTRACT: The neural causes of stuttering remain unknown. One explanation comes from neuroimaging studies that have reported abnormal lateralization of activation in the brains of people who stutter. However, these findings are generally based on data from adults with a long history of stuttering, raising the possibility that the observed lateralization anomalies are compensatory rather than causal. The current study investigated lateralization of brain activity in language-related regions of interest in young children soon after the onset of stuttering. We tested 24 preschool-aged children, half of whom had a positive diagnosis of stuttering. All children participated in a picture-naming experiment whilst their brain activity was recorded by magnetoencephalography. Source analysis performed during an epoch prior to speech onset was used to assess lateralized activation in three regions of interest. Activation was significantly lateralized to the left hemisphere in both groups and not different between groups. This study shows for the first time that significant speech preparatory brain activation can be identified in young children during picture-naming and supports the contention that, in stutterers, aberrant lateralization of brain function may be the result of neuroplastic adaptation that occurs as the condition becomes chronic.
    Frontiers in Human Neuroscience 05/2014; 8:354. DOI:10.3389/fnhum.2014.00354 · 3.63 Impact Factor
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    • "For each subject, a regular grid-based mesh (∼400,000 nodes, ∼450,000 linear elements, ∼2 mm average edge length) was created and the so-called forward matrix (the values of the electric potential at each sensor due to every cortical source) was computed [18]. The inverse localization technique employed has been widely used for the study of epilepsy [20] [21] [22] and its technical details have been comprehensively explored elsewhere [23] [24], particularly in our previous publication [25]. Briefly, source localization is performed using a minimum-norm inverse linear operator [26] which seeks to minimize the expected difference between the estimated and the true inverse solution. "
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    ABSTRACT: Objective: To inverse-localize epileptiform cortical electrical activity recorded from severe traumatic brain injury (TBI) patients using electroencephalography (EEG). Methods: Three acute TBI cases were imaged using computed tomography (CT) and multimodal magnetic resonance imaging (MRI). Semi-automatic segmentation was performed to partition the complete TBI head into 25 distinct tissue types, including 6 tissue types accounting for pathology. Segmentations were employed to generate a finite element method model of the head, and EEG activity generators were modeled as dipolar currents distributed over the cortical surface. Results: We demonstrate anatomically faithful localization of EEG generators responsible for epileptiform discharges in severe TBI. By accounting for injury-related tissue conductivity changes, our work offers the most realistic implementation currently available for the inverse estimation of cortical activity in TBI. Conclusion: Whereas standard localization techniques are available for electrical activity mapping in uninjured brains, they are rarely applied to acute TBI. Modern models of TBI-induced pathology can inform the localization of epileptogenic foci, improve surgical efficacy, contribute to the improvement of critical care monitoring and provide guidance for patient-tailored treatment. With approaches such as this, neurosurgeons and neurologists can study brain activity in acute TBI and obtain insights regarding injury effects upon brain metabolism and clinical outcome.
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