Shirin Sarkari

Does magnetoencephalography add to scalp video-EEG as a diagnostic tool in epilepsy surgery?

Objective: The authors evaluated the sensitivity and selectivity of interictal magnetoencephalography (MEG) versus prolonged ictal and interictal scalp video-electroencephalography (V-EEG) in order to identify patient groups that would benefit from preoperative MEG testing. Methods: The authors evaluated 113 consecutive patients with medically refractory epilepsy who underwent surgery. The epileptogenic region predicted by interictal and ictal V-EEG and MEG was defined in relation to the resected area as perfectly overlapping with the resected area, partially overlapping, or nonoverlapping. Results: The sensitivity of a 30-minute interictal MEG study for detecting clinically significant epileptiform activity was 79.2%. Using MEG, we were able to localize the resected region in a greater proportion of patients (72.3%) than with noninvasive V-EEG (40%). MEG contributed to the localization of the resected region in 58.8% of the patients with a nonlocalizing V-EEG study and 72.8% of the patients for whom V-EEG only partially identified the resected zone. Overall, MEG and V-EEG results were equivalent in 32.3% of the cases, and additional localization information was obtained using MEG in 40% of the patients. Conclusion: MEG is most useful for presurgical planning in patients who have either partially or nonlocalizing V-EEG results.

Reorganization of language-specific cortex in patients with lesions or mesial temporal epilepsy

Objective: To examine brain activation profiles for receptive language function, using magnetoencephalography (MEG), in patients with left hemisphere space-occupying lesions and patients with left temporal lobe epilepsy due to mesial temporal sclerosis (MTS) and to evaluate whether cross- and intrahemispheric plasticity for language varied as a function of lesion type or location. Methods: Twenty-one patients with MTS and 23 lesional patients underwent preoperative language mapping while performing a word recognition task. The anatomic location of late activity sources was determined by co-registering MEG coordinates onto structural MRI scans. A language laterality index was calculated based on the number of activity sources in each hemisphere. The location of language-specific activity was examined in relation to its proximity or overlap with Wernicke’s area. Results: A higher incidence of atypical language lateralization was noted among patients with MTS than lesional patients (43 vs 13%). The majority of MTS patients with early seizure onset (before age 5) showed atypical language lateralization. In contrast, the precise location of receptive language-specific cortex within the dominant hemisphere was found to be atypical (outside of Wernicke’s area) in 30% of lesional patients and only 14% of MTS patients. Conclusions: There is an increased probability of a partial or total displacement of key components of the brain mechanism responsible for receptive language function to the nondominant hemisphere in mesial temporal sclerosis patients. Early onset of seizures is strongly associated with atypical language lateralization. Lesions in the dominant hemisphere tend to result in an intrahemispheric reorganization of linguistic function.

Toward the substitution of invasive electroencephalography in epilepsy surgery.

The authors compared the localization accuracy of interictal magnetoencephalography (MEG) with ictal and interictal invasive video electroencephalography (VEEG) in identifying the epileptogenic zone in epilepsy surgery candidates. Forty-one patients, 29 with temporal lobe epilepsy (TLE) and 12 with extratemporal lobe epilepsy (ETLE), participated. Only patients with interictal changes during the MEG recordings were included. A comparison of the accuracy of invasive VEEG and MEG seizure zone identification was based on the degree of overlap between the location of the actual surgical resection and the zone identified by each method, and the success of surgery in reducing seizure activity. No statistical differences were observed between the accuracy of invasive VEEG and MEG in determining the location of the seizure zone across TLE and ETLE cases. Invasive VEEG and MEG localization judgments were correct in 54% and 56% of the cases, respectively. Separate group analyses suggested that MEG may be less beneficial relative to invasive VEEG in ETLE than TLE cases. MEG is of statistically equivalent accuracy to invasive VEEG, despite the fact that its use has not reached optimal conditions. The authors predict the replacement of the more invasive procedure with MEG in the near future for TLE cases, subsequent to the optimization of the conditions under which preoperative MEG is performed.

Integrating sensory and motor mapping in a comprehensive MEG protocol: clinical validity and replicability.

Considerable evidence supports the idea of magnetoencephalography (MEG) being a valuable noninvasive tool for presurgical mapping of sensory and motor functions. In this study, we test the validity and replicability of a new experimental paradigm for simultaneous sensory and motor mapping using MEG recordings. This comprehensive sensorimotor protocol (CSSMP), where external mechanic stimulation serves as a cue for voluntary movements, allows the recording of sensory and motor cortical responses during a single activation task. The stability and replicability of MEG-derived recordings during this paradigm were tested in a group of eight neurologically normal volunteers and six patients with perirolandic lesions. We found that a common sensorimotor cortical network, engaging sensory (S1, S2) and motor (M1) areas, was reliably activated in all subjects and patients and that the results remained exceptionally stable over time. Additionally, the clinical validity of the MEG-derived maps of activation was tested through intraoperative electrocortical stimulation mapping in the group of patients. The MEG-derived anatomical maps for specific sensory (S1) and motor (M1) responses were verified, by direct cortical mapping, and confirmed with the patients surgical outcome. The results of this validation study show that the so-called CSSMP is a reliable and reproducible method for assessing simultaneously sensory and motor areas. This method minimizes methodological problems and improves our knowledge of the spatiotemporal organization of the sensorimotor cortical network and helps to optimize the surgical management of patients with perirolandic lesions.

Intensive Instruction Affects Brain Magnetic Activity Associated with Oral Word Reading in Children with Persistent Reading Disabilities

Fifteen children ages 7 to 9 years who had persistent reading difficulties despite adequate instruction were provided with intensive tutorial interventions. The interventions targeted deficient phonological processing and decoding skills for 8 weeks (2 hours per day) followed by an 8-week, 1-hour-per-day intervention that focused on the development of reading fluency skills. Spatiotemporal brain activation profiles were obtained at baseline and after each 8-week intervention program using magnetoencephalography during the performance of an oral sight-word reading task. Changes in brain activity were found in the posterior part of the middle temporal gyrus (Brodmanns Area [BA] 21: increased degree of activity and reduced onset latency), the lateral occipitotemporal region (BA 19/37: decreased onset latency of activation), and the premotor cortex (increased onset latency). Overall changes associated with the intervention were primarily normalizing, as indicated by (a) increased activity in a region that is typically involved in lexical—semantic processing (BA 21) and (b) a shift in the relative timing of regional activity in temporal and frontal cortices to a pattern typically seen in unimpaired readers. These findings extend previous results in demonstrating significant changes in the spatiotemporal profile of activation associated with word reading in response to reading remediation.

Organization of receptive language-specific cortex before and after left temporal lobectomy

Objective: To examine brain activation associated with receptive language in patients with left temporal lobe epilepsy (TLE) before and after an anterior temporal lobectomy using magnetoencephalography (MEG), and to evaluate which patients were most likely to show a change in the lateralization and localization of the mechanisms supporting receptive language and if such changes were associated with neuropsychological function. Methods: Twelve patients with left TLE underwent preoperative Wada testing, and pre- and postoperative neuropsychological testing and MEG language mapping. The anatomic location of receptive language-related activity sources observed with MEG was determined by coregistering MEG data with structural MRI scans. Language laterality indices were calculated based on the number of reproducible activity sources in each hemisphere. The proximity of language-specific activity sources to Wernickes area was also examined. Results: Although the small sample size precluded formal statistical analyses, patients with atypical (bilateral) hemispheric dominance preoperatively were more likely than patients with typical (left-hemisphere) dominance to show evidence of increased right hemisphere participation in language functions after surgery. Patients with left hemispheric dominance preoperatively were more likely to show intrahemispheric changes involving a slight inferior shift of the putative location of Wernickes area. Patients with bilateral representation tended to perform worse on neuropsychological test measures obtained both pre- and postoperatively. Conclusion: Interhemispheric functional reorganization of language-specific areas may occur in patients undergoing left anterior temporal lobectomy. Intrahemispheric reorganization may take place even when the resection does not directly impinge upon Wernickes area.

Early development of neurophysiological processes involved in normal reading and reading disability: a magnetic source imaging study.

This longitudinal study examined the development of the brain mechanism involved in phonological decoding in beginning readers using magnetic source imaging. Kindergarten students were assigned to 2 groups: those who showed mastery of skills that are important predictors of proficient reading (low-risk group) and those who initially did not show mastery but later benefited from systematic reading instruction and developed average-range reading skills at the end of Grade 1 (high-risk responders). Spatiotemporal profiles of brain activity were obtained during performance of letter-sound and pseudoword naming tasks before and after Grade 1 instruction. With few exceptions, low-risk children showed early development of brain activation profiles that are typical of older skilled readers. Provided that temporoparietal and visual association areas were recruited into the brain mechanism that supported reading, the majority of high-risk responder children benefited from systematic reading instruction and developed adequate reading abilities.

Multimodality neuroimaging evaluation improves the detection of subtle cortical dysplasia in seizure patients

Abstract The purpose of this study is to investigate if multimodality neuroimaging evaluation increases the detection of subtle focal cortical dysplasia as part of an epilepsy surgery evaluation. Three patients with normal magnetic resonance imaging and histopathological findings of focal cortical dysplasia were reviewed. Their magnetoencephalography recordings were performed on whole-head magnetoencephalography system. Magnetic resonance images were re-evaluated with special inspection in limited regions guided by magnetoencephalography spike localization. Two patients had ictal and interictal single photon emission computed tomography study after administration of Tc99m ECD. In two patients we found tiny focal abnormalities including slightly increased cortical thickness and blurred gray–white matter junction at the locations of interictal events after re-evaluation of the MR images indicating focal cortical dysplasia. The third patient showed focal atrophic change. All patients are seizure free after surgery. Both ictal and interictal single photon emission computed tomography showed hyperperfusion in the dysplastic cortex regions. Multimodality neuroimaging study can improve the detection of focal cortical dysplasia. Normal magnetic resonance images should be re-evaluated for subtle signs of focal cortical dysplasia especially when magnetoencephalography recording demonstrate focal epileptic discharges.

A comparison of functional MRI and magnetoencephalography for receptive language mapping

We compared functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) for the mapping of receptive language function. Participants performed the same language task in the two different imaging environments. MEG activation profiles showed prominent bilateral activity in superior temporal gyrus and left-lateralized activity in middle temporal gyrus. fMRI activation profiles revealed bilateral activity in prefrontal, superior temporal, middle temporal, and visual areas. Laterality quotients derived from the two modalities showed poor agreement between the two methods for commonly active regions of interest. Locations of peak activity also varied considerably within participants between the two methods.

Atypical Language Representation in Patients with Chronic Seizure Disorder and Achievement Deficits with Magnetoencephalography

Summary:  Purpose: To characterize the relation between hemispheric asymmetries in language‐specific brain activity and reading/spelling achievement by using magnetoencephalography (MEG).