Rebecca L. Billingsley

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.

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.

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.

Spatiotemporal patterns of language-specific brain activity in patients with chronic aphasia after stroke using magnetoencephalography

Six participants with chronic aphasia secondary to first-ever ischemic stroke within the middle cerebral artery (MCA) distribution of the left hemisphere and six neurologically intact controls of similar age were given a running recognition memory task for words while the magnetic flux normal to the scalp surface was measured with a whole-head neuromagnetometer. This task had been previously shown to be valid for the localization and lateralization of brain activity specific to receptive language function. As expected, patients exhibited relatively decreased activation in areas known to be involved in receptive language function, including superior temporal gyrus (STG) in the left hemisphere, as well as increased activation of areas outside of the left STG that might potentially support language function. Decreased activation within left STG was associated with a reduction in receptive language in patients, as was increased activation outside of left STG. Results support hypotheses suggesting that peri-lesional areas outside premorbid language areas may assume receptive language function after aphasia secondary to stroke, but that better recovery occurs when putative premorbid language areas are able to normalize.

Spatio-Temporal Cortical Dynamics of Phonemic and Semantic Fluency

ABSTRACT Hemodynamic brain imaging and lesion studies have suggested differential involvement of expressive language-related cortical regions based on the phonemic versus semantic characteristics of verbal cues. The aims of this study were: 1) to elucidate the relative timing of the activity of inferior frontal and anterior insular versus motor and supplementary motor cortex during a fluency task and 2) to assess potential differences in the location or timing of activity in anterior and posterior language areas based on letter versus category cues. Using magnetic source imaging (MSI), we found significantly earlier onset latencies and a greater number of activity sources in motor and supplementary motor compared with inferior frontal and anterior insular regions. We also observed greater left versus right hemispheric asymmetry of activation for letter compared with category cues. This study provides new insights into cortico-cortical interactions during expressive language tasks.

Spatio-temporal brain activation profiles associated with line bisection judgments and double simultaneous visual stimulation

We used magnetic source imaging (MSI) to investigate the spatio-temporal patterns of brain activity associated with line bisection judgments and double simultaneous visual stimulation in 14 healthy adults. Consistent with lesion and hemodynamic neuroimaging studies, we found the greatest number of activity sources in right inferior parietal cortex. These sources were most prominent, on average, between 200 and 300 ms after the onset of single (left, right, or center) target stimuli. A greater number of significant activity sources were found in right inferior parietal, occipital, and prefrontal cortices during bilateral compared with unilateral stimulus presentation. Based on these observations, we suggest that a more parsimonious physiological explanation of visual extinction than the hemispheric rivalry account may be the additional neuronal excitation required in right occipital and parietal cortices for accurate bilateral visual perception.

Functional neuroimaging contributions to neurolinguistics

What has functional neuroimaging contributed to linguistics in general and to neurolinguistics in particular? And what can one expect, within reason, that it might contribute in the future? These are the basic questions that the contributors to this special issue of the Journal of Neurolinguistics, editors included, undertook to address. Clearly, questions of this sort may be addressed in at least two very distinct ways: Directly, through lengthy commentaries on the literature and, indirectly, with minimal critical comment, and emphasis on the juxtaposition of specific studies representative of the extant literature. We have chosen the latter approach, which places the responsibility of appraisal squarely on the reader, who is the ultimate consumer of the literature, and we have reserved for ourselves the role of facilitators, a role that we believe we can fulfill in two ways. First, by soliciting a set of papers that represent fairly accurately the contemporary literature on applications of functional neuroimaging methods, to problems in neurolinguistics. Second, by bringing to the reader’s attention technical issues, awareness of which is essential for an accurate evaluation of that literature. It appears, at least on the surface, that we have discharged our first responsibility satisfactorily: The sample of the works solicited for this special issue of this Journal, appears to be fairly representative of the caliber of publications one encounters in all professional journals. They are also representative in terms of the relative frequency of use of particular imaging methods (most of them involve functional magnetic resonance imaging or fMRI) and of geographic dispersion of the contributor’s country of residence and work (seven countries and three continents are represented), in terms of genre (the papers include one case study, three critical reviews and seven reports of typical experiments) and in terms of specific topic (bilingual brain organization, verbal working memory, phonological and semantic processing, hemispheric specialization within prefrontal cortex, neural components of reading, developmental changes in lexical processing, and the localization of syntactic processing mechanisms). Clearly, a small sample of 11 papers cannot represent all trends, whether theoretical or technical, and all shades of opinion prevailing in the field, but we believe this sample provides a fairly accurate picture of the most prevailing trends and opinions. To discharge the second responsibility we have assumed as editors of this Special Issue, we are summarizing below some key concepts that the reader ought to keep in mind in

Functional brain imaging of language: criteria for scientific merit and supporting data from magnetic source imaging

Abstract We propose five separate criteria for establishing the clinical and research utility of a functional neuroimaging method for the study of language. These criteria are the functional specificity, reliability, validity, spatial and temporal resolution, and logistical ease of the technique for studying language processes in patient and control populations. We describe the newest of the functional neuroimaging techniques, magnetic source imaging, and its advantages in satisfying these criteria. Finally, we review a series of language studies that have revealed dissociations between the relative contributions of superior temporal and middle and mesial temporal cortices in phonological versus semantic processing.