Optimizing estimation of hemispheric dominance for language using magnetic source imaging

Abstract

The efficacy of magnetoencephalography (MEG) as an alternative to invasive methods for investigating the cortical representation of language has been explored in several studies. Recently, studies comparing MEG to the gold standard Wada procedure have found inconsistent and often less-than accurate estimates of laterality across various MEG studies. Here we attempted to address this issue among normal right-handed adults (N=12) by supplementing a well-established MEG protocol involving word recognition and the single dipole method with a sentence comprehension task and a beamformer approach localizing neural oscillations. Beamformer analysis of word recognition and sentence comprehension tasks revealed a desynchronization in the 10–18 Hz range, localized to the temporo-parietal cortices. Inspection of individual profiles of localized desynchronization (10–18 Hz) revealed left hemispheric dominance in 91.7% and 83.3% of individuals during the word recognition and sentence comprehension tasks, respectively. In contrast, single dipole analysis yielded lower estimates, such that activity in temporal language regions was left-lateralized in 66.7% and 58.3% of individuals during word recognition and sentence comprehension, respectively. The results obtained from the word recognition task and localization of oscillatory activity using a beamformer appear to be in line with general estimates of left hemispheric dominance for language in normal right-handed individuals. Furthermore, the current findings support the growing notion that changes in neural oscillations underlie critical components of linguistic processing.

MEG imaging of recurrent gliomas reveals functional plasticity of hemispheric language specialization

“…Compared to the IAP results, the combined LI exhibited a test sensitivity and specificity of 100 and 96%, respectively, using a LI threshold of ±0.1 (Findlay et al, ). These results are aligned with previous studies and further establish MEG based lateralization techniques as valid methods of language dominance determination (Castillo et al, ; Frye et al, ; Pang et al, ; Passaro et al, ; Salmelin, ).…”

“…Because our language lateralization algorithm is MEG‐based, it has the advantage of being noninvasive (and thus not subject to the complications of the IAP; Wada, ). In most cases, the language LI can replace the IAP entirely, and is frequently incorporated into the standard presurgical imaging battery (Breier, Billingsley‐Marshall, Pataraia, Castillo, & Papanicolaou, ; Doss, Zhang, Risse, & Dickens, ; Frye, Rezaie, & Papanicolaou, ; Pang, Wang, Malone, Kadis, & Donner, ; Passaro et al, ). By repeating the same verb generation task at each scan, we are able to compare subsequent scans to identify changes in language laterality, over time, on a patient‐by‐patient basis.…”

Is it time to replace the Wada test and put awake craniotomy to sleep?

“…A second basic and common limitation to the noninvasive methods (MEG, PET, and fMRI) is related to the phenomenon of bilateral activation and consists in the determination of the appropriate ratio of the amount of activation that indicates actual lateralization of language or memory. This problem, however, has been largely solved in the context of prospective studies where the so‐called laterality index (LI) has been established for both MEG and fMRI …”

Language Lateralization Represented by Spatiotemporal Mapping of Magnetoencephalography

“…Several researchers have demonstrated that the optimization may be important for determining laterality by MEG. 33 In theory, dSPM can represent all the magnetic fields by applying a distributed source model. 13,20 Therefore, dSPM analysis does not have a concept of the selection criteria of the adequate sources.…”