Abstracts

Rationale: Comprehensive localization of eloquent cortex is essential for planning surgical interventions in refractory epilepsy. Magnetoencephalography (MEG) has become increasingly popular for localization and characterization of seizure disorders; the technology is also proving useful for mapping eloquent processes, such as motor, somatosensory, and language functions. To date, the most successful language mapping procedures in MEG involve dipole fitting to receptive (primarily posterior) language cortices, particularly in adults. The most popular language mapping protocols and analyses do not identify expressive (anterior) language networks, and work to-date has not controlled for task difficulty when assessing young children and adolescents.Methods: We present a case series, characterizing changes in cortical activity associated with two developmentally-appropriate covert expressive language tasks in healthy children/adolescents (n = 5) and children/adolescents with intractable epilepsy (n = 5). Participants silently name or generate verbs to picture stimuli while MEG is recorded. The data are assessed using differential beamformer analyses, to characterize neuronal changes associated with task completion. The beamformer approach employs spatial filtering, and is appropriate for identification of multiple sources. Using differential beamforming, we estimate source power to characterize neuronal changes (in terms of latency, frequency, and location) associated with active versus baseline states. This differential approach has been shown to correlate well with the BOLD (fMRI) signal, unlike traditional dipole approaches, possibly because differential beamformer retains information that is not phase-locked.Results: We find these developmentally-appropriate tasks valuable for assessment of expressive language in young and school-aged children. The differential beamformer analyses demonstrate synchronous and desynchronous changes associated with expressive language, particularly changes occurring over the inferior frontal lobes.Conclusions: In the future, this protocol may be used to lateralize and localize expressive language in healthy children and in those with intractable epilepsy. (DSK is funded, in part, through a Studentship from the Ontario Student Opportunity Trust Fund - Hospital for Sick Children Foundation Student Scholarship Program, and through a Doctoral Research Award from CIHR in partnership with Epilepsy Canada.)