Abstracts

Rationale: Magnetic source imaging (MSI) for receptive language localization is routinely performed on inpatients undergoing pre-surgical work-ups. As part of the inpatient work-up, the patients may be subjected to variable amounts of sleep-deprivation. The effect of varying levels of alertness on the localization of receptive language by MSI has not been evaluated.Methods: We analyzed the results of six magnetoencephalography (MEG) studies done on a single healthy volunteer in a series of different states of alertness. Two studies were obtained after 24 hours of continuous sleep-deprivation, two studies were obtained after a normal night’s sleep, and two studies were obtained after a normal night’s sleep with the subject taking 100 mg of modafinil upon awakening. The first study in each state was obtained between 9 AM and 10 AM to coincide with peak circadian alertness and the second between 2 PM and 3 PM to coincide with peak circadian daytime drowsiness. A brain magnetic resonance imaging study was obtained prior to the MEG studies and was normal. MEG recordings were conducted using a 248-channel MEG gradiometer system (4-D Neuroimaging, San Diego, CA). Maps of receptive language function were derived from MEG recordings obtained in the participant in the context of a continuous word recognition task. The stability across conditions in the topography (x,y,z values of derived dipoles), and the amplitude of the recorded magnetic fields (RMS) and estimated sources (Q) was tested.Results: There were no significant differences in topography to report. The amplitude of the estimated dipoles in Wernicke’s area showed a lower amplitude (values of Q) and the recorded magnetic fields were significantly weaker in a single session, that obtained after a full night’s sleep and 100 mg of modafinil, recorded between 9 and 10 AM (the session corresponding to maximal alertness).Conclusions: MSI of receptive language remains topographically stable across a range of alertness. These results may allay concerns that the sleep deprivation that frequently occurs during pre-surgical epilepsy monitoring unit hospitalizations will compromise the accuracy of receptive language localization by MEG. Further investigation to determine what changes can be detected in MEG recordings obtained in states of variable alertness is warranted.