Auditory Functional Mapping. Validation by simultaneous depth and MEG recordings

Abstract

Objectives Hemispheric dominance for language is one of the most important to predict both risks of language production and verbal memory impairment. Evoked activities recorded from depth electrodes in the auditory areas have been proved to be efficient to reveal dominant hemisphere [1] . Similar information can also be obtained for non-invasive recordings (EEG or MEG) [2] . However, reconstruction of a cortical brain area from surface recordings is subject to the use of “inverse problems” that are still under development. Methods We have investigated patients with depth electrodes from up to 219 contacts with contacts located in the auditory areas and with MagnetoEncephaloGraphy. Thanks to technical developments, recordings have been performed simultaneously [3] . We used verbal sounds/BA/and/PA/are known to induce different cortical responses depending on the hemispheric lateralization [1] . Activity from virtual electrodes have been reconstructed from MEG recording using beam forming approach. Coordinates of the virtual electrodes have been taken from the depth electrodes contacts measured from IRM and CT scans. Results Reconstructions of virtual electrodes have been compared with recordings from the depth electrode. They presented similar time courses in both auditory and non-auditory areas. However, responses obtained from virtual electrodes are more spread than the invasive ones. General shapes and latencies of the event were correctly reconstructed allowing to evaluate the cerebral dominance from MEG data. It was also demonstrated in this study that close results can be obtained without MRI information. Conclusion Inverse solutions are known to be subject to a “leakage” effect that tends to spread the solution over a larger space than found with the seeg recordings. However, this demonstrates the ability of the MEG to unravel the cortical activity on a non-invasive way. Furthermore, the signals were properly reconstructed especially regarding the timing.