title: Localising the auditory N1m with event-related beamformers: localisation accuracy following bilateral and unilateral stimulation.
abstract: The auditory evoked N1m-P2m response complex presents a challenging case for MEG source-modelling, because symmetrical, phase-locked activity occurs in the hemispheres both contralateral and ipsilateral to stimulation. Beamformer methods, in particular, can be susceptible to localisation bias and spurious sources under these conditions. This study explored the accuracy and efficiency of event-related beamformer source models for auditory MEG data under typical experimental conditions: monaural and diotic stimulation; and whole-head beamformer analysis compared to a half-head analysis using only sensors from the hemisphere contralateral to stimulation. Event-related beamformer localisations were also compared with more traditional single-dipole models. At the group level, the event-related beamformer performed equally well as the single-dipole models in terms of accuracy for both the N1m and the P2m, and in terms of efficiency (number of successful source models) for the N1m. The results yielded by the half-head analysis did not differ significantly from those produced by the traditional whole-head analysis. Any localisation bias caused by the presence of correlated sources is minimal in the context of the inter-individual variability in source localisations. In conclusion, event-related beamformers provide a useful alternative to equivalent-current dipole models in localisation of auditory evoked responses.
authors.affiliation: Aston Brain Centre, School of Life and Health Sciences, Aston University, Birmingham, B4 7ET, UK.|Sir Peter Mansfield Imaging Centre, Department of Physics, University of Nottingham, Nottingham , NG7 2QL , UK.
authors.forename: Lauren
authors.initials: L
authors.lastname: Gascoyne
authors.affiliation: Aston Brain Centre, School of Life and Health Sciences, Aston University, Birmingham, B4 7ET, UK.
authors.forename: Paul L
authors.initials: PL
authors.lastname: Furlong
authors.affiliation: Department of Clinical Neurophysiology and Magnetoencephalography Center, VU University Medical Center, 1081 HV Amsterdam, the Netherlands.
authors.forename: Arjan
authors.initials: A
authors.lastname: Hillebrand
authors.affiliation: Aston Brain Centre, School of Life and Health Sciences, Aston University, Birmingham, B4 7ET, UK.
authors.forename: Siân F
authors.initials: SF
authors.lastname: Worthen
authors.affiliation: Aston Brain Centre, School of Life and Health Sciences, Aston University, Birmingham, B4 7ET, UK.
authors.forename: Caroline
authors.initials: C
authors.lastname: Witton
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D000368:Aged; D001921:Brain / Q000502:physiology*; D005072:Evoked Potentials, Auditory; D005260:Female; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D008875:Middle Aged; D013017:Sound Localization