title: MEG Adaptation Resolves the Spatiotemporal Characteristics of Face-Sensitive Brain Responses.
abstract: An unresolved goal in face perception is to identify brain areas involved in face processing and simultaneously understand the timing of their involvement. Currently, high spatial resolution imaging techniques identify the fusiform gyrus as subserving processing of invariant face features relating to identity. High temporal resolution imaging techniques localize an early latency evoked component-the N/M170-as having a major generator in the fusiform region; however, this evoked component is not believed to be associated with the processing of identity. To resolve this, we used novel magnetoencephalographic beamformer analyses to localize cortical regions in humans spatially with trial-by-trial activity that differentiated faces and objects and to interrogate their functional sensitivity by analyzing the effects of stimulus repetition. This demonstrated a temporal sequence of processing that provides category-level and then item-level invariance. The right fusiform gyrus showed adaptation to faces (not objects) at ∼150 ms after stimulus onset regardless of face identity; however, at the later latency of ∼200-300 ms, this area showed greater adaptation to repeated identity faces than to novel identities. This is consistent with an involvement of the fusiform region in both early and midlatency face-processing operations, with only the latter showing sensitivity to invariant face features relating to identity.
  
  
  CONCLUSIONS
  Neuroimaging techniques with high spatial-resolution have identified brain structures that are reliably activated when viewing faces and techniques with high temporal resolution have identified the time-varying temporal signature of the brain's response to faces. However, until now, colocalizing face-specific mechanisms in both time and space has proven notoriously difficult. Here, we used novel magnetoencephalographic analysis techniques to spatially localize cortical regions with trial-by-trial temporal activity that differentiates between faces and objects and to interrogate their functional sensitivity by analyzing effects of stimulus repetition on the time-locked signal. These analyses confirm a role for the right fusiform region in early to midlatency responses consistent with face identity processing and convincingly deliver upon magnetoencephalography's promise to resolve brain signals in time and space simultaneously.
authors.affiliation: York Neuroimaging Centre, University of York, Heslington, York YO10 5NY, United Kingdom.
authors.forename: Michael I G
authors.initials: MI
authors.lastname: Simpson
authors.affiliation: York Neuroimaging Centre, University of York, Heslington, York YO10 5NY, United Kingdom.
authors.forename: Sam R
authors.initials: SR
authors.lastname: Johnson
authors.affiliation: School of Psychological Sciences, University of Manchester, Manchester M13 9PL, United Kingdom.
authors.forename: Garreth
authors.initials: G
authors.lastname: Prendergast
authors.affiliation: Department of Computer Science, University of York, Heslington, York YO10 5GH, United Kingdom.
authors.forename: Athanasios V
authors.initials: AV
authors.lastname: Kokkinakis
authors.affiliation: UCL Institute of Neurology, University College London, Queens Square, London WC1N 3BG, United Kingdom, and.
authors.forename: Eileanoir
authors.identifier: http://orcid.org/0000-0002-5271-0747
authors.initials: E
authors.lastname: Johnson
authors.affiliation: York Neuroimaging Centre, University of York, Heslington, York YO10 5NY, United Kingdom.
authors.forename: Gary G R
authors.initials: GG
authors.lastname: Green
authors.affiliation: York Neuroimaging Centre, University of York, Heslington, York YO10 5NY, United Kingdom, School of Psychology and Counseling, Queensland University of Technology, Kelvin Grove, Queensland 4059, Australia patrick.johnston@qut.edu.au.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Johnston
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D001921:Brain / Q000502:physiology*; D000066499:Facial Recognition / Q000502:physiology*; D005260:Female; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods*; D008297:Male; D009415:Nerve Net / Q000502:physiology; D010775:Photic Stimulation / Q000379:methods*; D013028:Space Perception / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult
keywords: M170; MEG; faces; source localization; visual perception