Localizing evoked and induced responses to faces using magnetoencephalography.
Bottom Line: Recently, a number of studies have used magnetoencephalography (MEG) to try to record these responses non-invasively - in many cases using source analysis techniques based on the beamforming method.We localized the gamma-band response to bilateral lateral occipital cortex, and both the gamma-band response and the M170-evoked response to the right fusiform gyrus.These findings help to establish that MEG beamforming can localize face-specific responses in time, frequency and space with good accuracy (when validated against established findings from functional magnetic resonance imaging and intracranial recordings), as well as contributing to the establishment of best methodological practice for the use of the beamformer method to measure face-specific responses.
Affiliation: Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, 70 Park Place, Cardiff, CF10 3AT, Wales, UK.Show MeSH
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Mentions: For the M170 analysis (see Fig.9A) a single area was found in which the faces produced enhanced source power relative to scrambled stimuli. This was situated in a posterior region of ventro-temporal cortex, close to the region of fusiform gyrus for which we found a gamma amplitude enhancement for faces, but shifted somewhat anteriorally and superiorally so that the most significant voxel occurred in the adjacent white matter (Talairach coordinates: + 37.1, −55.2, −1.0). To explore the time course of this effect we performed a virtual sensor analysis of this response by finding local maxima in the approximate location of this effect in individual-level images of between-condition differences (two participants were excluded from this analysis due to absence of a local maximum in the area of interest). Consistent with our attribution of this effect to the M170 ERF, the major difference between conditions was a prominent peak around 140 ms to face stimuli, which was almost entirely absent when the stimuli were scrambled (Fig.10A).
Affiliation: Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, 70 Park Place, Cardiff, CF10 3AT, Wales, UK.