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Ipek Oruc, Teresa Cheung, Kirsten Dalrymple, Chris Fox, Giuseppe Iaria, Todd Handy, Jason Barton; Residual face-selectivity of the N170 and M170 is related to the status of the occipital and fusiform face areas in acquired prosopagnosia. Journal of Vision 2010;10(7):585. doi: 10.1167/10.7.585.
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Event-related potentials (ERP) using scalp EEG recordings demonstrate that a difference between the perception of face and non-face object stimuli is evident in the N170 potential, usually larger over the posterior regions of the right hemisphere. A similar phenomenon is noted in the M170 potential in magnetoencephalography (MEG). The anatomic origins of this face-selective N170 remain uncertain, with proposals that it may reflect contributions from the FFA, STS or both. To investigate this, we studied the face-selective N170 using ERP and M170 using MEG in patients with acquired prosopagnosia. Significance of face/object contrasts in single-subject ERP were based on nonparametric bootstrap confidence intervals. All patients had undergone extensive neuropsychological and behavioural testing, as well as structural and functional MRI with a dynamic face localizer (Fox et al, Human Brain Mapping 2009) to characterize the post-lesion status of their core face-processing network, namely the FFA, STS and OFA. Two patients had right or bilateral anterior temporal damage from herpes encephalitis, sparing all components of the core network. The ERP data showed that, despite their prosopagnosia, they still showed a significant difference between faces and objects in the N170 over the right occipitotemporal regions, which was confirmed in the M170 using MEG in one patient. Three patients had occipitotemporal damage, two with loss of the FFA alone and one with loss of the FFA and OFA. Two of these subjects showed no difference between faces and objects in either the N170 or M170; however one subject with loss of the FFA alone did show a residual face-selective N170. We conclude that STS survival is insufficient on its own to generate a face-selective N170 in some patients, but on the other hand loss of the FFA alone does not always eliminate this electrophysiological phenomenon.
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