Decoding face categories in diagnostic subregions of primary visual cortex

• Published in: The European journal of neuroscience 2013-04, Vol.37 (7), p.1130-1139
• Main Authors: Petro, Lucy S., Smith, Fraser W., Schyns, Philippe G., Muckli, Lars
• Format: Article
• Language: English
• Subjects: Adult; Biological and medical sciences; Brain Mapping; diagnostic information; Eye; Eye and associated structures. Visual pathways and centers. Vision; Facial Expression; Female; fMRI; Form Perception; Fundamental and applied biological sciences. Psychology; Humans; Magnetic Resonance Imaging; Male; Models, Neurological; Mouth; multivariate pattern classification; Neurosystems; Vertebrates: nervous system and sense organs; Visual Cortex - physiology
• ISSN: 0953-816X; 1460-9568
• DOI: 10.1111/ejn.12129

Higher visual areas in the occipitotemporal cortex contain discrete regions for face processing, but it remains unclear if V1 is modulated by top‐down influences during face discrimination, and if this is widespread throughout V1 or localized to retinotopic regions processing task‐relevant facial features. Employing functional magnetic resonance imaging (fMRI), we mapped the cortical representation of two feature locations that modulate higher visual areas during categorical judgements – the eyes and mouth. Subjects were presented with happy and fearful faces, and we measured the fMRI signal of V1 regions processing the eyes and mouth whilst subjects engaged in gender and expression categorization tasks. In a univariate analysis, we used a region‐of‐interest‐based general linear model approach to reveal changes in activation within these regions as a function of task. We then trained a linear pattern classifier to classify facial expression or gender on the basis of V1 data from ‘eye’ and ‘mouth’ regions, and from the remaining non‐diagnostic V1 region. Using multivariate techniques, we show that V1 activity discriminates face categories both in local ‘diagnostic’ and widespread ‘non‐diagnostic’ cortical subregions. This indicates that V1 might receive the processed outcome of complex facial feature analysis from other cortical (i.e. fusiform face area, occipital face area) or subcortical areas (amygdala). Using fMRI, we mapped the cortical representation of the eyes and mouth in V1. We measured the BOLD signal whilst subjects engaged in gender and expression categorization tasks of identical faces. With univariate and multivariate analyses, we reveal activity changes within “eye” and “mouth” regions, as well as the remaining V1, as a function of task. Thus a high level constraint such as face categorization task influences V1, possibly via top‐down activity from face areas or subcortical input.