title: Visual object agnosia is associated with a breakdown of object-selective responses in the lateral occipital cortex.
abstract: Patients with visual object agnosia fail to recognize the identity of visually presented objects despite preserved semantic knowledge. Object agnosia may result from damage to visual cortex lying close to or overlapping with the lateral occipital complex (LOC), a brain region that exhibits selectivity to the shape of visually presented objects. Despite this anatomical overlap the relationship between shape processing in the LOC and shape representations in object agnosia is unknown. We studied a patient with object agnosia following isolated damage to the left occipito-temporal cortex overlapping with the LOC. The patient showed intact processing of object structure, yet often made identification errors that were mainly based on the global visual similarity between objects. Using functional Magnetic Resonance Imaging (fMRI) we found that the damaged as well as the contralateral, structurally intact right LOC failed to show any object-selective fMRI activity, though the latter retained selectivity for faces. Thus, unilateral damage to the left LOC led to a bilateral breakdown of neural responses to a specific stimulus class (objects and artefacts) while preserving the response to a different stimulus class (faces). These findings indicate that representations of structure necessary for the identification of objects crucially rely on bilateral, distributed coding of shape features.
authors.affiliation: Division of Neurorehabilitation, Department of Clinical Neurosciences, Geneva University Hospitals, Geneva, Switzerland; Laboratory of Cognitive Neurorehabilitation, Department of Clinical Neurosciences, Medical School, University of Geneva, Geneva, Switzerland; Faculty of Psychology and Educational Sciences, University of Geneva, Geneva, Switzerland. Electronic address: radek.ptak@hcuge.ch.
authors.forename: Radek
authors.initials: R
authors.lastname: Ptak
authors.affiliation: Department of Radiology and Medical Informatics, University of Geneva, Geneva, Switzerland.
authors.forename: François
authors.initials: F
authors.lastname: Lazeyras
authors.affiliation: Division of Neurorehabilitation, Department of Clinical Neurosciences, Geneva University Hospitals, Geneva, Switzerland; Laboratory of Cognitive Neurorehabilitation, Department of Clinical Neurosciences, Medical School, University of Geneva, Geneva, Switzerland.
authors.forename: Marie
authors.initials: M
authors.lastname: Di Pietro
authors.affiliation: Division of Neurorehabilitation, Department of Clinical Neurosciences, Geneva University Hospitals, Geneva, Switzerland; Laboratory of Cognitive Neurorehabilitation, Department of Clinical Neurosciences, Medical School, University of Geneva, Geneva, Switzerland.
authors.forename: Armin
authors.initials: A
authors.lastname: Schnider
authors.affiliation: Department of Radiology and Medical Informatics, University of Geneva, Geneva, Switzerland.
authors.forename: Stéphane R
authors.initials: SR
authors.lastname: Simon
mesh_terms: D000368:Aged; D000377:Agnosia / Q000209:etiology / Q000503:physiopathology*; D001921:Brain / Q000473:pathology / Q000503:physiopathology*; D001931:Brain Mapping; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009778:Occipital Lobe / Q000503:physiopathology*; D021641:Recognition, Psychology / Q000502:physiology; D013028:Space Perception / Q000502:physiology*; D013702:Temporal Lobe / Q000503:physiopathology*
keywords: Functional MRI; Lateral occipital cortex; Object recognition; Visual object agnosia