FUNCTIONAL NEUROANATOMY OF FACE AND OBJECT PROCESSING

TLDR

Studies of brain‑damaged patients have shown that lesions in occipital and temporal lobes can cause prosopagnosia, yet the specific functional roles of the identified face‑processing cortical areas and their exclusivity remain unclear. This study uses PET to investigate whether distinct cortical regions are uniquely devoted to face processing in normal adults. Six tasks involving gratings, face gender, face identity, and object recognition were performed while rCBF was measured with PET and mapped onto MR images, then compared by subtraction. Gratings activated striate and extrastriate cortex; face gender engaged right extrastriate, face identity recruited bilateral fusiform, anterior temporal, and right parahippocampal regions, whereas object recognition activated left occipito‑temporal cortex, demonstrating a ventro‑medial right‑hemisphere specialization for face recognition and a clear dissociation from object processing.

Abstract

Studies of brain-damaged patients have revealed the existence of a selective impairment of face processing, prosopagnosia, resulting from lesions at different loci in the occipital and temporal lobes. The results of such studies have led to the identification of several cortical areas underlying the processing of faces, but it remains unclear what functional aspects of face processing are served by these areas and whether they are uniquely devoted to the processing of faces. The present study addresses these questions in a positron emission tomography (PET) study of regional cerebral blood flow in normal adults, using the 15 oxygen water bolus technique. The subjects participated in six tasks (with gratings, faces and objects), and the resulting level of cerebral activation was mapped on images of the subjects' cerebral structures obtained through magnetic resonance and was compared between tasks using the subtraction method. Compared with a fixation condition, regional cerebral blood flow (rCBF) changes were found in the striate and extrastriate cortex when subjects had to decide on the orientation of sine-wave gratings. A face-gender categorization resulted in activation changes in the right extrastriate cortex, and a face-identity condition produced additional activation of the fusiform gyrus and anterior temporal cortex of both hemispheres, and of the right parahippocampal gyrus and adjacent areas. Cerebral activation during an object-recognition task occurred essentially in the left occipito-temporal cortex and did not involve the right hemisphere regions specifically activated during the face-identity task. The results provide the first empirical evidence from normal subjects regarding the crucial role of the ventro-medial region of the right hemisphere in face recognition, and they offer new information about the dissociation between face and object processing.