Abnormal face identity coding in the middle fusiform gyrus of two brain-damaged prosopagnosic patients (original) (raw)
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A functional MRI study of face recognition in patients with prosopagnosia
Neuroreport, 2001
An fMRI investigation was conducted to determine whether patients with impaired face recognition, a de®cit known as prosopagnosia, would show functional activation in the fusiform gyrus, the neural substrate for face processing, when viewing faces. While the patients did show activation in the fusiform gyrus, with signi®cantly more voxels in posterior areas than their control subjects, this activation was not suf®cient for face processing. In one of the patients, the posterior activation was particularly evident in the left hemisphere, which is thought to be involved in feature-based strategies of face perception. We conclude that an increased reliance on feature-based processing in prosopagnosia leads to a recruitment of neurons in posterior regions of the fusiform gyrus, regions that are not ideally suited for processing faces.
Top-Down Activation of Fusiform Cortex without Seeing Faces in Prosopagnosia
Cerebral Cortex, 2010
Face processing can be modified by bottom-up and top-down influences, but it is unknown how these processes interact in patients with face-recognition impairments (prosopagnosia). We investigated a prosopagnosic with lesions in right occipital and left fusiform cortex but whose right fusiform gyrus is intact and still activated during face-processing tasks. P.S., a patient with a wellestablished and selective agnosia for faces, was instructed to detect the presence of either faces or houses in pictures with different amounts of noise. The right fusiform face area (FFA) showed reduced responses to face information when visual images were degraded with noise. However, her right FFA still activated to noise-only images when she was instructed to detect faces. These results reveal that fusiform activation is still selectively modulated by task demands related to the anticipation of a face, despite severe face-recognition deficits and the fact that no reliable stimulus-driven response is evoked by actual facial information. Healthy controls showed stimulus-driven responses to faces in fusiform, and in right but not left occipital cortex, suggesting that the latter area alone might provide insufficient facial information in P.S. These results provide a novel account for residual activation of the FFA and underscore the importance of controlling task demands during functional magnetic resonance imaging.
Neuropsychologia, 2006
We tested functional activation for faces in patient D.F., who following acquired brain damage has a profound deficit in object recognition based on form (visual form agnosia) and also prosopagnosia that is undocumented to date. Functional imaging demonstrated that like our control observers, D.F. shows significantly more activation when passively viewing face compared to scene images in an area that is consistent with the fusiform face area (FFA) (p < 0.01). Control observers also show occipital face area (OFA) activation; however, whereas D.F.'s lesions appear to overlap the OFA bilaterally. We asked, given that D.F. shows FFA activation for faces, to what extent is she able to recognize faces? D.F. demonstrated a severe impairment in higher level face processing-she could not recognize face identity, gender or emotional expression. In contrast, she performed relatively normally on many face categorization tasks. D.F. can differentiate faces from non-faces given sufficient texture information and processing time, and she can do this is independent of color and illumination information. D.F. can use configural information for categorizing faces when they are presented in an upright but not a sideways orientation and given that she also cannot discriminate half-faces she may rely on a spatially symmetric feature arrangement. Faces appear to be a unique category, which she can classify even when she has no advance knowledge that she will be shown face images. Together, these imaging and behavioral data support the importance of the integrity of a complex network of regions for face identification, including more than just the FFA-in particular the OFA, a region believed to be associated with low-level processing.
Neuropsychologia, 2011
Gaze-contingency is a method traditionally used to investigate the perceptual span in reading by selectively revealing/masking a portion of the visual field in real time. Introducing this approach in face perception research showed that the performance pattern of a brain-damaged patient with acquired prosopagnosia (PS) in a face matching task was reversed, as compared to normal observers: the patient showed almost no further decrease of performance when only one facial part (eye, mouth, nose, etc.) was available at a time (foveal window condition, forcing part-based analysis), but a very large impairment when the fixated part was selectively masked (mask condition, promoting holistic perception) (Van Belle, De Graef, Verfaillie, Busigny, & Rossion, 2010a; Van Belle, De Graef, Verfaillie, Rossion, & Lefèvre, 2010b). Here we tested the same manipulation in a recently reported case of pure prosopagnosia (GG) with unilateral right hemisphere damage (Busigny, Joubert, Felician, Ceccaldi, & Rossion, 2010). Contrary to normal observers, GG was also significantly more impaired with a mask than with a window, demonstrating impairment with holistic face perception. Together with our previous study, these observations support a generalized account of acquired prosopagnosia as a critical impairment of holistic (individual) face perception, implying that this function is a key element of normal human face recognition. Furthermore, the similar behavioral pattern of the two patients despite different lesion localizations supports a distributed network view of the neural face processing structures, suggesting that the key function of human face processing, namely holistic perception of individual faces, requires the activity of several brain areas of the right hemisphere and their mutual connectivity.
Neural basis of prosopagnosia: An fMRI study
Human Brain Mapping, 2002
Brain imaging research has identified at least two regions in human extrastriate cortex responding selectively to faces. One of these is located in the mid-fusiform gyrus (FFA), the other in the inferior occipital gyrus (IOG). We studied activation of these areas using fMRI in three individuals with severely impaired face recognition (one pure developmental and two childhood prosopagnosics). None of the subjects showed the normal pattern of higher fMRI activity to faces than to objects in the FFA and IOG or elsewhere. Moreover, in two of the patients, faces and objects produced similar activations in the regions corresponding to where the FFA and IOG are found in normal subjects. Our study casts light on the important role of FFA and IOG in the network of areas involved in face recognition, and indicates limits of brain plasticity. Hum. Brain Mapping 16:176 -182, 2002.
Face-selective Activation in a Congenital Prosopagnosic Subject
Journal of Cognitive Neuroscience, 2003
& Congenital prosopagnosia is a severe impairment in face identification manifested from early childhood in the absence of any evident brain lesion. In this study, we used fMRI to compare the brain activity elicited by faces in a congenital prosopagnosic subject (YT) relative to a control group of 12 subjects in an attempt to shed more light on the nature of the brain mechanisms subserving face identification. The facerelated activation pattern of YT in the ventral occipito-temporal cortex was similar to that observed in the control group on several parameters: anatomical location, activation profiles, and hemispheric laterality. In addition, using a modified vaseface illusion, we found that YT's brain activity in the facerelated regions manifested global grouping processes. However, subtle differences in the degree of selectivity between objects and faces were observed in the lateral occipital cortex. These data suggest that face-related activation in the ventral occipito-temporal cortex, although necessary, might not be sufficient by itself for normal face identification. &
A bilateral occipitotemporal network mediates face perception
Behavioural Brain Research, 2009
The aim of the present study was to further explore the neuronal mechanisms of face processing in healthy subjects which may help to understand the difficulties experienced by prosopagnosia subjects. A further goal was to compare face specific activation patterns in the right and left occipital face area (OFA) and fusiform face area (FFA) for famous faces, non-famous faces and caricatures of famous faces in four individuals suffering from developmental prosopagnosia (DP) and seven healthy controls, using functional magnetic resonance imaging and psychophysiological interaction analysis (PPI). Control subjects showed higher face related activations in the right compared to the left FFA. Caricatures of faces of famous people and photographs of non-famous faces yielded higher percent signal changes in the OFA and FFA compared to photographs of famous faces. These data support the idea that the OFA and FFA discriminate between familiar and new face representations. The activation patterns of DP subjects were heterogeneous, with none of the patients showing bilateral face related activations in both OFA and FFA. There was no evidence of a left hemispheric activation when the right homologue failed to be activated, supporting the view of a right hemispheric dominance in face perception. PPI analysis indicated a link between activation of the right FFA and the other three tested regions, the left FFA and the right and left OFA. In summary, all four face related brain regions appear to be necessary for successful face processing, and disruption of one component may lead to face recognition deficits.
Journal of Cognitive Neuroscience, 2005
& One of the most impressive disorders following brain damage to the ventral occipitotemporal cortex is prosopagnosia, or the inability to recognize faces. Although acquired prosopagnosia with preserved general visual and memory functions is rare, several cases have been described in the neuropsychological literature and studied at the functional and neural level over the last decades. Here we tested a braindamaged patient presenting a deficit restricted to the category of faces to clarify the nature of the missing and preserved components of the face processing system when it is selectively damaged. Following learning to identify 10 neutral and happy faces through extensive training, we investigated patient PS's recognition of faces using Bubbles, a response classification technique that sampled facial information across the faces in different bandwidths of spatial frequencies [Bubbles: A technique to reveal the use of information in recognition tasks. Vision Research, 41, 2261Research, 41, -2271Research, 41, , 2001. Although PS gradually used less information (i.e., the number of bubbles) to identify faces over testing, the total information required was much larger than for normal controls and decreased less steeply with practice. Most importantly, the facial information used to identify individual faces differed between PS and controls. Specifically, in marked contrast to controls, PS did not use the optimal eye information to identify familiar faces, but instead the lower part of the face, including the mouth and the external contours, as normal observers typically do when processing unfamiliar faces. Together, the findings reported here suggest that damage to the face processing system is characterized by an inability to use the information that is optimal to judge identity, focusing instead on suboptimal information. & D