Impaired face discrimination in acquired prosopagnosia is associated with abnormal response to individual faces in the right middle fusiform gyrus

in Cerebral Cortex (2006), 16(4), 574-586

The middle fusiform gyrus (MFG) and the inferior occipital gyrus (IOG) are activated by both detection and identification of faces. Paradoxically, patients with acquired prosopagnosia following lesions to ... [more ▼]

The middle fusiform gyrus (MFG) and the inferior occipital gyrus (IOG) are activated by both detection and identification of faces. Paradoxically, patients with acquired prosopagnosia following lesions to either of these regions in the right hemisphere cannot identify faces, but can still detect faces. Here we acquired functional magnetic resonance imaging (fMRI) data during face processing in a patient presenting a specific deficit in individual face recognition, following lesions encompassing the right IOG. Using an adaptation paradigm we show that the fMRI signal in the rMFG of the patient, while being larger in response to faces as compared to objects, does not differ between conditions presenting identical and distinct faces, in contrast to the larger response to distinct faces observed in controls. These results suggest that individual discrimination of faces critically depends on the integrity of both the rMFG and the rIOG, which may interact through re-entrant cortical connections in the normal brain. [less ▲]

Recovery from adaptation to facial identity is larger for upright than inverted faces in the human occipito-temporal cortex

in Neuropsychologia (2006), 44(6), 912-922

Human faces look more similar to each other when they are presented upside-down, leading to an increase of error rates and response times during individual face discrimination tasks. Here we used ... [more ▼]

Human faces look more similar to each other when they are presented upside-down, leading to an increase of error rates and response times during individual face discrimination tasks. Here we used functional magnetic resonance imaging (fMRI) to test the hypothesis that this perceived similarity leads to a lower recovery from identity adaptation for inverted faces than for upright faces in face-sensitive areas of the occipito-temporal cortex. Ten subjects were presented with blocks of upright and inverted faces, with the same face identity repeated consecutively in half of the blocks, and different facial identities repeated in the other blocks. When face stimuli were presented upright, the percent signal change in the bilateral middle fusiform gyrus (MFG) was larger for different faces as compared to same faces, replicating previous observations of a recovery from facial identity adaptation in this region. However, there was no significant recovery from adaptation when different inverted faces were presented. Most interestingly, the difference in activation between upright and inverted faces increased progressively during a block when different facial identities were presented. A similar pattern of activation was found in the left middle fusiform gyrus, but was less clear-cut in bilateral face-sensitive areas of the inferior occipital cortex. These findings show that the differential level of activation to upright and inverted faces in the fusiform gyrus is mainly due to a difference in recovery from adaptation, and they explain the discrepancies in the results reported in previous fMRI studies which compared the processing of upright and inverted faces. The lack of recovery from adaptation for inverted faces in the fusiform gyrus may underlie the face inversion effect (FIE), which takes place during perceptual encoding of individual face representations. [less ▲]

Processus attentionnels, mémoire de travail visuospatiale et genèse des représentations numériques: une approche neuropsychologique

Report (2005)

Face-sensitive responses in the occipital inferior cortex of normal humans through feedback inputs from the fusiform gyrus ?: Evidence from neuroimaging studies of brain-damaged prosopagnosic patients

Poster (2004, June)

In humans, neuroimaging studies have identified two major visual extrastriate areas presenting face-sensitive responses: in the inferior occipital cortex (‘occipital face area’, OFA), and the middle ... [more ▼]

In humans, neuroimaging studies have identified two major visual extrastriate areas presenting face-sensitive responses: in the inferior occipital cortex (‘occipital face area’, OFA), and the middle fusiform gyrus (the ‘fusiform face area’, FFA), with a right hemispheric dominance. It has been proposed that the OFA, located anteriorly to foveal V4v (Halgren et al., 1999), has a critical role in the early perception of facial features and provides the feedforward outputs to later stages of face processing in both the FFA and the STS (Haxby et al., 2000). However, we have recently reported a normal activation of the right FFA despite a lesion encompassing the region of the right OFA in a brain-damaged prosopagnosic patient, PS (Rossion et al., 2003), suggesting that the face-sensitive responses observed at the level of the OFA in normals may rather arise from feedback connections from the FFA. Here we provide complementary fMRI evidence supporting this view. First, the normal differential activation for faces and objects in the right FFA of PS was observed only for left visual field presentations and is thus unlikely to originate from contralateral intact regions of the occipital cortex (e.g. left OFA). Second, the time-course in the right FFA and left OFA of PS for centrally presented items suggests an earlier differential activity between faces and objects in the most anterior region, the FFA. Finally, we imaged another (prosop)agnosic patient (NS, Delvenne et al., 2004) with a lesion encompassing the right FFA but sparing all posterior visual areas, and failed to disclose any face-sensitive response in his nonetheless structurally and functionnally intact occipital cortex. Together, these findings illustrate the necessary role of both the right FFA and OFA for accurate face perception, and reinforce the hypothesis that a dominant (feedback) connection from the FFA to the OFA subtends face-sensitive responses observed in the latter area when processing faces. [less ▲]

The functionally defined right occipital and fusiform "face areas" discriminate novel from visually familiar faces

in NeuroImage (2003), 19(3), 877-883

Neuroimaging (PET and fMRI) studies have identified a set of brain areas responding more to faces than to other object categories in the visual extrastriate cortex of humans. This network includes the ... [more ▼]

Neuroimaging (PET and fMRI) studies have identified a set of brain areas responding more to faces than to other object categories in the visual extrastriate cortex of humans. This network includes the middle lateral fusiform gyrus (the fusiform face area, or FFA) as well as the inferior occipital gyrus (occipital face area, OFA). The exact functions of these areas in face processing remain unclear although it has been argued that their primary function is to distinguish faces from nonface object categories-"face detection"-or also to discriminate among faces, irrespective of their visual familiarity to the observer. Here, we combined the data from two previous positron emission tomography (PET) studies to show that the functionally defined face areas are involved in the automatic discrimination between unfamiliar faces and familiar faces. Consistent with previous studies, a face localizer contrast (faces-objects) revealed bilateral activation in the middle lateral fusiform gyrus (FFA, BA37) and in the right inferior occipital cortex (OFA, BA19). Within all the regions of the right hemisphere, larger levels of activation were found for unfamiliar as compared to familiar faces. These results suggest that the very same areas involved in categorizing faces at the basic or individual level, play a role in differentiating familiar faces from new faces, showing an overlap between visual and presemantic mnesic representations of faces in the right hemisphere. [less ▲]

A pet study of human skill learning: Changes in brain activity related to learning an orientation discrimination task

in Cortex: A Journal Devoted to the Study of the Nervous System and Behavior (2001), 37(2), 243-265

Using 15O-water 3D positron emission tomography we investigated the effect of training in orientation discrimination upon cerebral activity in healthy human adults. When subjects are trained in this ... [more ▼]

Using 15O-water 3D positron emission tomography we investigated the effect of training in orientation discrimination upon cerebral activity in healthy human adults. When subjects are trained in this discrimination task, they learn the visuo-motor stimulus-response association required by the task and they increase their perceptual abilities in orientation discrimination. The present study was designed to investigate the rCBF modifications related to both these learning processes induced by training in orientation discrimination. PET data were acquired on two separate days (before and after training). Comparing the activation pattern related to orientation discrimination before and after the training period we observed activity decreases located in the left cerebellar cortex, in the right precentral gyrus and bilaterally in the fusiform gyri. The only region showing an activity increase was located in the body of the right caudate nucleus. These findings confirm the role of the neostriatum in skill learning and highlight the importance of mechanisms resulting in cortical and cerebellar neuronal activity decreases in this type of learning. [less ▲]

Effect of familiarity on the processing of human faces

in NeuroImage (1999), 9(3), 278289

Most brain imaging studies on face perception have investigated the processing of unknown faces and addressed mainly the question of specific face processing in the human brain. The goal of this study was ... [more ▼]

Most brain imaging studies on face perception have investigated the processing of unknown faces and addressed mainly the question of specific face processing in the human brain. The goal of this study was to highlight the effects of familiarity on the visual processing of faces. Using [15O]water 3D Positron Emission Tomography, regional cerebral blood flow distribution was measured in 11 human subjects performing an identical task (gender categorization) on both unknown and known faces. Subjects also performed two control tasks (a face recognition task and a visual pattern discrimination task). They were scanned after a training phase using videotapes during which they had been familiarized with and learned to recognize a set of faces. Two major results were obtained. On the one hand, we found bilateral activations of the fusiform gyri in the three face conditions, including the so-called fusiform-face area, a region in the right fusiform gyrus specifically devoted to face processing. This common activation suggests that different cognitive tasks performed on known and unknown faces require the involvement of this fusiform region. On the other hand, specific regional cerebral blood flow changes were related to the processing of known and unknown faces. The left amygdala, a structure involved in implicit learning of visual representations, was activated by the categorization task on unknown faces. The same task on known faces induced a relative decrease of activity in early visual areas. These differences between the two categorization tasks reveal that the human brain processes known and unknown faces differently. [less ▲]

PET study of human voluntary saccadic eye movements in darkness: Effect of task repetition on the activation pattern

in European Journal of Neuroscience (1998), 10

Using H2(15)O 3D Positron Emission Tomography (PET), regional cerebral blood flow (rCBF) was measured in six human subjects under two different conditions: at rest and while performing self-paced ... [more ▼]

Using H2(15)O 3D Positron Emission Tomography (PET), regional cerebral blood flow (rCBF) was measured in six human subjects under two different conditions: at rest and while performing self-paced horizontal saccadic eye movements in darkness. These two conditions were repeated four times each. First, the comparison between the four saccadic and four resting conditions was investigated in a group and a single subject analysis. Saccades elicited bilateral rCBF increases in the medial part of the superior frontal gyrus (supplementary eye field), precentral gyrus (frontal eye field), superior parietal lobule, anterior medial part of the occipital lobe involving striate and extrastriate cortex (lingual gyrus and cuneus), and in the right inferior parietal lobule. At the subcortical level, activations were found in the left putamen. These results mainly replicate previous PET findings on saccadic control. Second, the interaction between the experimental conditions and their repetition was examined. When activations throughout repetition of the same saccadic task are compared, the supplementary eye fields show a progressive increase of activation. On the contrary, the activation in the cerebellum, left superior parietal lobule and left occipital cortex progressively decreases during the scanning session. Given the existence of such an interaction, the pattern of activations must be interpreted as a function of task repetition. This may be a factor explaining some apparent mismatch between different studies. [less ▲]

Specific activation related to proper name retrieval associated with faces

Poster (1997, October)

Orientation-specific training effect in visual orientation discrimination, a pet study

Poster (1996)