Guided saccades modulate object and face-specific activity in the fusiform gyrus

Atypical neural encoding of faces in individuals with autism spectrum disorder

Individuals with autism spectrum disorder (ASD) experience pervasive difficulties in processing social information from faces. However, the behavioral and neural mechanisms underlying social trait judgments of faces in ASD remain largely unclear. Here, we comprehensively addressed this question by employing functional neuroimaging and parametrically generated faces that vary in facial trustworthiness and dominance. Behaviorally, participants with ASD exhibited reduced specificity but increased inter-rater variability in social trait judgments. Neurally, participants with ASD showed hypo-activation across broad face-processing areas. Multivariate analysis based on trial-by-trial face responses could discriminate participant groups in the majority of the face-processing areas. Encoding social traits in ASD engaged vastly different face-processing areas compared to controls, and encoding different social traits engaged different brain areas. Interestingly, the idiosyncratic brain areas encoding social traits in ASD were still flexible and context-dependent, similar to neurotypicals. Additionally, participants with ASD also showed an altered encoding of facial saliency features in the eyes and mouth. Together, our results provide a comprehensive understanding of the neural mechanisms underlying social trait judgments in ASD.

Unrestricted eye movements strengthen effective connectivity from hippocampal to oculomotor regions during scene construction

Scene construction is a key component of memory recall, navigation, and future imagining, and relies on the medial temporal lobes (MTL). A parallel body of work suggests that eye movements may enable the imagination and construction of scenes, even in the absence of external visual input. There are vast structural and functional connections between regions of the MTL and those of the oculomotor system. However, the directionality of connections between the MTL and oculomotor control regions, and how it relates to scene construction, has not been studied directly in human neuroimaging. In the current study, we used dynamic causal modeling (DCM) to interrogate effective connectivity between the MTL and oculomotor regions using a scene construction task in which participants' eye movements were either restricted (fixed-viewing) or unrestricted (free-viewing). By omitting external visual input, and by contrasting free- versus fixed- viewing, the directionality of neural connectivity during scene construction could be determined. As opposed to when eye movements were restricted, allowing free-viewing during construction of scenes strengthened top-down connections from the MTL to the frontal eye fields, and to lower-level cortical visual processing regions, suppressed bottom-up connections along the visual stream, and enhanced vividness of the constructed scenes. Taken together, these findings provide novel, non-invasive evidence for the underlying, directional, connectivity between the MTL memory system and oculomotor system associated with constructing vivid mental representations of scenes.

Effects of Scene Properties and Emotional Valence on Brain Activations: A Fixation-Related fMRI Study

Temporal and spatial characteristics of fixations are affected by image properties, including high-level scene characteristics, such as object-background composition, and low-level physical characteristics, such as image clarity. The influence of these factors is modulated by the emotional content of an image. Here, we aimed to establish whether brain correlates of fixations reflect these modulatory effects. To this end, we simultaneously scanned participants and measured their eye movements, while presenting negative and neutral images in various image clarity conditions, with controlled object-background composition. The fMRI data were analyzed using a novel fixation-based event-related (FIBER) method, which allows the tracking of brain activity linked to individual fixations. The results revealed that fixating an emotional object was linked to greater deactivation in the right lingual gyrus than fixating the background of an emotional image, while no difference between object and background was found for neutral images. We suggest that deactivation in the lingual gyrus might be linked to inhibition of saccade execution. This was supported by fixation duration results, which showed that in the negative condition, fixations falling on the object were longer than those falling on the background. Furthermore, increase in the image clarity was correlated with fixation-related activity within the lateral occipital complex, the structure linked to object recognition. This correlation was significantly stronger for negative images, presumably due to greater deployment of attention towards emotional objects. Our eye-tracking results are in line with these observations, showing that the chance of fixating an object rose faster for negative images over neutral ones as the level of noise decreased. Overall, our study demonstrated that emotional value of an image changes the way that low and high-level scene properties affect the characteristics of fixations. The fixation-related brain activity is affected by the low-level scene properties and this impact differs between negative and neutral images. The high-level scene properties also affect brain correlates of fixations, but only in the case of the negative images.

Loss of extra-striatal phosphodiesterase 10A expression in early premanifest Huntington's disease gene carriers

Huntington's disease (HD) is a monogenic neurodegenerative disorder with an underlying pathology involving the toxic effect of mutant huntingtin protein primarily in striatal and cortical neurons. Phosphodiesterase 10A (PDE10A) regulates intracellular signalling cascades, thus having a key role in promoting neuronal survival. Using positron emission tomography (PET) with [(11)C]IMA107, we investigated the in vivo extra-striatal expression of PDE10A in 12 early premanifest HD gene carriers. Image processing and kinetic modelling was performed using MIAKAT™. Parametric images of [(11)C]IMA107 non-displaceable binding potential (BPND) were generated from the dynamic [(11)C]IMA107 scans using the simplified reference tissue model with the cerebellum as the reference tissue for nonspecific binding. We set a threshold criterion for meaningful quantification of [(11)C]IMA107 BPND at 0.30 in healthy control data; regions meeting this criterion were designated as regions of interest (ROIs). MRI-based volumetric analysis showed no atrophy in ROIs. We found significant differences in mean ROIs [(11)C]IMA107 BPND between HD gene carriers and healthy controls. HD gene carriers had significant loss of PDE10A within the insular cortex and occipital fusiform gyrus compared to healthy controls. Insula and occipital fusiform gyrus are important brain areas for the regulation of cognitive and limbic function that is impaired in HD. Our findings suggest that dysregulation of PDE10A-mediated intracellular signalling could be an early phenomenon in the course of HD with relevance also for extra-striatal brain areas.

Visual system integrity and cognition in early Huntington's disease

Posterior cortical volume changes and abnormal visuomotor performance are present in patients with Huntington's disease (HD). However, it is unclear whether posterior cortical volume loss contributes to abnormal neural activity, and whether activity changes predict cognitive dysfunction. Using magnetic resonance imaging (MRI), we investigated brain structure and visual network activity at rest in patients with early HD (n = 20) and healthy controls (n = 20). The symbol digit modalities test (SDMT) and subtests of the Visual Object and Space Perception Battery were completed offline. For functional MRI data, a group independent component analysis was used. Voxel-based morphometry was employed to assess regional brain atrophy, and 'biological parametric mapping' analyses were included to investigate the impact of atrophy on neural activity. Patients showed significantly worse visuomotor and visual object performance than controls. Structural analyses confirmed occipitotemporal atrophy. In patients and controls, two spatiotemporally distinct visual systems were identified. Patients showed decreased activity in the left fusiform cortex, and increased left cerebellar activity. These findings remained stable after correction for brain atrophy. Lower fusiform cortex activity was associated with lower SDMT performance and with higher disease burden scores. These associations were absent when cerebellar function was related to task performance and disease burden. The results of this study suggest that regionally specific functional abnormalities of the visual system can account for the worse visuomotor cognition in HD patients. However, occipital volume changes cannot sufficiently explain abnormal neural function in these patients.

Self-face recognition in children with autism spectrum disorders: a near-infrared spectroscopy study

It is assumed that children with autism spectrum disorders (ASD) have specificities for self-face recognition, which is known to be a basic cognitive ability for social development. In the present study, we investigated neurological substrates and potentially influential factors for self-face recognition of ASD patients using near-infrared spectroscopy (NIRS). The subjects were 11 healthy adult men, 13 normally developing boys, and 10 boys with ASD. Their hemodynamic activities in the frontal area and their scanning strategies (eye-movement) were examined during self-face recognition. Other factors such as ASD severities and self-consciousness were also evaluated by parents and patients, respectively. Oxygenated hemoglobin levels were higher in the regions corresponding to the right inferior frontal gyrus than in those corresponding to the left inferior frontal gyrus. In two groups of children these activities reflected ASD severities, such that the more serious ASD characteristics corresponded with lower activity levels. Moreover, higher levels of public self-consciousness intensified the activities, which were not influenced by the scanning strategies. These findings suggest that dysfunction in the right inferior frontal gyrus areas responsible for self-face recognition is one of the crucial neural substrates underlying ASD characteristics, which could potentially be used to evaluate psychological aspects such as public self-consciousness.

Controlled scanpath variation alters fusiform face activation

We investigated the influence of experimentally guided saccades and fixations on fMRI activation in brain regions specialized for face and object processing. Subjects viewed a static image of a face while a small fixation cross made a discrete jump within the image every 500 ms. Subjects were required to make a saccade and fixate the cross at its new location. Each run consisted of alternating blocks in which the subject was guided to make a series of saccades and fixations that constituted either a Typical or an Atypical face scanpath. Typical scanpaths were defined as a scanpath in which the fixation cross landed on the eyes or the mouth in 90% of all trials. Atypical scanpaths were defined as scanpaths in which the fixation cross landed on the eyes or mouth on 12% of all trials. The average saccade length was identical in both typical and atypical blocks, and both were preceded by a baseline block where the fixation cross made much smaller jumps in the middle of the screen. Within the functionally predefined face area of the ventral occipitotemporal cortex (VOTC), typical scanpaths evoked significantly more activity when compared to atypical scanpaths. A voxel-based analysis revealed a similar pattern in clusters of voxels located within VOTC, frontal eye fields, superior colliculi, intraparietal sulcus, and inferior frontal gyrus. These results demonstrate that fMRI activation is highly sensitive to the pattern of eye movements employed during face processing, and thus illustrates the potential confounding influence of uncontrolled eye movements for neuroimaging studies of face and object perception in normal and clinical populations.

Scanning strategies do not modulate face identification: eye-tracking and near-infrared spectroscopy study

BACKGROUND

During face identification in humans, facial information is sampled (seeing) and handled (processing) in ways that are influenced by the kind of facial image type, such as a self-image or an image of another face. However, the relationship between seeing and information processing is seldom considered. In this study, we aimed to reveal this relationship using simultaneous eye-tracking measurements and near-infrared spectroscopy (NIRS) in face identification tasks.

METHODOLOGY/PRINCIPAL FINDINGS

22 healthy adult subjects (8 males and 14 females) were shown facial morphing movies in which an initial facial image gradually changed into another facial image (that is, the subject's own face was changed to a familiar face). The fixation patterns on facial features were recorded, along with changes in oxyhemoglobin (oxyHb) levels in the frontal lobe, while the subjects identified several faces. In the self-face condition (self-face as the initial image), hemodynamic activity around the right inferior frontal gyrus (IFG) was significantly greater than in the familiar-face condition. On the other hand, the scanning strategy was similar in almost all conditions with more fixations on the eyes and nose than on other areas. Fixation time on the eye area did not correlate with changes in oxyHb levels, and none of the scanning strategy indices could estimate the hemodynamic changes.

CONCLUSIONS/SIGNIFICANCE

We conclude that hemodynamic activity, i.e., the means of processing facial information, is not always modulated by the face-scanning strategy, i.e., the way of seeing, and that the right IFG plays important roles in both self-other facial discrimination and self-evaluation.

Guided saccades modulate face- and body-sensitive activation in the occipitotemporal cortex during social perception

Functional magnetic resonance imaging (fMRI) has identified distinct brain regions in ventral occipitotemporal cortex (VOTC) and lateral occipitotemporal cortex (LOTC) that are differentially activated by pictures of faces and bodies. Recent work from our laboratory has shown that the strong LOTC activation evoked by bodies in which the face is occluded is attenuated when the occlusion is removed. We hypothesized that this attenuation may occur because subjects preferentially fixate upon faces when present in the scene. Here, we experimentally manipulated subjects' fixations while they viewed a static picture of a character whose face, hand, and torso were continuously visible throughout each run. The subject's saccades and fixations were guided by a small fixation cross that made discrete jumps to a new location every 500ms. Subjects were instructed to follow the fixation cross and make a button press whenever it changed size. In a series of blocks, the fixation cross shifted from locations on the face, on the hand, and to locations on a background image of a phase-scrambled face. In a second study, the fixation cross moved similarly, but the hand locations were changed to locations along the character's body or torso. A localizer task was used to identify face- and body-sensitive regions of LOTC. Body-sensitive regions were strongly activated when the subjects' saccades were guided over the character's torso relative to when the saccades were guided over the character's face. Little to no activity occurred in the body-sensitive region of LOTC when the subjects' saccades were guided over the character's hand. The localizer task was unable to differentiate body-sensitive regions in lateral VOTC from face-sensitive regions, or body-sensitive regions in medial VOTC from flower-sensitive regions. Guided saccades over the body strongly activated both lateral and medial VOTC. These results provide new insights into the function of body-sensitive visual areas in both LOTC and VOTC, and illustrate the potential confounding influence of uncontrolled eye movements for neuroimaging studies of social perception.