Fusion Channels of Non-Abelian Anyons from Angular-Momentum and Density-Profile Measurements.

We present a method to characterize non-Abelian anyons that is based only on static measurements and that does not rely on any form of interference. For geometries where the anyonic statistics can be revealed by rigid rotations of the anyons, we link this property to the angular momentum of the initial state. We test our method on the paradigmatic example of the Moore-Read state that is known to support excitations with non-Abelian statistics of Ising type. As an example, we reveal the presence of different fusion channels for two such excitations, a defining feature of non-Abelian anyons. This is obtained by measuring density-profile properties, like the mean square radius of the system or the depletion generated by the anyons. Our study paves the way to novel methods for characterizing non-Abelian anyons, both in the experimental and theoretical domains.

Time-of-Flight Measurements as a Possible Method to Observe Anyonic Statistics.

We propose a standard time-of-flight experiment as a method for observing the anyonic statistics of quasiholes in a fractional quantum Hall state of ultracold atoms. The quasihole states can be stably prepared by pinning the quasiholes with localized potentials and a measurement of the mean square radius of the freely expanding cloud, which is related to the average total angular momentum of the initial state, offers direct signatures of the statistical phase. Our proposed method is validated by Monte Carlo calculations for ν=1/2 and 1/3 fractional quantum Hall liquids containing a realistic number of particles. Extensions to quantum Hall liquids of light and to non-Abelian anyons are briefly discussed.

The γ-parameter of anomalous diffusion quantified in human brain by MRI depends on local magnetic susceptibility differences.

Motivated by previous results obtained in vitro, we investigated the dependence of the anomalous diffusion (AD) MRI technique on local magnetic susceptibility differences (Δχ) driven by magnetic field inhomogeneity in human brains. The AD-imaging contrast investigated here is quantified by the stretched-exponential parameter γ, extracted from diffusion weighted (DW) data collected by varying diffusion gradient strengths. We performed T2* and DW experiments in eight healthy subjects at 3.0T. T2*-weighted images at different TEs=(10,20,35,55)ms and DW-EPI images with fourteen b-values from 0 to 5000s/mm2 were acquired. AD-metrics and Diffusion Tensor Imaging (DTI) parameters were compared and correlated to R2* and to Δχ values taken from literature for the gray (GM) and the white (WM) matter. Pearson's correlation test and Analysis of Variance with Bonferroni post-hoc test were used. Significant strong linear correlations were found between AD γ-metrics and R2* in both GM and WM of the human brain, but not between DTI-metrics and R2*. Depending on Δχ driven magnetic field inhomogeneity, the new contrast provided by AD-γ imaging reflects Δχ due to differences in myelin orientation and iron content within selected regions in the WM and GM, respectively. This feature of the AD-γ imaging due to the fact that γ is quantified by using MRI, may be an alternative strategy to investigate, at high magnetic fields, microstructural changes in myelin, and alterations due to iron accumulation. Possible clinical applications might be in the field of neurodegenerative diseases.

Weighing the stigma of weight: An fMRI study of neural reactivity to the pain of obese individuals.

Explicit negative attitudes and blameful beliefs (e.g. poor diet, laziness) towards obese individuals are well documented and are pervasive even among health professionals. Here we sought to determine whether obesity stigma is reflected in a fundamental feature of intersubjectivity namely the automatic neural resonance with others' affective experiences. During fMRI, normal-weight female participants observed short clips depicting normal-weight (NW) and obese (Ob) models experiencing pain. Importantly, participants believed that half of the Ob were overweight due to a hormonal disorder (HormOb) and ignored the cause of obesity of the remaining models (Unknown obese models; UnkOb). Analyses of hemodynamic responses showed reduced activity to the pain of Ob compared to that of NW in areas associated with pain processing and early visual processing. The comparison between the two Ob conditions revealed a further decrease of activity to HormOb's pain compared to UnkOb's (and NW) pain in the right inferior frontal gyrus, an area associated with emotional resonance. Our study demonstrates that stigma for obese individuals can be observed at implicit levels, and that it is modulated by knowledge concerning the etiology of obesity, with the seemingly surprising result that obesity due to disease may result in greater stigmatization. Moreover, the perceived similarity with the models and the ambivalent emotion of pity may index biased brain responses to obese individuals' pain. The study highlights a possibly important neural link between resonance with the pain of others and obesity stigma.

Prospective memory: the combined impact of cognitive load and task focality.

Prospective Memory (PM) entails a set of executive processes primarily associated with the activation of frontal and parietal regions. Both the number of PM-targets to be monitored (i.e. task load) and the relationship between the type of PM-targets and the ongoing (ONG) task (i.e. task focality) can impact executive monitoring and PM performance. In the present imaging study, we manipulated load and focality of an event-based PM task to test the hypothesis that common resources engage in situations requiring high levels of cognitive control: that is, in high-load (i.e. monitor multiple PM-targets) and non-focal conditions (i.e. monitor at the same time letters' identity and color). We investigated monitoring-related and detection-related processes by assessing behavior and brain activity separately for ONG trials (monitoring) and PM-targets (detection). At the behavioral level, we found a significant interaction between load and focality during detection, with slowest reaction times for focal, high-load PM-targets. The imaging analyses of the detection phase revealed the activation of the left intraparietal sulcus in the high-load conditions. Both in the monitoring and the detection phases, we found overlapping effects of non-focality and low-load in the fusiform gyrus. Our results suggest that under low-load conditions, cognitive control operates via early selection mechanisms in the ventral occipito-temporal cortex. By contrast, high-load conditions entail control at later processing stages within the dorsal parietal cortex. We conclude that load and focality operate via different mechanisms, with the level of task load largely determining how cognitive control selects the most relevant information.

Action anticipation beyond the action observation network: a functional magnetic resonance imaging study in expert basketball players.

The ability to predict the actions of others is quintessential for effective social interactions, particularly in competitive contexts (e.g. in sport) when knowledge about upcoming movements allows anticipating rather than reacting to opponents. Studies suggest that we predict what others are doing by using our own motor system as an internal forward model and that the fronto-parietal action observation network (AON) is fundamental for this ability. However, multiple-duty cells dealing with action perception and execution have been found in a variety of cortical regions. Here we used functional magnetic resonance imaging to explore, in expert basketball athletes and novices, whether the ability to make early predictions about the fate of sport-specific actions (i.e. free throws) is underpinned by neural regions beyond the classical AON. We found that, although involved in action prediction, the fronto-parietal AON was similarly activated in novices and experts. Importantly, athletes exhibited relatively greater activity in the extrastriate body area during the prediction task, probably due to their expert reading of the observed action kinematics. Moreover, experts exhibited higher activation in the bilateral inferior frontal gyrus and in the right anterior insular cortex when producing errors, suggesting that they might become aware of their own errors. Correct action prediction induced higher posterior insular cortex activity in experts and higher orbito-frontal activity in novices, suggesting that body awareness is important for performance monitoring in experts, whereas novices rely more on higher-order decision-making strategies. This functional reorganization highlights the tight relationship between action anticipation, error awareness and motor expertise leading to body-related processing and differences in decision-making processes.

Anisotropic anomalous diffusion assessed in the human brain by scalar invariant indices.

A new method to investigate anomalous diffusion in human brain, inspired by the stretched-exponential model proposed by Hall and Barrick, is proposed here, together with a discussion about its potential application to cerebral white matter characterization. Aim of the work was to show the ability of anomalous diffusion indices to characterize white matter structures, whose complexity is only partially accounted by diffusion tensor imaging indices. MR signal was expressed as a stretched-exponential only along the principal axes of diffusion; whereas, in a generic direction, it was modeled as a combination of three stretched-exponentials. Indices to quantify the tissue anomalous diffusion and its anisotropy, independently of the experiment reference frame, were derived. Experimental results, obtained on 10 healthy subjects at 3T, show that the new parameters are highly correlated to intrinsic local geometry when compared with Hall and Barrick indices. Moreover, they offer a different contrast in white matter regions when compared with diffusion tensor imaging. Specifically, the new indices show a higher capability to discriminate among areas of the corpus callosum associated to different distribution in axonal densities, thus offering a new potential tool to detect more specific patterns of brain abnormalities than diffusion tensor imaging in the presence of neurological and psychiatric disorders.

The brain network underlying serial visual search: comparing overt and covert spatial orienting, for activations and for effective connectivity.

We used functional magnetic resonance imaging (fMRI) to investigate the brain basis of overt and covert forms of attention during search, while employing stringent control of both eye movements and attentional shifts. A factorial design compared overt and covert forms of goal-directed serial search versus stimulus-driven tracking. To match ocular changes and the number and magnitude of attention shifts across cells in the design, stimulus-driven tracking involved trial-specific "replay" of previous goal-directed eye movements. We found that, in terms of cortical activations, engagement of the dorsal fronto-parietal network by goal-directed attention did not depend on oculomotor requirements, being found similarly for covert attention, in accord with other work. However, analyses of effective connectivity (or "functional coupling") revealed that information flow within this network changed significantly as a function of both the task (goal-directed or stimulus-driven) and the overt versus covert form of attention. Additionally, we observed a distinct set of subcortical regions (pulvinar and caudate nucleus) engaged primarily during the covert form of goal-directed search. We conclude that dynamics within the dorsal fronto-parietal attentional system flexibly reorganize to integrate task demands and oculomotor requirements.

Neural basis of maternal communication and emotional expression processing during infant preverbal stage.

During the first year of life, exchanges and communication between a mother and her infant are exclusively preverbal and are based on the mother's ability to understand her infant's needs and feelings (i.e., empathy) and on imitation of the infant's facial expressions; this promotes a social dialog that influences the development of the infant self. Sixteen mothers underwent functional magnetic resonance imaging while observing and imitating faces of their own child and those of someone else's child. We found that the mirror neuron system, the insula and amygdala were more active during emotional expressions, that this circuit is engaged to a greater extent when interacting with one's own child, and that it is correlated with maternal reflective function (a measure of empathy). We also found, by comparing single emotions with each other, that joy expressions evoked a response mainly in right limbic and paralimbic areas; by contrast, ambiguous expressions elicited a response in left high order cognitive and motor areas, which might reflect cognitive effort.

Molecular Nanomagnets as Qubits with Embedded Quantum-Error Correction.

We show that molecular nanomagnets have a potential advantage in the crucial rush toward quantum computers. Indeed, the sizable number of accessible low-energy states of these systems can be exploited to define qubits with embedded quantum error correction. We derive the scheme to achieve this crucial objective and the corresponding sequence of microwave/radiofrequency pulses needed for the error correction procedure. The effectiveness of our approach is shown already with a minimal S = 3/2 unit corresponding to an existing molecule, and the scaling to larger spin systems is quantitatively analyzed.

High binaural coherence determines successful sound localization and increased activity in posterior auditory areas.

Our brain continuously receives complex combinations of sounds originating from different sources and relating to different events in the external world. Timing differences between the two ears can be used to localize sounds in space, but only when the inputs to the two ears have similar spectrotemporal profiles (high binaural coherence). We used fMRI to investigate any modulation of auditory responses by binaural coherence. We assessed how processing of these cues depends on whether spatial information is task relevant and whether brain activity correlates with subjects' localization performance. We found that activity in Heschl's gyrus increased with increasing coherence, irrespective of whether localization was task relevant. Posterior auditory regions also showed increased activity for high coherence, primarily when sound localization was required and subjects successfully localized sounds. We conclude that binaural coherence cues are processed throughout the auditory cortex and that these cues are used in posterior regions for successful auditory localization.

Interaural temporal and coherence cues jointly contribute to successful sound movement perception and activation of parietal cortex.

The perception of movement in the auditory modality requires dynamic changes in the input that reaches the two ears (e.g. sequential changes of interaural time differences; dynamic ITDs). However, it is still unclear as to what extent these temporal cues interact with other interaural cues to determine successful movement perception, and which brain regions are involved in sound movement processing. Here, we presented trains of white-noise bursts containing either static or dynamic ITDs, and we varied parametrically the level of binaural coherence (BC) of both types of stimuli. Behaviorally, we found that movement discrimination sensitivity decreased with decreasing levels of BC. fMRI analyses highlighted a network of temporal, frontal and parietal regions where activity decreased with decreasing BC. Critically, in the intra-parietal sulcus and the supra-marginal gyrus brain activity decreased with decreasing BC, but only for dynamic-ITD sounds (BC by ITD interaction). Thus, these regions activated selectively when the sounds contained both dynamic ITDs and high levels of BC; i.e. when subjects perceived sound movement. We conclude that sound movement perception requires both dynamic changes of the auditory input and effective sound-source localization, and that parietal cortex utilizes interaural temporal and coherence cues for the successful perception of sound movement.

Spatial attention can modulate audiovisual integration at multiple cortical and subcortical sites.

The role of attention in multisensory integration (MI) is presently uncertain, with some studies supporting an automatic, pre-attentive process and others suggesting possible modulation through selective attention. The goal of this functional magnetic resonance imaging study was to investigate the role of spatial attention on the processing of congruent audiovisual speech stimuli (here indexing MI). Subjects were presented with two simultaneous visual streams (speaking lips in the left and right visual hemifields) plus a single central audio stream (spoken words). In the selective attention conditions, the auditory stream was congruent with one of the two visual streams. Subjects attended to either the congruent or the incongruent visual stream, allowing the comparison of brain activity for attended vs. unattended MI while the amount of multisensory information in the environment and the overall attentional requirements were held constant. Meridian mapping and a lateralized 'speaking-lips' localizer were used to identify early visual areas and to localize regions responding to contralateral visual stimulations. Results showed that attention to the congruent audiovisual stimulus resulted in increased activation in the superior temporal sulcus, striate and extrastriate retinotopic visual cortex, and superior colliculus. These findings demonstrate that audiovisual integration and spatial attention jointly interact to influence activity in an extensive network of brain areas, including associative regions, early sensory-specific visual cortex and subcortical structures that together contribute to the perception of a fused audiovisual percept.

Modulation of human visual cortex by crossmodal spatial attention.

A sudden touch on one hand can improve vision near that hand, revealing crossmodal links in spatial attention. It is often assumed that such links involve only multimodal neural structures, but unimodal brain areas may also be affected. We tested the effect of simultaneous visuo-tactile stimulation on the activity of the human visual cortex. Tactile stimulation enhanced activity in the visual cortex, but only when it was on the same side as a visual target. Analysis of effective connectivity between brain areas suggests that touch influences unimodal visual cortex via back-projections from multimodal parietal areas. This provides a neural explanation for crossmodal links in spatial attention.

An fMRI study on the neural correlates of social conformity to a sexual minority.

Social conformity refers to the tendency to align one's own behaviors, beliefs and values to those of others. Little is known about social influence coming from a minority group. To test whether social pressure from sexual minorities triggers avoidance-motivated behaviors, we explored how being influenced by the preferences of gay peers modifies the behavioral and neural reactivity of individuals defined as in- vs. out- groups on the basis of sexual orientation. To this aim, we combined fMRI with a social conformity paradigm in which heterosexual and gay/bisexual (hereafter non-exclusively heterosexual, NEH) individuals provided with male body attractiveness ratings by a fictitious group of gay students may or may not alter their previous rating and may or may not conform to the mean. Behaviorally, conformity to the minority preference was found in in-group NEH more than in out-group heterosexuals. Analysis of BOLD signal showed that social pressure brought about increased brain activity in frontal and parietal regions associated with the detection of social conflict. These results show that members of a sexual majority group display a smaller level of conformity when a sexual minority group exerts social influence. However, the neural correlates of this modulation are yet to be clarified.

Crossmodal spatial influences of touch on extrastriate visual areas take current gaze direction into account.

Recent results indicate that crossmodal interactions can affect activity in cortical regions traditionally regarded as "unimodal." Previously we found that combining touch on one hand with visual stimulation in the anatomically corresponding hemifield could boost responses in contralateral visual cortex. Here we manipulated which visual hemifield corresponded to the location of the stimulated hand, by changing gaze direction such that right-hand touch could now arise in either the left or right visual field. Crossmodal effects on visual cortex switched from one hemisphere to the other, depending on gaze direction, regardless of whether the hand was seen. This indicates that crossmodal influences of touch upon visual cortex depend on spatial alignment for the multimodal stimuli, with gaze posture taken into account.

Episodic memory impairment in patients with Alzheimer's disease is correlated with entorhinal cortex atrophy. A voxel-based morphometry study.

The aims of this study were to investigate the pattern of cortical atrophy and the relationships between memory performances and the brain regions in Alzheimer's Disease (AD). optimized voxel-based morphometry (VBM) was applied to the MRI brain images of 18 probable AD and 18 healthy subjects (HS). Patients performed verbal and visuo-spatial episodic and shortterm memory tests. Contrasting of AD group with HS, and anatomobehavioural correlations were carried out in order to identify regional atrophic changes and neuro-cognitive aspects in AD group. We found evidence of gray matter (GM) volume reduction in AD in the medial temporal, parietal and frontal areas bilaterally and in the left anterior thalamic nuclei. Performance on the episodic memory delayed recall tests co-varied with GM volume in the left entorhinal cortex. The pattern of cortical atrophy likely reflects the heterogeneous level of dementia severity in our AD group. The anatomical region affected in the left hemisphere indicates a sufferance at multiple levels of the Polysynaptic Hippocampal Pathway, which is involved in declarative memory. Findings on the entorhinal cortex and the delayed memory scores support the role of the entorhinal cortex in episodic memory. Damage to the entorhinal cortex, deafferenting the hippocampus from neocortical inputs, interferes with episodic memory consolidation in AD patients.

Influence of gaze direction on crossmodal modulation of visual ERPS by endogenous tactile spatial attention.

Recent evidence indicates that the spatial direction of endogenous covert spatial attention in one sensory modality can crossmodally influence early processing of stimuli in a different modality. However, spatial locations are initially coded according to different frames of reference for different modalities (e.g., body-centered for touch versus retinocentric vision) and postural changes (e.g., gaze shifts) will realign these. Here, we used event-related potentials (ERPs) to investigate how the direction of endogenous tactile attention affects sensory-specific visual ERP components. Critically, by manipulating direction of gaze, we were able to test whether any crossmodal effects depend on visual and tactile projections to a common hemisphere, on common locations in external space, or on some combination of the two. We found that both P1 and N1 visual components were modulated according to the direction of endogenous tactile attention. While the P1 crossmodal effect followed purely hemispheric constraints, the attentional modulation of N1 appeared to combine both anatomical and external spatial constraints.

Spatial attention and crossmodal interactions between vision and touch.

In the present paper, we review several functional imaging studies investigating crossmodal interactions between vision and touch relating to spatial attention. We asked how the spatial unity of a multimodal event in the external world might be represented in the brain, where signals from different modalities are initially processed in distinct brain regions. The results highlight several links between visual and tactile spatial representations. First, we found that activity in the anterior part of the intraparietal sulcus was influenced by stimulus position independently of the modality of the stimulation. This is consistent with crossmodal interactions via sensory convergence from early modality-specific spatial maps to higher-order multimodal regions. Second, we found that stimulation in, or attention to, one modality could affect activity in areas dedicated to a different modality, in a spatially-specific manner. These spatial crossmodal effects in unimodal regions demonstrate congruous activity in anatomically distant brain areas that represent similar external locations, implicating a distributed network of spatial representations in crossmodal integration. Finally, the results suggest that the temporo-parietal junction may be involved in aspects of controlling spatial attention, for both vision and touch. A multimodal attentional system may influence activity in distinct brain areas representing common regions of space for different modalities, thus suggesting a link between spatial attention and crossmodal integration.

Motile areas of leech neurites are rich in microfilaments and two actin-binding proteins: gelsolin and profilin.

Cell motility is produced by changes in the dynamics and organization of actin filaments. The aim of the experiments described here was to test whether growing neurites contain two actin-binding proteins, gelsolin and profilin, that regulate polymerization of actin and affect non-neuronal cell motility. The distribution of gelsolin, profilin and the microfilaments was compared by immunocytochemistry of leech neurons growing in culture. We observed that microfilaments are enriched in the peripheral motile areas of the neurites. Both gelsolin and profilin are also concentrated in these regions. Gelsolin is abundant in filopodia and is associated with single identifiable microfilament bundles in lamellipodia. Profilin is not prominent in filopodia and shows a diffuse staining pattern in lamellipodia. The colocalization of gelsolin and profilin in motile, microfilament-rich areas supports the hypothesis that they synergistically regulate the actin dynamics that underlie neurite growth.