Disengagement of attention with spatial neglect: A systematic review of behavioral and anatomical findings

The present review examined the consequences of focal brain injury on spatial attention studied with cueing paradigms, with a particular focus on the disengagement deficit, which refers to the abnormal slowing of reactions following an ipsilesional cue. Our review supports the established notion that the disengagement deficit is a functional marker of spatial neglect and is particularly pronounced when elicited by peripheral cues. Recent research has revealed that this deficit critically depends on cues that have task-relevant characteristics or are associated with negative reinforcement. Attentional capture by task-relevant cues is contingent on damage to the right temporo-parietal junction (TPJ) and is modulated by functional connections between the TPJ and the right insular cortex. Furthermore, damage to the dorsal premotor or prefrontal cortex (dPMC/dPFC) reduces the effect of task-relevant cues. These findings support an interactive model of the disengagement deficit, involving the right TPJ, the insula, and the dPMC/dPFC. These interconnected regions play a crucial role in regulating and adapting spatial attention to changing intrinsic values of stimuli in the environment.

Intracortical recordings reveal vision-to-action cortical gradients driving human exogenous attention

Exogenous attention, the process that makes external salient stimuli pop-out of a visual scene, is essential for survival. How attention-capturing events modulate human brain processing remains unclear. Here we show how the psychological construct of exogenous attention gradually emerges over large-scale gradients in the human cortex, by analyzing activity from 1,403 intracortical contacts implanted in 28 individuals, while they performed an exogenous attention task. The timing, location and task-relevance of attentional events defined a spatiotemporal gradient of three neural clusters, which mapped onto cortical gradients and presented a hierarchy of timescales. Visual attributes modulated neural activity at one end of the gradient, while at the other end it reflected the upcoming response timing, with attentional effects occurring at the intersection of visual and response signals. These findings challenge multi-step models of attention, and suggest that frontoparietal networks, which process sequential stimuli as separate events sharing the same location, drive exogenous attention phenomena such as inhibition of return.

Fronto-parietal networks shape human conscious report through attention gain and reorienting

How do attention and consciousness interact in the human brain? Rival theories of consciousness disagree on the role of fronto-parietal attentional networks in conscious perception. We recorded neural activity from 727 intracerebral contacts in 13 epileptic patients, while they detected near-threshold targets preceded by attentional cues. Clustering revealed three neural patterns: first, attention-enhanced conscious report accompanied sustained right-hemisphere fronto-temporal activity in networks connected by the superior longitudinal fasciculus (SLF) II-III, and late accumulation of activity (>300 ms post-target) in bilateral dorso-prefrontal and right-hemisphere orbitofrontal cortex (SLF I-III). Second, attentional reorienting affected conscious report through early, sustained activity in a right-hemisphere network (SLF III). Third, conscious report accompanied left-hemisphere dorsolateral-prefrontal activity. Task modeling with recurrent neural networks revealed multiple clusters matching the identified brain clusters, elucidating the causal relationship between clusters in conscious perception of near-threshold targets. Thus, distinct, hemisphere-asymmetric fronto-parietal networks support attentional gain and reorienting in shaping human conscious experience.

Task relevance and negative reward modulate the disengagement deficit of patients with spatial neglect

Though motivational value is a recognized trigger of approach and avoidance behavior, less is known about the potential of reward to capture attention. We here explored whether positive or negative reward modulates the characteristic deficit of patients with left spatial neglect to disengage attention from an ipsilesional distracter. We built our study on recent observations showing that the disengagement deficit is exaggerated for distracters with target-defining features, indicating that task-relevance captures attention. Patients with left neglect and matched healthy controls were asked to react to lateralized, colored targets preceded by a peripheral cue. Crucially, the cue either possessed the color of the target and was thus task-relevant, or was followed by a positive, negative, or neutral symbolic reward. Neglect patients only exhibited a disengagement deficit when cues were task-relevant or were followed by a negative reward. This finding indicates that attentional selection is driven by task-relevance and negative reward, possibly through interactions between limbic and attention networks.

Machine learning algorithms on eye tracking trajectories to classify patients with spatial neglect

BACKGROUND AND OBJECTIVE

Eye-movement trajectories are rich behavioral data, providing a window on how the brain processes information. We address the challenge of characterizing signs of visuo-spatial neglect from saccadic eye trajectories recorded in brain-damaged patients with spatial neglect as well as in healthy controls during a visual search task.

METHODS

We establish a standardized pre-processing pipeline adaptable to other task-based eye-tracker measurements. We use traditional machine learning algorithms together with deep convolutional networks (both 1D and 2D) to automatically analyze eye trajectories.

RESULTS

Our top-performing machine learning models classified neglect patients vs. healthy individuals with an Area Under the ROC curve (AUC) ranging from 0.83 to 0.86. Moreover, the 1D convolutional neural network scores correlated with the degree of severity of neglect behavior as estimated with standardized paper-and-pencil tests and with the integrity of white matter tracts measured from Diffusion Tensor Imaging (DTI). Interestingly, the latter showed a clear correlation with the third branch of the superior longitudinal fasciculus (SLF), especially damaged in neglect.

CONCLUSIONS

The study introduces new methods for both the pre-processing and the classification of eye-movement trajectories in patients with neglect syndrome. The proposed methods can likely be applied to other types of neurological diseases opening the possibility of new computer-aided, precise, sensitive and non-invasive diagnostic tools.

From Action to Cognition: Neural Reuse, Network Theory and the Emergence of Higher Cognitive Functions

The aim of this article is to discuss the logic and assumptions behind the concept of neural reuse, to explore its biological advantages and to discuss the implications for the cognition of a brain that reuses existing circuits and resources. We first address the requirements that must be fulfilled for neural reuse to be a biologically plausible mechanism. Neural reuse theories generally take a developmental approach and model the brain as a dynamic system composed of highly flexible neural networks. They often argue against domain-specificity and for a distributed, embodied representation of knowledge, which sets them apart from modular theories of mental processes. We provide an example of reuse by proposing how a phylogenetically more modern mental capacity (mental rotation) may appear through the reuse and recombination of existing resources from an older capacity (motor planning). We conclude by putting arguments into context regarding functional modularity, embodied representation, and the current ontology of mental processes.

Visual but Not Auditory-Verbal Feedback Induces Aftereffects Following Adaptation to Virtual Prisms

Visuo-motor adaptation with optical prisms that displace the visual scene (prism adaptation, PA) has been widely used to study visuo-motor plasticity in healthy individuals and to decrease the lateralized bias of brain-damaged patients suffering from spatial neglect. Several factors may influence PA aftereffects, such as the degree of optical deviation (generally measured in dioptres of wedge prisms) or the direction of the prismatic shift (leftward vs. rightward). However, the mechanisms through which aftereffects of adaptation in healthy individuals and in neglect affect performance in tasks probing spatial cognition remain controversial. For example, some studies have reported positive effects of PA on auditory neglect, while other studies failed to obtain any changes of performance even in the visual modality. We here tested a new adaptation method in virtual reality to evaluate how sensory parameters influence PA aftereffects. Visual vs. auditory-verbal feedback of optical deviations were contrasted to assess whether rightward deviations influence manual and perceptual judgments in healthy individuals. Our results revealed that altered visual, but not altered auditory-verbal feedback induces aftereffects following adaptation to virtual prisms after 30-degrees of deviation. These findings refine current models of the mechanisms underlying the cognitive effects of virtual PA in emphasizing the importance of visual vs. auditory-verbal feedback during the adaptation phase on visuospatial judgments. Our study also specifies parameters which influence virtual PA and its aftereffect, such as the sensory modality used for the feedback.

The neural correlates of intermanual transfer

Intermanual transfer of motor learning is a form of learning generalization that leads to behavioral advantages in various tasks of daily life. It might also be useful for rehabilitation of patients with unilateral motor deficits. Little is known about neural structures and cognitive processes that mediate intermanual transfer. Previous studies have suggested a role for primary motor cortex (M1) and the supplementary motor area (SMA). Here, we investigated the functional neuroanatomy of intermanual transfer with a special emphasis on functional connectivity within the motor network and between motor regions and attentional networks, including the fronto-parietal executive control network and visual attention networks. We designed a finger tapping task, in which young, heathy subjects trained the non-dominant left hand in the MRI scanner. Behaviorally, transfer of sequence learning was observed in most cases, independently of the trained hand's performance. Pre- and post-training functional connectivity patterns of cortical motor seeds were investigated using generalized psychophysiological interaction analyses. Transfer was correlated with the strength of connectivity between the left premotor cortex and structures within the dorsal attention network (superior parietal cortex, left middle temporal gyrus) and executive control network (right prefrontal regions) during pre-training, relative to post-training. Changes in connectivity within the motor network, and more particularly between trained and untrained M1, as well as between the SMA and untrained M1, correlated with transfer after training. Together, these results suggest that the interplay between attentional, executive and motor networks may support processes leading to transfer, whereas, following training, transfer translates into increased connectivity within the motor network.

Periinfarct rewiring supports recovery after primary motor cortex stroke

After stroke restricted to the primary motor cortex (M1), it is uncertain whether network reorganization associated with recovery involves the periinfarct or more remote regions. We studied 16 patients with focal M1 stroke and hand paresis. Motor function and resting-state MRI functional connectivity (FC) were assessed at three time points: acute (<10 days), early subacute (3 weeks), and late subacute (3 months). FC correlates of recovery were investigated at three spatial scales, (i) ipsilesional non-infarcted M1, (ii) core motor network (M1, premotor cortex (PMC), supplementary motor area (SMA), and primary somatosensory cortex), and (iii) extended motor network including all regions structurally connected to the upper limb representation of M1. Hand dexterity was impaired only in the acute phase (P = 0.036). At a small spatial scale, clinical recovery was more frequently associated with connections involving ipsilesional non-infarcted M1 (Odds Ratio = 6.29; P = 0.036). At a larger scale, recovery correlated with increased FC strength in the core network compared to the extended motor network (rho = 0.71;P = 0.006). These results suggest that FC changes associated with motor improvement involve the perilesional M1 and do not extend beyond the core motor network. Core motor regions, and more specifically ipsilesional non-infarcted M1, could hence become primary targets for restorative therapies.

Abstract 25: Periinfarct Rewiring Supports Recovery After Primary Motor Cortex Stroke

Background and Purpose: After stroke restricted to the primary motor cortex (M1), it is uncertain whether network reorganization associated with motor recovery involves the periinfarct or more remote brain regions. In humans, the challenge is to recruit patients with similar lesions in size and location.

Methods: We studied 16 patients with focal M1 stroke and hand paresis. Motor function and resting-state MRI functional connectivity (FC) were studied at three time points: acute (<10 days), early subacute (3 weeks), and late subacute (3 months). FC correlates of motor recovery were investigated at three spatial scales, i) ipsilesional non-infarcted M1, ii) core motor network (including M1, premotor cortex (PMC), supplementary motor area (SMA), and primary somatosensory cortex), and iii) extended motor network including all regions structurally connected to the upper limb representation of M1.

Results: Hand dexterity was impaired only in the acute phase ( P =0.036). At a small spatial scale, improved dexterity was associated with increased FC involving mainly the ipsilesional non-infarcted M1 and contralesional motor regions (cM1: rho=0.732; P =0.004; cPMC: rho=0.837, P <0.001; cSMA: rho=0.736; P =0.004). At a larger scale, motor recovery correlated with the relative increase in total FC strength in the core motor network compared to the extended motor network (rho=0.71; P =0.006).

Conclusions: FC changes associated with motor improvement involve the perilesional M1 and do not extend beyond the core motor network. The ipsilesional non-infarcted M1 and core motor regions could hence be primary targets for future restorative therapies.

Virtual prism adaptation for spatial neglect: A double-blind study

ABSTRACTPrismatic adaptation (PA) with wedge prisms is a non-invasive technique used in the rehabilitation of patients suffering from spatial neglect. Unfortunately, as for many behavioural intervention techniques, it is nearly impossible to achieve adequate blinding using wedge prisms, and the potential benefit of PA in the rehabilitation of neglect remains controversial. In order to study an alternative to wedge prism, we examine whether virtual PA at different degrees of deviation may alleviate signs of neglect in a double-blind design. Fifteen neglect patients participated in three adaptation sessions, which differed by the degree of deviation (0°, 15°, or 30°). Performance in line bisection and item cancellation tasks was measured in virtual reality immediately before and after adaptation. Session allocation was concealed from patients and the examiner. Despite the presence of robust, dose-dependent effects of virtual PA on Open-Loop Pointing (OLP), no transfer to line bisection and item cancellation tests were observed. None of the patients were aware of differences between sessions. Virtual PA did not result in visuo-motor transfer effects despite inducing significant adaptation effects in OLP. Together with recent negative findings of randomized-controlled trials, these findings cast doubt on the general efficacy of PA as a rehabilitation method of spatial neglect.

Discrete Patterns of Cross-Hemispheric Functional Connectivity Underlie Impairments of Spatial Cognition after Stroke

Despite intense research, the neural correlates of stroke-induced deficits of spatial cognition remain controversial. For example, several cortical regions and white-matter tracts have been designated as possible anatomic predictors of spatial neglect. However, many studies focused on local anatomy, an approach that does not harmonize with the notion that brain-behavior relationships are flexible and may involve interactions among distant regions. We studied in humans of either sex resting-state fMRI connectivity associated with performance in line bisection, reading and visual search, tasks commonly used for he clinical diagnosis of neglect. We defined left and right frontal, parietal, and temporal areas as seeds (or regions of interest, ROIs), and measured whole-brain seed-based functional connectivity (FC) and ROI-to-ROI connectivity in subacute right-hemisphere stroke patients. Performance on the line bisection task was associated with decreased FC between the right fusiform gyrus and left superior occipital cortex. Complementary increases and decreases of connectivity between both temporal and occipital lobes predicted reading errors. In addition, visual search deficits were associated with modifications of FC between left and right inferior parietal lobes and right insular cortex. These distinct connectivity patterns were substantiated by analyses of FC between left- and right-hemispheric ROIs, which revealed that decreased interhemispheric and right intrahemispheric FC was associated with higher levels of impairment. Together, these findings indicate that intrahemispheric and interhemispheric cooperation between brain regions lying outside the damaged area contributes to spatial deficits in a way that depends on the different cognitive components recruited during reading, spatial judgments, and visual exploration.SIGNIFICANCE STATEMENT Focal damage to the right cerebral hemisphere may result in a variety of deficits, often affecting the domain of spatial cognition. The neural correlates of these disorders have traditionally been studied with lesion-symptom mapping, but this method fails to capture the network dynamics that underlie cognitive performance. We studied functional connectivity in patients with right-hemisphere stroke and found a pattern of correlations between the left and right temporo-occipital, inferior parietal, and right insular cortex that were distinctively predictive of deficits in reading, spatial judgment, and visual exploration. This finding reveals the importance of interhemispheric interactions and network adaptations for the manifestation of spatial deficits after damage to the right hemisphere.

Impaired visual search with paradoxically increased facilitation by emotional features after unilateral pulvinar damage

Posterior thalamic pulvinar nuclei have been implicated in different aspects of spatial attention, but their exact role in humans remain unclear. Most neuropsychological studies of attention deficits after pulvinar lesion have concerned single patients or small samples. Here we examined a group of 13 patients with focal damage to posterior thalamus on a visual search task with faces, allowing us to test several hypotheses concerning pulvinar function in controlling attention to visually salient or emotionally significant stimuli. Our results identified two subgroups of thalamic patients with distinct patterns of attentional responsiveness to emotional and colour features in face targets. One group with lesions located in anterior and ventral portions of thalamus showed intact performance, with a normal facilitation of visual search for faces with emotional (fearful or happy) expressions on both side of space, similar to healthy controls. By contrast, a second group showed a slower and poorer detection of face targets, most severe for neutral faces, but with a paradoxically enhanced facilitation by both colour and emotional features. This second group had lesions centred on the pulvinar, involving mainly the dorso-medial sectors in patients showing enhanced effects of colour features, but extending to more dorso-lateral sectors in those with enhanced effects of emotional features. These findings reveal that pulvinar nuclei are not critical for orienting attention to emotionally or visually salient features, but instead provide new evidence in support of previous hypotheses suggesting an important role in controlling attention in visual scenes with distracting information.

Does Intraneuronal Accumulation of Carboxyl-terminal Fragments of the Amyloid Precursor Protein Trigger Early Neurotoxicity in Alzheimer’s Disease?

Background:

Alzheimer’s disease (AD) is associated with extracellular accumulation and aggregation of amyloid β (Aβ) peptides ultimately seeding in senile plaques. Recent data show that their direct precursor C99 (βCTF) also accumulates in AD-affected brain as well as in AD-like mouse models. C99 is consistently detected much earlier than Aβ, suggesting that this metabolite could be an early contributor to AD pathology. C99 accumulates principally within endolysosomal and autophagic structures and its accumulation was described as both a consequence and one of the causes of endolysosomalautophagic pathology, the occurrence of which has been documented as an early defect in AD. C99 was also accompanied by C99-derived C83 (αCTF) accumulation occurring within the same intracellular organelles. Both these CTFs were found to dimerize leading to the generation of higher molecular weight CTFs, which were immunohistochemically characterized in situ by means of aggregate-specific antibodies.

Discussion:

Here, we discuss studies demonstrating a direct link between the accumulation of C99 and C99-derived APP-CTFs and early neurotoxicity. We discuss the role of C99 in endosomal-lysosomalautophagic dysfunction, neuroinflammation, early brain network alterations and synaptic dysfunction as well as in memory-related behavioral alterations, in triple transgenic mice as well as in newly developed AD animal models.

Conclusion:

This review summarizes current evidence suggesting a potential role of the β -secretasederived APP C-terminal fragment C99 in Alzheimer’s disease etiology

Influence of reward learning on visual attention and eye movements in a naturalistic environment: A virtual reality study

Rewards constitute crucial signals that motivate approach behavior and facilitate the perceptual processing of objects associated with favorable outcomes in past encounters. Reward-related influences on perception and attention have been reliably observed in studies where a reward is paired with a unidimensional low-level visual feature, such as the color or orientation of a line in visual search tasks. However, our environment is drastically different and composed of multidimensional and changing visual features, encountered in complex and dynamic scenes. Here, we designed an immersive virtual reality (VR) experiment using a 4-frame CAVE system to investigate the impact of rewards on attentional orienting and gaze patterns in a naturalistic and ecological environment. Forty-one healthy participants explored a virtual forest and responded to targets appearing on either the left or right side of their path. To test for reward-induced biases in spatial orienting, targets on one side were associated with high reward, whereas those on the opposite side were paired with a low reward. Eye-movements recording showed that left-side high rewards led to subsequent increase of eye gaze fixations towards this side of the path, but no such asymmetry was found after exposure to right-sided high rewards. A milder spatial bias was also observed after left-side high rewards during subsequent exploration of a virtual castle yard, but not during route turn choices along the forest path. Our results indicate that reward-related influences on attention and behavior may be better learned in left than right space, in line with a right hemisphere dominance, and could generalize to another environment to some extent, but not to spatial choices in another decision task, suggesting some domain- or context-specificity. This proof-of-concept study also outlines the advantages and the possible drawbacks of the use of the 3D CAVE immersive platform for VR in neuroscience.

Value-driven attentional capture in neglect

OBJECTIVE

Recent studies suggest that motivational cues such as rewards may be a powerful determinant of attentional selection, both in healthy subjects and in brain-damaged patients suffering from neglect. However, the exact brain mechanisms underlying these effects and their relation to other well-known attentional systems are still poorly known.

METHODS

We designed a visual search paradigm to examine how value-based attentional priority could modulate spatial orienting in patients with pathological biases due to neglect after right hemispheric stroke. Targets were preceded by exogenous valid or invalid spatial cues, in the presence or absence of distractors that were associated with high reward values subsequent to an initial reinforcement training phase.

RESULTS

We found that the learned reward value of distractors interfered with spatial reorienting toward the left (neglected) side when neglect patients were invalidly cued to the right side. Moreover, the presence of reward-associated distractors in the contralesional field interfered most with the detection of task-relevant targets on the same side, and this interference was exaggerated with more severe neglect. Voxelwise anatomical lesion analysis indicated that damage to the right angular gyrus, as well as lateral occipital and inferior temporal areas of the right hemisphere, were associated with stronger value-driven attentional effects.

CONCLUSIONS

Visual stimuli previously associated with rewards receive higher attentional priority during visual search despite pathological spatial biases due to neglect, and thus interfere with orienting to contralesional targets, presumably by competing with top-down mechanisms controlling exogenous spatial attention. Reward signals may bias neural activity evoked by visual stimuli, independent of conscious control, through a common priority map integrating several different attentional influences. These results do not only provide novel insights to link spatial orienting and motivational signals within current models of attention, but also open new perspectives that may usefully be exploited for neurological rehabilitation strategies in patients suffering from attentional deficits and neglect.

Does the insula contribute to emotion-related distortion of time? A neuropsychological approach

The literature points to a large distributed brain network involved in the estimation of time. Among these regions, the role of the insular cortex is still poorly understood. At the confluence of emotional, interoceptive, and environmental signals, this brain structure has been proposed to underlie awareness of the passage of time and emotion related time dilation. Yet, this assumption has not been tested so far. This study aimed at exploring how a lesion of the insula affects subjective duration, either in an emotional context or in a non-emotional context. Twenty-one patients with a stroke affecting the insula, either left or right, were studied for their perception of sub and supra second durations. A verbal estimation task and a temporal bisection task were used with either pure tones or neutral and emotional sounds lasting between 300 and 1500 ms and presented monaurally. Results revealed that patients with a right insular lesion, showed less temporal sensitivity than both control participants and patients with a left insular lesion. Unexpectedly, emotional effects were similar in patients and control participants. Altogether, these results suggest a specific role of the right insula in the discrimination of durations, but not in emotion related temporal distortion. In addition, an ear × emotion interaction in control participants suggests that temporal processing of positive and negative sounds may be lateralized in the brain.

Cross-modal integration during value-driven attentional capture

A growing body of evidence suggests that reward may be a powerful determinant of attentional selection. To date, the study of value-based attentional capture has been mainly focused on the visual sensory modality. It is yet unknown how reward information is communicated and integrated across the different senses in order to resolve between competing choices during selective attention. Our study investigated the interference produced by an auditory reward-associated distractor when a semantically-related visual target was concurrently presented. We measured both manual and saccadic response times towards a target image (drum or trumpet), while an irrelevant sound (congruent or incongruent instrument) was heard. Each sound was previously associated with either a high or a low reward. We found that manual responses were slowed by a high-reward auditory distractor when sound and image were semantically congruent. A similar effect was observed for saccadic responses, but only for participants aware of the past reward contingencies. Auditory events associated with reward value were thus capable of involuntarily capturing attention in the visual modality. This reward effect can mitigate cross-modal semantic integration and appears to be differentially modulated by awareness for saccadic vs. manual responses. Together, our results extend previous work on value-driven attentional biases in perception by showing that these may operate across sensory modalities and override cross-modal integration for semantically-related stimuli. This study sheds new light on the potential implication of brain regions underlying value-driven attention across sensory modalities.

Cortico-thalamic disconnection in a patient with supernumerary phantom limb

Supernumerary phantom limb (SPL) designates the experience of an illusory additional limb occurring after brain damage. Functional neuroimaging during SPL movements documented increased response in the ipsilesional supplementary motor area (SMA), premotor cortex (PMC), thalamus and caudate. This suggested that motor circuits are important for bodily related cognition, but anatomical evidence is sparse. Here, we tested this hypothesis by studying an extremely rare patient with chronic SPL, still present 3 years after a vascular stroke affecting cortical and subcortical right-hemisphere structures. Anatomical analysis included an advanced in vivo reconstruction of white matter tracts using diffusion-based spherical deconvolution. This reconstruction demonstrated a massive and relatively selective disconnection between anatomically preserved SMA/PMC and the thalamus. Our results provide strong anatomical support for the hypothesis that cortico-thalamic loops involving motor-related circuits are crucial to integrate sensorimotor processing with bodily self-awareness.

How Does Awareness Modulate Goal-Directed and Stimulus-Driven Shifts of Attention Triggered by Value Learning?

In order to behave adaptively, attention can be directed in space either voluntarily (i.e., endogenously) according to strategic goals, or involuntarily (i.e., exogenously) through reflexive capture by salient or novel events. The emotional or motivational value of stimuli can also strongly influence attentional orienting. However, little is known about how reward-related effects compete or interact with endogenous and exogenous attention mechanisms, particularly outside of awareness. Here we developed a visual search paradigm to study subliminal value-based attentional orienting. We systematically manipulated goal-directed or stimulus-driven attentional orienting and examined whether an irrelevant, but previously rewarded stimulus could compete with both types of spatial attention during search. Critically, reward was learned without conscious awareness in a preceding phase where one among several visual symbols was consistently paired with a subliminal monetary reinforcement cue. Our results demonstrated that symbols previously associated with a monetary reward received higher attentional priority in the subsequent visual search task, even though these stimuli and reward were no longer task-relevant, and despite reward being unconsciously acquired. Thus, motivational processes operating independent of conscious awareness may provide powerful influences on mechanisms of attentional selection, which could mitigate both stimulus-driven and goal-directed shifts of attention.

How motivation and reward learning modulate selective attention

Motivational stimuli such as rewards elicit adaptive responses and influence various cognitive functions. Notably, increasing evidence suggests that stimuli with particular motivational values can strongly shape perception and attention. These effects resemble both selective top-down and stimulus-driven attentional orienting, as they depend on internal states but arise without conscious will, yet they seem to reflect attentional systems that are functionally and anatomically distinct from those classically associated with frontoparietal cortical networks in the brain. Recent research in human and nonhuman primates has begun to reveal how reward can bias attentional selection, and where within the cognitive system the signals providing attentional priority are generated. This review aims at describing the different mechanisms sustaining motivational attention, their impact on different behavioral tasks, and current knowledge concerning the neural networks governing the integration of motivational influences on attentional behavior.

How does reward compete with goal-directed and stimulus-driven shifts of attention?

In order to behave adaptively, attention can be directed in space either voluntarily (i.e. endogenously) according to strategic goals, or involuntarily (i.e. exogenously) through reflexive capture by salient or novel events. The emotional or motivational values of stimuli can also influence attentional orienting. However, little is known about how reward-related effects compete or interact with endogenous and exogenous attention mechanisms. Here we designed a visual search paradigm in which goal-driven and stimulus-driven shifts of attention were manipulated by classic spatial cueing procedures, while an irrelevant, but previously rewarded stimulus also appeared as a distractor and hence competed with both types of spatial attention during search. Our results demonstrated that stimuli previously associated with a high monetary reward received higher attentional priority in the subsequent visual search task, even though these stimuli and reward were no longer task-relevant, mitigating the attentional orienting induced by both endogenous and exogenous cues.

Biodegradability of fluorinated fire-fighting foams in water

Fluorinated fire-fighting foams may be released into the environment during fire-fighting activities, raising concerns due to the potential environmental and health impacts for some fluorinated organics. The current study investigated (1) the biodegradability of three fluorinated fire-fighting foams, and (2) the applicability of current standard measures used to assess biodegradability of fluorinated fire-fighting foams. The biodegradability of three fluorinated fire-fighting foams was evaluated using a 28-day dissolved organic carbon (DOC) Die-Away Test. It was found that all three materials, diluted in water, achieved 77-96% biodegradability, meeting the criteria for "ready biodegradability". Defluorination of the fluorinated organics in the foam during biodegradation was measured using ion chromatography. It was found that the fluorine liberated was 1-2 orders of magnitude less than the estimated initial amount, indicating incomplete degradation of fluorinated organics, and incomplete CF bond breakage. Published biodegradability data may utilize biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total organic carbon (TOC) metrics to quantify organics. COD and TOC of four fluorinated compounds were measured and compared to the calculated carbon content or theoretical oxygen demand. It was found that the standard dichromate-based COD test did not provide an accurate measure of fluorinated organic content. Thus published biodegradability data using COD for fluorinated organics quantification must be critically evaluated for validity. The TOC measurements correlated to an average of 91% of carbon content for the four fluorinated test substances, and TOC is recommended for use as an analytical parameter in fluorinated organics biodegradability tests.

Cortical control of Inhibition of Return: exploring the causal contributions of the left parietal cortex

Inhibition of Return (IOR) refers to longer response times (RTs) when processing information from an already inspected spatial location. This effect encourages orienting towards novel locations and may be hence adaptive to efficiently explore our environment. In a previous study (Bourgeois, Chica, Valero-Cabre, & Bartolomeo, 2013), we demonstrated that repetitive Transcranial Magnetic Stimulation (rTMS) over right hemisphere parietal sites, such as the intra-parietal sulcus (IPS), or the temporo-parietal junction (TPJ), lastingly interfered with manual but not saccadic IOR, for ipsilateral right-sided targets. For contralateral left-sided targets, rTMS over the right IPS, but not over the right TPJ, impaired both manual and saccadic IOR. In the present study, we investigated hemispheric differences in the cortical control of IOR by stimulating left parietal sites with the same design. Contrary to the stimulation of the right hemisphere, rTMS over the left IPS or TPJ did not produce significant modulations of either manual or saccadic IOR. This evidence extends to IOR the validity of current models of hemispheric asymmetries in the control of visuospatial attention.

Cortical control of inhibition of return: evidence from patients with inferior parietal damage and visual neglect

Inhibition of return (IOR) refers to slower reaction times to targets presented at previously stimulated or inspected locations. This phenomenon biases orienting towards novel locations and is functional to an effective exploration of the environment. Patients with right brain damage and left visual neglect explore their environment asymmetrically, with strong difficulties to orient attention to left-sided objects. We show for the first time a dissociation between manual and saccadic IOR in neglect. Our patients demonstrated facilitation, instead of inhibition, for repeated right-sided targets with manual responses, but normal IOR to right-sided targets with saccadic responses. All neglect patients had damage to the supramarginal gyrus in the right parietal lobe, or to its connections with the ipsilateral prefrontal cortex. We concluded that IOR with manual responses relies on fronto-parietal attentional networks in the right hemisphere, whose functioning is typically impaired in neglect patients. Saccadic IOR may instead depend on circuits less likely to be damaged in neglect, such as the retinotectal visual pathway.

High rates of active hepatitis B and C co-infections in HIV-1 infected Cameroonian adults initiating antiretroviral therapy

OBJECTIVES

To investigate the presence of hepatitis B virus (HBV) DNA and hepatitis C virus (HCV) RNA in HIV-infected patients initiating antiretroviral therapy in Cameroon.

METHODS

Baseline blood samples from 169 patients were tested retrospectively for hepatitis B surface antigens (HBsAg), anti-hepatitis B core (anti-HBc), anti-HCV and - if HBsAg or anti-HCV result was positive or indeterminate - for HBV DNA or HCV RNA, respectively, using the Cobas Ampliprep/Cobas TaqMan quantitative assay (Roche Diagnostics GmbH, Mannheim, Germany).

RESULTS

HBV DNA was detected in 14 of the 18 patients with positive or indeterminate HBsAg results [8.3% of the total study population, 95% confidence interval (CI) 4.6-13.5]. The median HBV viral load was 2.47 x 10(7) IU/mL [interquartile range (IQR) 3680-1.59 x 10(8); range 270 to >2.2 x 10(8)]. Twenty-one patients (12.4%, 95% CI 7.9-18.4) were found with HCV RNA (all with positive HCV serology). The median HCV viral load was 928 000 IU/mL (IQR 178 400-2.06 x 10(6); range 640-5.5 x 10(6)). No patient was co-infected with HBV and HCV. In multivariate analysis, HCV co-infection was associated with greater age [>or=45 years vs. <45 years, odds ratio (OR) 11.89, 95% CI 3.49-40.55, P<0.001] and abnormal serum alanine aminotransferase level [>or=1.25 x upper limit of normal (ULN) vs. <1.25 x ULN, OR 7.81, 95% CI 1.54-39.66, P=0.01]; HBV co-infection was associated with abnormal serum aspartate aminotransferase level (OR 4.33, 95% CI 1.32-14.17, P=0.02).

CONCLUSIONS

These high rates of active HBV and HCV co-infections in HIV-positive Cameroonian patients requiring antiretroviral therapy underline the need to promote: (i) screening for HBV and HCV before treatment initiation; (ii) accessibility to tenofovir (especially in HBV-endemic African countries); and (iii) accessibility to treatment for HBV and HCV infections.

Dynamical mean field theory of an effective three-band model for NaxCoO2

We derive an effective Hamiltonian for highly correlated t_{2g} states centered at the Co sites of NaxCoO2. The essential ingredients of the model are an O mediated hopping, a trigonal crystal-field splitting, and on-site effective interactions derived from the exact solution of a multiorbital model in a CoO6 cluster, with parameters determined previously. The effective model is solved by dynamical mean field theory. We obtain a Fermi surface and electronic dispersion that agrees well with angle-resolved photoemission spectra. Our results also elucidate the origin of the "sinking pockets" in different doping regimes.