The Role of Frontoparietal Cortex across the Functional Stages of Visual Search.

Areas in frontoparietal cortex have been shown to be active in a range of cognitive tasks and have been proposed to play a key role in goal-driven activities (Dosenbach, N. U. F., Fair, D. A., Miezin, F. M., Cohen, A. L., Wenger, K. K., Dosenbach, R. A. T., et al. Distinct brain networks for adaptive and stable task control in humans. Proceedings of the National Academy of Sciences, U.S.A., 104, 11073-11078, 2007; Duncan, J. The multiple-demand (MD) system of the primate brain: Mental programs for intelligent behavior. Trends in Cognitive Sciences, 14, 172-179, 2010). Here, we examine the role this frontoparietal system plays in visual search. Visual search, like many complex tasks, consists of a sequence of operations: target selection, stimulus-response (SR) mapping, and response execution. We independently manipulated the difficulty of target selection and SR mapping in a novel visual search task that involved identical stimulus displays. Enhanced activity was observed in areas of frontal and parietal cortex during both difficult target selection and SR mapping. In addition, anterior insula and ACC showed preferential representation of SR-stage information, whereas the medial frontal gyrus, precuneus, and inferior parietal sulcus showed preferential representation of target selection-stage information. A connectivity analysis revealed dissociable neural circuits underlying visual search. We hypothesize that these circuits regulate distinct mental operations associated with the allocation of spatial attention, stimulus decisions, shifts of task set from selection to SR mapping, and SR mapping. Taken together, the results show frontoparietal involvement in all stages of visual search and a specialization with respect to cognitive operations.

Category-length and category-strength effects using images of scenes.

Global matching models have provided an important theoretical framework for recognition memory. Key predictions of this class of models are that (1) increasing the number of occurrences in a study list of some items affects the performance on other items (list-strength effect) and that (2) adding new items results in a deterioration of performance on the other items (list-length effect). Experimental confirmation of these predictions has been difficult, and the results have been inconsistent. A review of the existing literature, however, suggests that robust length and strength effects do occur when sufficiently similar hard-to-label items are used. In an effort to investigate this further, we had participants study lists containing one or more members of visual scene categories (bathrooms, beaches, etc.). Experiments 1 and 2 replicated and extended previous findings showing that the study of additional category members decreased accuracy, providing confirmation of the category-length effect. Experiment 3 showed that repeating some category members decreased the accuracy of nonrepeated members, providing evidence for a category-strength effect. Experiment 4 eliminated a potential challenge to these results. Taken together, these findings provide robust support for global matching models of recognition memory. The overall list lengths, the category sizes, and the number of repetitions used demonstrated that scene categories are well-suited to testing the fundamental assumptions of global matching models. These include (A) interference from memories for similar items and contexts, (B) nondestructive interference, and (C) that conjunctive information is made available through a matching operation.

Bispecific Antibodies Targeting Different Epitopes on the HIV-1 Envelope Exhibit Broad and Potent Neutralization.

UNLABELLED: The potency and breadth of the recently isolated neutralizing human monoclonal antibodies to HIV-1 have stimulated interest in their use to prevent or to treat HIV-1 infection. Due to the antigenically diverse nature of the HIV-1 envelope (Env), no single antibody is highly active against all viral strains. While the physical combination of two broadly neutralizing antibodies (bNAbs) can improve coverage against the majority of viruses, the clinical-grade manufacturing and testing of two independent antibody products are time and resource intensive. In this study, we constructed bispecific immunoglobulins (IgGs) composed of independent antigen-binding fragments with a common Fc region. We developed four different bispecific IgG variants that included antibodies targeting four major sites of HIV-1 neutralization. We show that these bispecific IgGs display features of both antibody specificities and, in some cases, display improved coverage over the individual parental antibodies. All four bispecific IgGs neutralized 94% to 97% of antigenically diverse viruses in a panel of 206 HIV-1 strains. Among the bispecific IgGs tested, VRC07 × PG9-16 displayed the most favorable neutralization profile. It was superior in breadth to either of the individual antibodies, neutralizing 97% of viruses with a median 50% inhibitory concentration (IC50) of 0.055 µg/ml. This bispecific IgG also demonstrated in vivo pharmacokinetic parameters comparable to those of the parental bNAbs when administered to rhesus macaques. These results suggest that IgG-based bispecific antibodies are promising candidates for the prevention and treatment of HIV-1 infection in humans. IMPORTANCE: To prevent or treat HIV-1 infection, antibodies must potently neutralize nearly all strains of HIV-1. Thus, the physical combination of two or more antibodies may be needed to broaden neutralization coverage and diminish the possibility of viral resistance. A bispecific antibody that has two different antibody binding arms could potentially display neutralization characteristics better than those of any single parental antibody. Here we show that bispecific antibodies contain the binding specificities of the two parental antibodies and that a single bispecific antibody can neutralize 97% of viral strains with a high overall potency. These findings support the use of bispecific antibodies for the prevention or treatment of HIV-1 infection.

The spider does not always win the fight for attention: Disengagement from threat is modulated by goal set.

Stimulus-driven preferential attention to threat can be modulated by goal-driven attention. However, it remains unclear how this goal-driven modulation affects specific attentional components implied in threat interference. We hypothesise that goal-driven modulation most strongly impacts delayed disengagement from threat. A spatial cueing task was used that disentangles delayed disengagement from attentional capture by tightly manipulating the locus of attention at the time of target onset. Different top-down goals were induced by instructing participants to identify bird/fish targets (Experiment 1) or spider/cat targets (Experiment 2) among animal non-targets. Delayed disengagement from a non-target spider was observed only when the spider was part of the target set, not when it was task-irrelevant. This corroborates evidence that threat stimuli do not necessarily override goal-driven attentional control and that extended processing of threatening distractors is not obligatory.

Boston type craniosynostosis: report of a second mutation in MSX2.

We describe a family that segregated an autosomal dominant form of craniosynostosis characterized by variable expression and limited extra-cranial features. Linkage analysis and genome sequencing were performed to identify the underlying genetic mutation. A c.443C>T missense mutation in MSX2, which predicts p.Pro148Leu was identified and segregated with the disease in all affected family members. One other family with autosomal dominant craniosynostosis (Boston type) has been reported to have a missense mutation in MSX2. These data confirm that missense mutations altering the proline at codon 148 of MSX2 cause dominantly inherited craniosynostosis.

Complex craniosynostosis is associated with the 2p15p16.1 microdeletion syndrome.

In a screening project of patients with (complex) craniosynostosis using genomic arrays, we identified two patients with craniosynostosis and microcephaly with a deletion in the 2p15p16.1 chromosomal region. This region has been associated with a new microdeletion syndrome, for which patients have various features in common, including microcephaly and intellectual disability. Deletions were identified using Affymetrix 250K SNP array and further characterized by fluorescence in situ hybridization (FISH) analysis and qPCR. The deletions in our two patients overlapped within the 2p15p16.1 microdeletion syndrome area and were 6.8 and 6.9 Mb in size, respectively. FISH and qPCR confirmed the presence of only one copy in this region. Finemapping of the breakpoints indicated precise borders in our patients and were further finemapped in two other previously reported patients. Clinical features of patients with deletions in the 2p15p16.1 region vary. Including data from our patients, now eight out of nine reported patients have microcephaly, one of the major features, and all had intellectual disability. The current reported two patients add different forms of craniosynostosis to the clinical spectrum of this recently recognized microdeletion syndrome.

Sleep apnoea in syndromic craniosynostosis occurs independent of hindbrain herniation.

PURPOSE: Hindbrain herniation (HH) is frequently found in syndromic craniosynostosis. It may cause impairment of the respiratory centres and manifest as sleep-disordered breathing. Our aim was to quantify sleep apnoea caused by HH in children with syndromic craniosynostosis. METHODS: Seventy-one children with syndromic and complex craniosynostosis (aged 0-18 years) underwent prospective magnetic resonance imaging and a sleep study. The position of the cerebellar tonsils and respiratory parameters were evaluated and analysed. None of the included patients had undergone previous foramen magnum decompression. RESULTS: HH was present in 35% of the patients and was more frequent in children with Crouzon syndrome (63%) than in other types of craniosynostosis (p = .018). There was a positive association between the position of the cerebellar tonsils and papilledema (p = .002). Sleep studies of children with craniosynostosis and HH were not different from those without HH. Obstructive sleep apnoea syndrome was not more prevalent in children with HH compared to those without HH (p = .12). A cluster analysis using indices of apnoea revealed that three new clusters between which age was significantly different (p = .025). CONCLUSION: Sleep apnoea in syndromic craniosynostosis is not caused by HH. Rather, our evidence suggests that sleep-disordered breathing in craniosynostosis may be caused by brain stem immaturity in young children or upper airway obstruction. Therefore, as long as the child remains asymptomatic, our preferred management of HH is to be conservative and provide regular neurosurgical follow-up.

Assessment of white matter microstructural integrity in children with syndromic craniosynostosis: a diffusion-tensor imaging study.

PURPOSE: To assess whether architectural alterations exist in the white matter of patients with syndromic and complex craniosynostosis. MATERIALS AND METHODS: The medical ethics committee approved this study. Written informed consent was obtained from parents or guardians before imaging. A prospective study was performed in children with syndromic and complex craniosynostosis aged 6-14 years. Forty-five patients were included: four had Apert syndrome, 14 had Crouzon-Pfeiffer syndrome, eight had Muenke syndrome, 11 had Saethre-Chotzen syndrome, and eight had complex craniosynostosis. In addition, seven control subjects were evaluated. For diffusion-tensor imaging, an echo-planar sequence was used with a diffusion gradient (b = 1000 sec/mm(2)) applied in 25 noncollinear directions. Regions of interest (ROIs) were placed in the following white matter structures: pontine crossing tract, corticospinal tracts, medial cerebral peduncles, uncinate fasciculus (measured bilaterally), anterior commissure, frontal and occipital white matter (measured bilaterally), fornix, corpus callosum (measured in the genu and splenium), and corpus cingulum (measured bilaterally). Eigenvalues were measured in all ROIs and fractional anisotropy (FA) was calculated. RESULTS: Across all measured ROIs, FA values were generally lower in all patients combined than in the control subjects (P < .001). There were no significant differences among subgroups of patients. CONCLUSION: Diffusion-tensor imaging measurements of white matter tracts reveal significant white matter integrity differences between children with craniosynostosis and healthy control subjects. This could imply that the developmental delays seen in these patients could be caused by the presence of a primary disorder of the white matter microarchitecture.

Papilledema in isolated single-suture craniosynostosis: prevalence and predictive factors.

The purpose of this retrospective study was to assess the prevalence of papilledema in patients with isolated craniosynostosis. Second, we wanted to assess if the presence of ventricular dilatation on computed tomography (CT) scan is a predictive factor for the occurrence of papilledema. We included 205 consecutive children with an isolated single-suture craniosynostosis, who had at least 1 fundus examination. Preoperative CT scans of the brain were examined for the presence of ventricular dilatation.Papilledema developed in 14 of 205 patients: 10 developed papilledema before surgery and 4 during the follow-up period. Ten of the patients with papilledema had a synostosis of the sagittal suture, and 4 of the metopic suture. Prevalence of papilledema in scaphocephaly was 9.7%, and in trigonocephaly, 5.6%. Based on evaluation of all CT scans, ventricular dilatation seemed not to be a predictive factor for papilledema in children with isolated craniosynostosis.The incidence of papilledema in almost 10% of scaphocephaly patients is remarkably higher than expected. Therefore, we recommend routine preoperative screening, especially for patients with scaphocephaly, but also for patients with trigonocephaly. Postoperative screening is recommended in all patients when there is any uncertainty.

Evidence against the Detectability of a Hippocampal Place Code Using Functional Magnetic Resonance Imaging.

Individual hippocampal neurons selectively increase their firing rates in specific spatial locations. As a population, these neurons provide a decodable representation of space that is robust against changes to sensory- and path-related cues. This neural code is sparse and distributed, theoretically rendering it undetectable with population recording methods such as functional magnetic resonance imaging (fMRI). Existing studies nonetheless report decoding spatial codes in the human hippocampus using such techniques. Here we present results from a virtual navigation experiment in humans in which we eliminated visual- and path-related confounds and statistical limitations present in existing studies, ensuring that any positive decoding results would represent a voxel-place code. Consistent with theoretical arguments derived from electrophysiological data and contrary to existing fMRI studies, our results show that although participants were fully oriented during the navigation task, there was no statistical evidence for a place code.

Neural Correlates of Temporal Complexity and Synchrony during Audiovisual Correspondence Detection.

We often perceive real-life objects as multisensory cues through space and time. A key challenge for audiovisual integration is to match neural signals that not only originate from different sensory modalities but also that typically reach the observer at slightly different times. In humans, complex, unpredictable audiovisual streams lead to higher levels of perceptual coherence than predictable, rhythmic streams. In addition, perceptual coherence for complex signals seems less affected by increased asynchrony between visual and auditory modalities than for simple signals. Here, we used functional magnetic resonance imaging to determine the human neural correlates of audiovisual signals with different levels of temporal complexity and synchrony. Our study demonstrated that greater perceptual asynchrony and lower signal complexity impaired performance in an audiovisual coherence-matching task. Differences in asynchrony and complexity were also underpinned by a partially different set of brain regions. In particular, our results suggest that, while regions in the dorsolateral prefrontal cortex (DLPFC) were modulated by differences in memory load due to stimulus asynchrony, areas traditionally thought to be involved in speech production and recognition, such as the inferior frontal and superior temporal cortex, were modulated by the temporal complexity of the audiovisual signals. Our results, therefore, indicate specific processing roles for different subregions of the fronto-temporal cortex during audiovisual coherence detection.

Broadly neutralizing antibodies targeting the HIV-1 envelope V2 apex confer protection against a clade C SHIV challenge.

Neutralizing antibodies to the V2 apex antigenic region of the HIV-1 envelope (Env) trimer are among the most prevalent cross-reactive antibodies elicited by natural infection. Two recently described V2-specific antibodies, PGDM1400 and CAP256-VRC26.25, have demonstrated exquisite potency and neutralization breadth against HIV-1. However, little data exist on the protective efficacy of V2-specific neutralizing antibodies. We created a novel SHIV-325c viral stock that included a clade C HIV-1 envelope and was susceptible to neutralization by both of these antibodies. Rhesus macaques received a single infusion of either antibody at three different concentrations (2, 0.4, and 0.08 mg/kg) before challenge with SHIV-325c. PGDM1400 was fully protective at the 0.4 mg/kg dose, whereas CAP256-VRC26.25-LS was fully protective even at the 0.08 mg/kg dose, which correlated with its greater in vitro neutralization potency against the challenge virus. Serum antibody concentrations required for protection were <0.75 µg/ml for CAP256-VRC26.25-LS. These data demonstrate unprecedented potency and protective efficacy of V2-specific neutralizing antibodies in nonhuman primates and validate V2 as a potential target for the prevention of HIV-1 infection in passive immunization strategies in humans.

Threat captures attention, but not automatically: Top-down goals modulate attentional orienting to threat distractors.

The rapid orienting of attention to potential threats has been proposed to proceed outside of top-down control. However, paradigms that have been used to investigate this have struggled to separate the rapid orienting of attention (i.e. capture) from the later disengagement of focal attention that may be subject to top-down control. Consequently, it remains unclear whether and to what extent orienting to threat is contingent on top-down goals. The current study manipulated the goal-relevance of threat distractors (spiders), whilst a strict top-down attentional set was encouraged by presenting the saliently colored target and the threat distracter simultaneously for a limited time. The goal-relevance of threatening distractors was manipulated by including a spider amongst the possible target stimuli (Experiment 1: spider/cat targets) or excluding it (Experiment 2: bird/fish targets). Orienting and disengagement were disentangled by cueing attention away from or towards the threat prior to its onset. The results indicated that the threatening spider distractors elicited rapid orienting of attention when spiders were potentially goal-relevant (Experiment 1) but did so much less when they were irrelevant to the task goal (Experiment 2). Delayed disengagement from the threat distractors was even more strongly contingent on the task goal and occurred only when a spider was a possible target. These results highlight the role of top-down goals in attentional orienting to and disengagement from threat.

Venous hypertension in syndromic and complex craniosynostosis: the abnormal anatomy of the jugular foramen and collaterals.

UNLABELLED: Why craniosynostosis patients develop elevated intracranial pressure (ICP) is still a mystery. Our aim was to investigate jugular foramen size and its relation to venous hypertension and elevated ICP. Secondly, we evaluated whether occipital collateral veins develop as a compensatory mechanism for elevated ICP. We conducted a prospective study in 41 children with craniosynostosis who underwent a 3D-CT-angiography. We evaluated the anatomical course of the jugular vein, the diameter of the jugular foramen and the relation to the presence of papilledema. Additionally, we studied the anatomical variations of the cerebral venous drainage system. The diameter of the jugular foramen was significantly smaller in our patients. Abnormal venous collaterals were most often observed in patients with Apert, Crouzon-Pfeiffer and Saethre-Chotzen syndrome, even in children under two years of age. There was no significant difference in the number of collateral veins in patients with or without papilledema. Collaterals appear to reflect an inborn abnormality of the venous system, rather than a compensating mechanism for elevated ICP. This study confirms the presence of jugular foraminal narrowing in craniosynostosis patients and an abnormal venous system, which may predispose to elevated ICP. LEVEL OF EVIDENCE: Diagnostic II.

Flavocytochrome P450 BM3: an update on structure and mechanism of a biotechnologically important enzyme.

Since its discovery in the 1980s, the fatty acid hydroxylase flavocytochrome P450 (cytochrome P450) BM3 (CYP102A1) from Bacillus megaterium has been adopted as a paradigm for the understanding of structure and mechanism in the P450 superfamily of enzymes. P450 BM3 was the first P450 discovered as a fusion to its redox partner--a eukaryotic-like diflavin reductase. This fact fuelled the interest in soluble P450 BM3 as a model for the mammalian hepatic P450 enzymes, which operate a similar electron transport chain using separate, membrane-embedded P450 and reductase enzymes. Structures of each of the component domains of P450 BM3 have now been resolved and detailed protein engineering and molecular enzymology studies have established roles for several amino acids in, e.g. substrate binding, coenzyme selectivity and catalysis. The potential of P450 BM3 for biotechnological applications has also been recognized, with variants capable of industrially important transformations generated using rational mutagenesis and forced evolution techniques. This paper focuses on recent developments in our understanding of structure and mechanism of this important enzyme and highlights important problems still to be resolved.