抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Let's read! We will often find out this sentence everywhere. When still being a kid, mom used to order us to always read, so did the teacher. Some books are fully read in a week and we need the obligation to support reading. What about now? Do you still love reading? Is reading only for you who have obligation? Absolutely not! We here offer you a new book enPDFd the perception of the visual world to read.

The Perception of the Visual World. By James J. Gibson. U.S.A.: Houghton Mifflin Company, 1950 (George Allen & Unwin, Ltd., London). Price 35s.

The journal of neuroscience : the official journal of the Society for Neuroscience.

Autism is a complex neurodevelopmental condition, and little is known about its neurobiology Much of autism research has focused on the social, communication and cognitive difficulties associated with the condition However, the recent revision of the diagnostic criteria for autism has brought another key domain of autistic experience into focus: sensory processing Here, we review the properties of sensory processing in autism and discuss recent computational and neurobiological insights arising from attention to these behaviours We argue that sensory traits have important implications for the development of animal and computational models of the condition Finally, we consider how difficulties in sensory processing may relate to the other domains of behaviour that characterize autism

Sensory perception in autism

Discoveries over the past two decades demonstrate that regions distributed throughout the association cortex, often called the default network, are suppressed during tasks that demand external attention and are active during remembering, envisioning the future and making social inferences. This Review describes progress in understanding the organization and function of networks embedded within these association regions. Detailed high-resolution analyses of single individuals suggest that the default network is not a single network, as historically described, but instead comprises multiple interwoven networks. The multiple networks share a common organizational motif (also evident in marmoset and macaque anatomical circuits) that might support a general class of processing function dependent on internally constructed rather than externally constrained representations, with each separate interwoven network specialized for a distinct processing domain. Direct neuronal recordings in humans and monkeys reveal evidence for competitive relationships between the internally and externally oriented networks. Findings from rodent studies suggest that the thalamus might be essential to controlling which networks are engaged through specialized thalamic reticular neurons, including antagonistic subpopulations. These association networks (and presumably thalamocortical circuits) are expanded in humans and might be particularly vulnerable to dysregulation implicated in mental illness. The brain’s default network is thought to comprise a set of regions in the association cortex. Randy Buckner and Lauren DiNicola review findings from humans, monkeys and rodents indicating that multiple subnetworks make up the default network and explore the implications of these observations.

The brain’s default network: updated anatomy, physiology and evolving insights

If you were to ask someone in the street what they find most fascinating about the human brain the chances are they will tell you about a strange neuropsychological case study in which the patient presents with an odd and intriguingly specific deficit. Perhaps they lost the ability to recognize faces, tasted in colors or could no longer navigate familiar environments. Neuropsychological case studies, it turns out, are thus intrinsically fascinating to both scientists and the general public alike. Consistent with this general tenet, the case of ‘Davida’ reported by Vannuscorps et al. (Vannuscorps et al., 2021) is no exception. Davida, a right-handed young woman who is unremarkable in terms of her medical, neuropsychological, and neurological history nevertheless presents with a specific deficit in which she perceives 2D bounded shapes, defined by sharp edges of high contrast, as either inverted, mirror-reversed or plane-rotated by 90 or 180 degrees. Remarkably, her ability to judge the shape, size, location, distance, and tilt of 2D stimuli is no different from controls and her perception of 3D, strongly blurred or very low contrast shapes is intact—a curious case if ever there was one. When reading case-studies one can be left questioning the depth and breadth of the testing, wishing that further tests had been conducted to rule out all manner of possible explanations. Of course, time is tight when conducting these studies, but that sense of a missed opportunity can persist, nevertheless. That is not the case when reading Vannuscorps et al. Over the course of two years, Davida completed six experimental phases comprising over fifty individual experiments. Within these, many of the conceivable adaptations and modifications to the experimental set-up were tested including, but not limited to, visual, auditory, and somatosensory perception, visual illusions, object naming, object matching and drawing/tracing—a monumental achievement for both the researchers and Davida herself. Collectively, these data provide a benchmark for comprehensive behavioral profiling in such casestudies. The fact that Davida systematically mis-perceives 2D shapes defined by sharp and high contrast edges as either reversed or plane-rotated and yet perceives low contrast 2D shapes and 3D shapes correctly, suggests a dissociation between the visual information originating from the parvocellular and magnocellular pathways, pointing to a failure to integrate parvocellular information correctly. But, perhaps the most intriguing implication of Davida’s behavioral profile is that the implied cortical locus of her deficit lies at an intermediate stage of visual processing, somewhere between retinotopic based frames of representation in early visual cortex (e.g., V1-V3) (Wandell et al., 2007), and more abstract spatiotopic and bodycentered coordinate systems that are presumably computed more anterior in the brain (Groen et al., 2021). Vannuscorps et al. term this type of representation “intermediate shape-centered representation” (ISCR) and argue that these are distinct from subsequent and deeper levels of representation that underpin conscious perception and action. A critical and obvious question emerging is thus, where is the most likely cortical locus for such ISCRs within the visual hierarchy? Although no neuroimaging results were reported here, Vannuscorps et al. argue that cortical areas LO1-LO2 (Larsson & Heeger, 2006) are suitable candidates, and several known features of LO1LO2 support their claim. For instance, LO1-LO2 play

The search for shape-centered representations

Braille reading and other tactile discrimination tasks recruit the visual cortex of both blind and normally sighted individuals undergoing short-term visual deprivation. Prior functional magnetic resonance imaging (fMRI) work in patient S, a visually impaired adult with the rare ability to read both highly magnified print visually and Braille by touch, found that foveal representations of S9s visual cortex were recruited during tactile perception, whereas peripheral regions were recruited during visual perception. Here, we test the causal nature of tactile responses in the visual cortex of S by combining tactile and visual psychophysics with repetitive transcranial magnetic stimulation (rTMS). First, we replicate this prior fMRI work in S. Second, we demonstrate that transient disruption of S9s foveal visual cortex has no measurable impact on S9s tactile processing performance compared to that of healthy controls - a pattern not predicted by the fMRI results. Third, stimulation of foveal visual cortex maximally disrupted visual processing performance in both S and controls, suggesting the possibility of preserved visual function within S9s foveal cortex. Finally, stimulation of somatosensory cortex induced the expected disruption to tactile processing performance in both S and controls. These data suggest that tactile responses in S9s foveal representation reflect unmasking of latent connections between visual and somatosensory cortices and not behaviourally relevant cross-modal plasticity. Unlike studies in congenitally blind individuals, it is possible that the absence of complete visual loss in S has limited the degree of causally impactful cross-modal reorganisation.

/pdf/regions-of-visual-cortex-responding-to-tactile-stimulation-46ed902zpx.pdf

Regions of visual cortex responding to tactile stimulation in an individual with longstanding low vision are not causally involved in tactile processing performance

Human visual cortex is organised broadly according to two major principles: retinotopy (the spatial mapping of the retina in cortex) and category-selectivity (preferential responses to specific categories of stimuli). Historically, these principles were considered anatomically separate, with retinotopy restricted to the occipital cortex and category-selectivity emerging in lateral-occipital and ventral-temporal cortex. Contrary to this assumption, recent studies show that category-selective regions exhibit systematic retinotopic biases. It is unclear, however, whether responses within these regions are more strongly driven by retinotopic location or by category preference, and if there are systematic differences between category-selective regions in the relative strengths of these preferences. Here, we directly compare spatial and category preferences by measuring fMRI responses to scene and face stimuli presented in the left or right visual field and computing two bias indices: a spatial bias (response to the contralateral minus ipsilateral visual field) and a category bias (response to the preferred minus non-preferred category). We compare these biases within and between scene- and face-selective regions across the lateral and ventral surfaces of visual cortex. We find an interaction between surface and bias: lateral regions show a stronger spatial than category bias, whilst ventral regions show the opposite. These effects are robust across and within subjects, and reflect large-scale, smoothly varying gradients across both surfaces. Together, these findings support distinct functional roles for lateral and ventral category-selective regions in visual information processing in terms of the relative importance of spatial information.

https://www.biorxiv.org/content/biorxiv/early/2021/05/06/2021.05.06.442603.full.pdf

Direct comparison of category and spatial selectivity in human occipitotemporal cortex

The blind spot is a region in the temporal monocular visual field in humans, which corresponds to a physiological scotoma within the nasal hemi-retina. This region has no photoreceptors, so is insensitive to visual stimulation. There is no corresponding perceptual scotoma because the visual stimulation is “filled-in” by the visual system. Investigations of visual perception in and around the blind spot allow us to investigate this filling-in process. However, because the location and size of the blind spot are individually variable, experimenters must first map the blind spot in every observer. We present an open-source tool, which runs in Psychopy software, to estimate the location and size of the blind spot psychophysically. The tool will ideally be used with an Eyelink eye-tracker (SR Research), but it can also run in standalone mode. Here, we explain the rationale for the tool and demonstrate its validity in normally-sighted observers. We develop a detailed map of the blind spot in one observer. Then, in a group of 12 observers, we propose a more efficient, pragmatic method to define a “safe zone” within the blind spot, for which the experimenter can be fully confident that visual stimuli will not be seen. Links are provided to this open-source tool and a manual.

/pdf/did-you-see-it-a-python-tool-for-psychophysical-assessment-hhougrg8p8.pdf

Did you see it? A Python tool for psychophysical assessment of the human blind spot

Human medial parietal cortex (MPC) is recruited during multiple cognitive processes. Previously, we demonstrated regions specific to recall of people or places and proposed that the functional organization of MPC mirrors the category selectivity defining the medial-lateral axis of ventral temporal cortex (VTC). However, prior work considered recall of people and places only and VTC also shows object-selectivity sandwiched between face- and scene-selective regions. Here, we tested a strong prediction of our proposal: like VTC, MPC should show a region specifically recruited during object recall, and its relative cortical position should mirror the one of VTC. While responses during people and place recall showed a striking replication of prior findings, we did not observe any evidence for object-recall effects within MPC, which differentiates it from the spatial organization in VTC. Importantly, beyond MPC, robust recall-effects were observed for people, places, and objects on the lateral surface of the brain. Place-recall effects were present in the angular gyrus, frontal eye fields and peripheral portions of early visual cortex, whereas people-recall selectively drove response in the right posterior superior temporal sulcus. Object-recall effects were largely restricted to a region posterior to left somatosensory cortex, in the vicinity of the supramarginal gyrus. Taken together, these data demonstrate that while there are distributed regions active during recall of people, places and objects, the functional organization of MPC does not mirror the medial-lateral axis of VTC but reflects only the most salient features of that axis - namely representations of people and places. Significance statement Human medial parietal cortex (MPC) is recruited during multiple cognitive. Recently, we proposed a framework for interpreting the functional organization of MPC by suggesting that it reflects the categorical preferences for people and places that is evident also in ventral temporal cortex (VTC). Because VTC also exhibits selectivity for objects, we here extend this framework to test whether MPC also shows object selectivity during recall. Robust people and place recall effects were evident in MPC, but we found no evidence for object-recall within MPC, suggesting that MPC and VTC are not mirror-copies of each other. Together, these data suggest that the functional organization of MPC reflects the most salient categorical representations within VTC for people and places.

Edward H. Silson

Papers

The search for shape-centered representations

Regions of visual cortex responding to tactile stimulation in an individual with longstanding low vision are not causally involved in tactile processing performance

Direct comparison of category and spatial selectivity in human occipitotemporal cortex

Did you see it? A Python tool for psychophysical assessment of the human blind spot

Distributed cortical regions for the recall of people, places and objects