Fix your eyes in the space you could reach: neurons in the macaque medial parietal cortex prefer gaze positions in peripersonal space

Interacting in the peripersonal space requires coordinated arm and eye movements to visual targets in depth. In primates, the medial posterior parietal cortex (PPC) represents a crucial node in the process of visual-to-motor signal transformations. The medial PPC area V6A is a key region engaged in the control of these processes because it jointly processes visual information, eye position and arm movement related signals. However, to date, there is no evidence in the medial PPC of spatial encoding in three dimensions. Here, using single neuron recordings in behaving macaques, we studied the neural signals related to binocular eye position in a task that required the monkeys to perform saccades and fixate targets at different locations in peripersonal and extrapersonal space. A significant proportion of neurons were modulated by both gaze direction and depth, i.e., by the location of the foveated target in 3D space. The population activity of these neurons displayed a strong preference for peripersonal space in a time interval around the saccade that preceded fixation and during fixation as well. This preference for targets within reaching distance during both target capturing and fixation suggests that binocular eye position signals are implemented functionally in V6A to support its role in reaching and grasping.     

虚拟环境下距离知觉的加工与整合

距离知觉是判断环境中自我与物体之间的距离或者是物体与物体之间的距离,本文简要介绍了虚拟环境下的距离信息线索的加工以及多感官的整合,系统回顾近年来对距离知觉的研究与探索,并对其进行评价.最后,讨论了运用虚拟现实技术研究距离知觉的一些局限性,并对于未来的研究趋势进行了展望.     

Quantifying the similarities within fold space

We have used GRATH, a graph-based structure comparison algorithm, to map the similarities between the different folds observed in the CATH domain structure database. Statistical analysis of the distributions of the fold similarities has allowed us to assess the significance for any similarity. Therefore we have examined whether it is best to represent folds as discrete entities or whether, in fact, a more accurate model would be a continuum wherein folds overlap via common motifs. To do this we have introduced a new statistical measure of fold similarity, termed gregariousness. For a particular fold, gregariousness measures how many other folds have a significant structural overlap with that fold, typically comprising 40% or more of the larger structure. Gregarious folds often contain commonly occurring super-secondary structural motifs, such as beta-meanders, greek keys, alpha-beta plait motifs or alpha-hairpins, which are matching similar motifs in other folds. Apart from one example, all the most gregarious folds matching 20% or more of the other folds in the database, are alpha-beta proteins. They also occur in highly populated architectural regions of fold space, adopting sandwich-like arrangements containing two or more layers of alpha-helices and beta-strands.Domains that exhibit a low gregariousness, are those that have very distinctive folds, with few common motifs or motifs that are packed in unusual arrangements. Most of the superhelices exhibit low gregariousness despite containing some commonly occurring super-secondary structural motifs. In these folds, these common motifs are combined in an unusual way and represent a small proportion of the fold (<10%). Our results suggest that fold space may be considered as continuous for some architectural arrangements (e.g. alpha-beta sandwiches), in that super-secondary motifs can be used to link neighbouring fold groups. However, in other regions of fold space much more discrete topologies are observed with little similarity between folds.     

Maternal perception of fetal motor activity.

A technique using real-time ultrasound for comprehensive recording of fetal motor activity was used in 20 subjects in the third trimester of pregnancy. Maternal awareness of fetal movement correlated with the number of fetal parts contributing to the movement but not with maternal parity or obesity, gestational age, placental site, or duration of the fetal movement. Some subjects recorded fetal breathing, passive fetal displacement, and Braxton Hicks''s contractions as fetal movement. Most of our subjects were consistent and accurate in their perception of major fetal movements, but a few were inconsistent and one was completely unaware of major fetal movements. These results suggest that kick counts kept by most mothers will be accurate. Low counts of fetal movement should be an indication for fetal monitoring by other means and not, unconfirmed, for intervention.     

The peri-saccadic perception of objects and space

Eye movements affect object localization and object recognition. Around saccade onset, briefly flashed stimuli appear compressed towards the saccade target, receptive fields dynamically change position, and the recognition of objects near the saccade target is improved. These effects have been attributed to different mechanisms. We provide a unifying account of peri-saccadic perception explaining all three phenomena by a quantitative computational approach simulating cortical cell responses on the population level. Contrary to the common view of spatial attention as a spotlight, our model suggests that oculomotor feedback alters the receptive field structure in multiple visual areas at an intermediate level of the cortical hierarchy to dynamically recruit cells for processing a relevant part of the visual field. The compression of visual space occurs at the expense of this locally enhanced processing capacity.     

以Ca-Ca距离为基础的构象空间的可视化研究

蛋白质结构构象呈现明显的规律,研究其在特定构象空间的分布对蛋白质结构预测和模拟具有重要意义。本文以449个非冗余的高分辨串蛋白质结构为材料,以Ga-Ga距离向量代表蛋白质片段。然后利用主成分分析方法,建立蛋白质片段构象空间的可视化构图,并且单个蛋白质分子可以映射到该空间形成一个顺序连接的路径。从而,可以很直观的分析各长度片段（4-9个残基的片段）的分布情况及其内在的连接关系。图形显示了明显的聚集性,以及各种类型片段与二级结构明显的对应关系。     

Human motor cortex excitability during the perception of others' action

Neuroscience research during the past ten years has fundamentally changed the traditional view of the motor system. In monkeys, the finding that premotor neurons also discharge during visual stimulation (visuomotor neurons) raises new hypotheses about the putative role played by motor representations in perceptual functions. Among visuomotor neurons, mirror neurons might be involved in understanding the actions of others and might, therefore, be crucial in interindividual communication. Functional brain imaging studies enabled us to localize the human mirror system, but the demonstration that the motor cortex dynamically replicates the observed actions, as if they were executed by the observer, can only be given by fast and focal measurements of cortical activity. Transcranial magnetic stimulation enables us to instantaneously estimate corticospinal excitability, and has been used to study the human mirror system at work during the perception of actions performed by other individuals. In the past ten years several TMS experiments have been performed investigating the involvement of motor system during others' action observation. Results suggest that when we observe another individual acting we strongly 'resonate' with his or her action. In other words, our motor system simulates underthreshold the observed action in a strictly congruent fashion. The involved muscles are the same as those used in the observed action and their activation is temporally strictly coupled with the dynamics of the observed action.     

Disruption of space perception due to cortical lesions

Space control has for a long time been considered a unitary function. The structure associated with this function was the right parietal lobe. Hemispheric specialization for space appeared to make it automatically a human-specific function. However, recent primate research shows different regions of the parietal lobes to be differently involved with space control. A review of the literature, together with own cases shows that there is ample evidence of a modular organization of space control in humans on the basis of specific deficits subsequent to circumscribed cerebral lesions. Lesions influence differentially retinotopic, spatiotopic, egocentric, and allocentric frames of references. They also influence differentially the attention to far or near space, or to global or local features of space. Moreover, preattentive processes can be studied in the neglected hemispace of humans and prove to be sensible to the meaning of visual stimuli. Space representation and attentional mechanisms that seem to operate on these representations are organized in our brain in a very modular fashion, similar to the modularity of visual submodalities. There is probably not a unified space representation in the parietal lobes, but distributed functional modules. Thus, the study of visual optic recognition, either by the brain or by machines, is inconceivable without considering space, attention and awareness.     

Multisensory contributions to the 3-D representation of visuotactile peripersonal space in humans: evidence from the crossmodal congruency task.

In order to determine precisely the location of a tactile stimulus presented to the hand it is necessary to know not only which part of the body has been stimulated, but also where that part of the body lies in space. This involves the multisensory integration of visual, tactile, proprioceptive, and even auditory cues regarding limb position. In recent years, researchers have become increasingly interested in the question of how these various sensory cues are weighted and integrated in order to enable people to localize tactile stimuli, as well as to give rise to the 'felt' position of our limbs, and ultimately the multisensory representation of 3-D peripersonal space. We highlight recent research on this topic using the crossmodal congruency task, in which participants make speeded elevation discrimination responses to vibrotactile targets presented to the thumb or index finger, while simultaneously trying to ignore irrelevant visual distractors presented from either the same (i.e., congruent) or a different (i.e., incongruent) elevation. Crossmodal congruency effects (calculated as performance on incongruent-congruent trials) are greatest when visual and vibrotactile stimuli are presented from the same azimuthal location, thus providing an index of common position across different sensory modalities. The crossmodal congruency task has been used to investigate a number of questions related to the representation of space in both normal participants and brain-damaged patients. In this review, we detail the major findings from this research, and highlight areas of convergence with other cognitive neuroscience disciplines.     

Organization of space perception: neural representation of three-dimensional space in the posterior parietal cortex.

The representation of perceptual space in the posterior parietal cortex can be divided into at least two categories: far space, beyond arm's reach, and peripersonal space, within arm's reach. These are encoded by different groups of neurons that are closely related to the control of gaze and the guidance of arm and hand movement, respectively.     

Influence of long-term intracortical microstimulation on the motor cortex

Long-term (0.5–1 s) stimulation of the hand region of the motor cortex in both macaque and human through a microelectrode by a series of biphasic current pulses of small amplitude evokes different complex, coordinated movements of the hand. There are two different opinions on how these movements are produced. The first hypothesis associates the movements with the presence of specific subregions in the motor cortex, which reflect different ethologically relevant categories of movement. According to the second hypothesis, these evoked complex movements are the artifacts of electrical stimulation. This article discusses the results of a number of studies in favor of each of the hypotheses. The conclusion about the validity of the first hypothesis is based on the analysis of the results of microstimulation and their comparison with the data obtained by the latest methods without the use of electric current. Moreover, this finding suggests the possibility of testing the condition changes of the monkey motor cortex through analysis the characteristics of the movements caused by long-term microstimulation.     

Exploring the conformational space of membrane protein folds matching distance constraints

Herein we present a computational technique for generating helix-membrane protein folds matching a predefined set of distance constraints, such as those obtained from NMR NOE, chemical cross-linking, dipolar EPR, and FRET experiments. The purpose of the technique is to provide initial structures for local conformational searches based on either energetic considerations or ad-hoc scoring criteria. In order to properly screen the conformational space, the technique generates an exhaustive list of conformations within a specified root-mean-square deviation (RMSD) where the helices are positioned in order to match the provided distances. Our results indicate that the number of structures decreases exponentially as the number of distances increases, and increases exponentially as the errors associated with the distances increases. We also found the number of solutions to be smaller when all the distances share one helix in common, compared to the case where the distances connect helices in a daisy-chain manner. We found that for 7 helices, at least 15 distances with errors up to 8 A are needed to produce a number of solutions that is not too large to be processed by local search refinement procedures. Finally, without energetic considerations, our enumeration technique retrieved the transmembrane domains of Bacteriorhodopsin (PDB entry1c3w), Halorhodopsin (1e12), Rhodopsin (1f88), Aquaporin-1 (1fqy), Glycerol uptake facilitator protein (1fx8), Sensory Rhodopsin (1jgj), and a subunit of Fumarate reductase flavoprotein (1qlaC) with Calpha level RMSDs of 3.0 A, 2.3 A, 3.2 A, 4.6 A, 6.0 A, 3.7 A, and 4.4 A, respectively.     

Spatial distance and reactivity traits alter the positive perception of brushing by ewes

Gentle handling seems to elicit positive states in sheep. The study investigated whether spatial distance alters sheep responses to brushing and whether spatial distance is influenced by reactivity. Twenty Romane ewes were assessed in three sessions: in Sessions 1 and 3, one grid separated the test animal from pen mates, with no distance between them, and in Session 2 two grids separated the test animal from pen mates by a distance of about 1.7 m. Ewes had been genetically selected for low (R−) or high (R+) behavioural reactivity to social isolation. Body postures, head orientation, ear postures, closed and half-closed eyes, tail wagging and feeding behaviour, in addition to heart rate (HR) and HR variability, as the root mean square of successive differences (RMSSD), standard deviation of all normal-to-normal (NN) intervals (SDNN), RMSSD/SDNN ratio and ratio between low-frequency (LF) and high-frequency (HF) powers (LF/HF) were assessed. Data were analysed using generalized linear models and linear mixed models. Session, genetic line and phase (pre-, brushing and post-brushing) were considered fixed effects. Increased distance in Session 2 might not have influenced ewes’ responses. Fewer changes in ear postures were noted in Session 3 than 1 (P<0.01), suggesting that ewes were more relaxed in Session 3. The RMSSD/SDNN ratio was higher mainly during brushing in Sessions 1 and 3 (P<0.05), indicating that ewes were more relaxed during brushing, and at no distance between pen mates. However, spatial distance influenced R− and R+ ewes’ responses; R+ ewes performed more asymmetric ear postures in Session 2 than 1 and 3 (P<0.01), and in Session 3 than 1 (P<0.01), indicating that spatial distance had a negative effect on R+ ewes. Low reactive ewes spent less time on horizontal ear postures in Session 2 than 1 and 3 (P<0.01), and R+ ewes spent more time on horizontal postures in Session 1 than 3 (P<0.01). Curiously, R− ewes spent more time eating and ruminating in Session 3 than 1 (P<0.01), and in Session 2 than 1 and 3 (P<0.01), whereas R+ ewes ate and ruminated more in Session 1 than 3 (P<0.05). Higher HR was found among R− ewes in Session 2 than 1 and 3, and in Session 3 than 1 (P<0.01). High reactive ewes showed higher HR in Session 1 than 3 (P<0.01). The findings suggest that the social context might influence sheep responses to gentle handling, and the effects depend on their reactivity traits.     

Visually mediated motor planning in the escape response of Drosophila

A key feature of reactive behaviors is the ability to spatially localize a salient stimulus and act accordingly. Such sensory-motor transformations must be particularly fast and well tuned in escape behaviors, in which both the speed and accuracy of the evasive response determine whether an animal successfully avoids predation [1]. We studied the escape behavior of the fruit fly, Drosophila, and found that flies can use visual information to plan a jump directly away from a looming threat. This is surprising, given the architecture of the pathway thought to mediate escape [2, 3]. Using high-speed videography, we found that approximately 200 ms before takeoff, flies begin a series of postural adjustments that determine the direction of their escape. These movements position their center of mass so that leg extension will push them away from the expanding visual stimulus. These preflight movements are not the result of a simple feed-forward motor program because their magnitude and direction depend on the flies' initial postural state. Furthermore, flies plan a takeoff direction even in instances when they choose not to jump. This sophisticated motor program is evidence for a form of rapid, visually mediated motor planning in a genetically accessible model organism.     

Influence of body size on the electric current perception threshold]

Although the threshold for electric current perception is of great importance for safety considerations and safety regulations, important aspects remain unsolved, e.g. the role of age or body size. In the present study measurements of the perception threshold were performed in 790 persons aged between 18 and 82 years randomly selected from the general population. For the first time, the composition and size of the sample were selected such as to allow extrapolation to the general population. The results reveal not only statistically significant gender differences in the perception threshold but also statistically significant relationships between perception threshold and body size. The assumption that the differences in body size between men and women are responsible for the gender-specific difference in electric current perception threshold was not confirmed in this study.     

MEG responses to the perception of global structure within glass patterns

Background

The perception of global form requires integration of local visual cues across space and is the foundation for object recognition. Here we used magnetoencephalography (MEG) to study the location and time course of neuronal activity associated with the perception of global structure from local image features. To minimize neuronal activity to low-level stimulus properties, such as luminance and contrast, the local image features were held constant during all phases of the MEG recording. This allowed us to assess the relative importance of striate (V1) versus extrastriate cortex in global form perception.

Methodology/Principal Findings

Stimuli were horizontal, rotational and radial Glass patterns. Glass patterns without coherent structure were viewed during the baseline period to ensure neuronal responses reflected perception of structure and not changes in local image features. The spatial distribution of task-related changes in source power was mapped using Synthetic Aperture Magnetometry (SAM), and the time course of activity within areas of maximal power change was determined by calculating time-frequency plots using a Hilbert transform. For six out of eight observers, passive viewing of global structure was associated with a reduction in 10–20 Hz cortical oscillatory power within extrastriate occipital cortex. The location of greatest power change was the same for each pattern type, being close to or within visual area V3a. No peaks of activity were observed in area V1. Time-frequency analyses indicated that neural activity was least for horizontal patterns.

Conclusions

We conclude: (i) visual area V3a is involved in the analysis of global form; (ii) the neural signature for perception of structure, as assessed using MEG, is a reduction in 10–20 Hz oscillatory power; (iii) different neural processes may underlie the perception of horizontal as opposed to radial or rotational structure; and (iv) area V1 is not strongly activated by global form in Glass patterns.     

Distortions of subjective time perception within and across senses

Background

The ability to estimate the passage of time is of fundamental importance for perceptual and cognitive processes. One experience of time is the perception of duration, which is not isomorphic to physical duration and can be distorted by a number of factors. Yet, the critical features generating these perceptual shifts in subjective duration are not understood.

Methodology/Findings

We used prospective duration judgments within and across sensory modalities to examine the effect of stimulus predictability and feature change on the perception of duration. First, we found robust distortions of perceived duration in auditory, visual and auditory-visual presentations despite the predictability of the feature changes in the stimuli. For example, a looming disc embedded in a series of steady discs led to time dilation, whereas a steady disc embedded in a series of looming discs led to time compression. Second, we addressed whether visual (auditory) inputs could alter the perception of duration of auditory (visual) inputs. When participants were presented with incongruent audio-visual stimuli, the perceived duration of auditory events could be shortened or lengthened by the presence of conflicting visual information; however, the perceived duration of visual events was seldom distorted by the presence of auditory information and was never perceived shorter than their actual durations.

Conclusions/Significance

These results support the existence of multisensory interactions in the perception of duration and, importantly, suggest that vision can modify auditory temporal perception in a pure timing task. Insofar as distortions in subjective duration can neither be accounted for by the unpredictability of an auditory, visual or auditory-visual event, we propose that it is the intrinsic features of the stimulus that critically affect subjective time distortions.