Visuomotor synchronization in adults and seven- to eight-year-old children

A group of 22 seven- to eight-year-old children and a group of 17 adults participated in the experiment in which they synchronized their movements (pressing a button) with an isochronous sequence of visual stimuli. The period of the sequence was varied between 500 to 2000 ms at a step of 300 ms. Two consecutive phases of visuomotor synchronization were studied: the initiation phase, which corresponds to the process of transition between responding to a visual stimulus to stable synchronization with them, and the synchronization phase. The initiation phase was characterized by the shape and duration of the asynchrony time course (relaxation curve). The statistical properties of asynchrony were analyzed in terms of the phase correction of the central timer. It was shown that (1) the range of successful visuomotor synchronization was narrower in seven- to eight-year-old children than in adults (from 600–700 ms to ∼1700 ms); (2) the initiation phase duration was about the same in seven- to eight-year-old children and adults, and typical shapes of individual relaxation curves were similar in both adults and children; (3) although the statistical properties of asynchrony were comparable in children and adults, the mechanism of phase correction of the central timer operated at a lower correction gain factor in children than in adults. In children, the phase correction process was also characterized by a substantially higher level of the central and motor noise, which leads to higher asynchrony variability and more frequent and longer synchronization losses.     

Priming, initiation and synchronization of the segmentation clock by deltaD and deltaC

Zebrafish somitogenesis is governed by a segmentation clock that generates oscillations in expression of several Notch pathway genes, including her1, her7 and deltaC. Using a combination of pharmacological inhibition and Mendelian genetics, we show that DeltaD and DeltaC, two Notch ligands, represent functionally distinct signals within the segmentation clock. Using high-resolution fluorescent in situ hybridization, the oscillations were divided into phases based on eight distinct subcellular patterns of mRNA localization for 140,000 cells. her1, her7 and deltaC expression was examined in wild-type, deltaD(-/-) and deltaC(-/-) embryos. We identified areas within the tailbud where the clock is set up in the progenitor cells (priming), where the clock starts running (initiation), and where the clocks of neighbouring cells are entrained (synchronization). We find that the clocks of motile cells are primed by deltaD in a progenitor zone in the posterior tailbud and that deltaD is required for cells to initiate oscillations on exiting this zone. Oscillations of adjacent cells are synchronized and amplified by deltaC in the posterior presomitic mesoderm as cell movement subsides and cells maintain stable neighbour relationships.     

Nucleation and decay initiation are the stiffness-sensitive phases of focal adhesion maturation

A cell plated on a two-dimensional substrate forms adhesions with that surface. These adhesions, which consist of aggregates of various proteins, are thought to be important in mechanosensation, the process by which the cell senses and responds to the mechanical properties of the substrate (e.g., stiffness). On the basis of experimental measurements, we model these proteins as idealized molecules that can bind to the substrate in a strain-dependent manner and can undergo a force-dependent state transition. The model forms molecular aggregates that are similar to adhesions. Substrate stiffness affects whether a simulated adhesion is initially formed and how long it grows, but not how that adhesion grows or shrinks. Our own experimental tests support these predictions, suggesting that the mechanosensitivity of adhesions is an emergent property of a simple molecular-mechanical system.     

Visuomotor transformations: early cortical mechanisms of reaching

Recent studies of visually guided reaching in monkeys support the hypothesis that the visuomotor transformations underlying arm movements to spatial targets involve a parallel mechanism that simultaneously engages functionally related frontal and parietal areas linked by reciprocal cortico-cortical connections. The neurons in these areas possess similar combinations of response properties. The multimodal combinatorial properties of these neurons and the gradient architecture of the parieto-frontal network emerge as a potential substrate to link the different sensory and motor signals that arise during reaching behavior into common hybrid reference frames. This convergent combinatorial process is evident at early stages of visual information processing in the occipito-parietal cortex, suggesting the existence of re-entrant motor influences on cortical areas once believed to have only visual functions.     

Visuomotor functions of the lateral pre-motor cortex

Recent studies have provided new insights into the visuomotor functions of the dorsal and ventral regions of the lateral pre-motor cortex. Anatomical and physiological investigations in non-human primates have demonstrated that these regions have differing patterns of cortical connectivity and distinctive neuronal responses. Brain-imaging techniques and lesion studies have begun to probe the functions of homologous regions in humans.     

The effect of cell synchronization on the efficiency of stable gene transfer by electroporation

We synchronized thymidine kinase deficient mouse Ltk-cells by two different methods, hydroxyurea double-block treatment or aphidicolin single-block treatment and transformed them with the cloned herpes simplex virus thymidine kinase gene at various time intervals by the electroporation technique. Marked enhancement of stable transformation efficiency was observed at the time corresponding to the peak of G2/M phase. These results suggest that the G2/M phase is the most efficient period for stable gene transfer by electroporation.     

Membrane binding events in the initiation and propagation phases of tissue factor-initiated zymogen activation under flow

This study investigates the dynamics of zymogen activation when both extrinsic tenase and prothrombinase are assembled on an appropriate membrane. Although the activation of prothrombin by surface-localized prothrombinase is clearly mediated by flow-induced dilutional effects, we find that when factor X is activated in isolation by surface-localized extrinsic tenase, it exhibits characteristics of diffusion-mediated activation in which diffusion of substrate to the catalytically active region is rate-limiting. When prothrombin and factor X are activated coincident with each other, competition for available membrane binding sites masks the diffusion-limiting effects of factor X activation. To verify the role of membrane binding in the activation of factor X by extrinsic tenase under flow conditions, we demonstrate that bovine lactadherin competes for both factor X and Xa binding sites, limiting factor X activation and forcing the release of bound factor Xa from the membrane at a venous shear rate (100 s(-1)). Finally, we present steady-state models of prothrombin and factor X activation under flow showing that zymogen and enzyme membrane binding events further regulate the coagulation process in an open system representative of the vasculature geometry.     

Development of chemically stable solid phases for the target isolation with reduced nonspecific binding proteins

Poly(methacrylate) matrices for affinity resins were designed and synthesized based on our previous results that nonspecific protein absorption on affinity resins strongly depended on their hydrophobic property. The novel affinity resins bearing FK506 (6a, 6b) captured specific binding protein, FKBP12, with a small amount of nonspecific binding proteins. The amount of nonspecific binding proteins on 6a-6b was much reduced compared to that on commercially available poly(methacrylate) resins, Toyopearl (8), and was almost the same as that on one of the most popular resins, Affigel (9). Interestingly, 6a and 6b could isolate FKBP52 as a specific binding protein as well, although 8 and 9 could not.     

Independent regulation of initiation and maintenance phases of Hoxa3 expression in the vertebrate hindbrain involve auto- and cross-regulatory mechanisms

During development of the vertebrate hindbrain, Hox genes play multiple roles in the segmental processes that regulate anteroposterior (AP) patterning. Paralogous Hox genes, such as Hoxa3, Hoxb3 and Hoxd3, generally have very similar patterns of expression, and gene targeting experiments have shown that members of paralogy group 3 can functionally compensate for each other. Hence, distinct functions for individual members of this family may primarily depend upon differences in their expression domains. The earliest domains of expression of the Hoxa3 and Hoxb3 genes in hindbrain rhombomeric (r) segments are transiently regulated by kreisler, a conserved Maf b-Zip protein, but the mechanisms that maintain expression in later stages are unknown. In this study, we have compared the segmental expression and regulation of Hoxa3 and Hoxb3 in mouse and chick embryos to investigate how they are controlled after initial activation. We found that the patterns of Hoxa3 and Hoxb3 expression in r5 and r6 in later stages during mouse and chick hindbrain development were differentially regulated. Hoxa3 expression was maintained in r5 and r6, while Hoxb3 was downregulated. Regulatory comparisons of cis-elements from the chick and mouse Hoxa3 locus in both transgenic mouse and chick embryos have identified a conserved enhancer that mediates the late phase of Hoxa3 expression through a conserved auto/cross-regulatory loop. This block of similarity is also present in the human and horn shark loci, and contains two bipartite Hox/Pbx-binding sites that are necessary for its in vivo activity in the hindbrain. These HOX/PBC sites are positioned near a conserved kreisler-binding site (KrA) that is involved in activating early expression in r5 and r6, but their activity is independent of kreisler. This work demonstrates that separate elements are involved in initiating and maintaining Hoxa3 expression during hindbrain segmentation, and that it is regulated in a manner different from Hoxb3 in later stages. Together, these findings add further strength to the emerging importance of positive auto- and cross-regulatory interactions between Hox genes as a general mechanism for maintaining their correct spatial patterns in the vertebrate nervous system.     

第一和第二语言Stroop任务中EEG同步化分析

采用基于多元自回归的瞬时EEG相干方法研究了十位汉英双语者执行Stroop任务时脑神经电活动及其功能皮层区的协同作用。结果显示：在β1(13-18Hz)频段,无论是汉语(第一语言,L1)还是英语(第二语言,L2)呈现的刺激,不一致条件的EEG相干值明显大于一致条件的EEG相干值,表明β1频段对刺激类型敏感;与L2相比,L1的Stroop任务中,额一顶区的相干值显著增强。EEG相干值反映了不同脑皮层间的相互作用强度。因此研究结果表明：判断和处理冲突信息(如Stroop的不一致条件)时脑功能皮层区之间的协同作用增强;相对于第二语言,第一语言处理过程中额一顶区之间的通信协作增加。     

Sensory integration: hierarchy and synchronization

This is the first in the series of mini-reviews devoted to the basic problems and most important effects of attention in terms of neuronal modeling. We believe that the absence of the unified view on wealth of new date on attention is the main obstacle for further understanding of higher nervous activity. The present work deals with the main ground problem of reconciling two competing architectures designed to integrate the sensory information in the brain. The other mini-reviews will be concerned with the remaining five or six problems of attention, all of them to be ultimately resolved uniformly in the framework of small modification of dominant model of attention and memory.     

Analysis of elicited EEG synchronization and desynchronization in emotional activation: temporal and topographic characteristics

Event-related synchronization (ERS) and desynchronization (ERD) in delta, theta1, theta2, alpha1, alpha2, beta1, beta2, beta3, and gamma were measured in 20 healthy right-handed subjects in response to IAPS stimuli with low, moderate, and high arousal reactions. The 62-channel EEG was simultaneously recorded while subjects viewed sequentially presented pictures and subjectively rated them after each presentation. The results show that emotionally loaded stimuli induced higher ERS in the delta, theta1, theta2, beta1, beta3, and gamma bands along with combined ERD and ERS effects in alpha2 band. As to hemispheric asymmetries, the effects of emotional arousal were restricted not only to right parietal (theta1 and theta2 ERS, alpha2 ERD) but also to left frontal (theta2 ERS) regions. In terms of affective chronometry, lower theta was the first to catch the affective salience of incoming stimuli (time window 0-600 ms after the stimulus input). For theta2, alpha2, and gamma bands this process was delayed to 600-1000 ms.