Delayed perceptual awareness in rapid perceptual decisions

The flourishing of studies on the neural correlates of decision-making calls for an appraisal of the relation between perceptual decisions and conscious perception. By exploiting the long integration time of noisy motion stimuli, and by forcing human observers to make difficult speeded decisions--sometimes a blind guess--about stimulus direction, we traced the temporal buildup of motion discrimination capability and perceptual awareness, as assessed trial by trial through direct rating. We found that both increased gradually with motion coherence and viewing time, but discrimination was systematically leading awareness, reaching a plateau much earlier. Sensitivity and criterion changes contributed jointly to the slow buildup of perceptual awareness. It made no difference whether motion discrimination was accomplished by saccades or verbal responses. These findings suggest that perceptual awareness emerges on the top of a developing or even mature perceptual decision. We argue that the middle temporal (MT) cortical region does not confer us the full phenomenic depth of motion perception, although it may represent a precursor stage in building our subjective sense of visual motion.     

Paradoxical inward rib cage motion during rapid eye movement sleep in infants and young children

In neonates, rib cage motion on inspiration during rapid eye movement sleep is almost exclusively paradoxical. We wondered whether or not duration of paradoxical inward rib cage motion on inspiration during rapid eye movement sleep decreases in infancy and early childhood. Thirteen healthy infants from 7 to 31 months of age were tested during natural afternoon naps. Electroencephalogram, electrooculogram and electromyogram were all recorded. Airflow was measured by nasal and buccal thermistors, abdominal and rib cage anteroposterior diameters by magnetometers. Transcutaneous partial pressure of O2 was monitored. Diaphragmatic electromyographic activity was recorded using surface electrodes. The average total sleep time was 138 min ranging from 107 to 186 and rapid eye movement sleep time amounted to 15% of total sleep time ranging from 6 to 25. During rapid eye movement sleep, the total duration of paradoxical inward rib cage motion was measured and expressed as a percentage of rapid eye movement sleep time. We found that duration of paradoxical inward rib cage motion during rapid eye movement sleep decreased significantly with age (r = -0.66, P less than 0.02) which may be explained by the changes in chest wall compliance and geometry of the rib cage occurring with growth. We observed no decrease in transcutaneous partial pressure in O2 during paradoxical inward rib cage motion during rapid eye movement sleep in infants in contrast to that reported in neonates.     

A novel acoustic evaluation system of scratching in mouse dermatitis: rapid and specific detection of invisibly rapid scratch in an atopic dermatitis model mouse

Scratching is an essential and a skin specific behavior induced by itching, which is a common symptom of atopic dermatitis (AD) and other types of dermatitis. Itching sensation and scratching are closely associated and thus scratching times are currently used for evaluating itching in animal models. However, objective measuring systems of scratching to assess the grade of dermatitis and the effectiveness of anti-pruritic drugs in animal dermatitis models are lacking. To investigate a quantitative evaluation system for itching, we have developed a novel acoustic scratching counting system and compared its accuracy with time-consuming slow-motion video recording system. We have also objectively evaluated the efficacy of an antihistamine using this novel system. Scratching behavior of an AD model mouse (K14 driven IL-18 transgenic mouse) was recorded visually and acoustically. Specific scratching sound produced by mice was recorded and counted using a software we have developed, and the results obtained using our acoustic system were not statistically different from data obtained using slow motion video system. Surprisingly, mice scratched more than 10 times/second, which was invisibly rapid motion and revealed inaccuracy of conventional hand counting system. Results were identical to that of measured by 10 times time costing slow-motion video analysis. The antihistamine is clearly effective for suppression of scratching as demonstrated using this objective and accurate method. This novel motion analysis system will open a window for physiological and pathological analysis for animal models and development of anti-pruritic drugs.     

Hypometabolism in torpid goldsinny wrasse subjected to rapid reductions in seawater temperature

Goldsinny Ctenolabrus rupestris were subjected to rapid, environmentally realistic, reductions in temperature at 2° C increments from 10 to 4° C over a 3-day period in full-strength sea water. In separate experiments, oxygen uptake measurements and ultrasound recordings of heart rate and opercular motion were carried out at regular intervals over the same temperature regime. Mean oxygen uptake rates fell from 0.042 to 0.028 ml O₂ g⁻¹ h⁻¹ between 10 and 6° C respectively (Q₁₀=2.71). Between 6 and 4° C mean rates decreased from 0.028 to 0.008 ml O₂ g⁻¹ h⁻¹ (Q₁₀=542). Mean opercular motion and heart beat rates decreased from 49.5 and 60.3 beats min⁻¹ respectively at 10° C to 18.7 and 18.0 beats min⁻¹ respectively at 4° C. Most goldsinny subjected to 4° C were observed in a torpid state and would not react to external stimulation. Opercular motion was erratic at 4° C and would at times cease altogether for periods up to 1.3 min duration. Heart movement was diffcult to detect at 4° C and may also have ceased for prolonged periods. Q₁₀ values for opercular motion and heart beat rates recorded between 6 and 4° C were 6.39 and 24.52 respectively compared with values of 2.42 and 2.93 respectively recorded between 10 and 8° C. Such large depressions in metabolism appear not to have been reported previously for a marine fish species. No goldsinny mortalities were recorded at any temperature. The possibility that hypometabolic torpor is an adaptive strategy for goldsinny survival at low environmental temperatures is discussed.     

Steady-state polarization from cylindrically symmetric fluorophores undergoing rapid restricted motion.

Steady-state fluorescence polarization measurements provide a relatively simple method for investigating the orientation of molecular components in ordered biological systems. However, the observed fluorescence polarization ratios also depend on any mobility of the fluorophores on the time scale of the fluorescence lifetime. Such mobility commonly arises from incomplete immobilization of a fluorescent probe on the macromolecule of interest. A theoretical formalism is presented for the interpretation of steady-state fluorescence polarization ratios in the presence of such rapid fluorophore motion. It is assumed that the fluorophores move freely within a cone between absorption and emission of a photon. Only one new parameter is introduced to describe fluorophore motion, the semi-angle of the cone, and this can be measured in separate experiments on an isotropic system. The fluorophore orientations are assumed to have cylindrical symmetry, but the symmetry axis need not be in the same plane as the center axes of the absorption and emission cones. This geometry applies to muscle and other biological fibers.     

Jerk-cost modulations during the practice of rapid arm movements

We examined how hand-trajectory smoothness changed during the practice of a motor task where smoothness was quantified by jerk-cost. Four human subjects each moved his nondominant arm between an upper target and a lower target, while circumnavigating a barrier that extended outward from the vertical plane of the targets. The two targets and the barrier placed boundary constraints on hand trajectories, but the motion was not restrained in any other way. Arm movements were recorded on high-speed ciné film, and linear and angular kinematical data were obtained for all arm segments. In each of 100 practice trials, subjects attempted to minimize movement time. After the practice trials, subjects repeated the same motor task but at movement times corresponding to the slowest, mid-range and fastest motion that had occurred during practice. Thus, jerk-cost could be compared for movements of different speeds during practice and after practice. Because the movement task contained several changes in hand-path direction, the changes in the vector characteristics of the hand accelerations were expected to be important for explaining the modulations in jerk-cost with practice. Total jerk-cost, therefore, was calculated as well as the separate magnitudinal and directional jerk-cost components. During practice, total movement time decreased, hand paths became more parabolic in shape, and significant changes occurred in hand acceleration magnitude, direction, and timing. Total jerk-cost and the magnitudinal and directional jerk-cost components were significantly less when slowest hand movements were compared after practice versus during practice. The decrease in jerk-cost indicated an increased smoothness of the practiced movements.K. Schneider was supported by the German Research Association (Deutsche Forschungsgemeinschaft)     

Visual motion and rapid auditory processing are solid endophenotypes of developmental dyslexia

Although a genetic component is known to have an important role in the etiology of developmental dyslexia (DD), we are far from understanding the molecular etiopathogenetic pathways. Reduced measures of neurobiological functioning related to reading (dis)ability, i.e. endophenotypes (EPs), are promising targets for gene finding and the elucidation of the underlying mechanisms. In a sample of 100 nuclear families with DD (229 offspring) and 83 unrelated typical readers, we tested whether a set of well‐established, cognitive phenotypes related to DD [i.e. rapid auditory processing (RAP), rapid automatized naming (RAN), multisensory nonspatial attention and visual motion processing] fulfilled the criteria of the EP construct. Visual motion and RAP satisfied all testable criteria (i.e. they are heritable, associate with the disorder, co‐segregate with the disorder within a family and represent reproducible measures) and are therefore solid EPs of DD. Multisensory nonspatial attention satisfied three of four criteria (i.e. it associates with the disorder, co‐segregates with the disorder within a family and represents a reproducible measure) and is therefore a potential EP for DD. Rapid automatized naming is heritable but does not meet other criteria of the EP construct. We provide the first evidence of a methodologically and statistically sound approach for identifying EPs for DD to be exploited as a solid alternative basis to clinical phenotypes in neuroscience.     

Quantitative detection of rapid motions in spectrin by NMR

Previous high resolution proton NMR data on human erythrocyte spectrin molecules has indicated the existence of regions exhibiting rapid internal motions within the intact molecules [L. W.-M. Fung, H.-Z. Lu, R. P. Hjelm, jr, M. E. Johnson, FEBS Lett., 197, 234 (1986)]. We have extended the studies by developing quantitative NMR methods to determine the fraction of spectrin protons exhibiting rapid internal motions, in both the isolated molecule and within the spectrin-actin network. Using both one-pulse and spin echo pulse sequences, we find that the fraction of the protons in rapid motion is about 15% of the total protons in the spectrin molecule at 37 degrees C in phosphate buffer with 150 mM NaCl at pH 7.4. Quantitative information on these rapid motions will be important in understanding the structural, mechanical and functional properties of spectrin molecules, as well as in understanding filamentous protein structures in general.     

The initiation and control of rapid flight maneuvers in fruit flies

Fruit flies alter flight direction by generating rapid, stereotypedturns, called saccades. The successful implementation of thesequick turns requires a well-tuned orchestration of neural circuits,musculo-skeletal mechanics, and aerodynamic forces. The changesin wing motion required to accomplish a saccade are quite subtle,as dictated by the inertial dynamics of the fly's body. A flyfirst generates torque to begin accelerating in the intendeddirection, but then must quickly create counter-torque to decelerate.Several lines of evidence suggest that the initial turn is initiatedby visual expansion, whereas the subsequent counter-turn istriggered by the gyroscopic halteres. This integrated analysisindicates how the functional organization of neural circuitscontrolling behavior is rigidly constrained by the physicalinteraction between an animal and the external world.     

Model of chromosome motility in Drosophila embryos: adaptation of a general mechanism for rapid mitosis

During mitosis, ensembles of dynamic MTs and motors exert forces that coordinate chromosome segregation. Typically, chromosomes align at the metaphase spindle equator where they oscillate along the pole-pole axis before disjoining and moving poleward during anaphase A, but spindles in different cell types display differences in MT dynamicity, in the amplitude of chromosome oscillations and in rates of chromatid-to-pole motion. Drosophila embryonic mitotic spindles, for example, display remarkably dynamic MTs, barely detectable metaphase chromosome oscillations, and a rapid rate of "flux-pacman-dependent" anaphase chromatid-to-pole motility. Here we develop a force-balance model that describes Drosophila embryo chromosome motility in terms of a balance of forces acting on kinetochores and kMTs that is generated by multiple polymer ratchets and mitotic motors coupled to tension-dependent kMT dynamics. The model shows that i), multiple MTs displaying high dynamic instability can drive steady and rapid chromosome motion; ii), chromosome motility during metaphase and anaphase A can be described by a single mechanism; iii), high kinetochore dynein activity is deployed to dampen metaphase oscillations, to augment the basic flux-pacman mechanism, and to drive rapid anaphase A; iv), modulation of the MT rescue frequency by the kinetochore-associated kinesin-13 depolymerase promotes metaphase chromosome oscillations; and v), this basic mechanism can be adapted to a broad range of spindles.     

Adaptations for rapid and forceful contraction in wing muscles of the male golden-collared manakin: sex and species comparisons

The courtship display of the male golden-collared manakin (Manacus vitellinus) of Panamanian rainforests is noteworthy for several types of whip-crack-like sounds created by a rapid overhead flip of the wings. We have hypothesized that this courtship behavior. which is not performed by females, is associated with steroid-sensitive and sexually dimorphic neuromuscular systems. Presumably, muscles creating the motion of the wingsnap in males are specialized for greater force generation and speed of contraction. We tested this hypothesis by examining mass, fiber diameter, metabolic enzyme activity, and myosin isoform expression in several muscles of male and female manakins and in both sexes of a non-wingsnapping bird, the zebra finch (Taenopygia guttata). We have identified three wing muscles, the scapulohumeralis caudalis, the supracoracoideus, and the pectoralis major, that differ in one or more of these characteristics across sex and species, suggesting they are specialized for faster contraction and greater force production in male manakins. These muscles normally function to raise and lower the wings during flight. As this movement is the principal motion of the wingsnap, these adaptations presumably underlie the performance of the wingsnap display.     

Stabilization of non-productive conformations underpins rapid electron transfer to electron-transferring flavoprotein

Crystal structures of protein complexes with electron-transferring flavoprotein (ETF) have revealed a dual protein-protein interface with one region serving as anchor while the ETF FAD domain samples available space within the complex. We show that mutation of the conserved Glu-165beta in human ETF leads to drastically modulated rates of interprotein electron transfer with both medium chain acyl-CoA dehydrogenase and dimethylglycine dehydrogenase. The crystal structure of free E165betaA ETF is essentially identical to that of wild-type ETF, but the crystal structure of the E165betaA ETF.medium chain acyl-CoA dehydrogenase complex reveals clear electron density for the FAD domain in a position optimal for fast interprotein electron transfer. Based on our observations, we present a dynamic multistate model for conformational sampling that for the wild-type ETF. medium chain acyl-CoA dehydrogenase complex involves random motion between three distinct positions for the ETF FAD domain. ETF Glu-165beta plays a key role in stabilizing positions incompatible with fast interprotein electron transfer, thus ensuring high rates of complex dissociation.     

Sustained and rapid chromosome movements are critical for chromosome pairing and meiotic progression in budding yeast

Telomere-led chromosome movements are a conserved feature of meiosis I (MI) prophase. Several roles have been proposed for such chromosome motion, including promoting homolog pairing and removing inappropriate chromosomal interactions. Here, we provide evidence in budding yeast that rapid chromosome movements affect homolog pairing and recombination. We found that csm4Δ strains, which are defective for telomere-led chromosome movements, show defects in homolog pairing as measured in a "one-dot/two-dot tetR-GFP" assay; however, pairing in csm4Δ eventually reaches near wild-type (WT) levels. Charged-to-alanine scanning mutagenesis of CSM4 yielded one allele, csm4-3, that confers a csm4Δ-like delay in meiotic prophase but promotes high spore viability. The meiotic delay in csm4-3 strains is essential for spore viability because a null mutation (rad17Δ) in the Rad17 checkpoint protein suppresses the delay but confers a severe spore viability defect. csm4-3 mutants show a general defect in chromosome motion but an intermediate defect in chromosome pairing. Chromosome velocity analysis in live cells showed that while average chromosome velocity was strongly reduced in csm4-3, chromosomes in this mutant displayed occasional rapid movements. Lastly, we observed that spo11 mutants displaying lower levels of meiosis-induced double-strand breaks showed higher spore viability in the presence of the csm4-3 mutation compared to csm4Δ. On the basis of these observations, we propose that during meiotic prophase the presence of occasional fast moving chromosomes over an extended period of time is sufficient to promote WT levels of recombination and high spore viability; however, sustained and rapid chromosome movements are required to prevent a checkpoint response and promote efficient meiotic progression.     

An integrated dielectrophoretic quartz crystal microbalance (DEP-QCM) device for rapid biosensing applications

A factor limiting the detection time of biological particles using a quartz crystal microbalance (QCM) system is the kinetics of the particles arriving within the sensing region of the crystal surface. A device has been developed which, for the first time, combines ac electro-kinetic particle manipulation with simultaneous acoustic sensing on an electrode surface. We have termed this device a dielectrophoretic quartz crystal microbalance (DEP-QCM). Particles within the system are rapidly driven by electro-hydrodynamic and dielectrophoretic forces on to the crystal surface. Frequency shift analysis of mass-loaded DEP-QCM, induced by fluid motion, has shown significant improvements in rates of detection based on particle concentration, with steady-state responses established by a factor of five times faster than other quartz crystal microbalance surface loading techniques described in the literature. Comparisons of the static fluid case for QCM devices revealed that particles with a concentration of less than 10(8) nano-spheres/ml could not be detected within a 1h time period when allowed to sediment.     

The role of intersegmental dynamics during rapid limb oscillations

The interactive dynamic effects of muscular, inertial and gravitational moments on rapid, multi-segmented limb oscillations were studied. Using three-segment, rigid-body equations of motion, hip, knee and ankle intersegmental dynamics were calculated for the steady-state cycles of the paw-shake response in adult spinal cats. Hindlimb trajectories were filmed to obtain segmental kinematics, and myopotentials of flexors and extensors at each of the three joints were recorded synchronously with the ciné film. The segmental oscillations that emerged during the paw-shake response were a consequence of an interplay between active and passive musculotendinous forces, inertial forces, and gravity. During steady-state oscillations, the amplitudes of joint excursions, peak angular velocities, and peak angular accelerations increased monotonically and significantly in magnitude from the proximal joint (hip) to the most distal joint (ankle). In contrast to these kinematic relationships, the maximal values of net moments at the hip and knee were equal in magnitude, but of significantly lower magnitude than the large net moment at the ankle joint. At both the ankle and the knee, the flexor and extensor muscle moments were equal, but at the hip the magnitude of the peak flexor muscle moment was significantly greater than the extensor muscle moment. Muscle moments at the hip not only acted to counterbalance accelerations of the more distal segments, but also acted to maintain the postural orientation of the hindlimb. Large muscle moments at the knee functioned to counterbalance the large inertial moments generated by the large angular accelerations of the paw. At the ankle, the muscle moments dominated the generation of the paw accelerations. At the ankle and the knee, muscle moments controlled limb dynamics by slowing and reversing joint motions, and the active muscle forces contributing to ankle and knee moments were derived from lengthening of active musculotendinous units. In contrast to the more distal joints, the active muscles crossing the hip predominantly shortened as a result of the interplay among inertial forces and gravitational moments. The muscle function and kinetic data explain key features of the complex interactions that occur between central control mechanisms and multi-segmented, oscillating limb segments during the paw-shake response.     

元宝枫生长旺季树干液流动态及影响因素

利用热扩散式边材液流探针和多种气象、土壤因子传感器组成的全自动数据采集系统和美国产Licor-6400光合测定系统,于夏秋季节对北京西山地区低山成林元宝枫单株边材液流动态和叶片蒸腾作用进行了系统观测。元宝枫树干边材液流变化受天气的影响,环境胁迫或环境的改善都能改变边材液流的波动特征。在正常情况下,边材液流的日变化呈单峰曲线:日出后树干液流迅速上升,峰值在中午前后出现,然后下降,在次日早晨前达到坡谷。最热月7月液流启动和进入坡谷的时间比其他各月早1~4 h。6月树干上位液流速率大于中位和下位,其他各月树干下位液流速率大于上位和中位,这种差距在7月达2~3倍。多元回归分析表明,在整个生长旺季,元宝枫边材液流变化深受气温、太阳辐射、空气相对湿度、土壤温度和风速等环境因子的影响,但在不同的观测时段和观测部位其影响的主导因子不完全相同,只有空气温度在任何情况下都是影响液流的主导因子;元宝枫边材液流的变异规律较好地说明了其耐旱的生态策略。     

Form and function of damselfish skulls: rapid and repeated evolution into a limited number of trophic niches

Background  

Damselfishes (Perciformes, Pomacentridae) are a major component of coral reef communities, and the functional diversity of their trophic anatomy is an important constituent of the ecological morphology of these systems. Using shape analyses, biomechanical modelling, and phylogenetically based comparative methods, we examined the anatomy of damselfish feeding among all genera and trophic groups. Coordinate based shape analyses of anatomical landmarks were used to describe patterns of morphological diversity and determine positions of functional groups in a skull morphospace. These landmarks define the lever and linkage structures of the damselfish feeding system, and biomechanical analyses of this data were performed using the software program JawsModel4 in order to calculate the simple mechanical advantage (MA) employed by different skull elements during feeding, and to compute kinematic transmission coefficients (KT) that describe the efficiency with which angular motion is transferred through the complex linkages of damselfish skulls.     

Uncoated endocytic vesicles require the unconventional myosin, Myo6, for rapid transport through actin barriers

After clathrin-mediated endocytosis, clathrin removal yields an uncoated vesicle population primed for fusion with the early endosome. Here we present the first characterization of uncoated vesicles and show that myo6, an unconventional myosin, functions to move these vesicles out of actin-rich regions found in epithelial cells. Time-lapse microscopy revealed that myo6-associated uncoated vesicles were motile and exhibited fusion and stretching events before endosome delivery, processes that were dependent on myo6 motor activity. In the absence of myo6 motor activity, uncoated vesicles remained trapped in the actin mesh, where they exhibited Brownian-like motion. Exit from the actin mesh occurred by a slow diffusion-based mechanism, delaying transferrin trafficking to the early endosome. Expression of a myo6 mutant that bound tightly to F-actin produced immobilized vesicles and blocked trafficking. Depolymerization of the actin cytoskeleton rescued this block and specifically accelerated transferrin delivery to the early endosome without affecting earlier steps in endocytosis. Therefore actin is a physical barrier impeding uncoated vesicle trafficking, and myo6 is recruited to move the vesicles through this barrier for fusion with the early endosome.     

A localized pattern photobleaching method for the concurrent analysis of rapid and slow diffusion processes.

A scanning pattern photobleaching method for the analysis of lateral transport is described and discussed. Fluorescence bleaching with a localized pattern allows for the concurrent analysis of motions over two very different characteristic distances: xi 0(-1), the repeat distance of the pattern, and W, the linear dimension of the illuminated region. The former motion is deduced from the decay of the modulation amplitude (of period xi 0(-1) of fluorescence scans with the attenuated pattern, the latter from the recovery of the average fluorescence intensity. Such analysis should prove useful for the study of samples with a wide range of diffusion coefficients, and for the separation of effects arising from lateral diffusion and association dynamics. Theoretical analyses are presented for three related problems: (a) the effect of pattern localization on the decay of the modulation amplitude, (b) the effect of the pattern modulation on the recovery of the average local fluorescence intensity, and (c) the effect of a limited diffusion space (with linear dimensions of only a few pattern periods) on the decay of the modulation amplitude.     

Consideration of dipole orientation angles yields accurate rate equations for energy transfer in the rapid diffusion limit.

Dipole-dipole energy transfer between suitable donor and acceptor chromophores is an important luminescence quenching mechanism and has been shown to be useful for distance determination at the molecular level. In the rapid diffusion limit, where the excited-state lifetime of the donor is long enough to allow the donor and acceptor to diffuse many times their average separation before deexcitation, it is usually assumed that the relative dipolar orientation is completely averaged due to rotational Brownian motion. Under this simplifying assumption, analytical expressions have been derived earlier for the energy transfer rate between donor and acceptor characterized by different geometries. Most such expressions, however, are only approximate because complete angular averaging is permitted only in a geometry that possesses spherical symmetry surrounding each chromophore. In this paper analytical expressions that correctly account for incomplete angle averaging due to steric hindrance are presented for several geometries. Each of the equations reveals a dependence of the energy transfer rate on chromophore orientation. It is shown that correctly accounting for this effect can lead to improvements in estimates of the distance of closest approach from measured quenching rates based on energy transfer experiments.