Imprint Behavior Research Articles

Single Vacancies and Vacancy Pairs in Tetragonal BaTiO3: A First Principles Study

The formation energies of single vacancies and vacancy pairs in the tetragonal BaTiO3 were studied using first principles computational method. The results show that under reduction conductions, oxygen vacancies have the lowest formation energy among single vacancies. For vacancy pairs, the formation energies of the Ba-O pair are lower than that of Ti-O under most thermodynamical conditions. Calculation of the polarization for system containing Ba-O vacancy pairs shows that depending on the direction of the electric dipole of the pair, the polarization is either enhanced or decreased, which may be related to the imprint behavior of ferroelectric materials.

Effect of electrode configurations on the process-induced imprint behavior of epitaxial Pb(Zr0.52Ti0.48)O3 capacitors

By using La0.7Sr0.3MnO3 (L) and SrRuO3 (S) electrodes, epitaxial Pb(Zr0.52Ti0.48)O3 (PZT) capacitors with different electrode configurations, i.e., L/PZT/L (from top to bottom) (a), S/PZT/S (b), S/PZT/L (c), and L/PZT/S (d), have been fabricated and the process-induced imprint was investigated. All as-grown capacitors are nearly imprint-free; however, after being annealed at 10−5 Torr of O2 the capacitors a (b) show a large negative (positive) imprinted polarization (P) state at zero electric-field (E), the capacitors c give strongly pinched P-E hysteresis loops, and the capacitors d are highly resistant to imprint failure. We show evidence that the internal fields could be attributed to the various oxygen-loss-related strain gradients at PZT top and bottom interfaces, induced during the annealing.

Effects of prenatal exposure to antithyroid drugs on imprinting behavior in chicks

Thyroid hormones play important roles in vertebrate brain development. However, there is little understanding of the direct effects of fetal thyroid dysfunction, i.e., not acquired through the mother, on learning ability. In the present study, we use a chick embryo as a fetal model to investigate the effects of prenatal exposure to antithyroid drugs on imprinting behavior in hatched chicks. Methimazole (MMI) at 20 µmol/egg or 5 µmol/egg of propylthiouracil (PTU) was administered to eggs on day 14 while the control was given only a vehicle. An imprinting test was conducted after the chicks hatched. Day-old chicks were exposed to a rotating training object for 150 min. The next day, the trained chicks were exposed to the training object and a novel object. The imprinting preference was represented as a preference score (PS) calculated as the rate of following the training object to following the training and novel objects. In the MMI-treated chicks, the PS was 0.68 ± 0.06 (range, 0.38–0.88), which was significantly lower than that in the control chicks (0.86 ± 0.04, p < 0.01). In the PTU-treated chicks, the PS was 0.69 ± 0.04 (range, 0.52–0.89), which was also significantly lower than that in the control (0.88 ± 0.02, p < 0.001). The present findings suggested that fetal thyroid dysfunction inhibited brain development, leading to impaired learning and memory. Our chick model can be considered useful for investigating the direct effects of prenatal exposure to antithyroid drugs or substances in the environment on learning ability after birth.

Demonstration of a Neural Circuit Critical for Imprinting Behavior in Chicks

Imprinting behavior in birds is elicited by visual and/or auditory cues. It has been demonstrated previously that visual cues are recognized and processed in the visual Wulst (VW), and imprinting memory is stored in the intermediate medial mesopallium (IMM) of the telencephalon. Alteration of neural responses in these two regions according to imprinting has been reported, yet direct evidence of the neural circuit linking these two regions is lacking. Thus, it remains unclear how memory is formed and expressed in this circuit. Here, we present anatomical as well as physiological evidence of the neural circuit connecting the VW and IMM and show that imprinting training during the critical period strengthens and refines this circuit. A functional connection established by imprint training resulted in an imprinting behavior. After the closure of the critical period, training could not activate this circuit nor induce the imprinting behavior. Glutamatergic neurons in the ventroposterior region of the VW, the core region of the hyperpallium densocellulare (HDCo), sent their axons to the periventricular part of the HD, just dorsal and afferent to the IMM. We found that the HDCo is important in imprinting behavior. The refinement and/or enhancement of this neural circuit are attributed to increased activity of HDCo cells, and the activity depended on NR2B-containing NMDA receptors. These findings show a neural connection in the telencephalon in Aves and demonstrate that NR2B function is indispensable for the plasticity of HDCo cells, which are key mediators of imprinting.

Neurobehavioral teratogenicity of perfluorinated alkyls in an avian model

Perfluorinated alkyls are widely-used agents that accumulate in ecosystems and organisms because of their slow rate of degradation. There is increasing concern that these agents may be developmental neurotoxicants and the present study was designed to develop an avian model for the neurobehavioral teratogenicity of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). Fertilized chicken eggs were injected with 5 or 10mg/kg of either compound on incubation day 0. On the day of hatching, imprinting behavior was impaired by both compounds. We then explored underlying mechanisms involving the targeting of protein kinase C (PKC) isoforms (α, β, γ) in the intermedial part of the hyperstriatum ventrale, the region most closely associated with imprinting. With PFOA exposure, cytosolic PKC concentrations were significantly elevated for all three isoforms; despite the overall increase in PKC expression, membrane-associated PKC was unaffected, indicating a defect in PKC translocation. In contrast, PFOS exposure evoked a significant decrease in cytosolic PKC, primarily for the β and γ isoforms, but again without a corresponding change in membrane-associated enzyme; this likely partial, compensatory increases in translocation to offset the net PKC deficiency. Our studies indicate that perfluorinated alkyls are indeed developmental neurotoxicants that affect posthatch cognitive performance but that the underlying synaptic mechanisms may differ substantially among the various members of this class of compounds, setting the stage for disparate outcomes later in life.

Mechanical stress induced voltage shift in polycrystalline Bi3.25La0.75Ti3O12 thin films

Imprint behavior of polycrystalline Bi3.25La0.75Ti3O12 thin films under stress was studied. The voltage shift along the positive voltage axis can be depressed by tensile stress while increased by compressive stress. With the measured voltage increasing, the voltage shift referred above increases and the increase trend gets enhanced under both compressive and tensile stress compared with that at zero stress. The asymmetric distribution of the trapped charged in films, which is caused by the increase of the in-plane polarization component for the domain reorientation induced by stress or for the voltage-assisted domain walls depinning, was considered the contribution to the voltage shift.

Genomic imprinting and communicative behaviour: Prader-Willi and Angelman syndrome

The kinship theory of genomic imprinting predicts that imprinted genes affect mother-child and child-child interactions. According to this theory paternally expressed genes will promote behaviours that increase costs of maternal investments and enable children to compete with siblings. Maternally expressed genes will promote behaviours that reduce the mother’s costs of child-rearing and enable children to engage in collaborative actions. Prader-Willi syndrome and Angelman syndrome are caused by the absence of expression of imprinted genes in 15q11-q13. Children with Prader-Willi syndrome lack the expression of paternally expressed genes; children with Angelman syndrome lack maternally expressed genes. The current paper discusses the role of imprinted genes in the development of communicative behaviours during the transition from breastfeeding to (consuming) solid food. Its focus is the possible role of imprinted genes in the development of empathy out of (reactive) crying, and in the development of behaviours necessary for joint action. Observed behavioural differences between children with Angelman and Prader-Willi syndrome, and data from mouse models on the effects of imprinted genes on brain development, are used to explore possible effects of imprinted genes. (Netherlands Journal of Psychology, 65, 78-88).

Neurobehavioral teratogenicity of sarin in an avian model

Nerve gas organophosphates like sarin are likely to be used in urban terrorism, leading to widespread exposures of pregnant women and young children. Here, we established a model for sarin neurobehavioral teratogenicity in the developing chick so as to explore the consequences of apparently subtoxic sarin exposure and the mechanisms underlying synaptic and behavioral deficits. Chicken eggs were injected with sarin (2, 6 and 12 μg/kg) on incubation days 2 and 6, treatments that did not decrease hatching and did not evoke dysmorphology. After hatching the chicks were tested for filial imprinting and neurochemical markers known to be critical for imprinting. Imprinting was reduced at 2 and 6 μg/kg but not at the highest dose. Acetylcholinesterase and choline acetyltransferase were unaffected but sarin reduced the concentration of the high-affinity choline transporter, the rate-limiting factor in acetylcholine utilization. The concentration of PKC isoforms was assessed in the imprinting-related intermediate part of the medial hyperstriatum ventrale, the region most closely associated with cholinergic function in imprinting behavior. Sarin reduced the concentration of all isoforms (α, β, γ) with a similar, biphasic dose–response curve to that seen for behavioral performance, a relationship noted in previous work with organophosphate pesticides. Our results indicate that otherwise subtoxic exposures to sarin produce neurodevelopmental deficits; since we utilized a chick model, which is devoid of maternal confounds that are present in mammalian development, the adverse effects of sarin are mediated directly in the developing organism.

Electrical investigations on metal/ferroelectric/insulator/semiconductor structures using poly[vinylidene fluoride trifluoroethylene] as ferroelectric layer for organic nonvolatile memory applications

Poly[vinylidene fluoride trifluoroethylene] (P[VDF/TrFE]) is a ferroelectric polymer and a candidate for the application in a ferroelectric field effect transistor, which is considered as a nonvolatile and nondestructive readout memory cell. In this contribution the authors focus on metal/ferroelectric/insulator/semiconductor capacitor structures with P[VDF/TrFE] as ferroelectric layer. Measuring the capacitance of Al/P[VDF/TrFE]/SiO2/Si stacks in dependence of the applied bias and analyzing the oxide capacitance in dependence of the thickness of the ferroelectric layer, they observe a formation of an interfacial nonferroelectric layer. This layer is responsible for reduced values of polarization profound for thinner P[VDF/TrFE] layers in this system. Capacitance-time measurements at such stacks show the possibility to distinguish between a higher and a lower capacitance state for more than 5 days. Long-time measurements revealed imprint and fatigue-like behavior.

IMPRINT BEHAVIOR OF FERROELECTRIC Pb(ZrTi)O3 THIN-FILM CAPACITORS IN THE EARLY STAGE

ABSTRACT Imprint behavior of Pb(Zr,Ti)O3 (PZT) thin-film capacitors in the early stage was carefully measured. The PZT films were formed on Pt/Ti/SiO2/Si substrates by chemical solution deposition (CSD) with sintering at 700°C, and a post-annealing was carried out at the same temperature after the deposition of top Pt electrodes by rf-magnetron sputtering. The imprint progresses of the PZT thin-film capacitors could be fitted by three equations with the same form, V shift = V 0 ln (1 + t/τ), but three diferent sets of parameters; V 0 and τ. This indicates that the conduction mechanisms of space charges which caused imprint changed by three steps with time progress. The first mechanism had less temperature dependence while the second one had remarkable temperature dependence. Whether the third one had temperature dependence or not was not clear because of data points were too few, it impacted a longtime imprint. From these results, we speculated that the imprint progresses were controlled by charge injection from electrodes due to first Fowler-Nordheim and seconde Schottky-emission in interfacial layers, and finally Poole-Frenkel conduction in film bodies.

Molecular imprinting and adsorption of metallothionein on nanocrystalline titania membranes

Metallothionein (MT) imprinted TiO 2 membrane was synthesized via surface sol–gel process, using MT as template and TiO 2 sol as imprinted matrix. Appropriate template cavities in the TiO 2 sol–gel membrane were formed after the template molecules were removed on treatment with 1% NaOH solution. In situ technique of quartz crystal microbalance (QCM) was employed to study the molecular imprinting behavior of MT on nanocrystalline titania membranes. The imprinted membrane showed selectivity recognition for MT as compared to the other proteins. The amount of adsorption increased with the increasing of MT concentration both on imprinted membrane and non-imprinted membrane. The adsorption amount increased with the increasing of pH on imprinted membrane.

Impact of glass temperature for thermal nanoimprint

To address the importance of the parameter glass transition temperature Tg for the choice of an adequate process temperature in a thermal nanoimprint process, three polymers with different values of Tg were investigated with respect to their imprint behaviors (poly)vinyl-chloride, (poly)styrene, and (poly)methyl-methacrylate. In order to evaluate the imprint results obtained at different temperatures, the volume of the polymer squeezed into the cavities was observed, and the temperature margins for the appearance of typical pattern size dependent failure types were derived. It turned out that despite the comparable molecular weight of these materials, the imprint temperature has to be chosen at different levels above Tg. Thus, Tg is not sufficient to characterize imprint polymers, and, in addition to the molecular weight, the viscosity at a definite temperature should be known. Tg alone can only indicate a lower limit for the process temperature.

The Effect of Metal-Film Thickness on Pattern Formation by Using Direct Imprint

This paper presents the use of the three-dimensional (3D) molecular dynamics (MD) simulation to demonstrate the direct imprint behavior between the metallic film and mold. The simulation considers the interaction of the mold and the defect-free metallic film during direct imprint process. The mold and the metallic film are made of nickel and aluminum, respectively, and are arranged in face-centered cubic (fcc) single crystal structures. Different imprint simulation conditions are implemented by changing the thickness of metal film; the formation mechanism, the hydrostatic phenomenon and the stress distribution of the metallic film are investigated. The imprint force applied to the mold, plastic atom ratio, and the formation ratios are calculated during direct imprint process. The relationship between the film thickness and the substrate effect are also investigated.

Activation of cholecystokinin neurons in the dorsal pallium of the telencephalon is indispensable for the acquisition of chick imprinting behavior

Chick imprinting behavior is a good model for the study of learning and memory. Imprinting object is recognized and processed in the visual wulst, and the memory is stored in the intermediate medial mesopallium in the dorsal pallium of the telencephalon. We identified chicken cholecystokinin (CCK)-expressing cells localized in these area. The number of CCK mRNA-positive cells increased in chicks underwent imprinting training, and these cells expressed nuclear Fos immunoreactivity at high frequency in these regions. Most of these CCK-positive cells were glutamatergic and negative for parvalbumin immunoreactivity. Semi-quantitative PCR analysis revealed that the CCK mRNA levels were significantly increased in the trained chicks compared with untrained chicks. In contrast, the increase in CCK- and c-Fos-double-positive cells associated with the training was not observed after closure of the critical period. These results indicate that CCK cells in the dorsal pallium are activated acutely by visual training that can elicit imprinting. In addition, the CCK receptor antagonist significantly suppressed the acquisition of memory. These results suggest that the activation of CCK cells in the visual wulst as well as in the intermediate medial mesopallium by visual stimuli is indispensable for the acquisition of visual imprinting.

Helen Crouse (1914–2006): Imprinting and Chromosome Behavior

HELEN Virginia Crouse died May 25, 2006, at age 91 in her home in Hayesville, North Carolina. She was a cytogeneticist par excellence who in the course of her studies coined the term “imprinting.” She also used the expression “controlling element,” which was employed in a different context by Barbara McClintock, her Ph.D. advisor. Helen Crouse was born September 12, 1914, to Charles C. and Margaret Ross Crouse. Her father was a train and trolley conductor; her mother was educated through the third grade. Helen grew up in Owings Mills, Maryland, together with her older sister, Marie Garrish. In 1935 she obtained her B.A. degree from Goucher College where she was elected to Phi Beta Kappa and her M.A. degree from Smith College a year later. While working on her Master's degree, Helen had obtained a fellowship for a brief stay at Cornell where she met Marcus Rhoades, who was raising corn there. After receiving her M.A., for the next 3 years she worked in the Department of Embryology at the Carnegie Institution of Washington in the laboratory of Charles W. Metz whom she had first met while a senior at Goucher College. In the Metz lab, Helen earned the grand sum of $1200/year! Metz was on the faculty at Johns Hopkins University, engaged in research on the lower dipteran fly, Sciara coprophila. In Metz's lab, Helen was introduced to this model organism and began her studies (Crouse and Smith-Stocking 1938; Crouse 1939; Metz and Crouse 1939), continuing to unravel the secrets of Sciara for the rest of her research career.

Imprinting modulates processing of visual information in the visual wulst of chicks

BackgroundImprinting behavior is one form of learning and memory in precocial birds. With the aim of elucidating of the neural basis for visual imprinting, we focused on visual information processing.ResultsA lesion in the visual wulst, which is similar functionally to the mammalian visual cortex, caused anterograde amnesia in visual imprinting behavior. Since the color of an object was one of the important cues for imprinting, we investigated color information processing in the visual wulst. Intrinsic optical signals from the visual wulst were detected in the early posthatch period and the peak regions of responses to red, green, and blue were spatially organized from the caudal to the nasal regions in dark-reared chicks. This spatial representation of color recognition showed plastic changes, and the response pattern along the antero-posterior axis of the visual wulst altered according to the color the chick was imprinted to.ConclusionThese results indicate that the thalamofugal pathway is critical for learning the imprinting stimulus and that the visual wulst shows learning-related plasticity and may relay processed visual information to indicate the color of the imprint stimulus to the memory storage region, e.g., the intermediate medial mesopallium.

Effect of Penetrating Irradiation on Polarization Reversal in PZT Thin Films

Spatially non-uniform imprint behavior induced by X-ray synchrotron, electron, and neutron irradiation has been investigated in Pb(Zr,Ti)O3 thin films. The obtained effects have been explained as a result of acceleration of the bulk screening process induced by irradiation. It has been shown that the spatial distribution of the internal bias field is determined by the domain pattern existing during irradiation. The microstructural changes in the structural characteristics during fatigue cycling have been revealed by high resolution synchrotron X-ray diffraction experiments. Their correlation with the evolution of the switching characteristics has been revealed and discussed.

Influence of different deposition conditions of top and bottom electrode on the reliability of Sr0.8Bi2.2Ta2O9 ferroelectric capacitors

In this study, the reliability (fatigue, imprint, and retention) of Pt/SBT/Pt capacitors was investigated. For non-integrated test capacitors, using a different process for top and bottom electrode formation, fatigue degradation is larger than for integrated capacitors using symmetric top and bottom electrode deposition process. Also, for the non-integrated capacitors, imprint behavior and retention loss were observed to depend on the voltage polarity. From hysteresis as well as leakage characteristics, these effects were attributed to the presence of a built-in field favoring the polarization of SBT from the bottom to the top electrode in non-integrated capacitors. The built-in field was attributed to defect generation during the top electrode sputtering at room temperature. For the integrated capacitors, whereby the top electrode is deposited using the same high temperature process (>150°C) as the bottom electrode, neither imprint degradation nor retention loss was observed under the applied conditions, showing excellent reliability of integrated SBT capacitors.

Simulation of flexoelectricity effect on imprint behavior of ferroelectric thin films

The impact of flexoelectricity on the imprint behavior in ferroelectric thin films has been investigated within the framework of Landau–Khalatnikov theory, by incorporating the coupling effect between the stress gradient and polarization. It is found that the imprint phenomenon can be in part induced by flexoelectricity. In the presence of flexoelectric coupling, the compressive stress shifts the hysteresis loop to the negative electric field axis, but the tensile stress shifts it to the opposite direction, which is in good agreement with experimental result. Besides, the characteristic length of stress distribution has a significant influence on the upper part of hysteresis loop. It highlights the pressing need to avoid the stress gradient in order to prevent degradation of device performance in ferroelectric thin films.

Anatomy of the Avian Hippocampal Formation

Increasing knowledge of the avian hippocampal formation (hippocampus and parahippocampal area) suggests that it plays a role in a variety of behaviors, such as homing, cache retrieving, visual discrimination, imprinting, and sexual behavior. Knowledge of the neural circuits in the hippocampal formation and its related areas or nuclei is important for the understanding of these functions. This review therefore describes the functional neuroanatomy of the avian hippocampal formations, i.e., its subdivisions, cytoarchitecture, and afferent and efferent connections. Evidence obtained by a combination of Nissl staining and tract-tracing shows that the pigeon hippocampal formation can be divided into seven subdivisions: dorsolateral (DL), dorsomedial (DM), triangular (Tr), V-shaped (V), magnocellular (Ma), parvocellular, and cell-poor regions. DL and DM can be further divided into dorsal and ventral, and lateral and medial portions, respectively. In the hippocampal formation, reciprocal connections are found between DL-DM, DL-Tr, DL-Ma, DM-Ma, DM-V, and Tr-V. Neurons in the V-shaped layer appear to be intrinsic neurons. Sensory inputs from higher order visual and olfactory stations enter DL and DM, are modified or integrated by intrinsic hippocampal circuitry, and the outputs are sent, via DL and DM, to various telencephalic nuclei, septum, and hypothalamus. The neural pathways indicate that the hippocampal formation plays a central role in the limbic system, which also includes the dorsolateral corticoid area, nucleus taeniae of the amygdala, posterior pallial amygdala, septum, medial part of the anterior dorsolateral nucleus of the thalamus, and the lateral mammillary nucleus. Connectional and comparative studies, including the use of kainic acid excitotoxicity, suggest that the V-shaped layer is comparable to the dentate gyrus of the mammalian hippocampal formation and DM to Ammon's horn and subiculum.