Direct Positive Feedback Research Articles

Driven by Social Comparisons: How Feedback about Coworkers’ Effort Influences Individual Productivity

Drawing on theoretical insights from research on social comparison processes, this article explores how managers can use performance feedback to sustain employees’ motivation and performance in organizations. Using a field experiment at a Japanese bank, we investigate the effects of valence (positive versus negative), type (direct versus indirect), and timing of feedback (one-shot versus persistent) on employee productivity. Our results show that direct negative feedback (e.g., an employee learns her performance falls in the bottom of her group) leads to improvements in employees’ performance, while direct positive feedback does not significantly impact performance. Furthermore, indirect negative feedback (i.e., the employee learns she is not in the bottom of her group) worsens productivity while indirect positive feedback (i.e., the employee learns she is not in the top of her group) does not affect it. Finally, both persistently positive and persistently negative feedback lead to improvements in employees’ performance. Together, our findings offer insight into the role of performance feedback in motivating productivity in repetitive tasks.

Positive Feedback Regulation between Phospholipase D and Wnt Signaling Promotes Wnt-Driven Anchorage-Independent Growth of Colorectal Cancer Cells

BackgroundAberrant activation of the canonical Wnt/β-catenin pathway occurs in almost all colorectal cancers and contributes to their growth, invasion and survival. Phopholipase D (PLD) has been implicated in progression of colorectal carcinoma However, an understanding of the targets and regulation of this important pathway remains incomplete and besides, relationship between Wnt signaling and PLD is not known.Methodology/Principal FindingsHere, we demonstrate that PLD isozymes, PLD1 and PLD2 are direct targets and positive feedback regulators of the Wnt/β-catenin signaling. Wnt3a and Wnt mimetics significantly enhanced the expression of PLDs at a transcriptional level in HCT116 colorectal cancer cells, whereas silencing of β-catenin gene expression or utilization of a dominant negative form of T cell factor-4 (TCF-4) inhibited expression of PLDs. Moreover, both PLD1 and PLD2 were highly induced in colon, liver and stomach tissues of mice after injection of LiCl, a Wnt mimetic. Wnt3a stimulated formation of the β-catenin/TCF complexes to two functional TCF-4-binding elements within the PLD2 promoter as assessed by chromatin immunoprecipitation assay. Suppressing PLD using gene silencing or selective inhibitor blocked the ability of β-catenin to transcriptionally activate PLD and other Wnt target genes by preventing formation of the β-catenin/TCF-4 complex, whereas tactics to elevate intracellular levels of phosphatidic acid, the product of PLD activity, enhanced these effects. Here we show that PLD is necessary for Wnt3a-driven invasion and anchorage-independent growth of colon cancer cells.Conclusion/SignificancePLD isozyme acts as a novel transcriptional target and positive feedback regulator of Wnt signaling, and then promotes Wnt-driven anchorage-independent growth of colorectal cancer cells. We propose that therapeutic interventions targeting PLD may confer a clinical benefit in Wnt/β-catenin-driven malignancies.

Indirect vegetation–soil moisture feedback with application to Holocene North Africa climate1

AbstractUsing a fully coupled climate–terrestrial ecosystem model, we demonstrate explicitly that an initial perturbation on vegetation induces not only a direct positive vegetation feedback, but also a significant indirect vegetation–soil moisture feedback. The indirect feedback is generated through either fractional cover change or soil moisture depletion. Both indirect feedback mechanisms are triggered by a vegetation perturbation, but involve subsequent effects of soil moisture and evaporation, indirectly. An increase in vegetation tends to reduce bare‐ground evaporation through either the area reduction in bare ground or the depletion of soil moisture; the reduced evaporation may then counter the initial plant transpiration, favoring a negative net vegetation feedback. Furthermore, grasses are more effective in inducing the indirect vegetation–soil feedbacks, because of their limited plant evapotranspiration and shallower roots that tend to change surface soil moisture, and, in turn, evaporation, effectively. In comparison, trees favor a direct positive vegetation feedback due to their strong plant transpiration on subsurface soil moisture as well as a lower albedo.

Systematic analysis of synchronized oscillatory neuronal networks reveals an enrichment for coupled direct and indirect feedback motifs

Synchronized bursting behavior is a remarkable phenomenon in neural dynamics. So, identification of the underlying functional structure is crucial to understand its regulatory mechanism at a system level. On the other hand, we noted that feedback loops (FBLs) are commonly used basic building blocks in engineering circuit design, especially for synchronization, and they have also been considered as important regulatory network motifs in systems biology. From these motivations, we have investigated the relationship between synchronized bursting behavior and feedback motifs in neural networks. Through extensive simulations of synthetic spike oscillation models, we found that a particular structure of FBLs, coupled direct and indirect positive feedback loops (PFLs), can induce robust synchronized bursting behaviors. To further investigate this, we have developed a novel FBL identification method based on sampled time-series data and applied it to synchronized spiking records measured from cultured neural networks of rat by using multi-electrode array. As a result, we have identified coupled direct and indirect PFLs. We therefore conclude that coupled direct and indirect PFLs might be an important design principle that causes the synchronized bursting behavior in neuronal networks although an extrapolation of this result to in vivo brain dynamics still remains an unanswered question.

Sexual Back Talk With Evolutionary Implications: Stimulation of the Drosophila Sex-Determination Gene Sex-lethal by Its Target transformer

We describe a surprising new regulatory relationship between two key genes of the Drosophila sex-determination gene hierarchy, Sex-lethal (Sxl) and transformer (tra). A positive autoregulatory feedback loop for Sxl was known to maintain somatic cell female identity by producing SXL-F protein to continually instruct the target gene transformer (tra) to make its feminizing product, TRA-F. We discovered the reciprocal regulatory effect by studying genetically sensitized females: TRA-F from either maternal or zygotic tra expression stimulates Sxl-positive autoregulation. We found female-specific tra mRNA in eggs as predicted by this tra maternal effect, but not predicted by the prevailing view that tra has no germline function. TRA-F stimulation of Sxl seems to be direct at some point, since Sxl harbors highly conserved predicted TRA-F binding sites. Nevertheless, TRA-F stimulation of Sxl autoregulation in the gonadal soma also appears to have a cell-nonautonomous aspect, unprecedented for somatic Sxl regulation. This tra-Sxl retrograde regulatory circuit has evolutionary implications. In some Diptera, tra occupies Sxl's position as the gene that epigenetically maintains female identity through direct positive feedback on pre-mRNA splicing. The tra-mediated Sxl feedback in Drosophila may be a vestige of regulatory redundancy that facilitated the evolutionary transition from tra to Sxl as the master sex switch.

Концепція Cа2+-функціональних одиниць у застосуванні до секреторних клітин слинних залоз личинки Chironomus plumosus

On the basis of analysis of experimental data received during investigation of Ca 2+ -transporting systems of secretory cells of salivary glands of Chironomus plumosus larvae, a conception of Ca 2+ -functional units has been proposed. According to this conception, Ca 2+ -functional unit is an abstract model which consists of with active and passive Ca 2+ -transporting systems and cellular membrane providing Ca 2+ cations compartmentalisation. There are type I (active and passive transporting systems located in the same membrane) and type II (active and passive transporting systems located in different membranes of the same cell) Ca 2+ -functional units. In both cases, Ca 2+ -functional unit is not a static structure, but a dynamic one, that ensure proper [Ca 2+ ] support in cytosol. It may be in three states: 1) resting state the is characterised by a dynamic balance between the influx and efflux of Ca 2+ flow; 2) active state of Ca 2+ influx (regarding cytosol) prevailing over the efflux; 3) inactive state (oppositely, Ca 2+ efflux prevailing over its influx). Factors which due to direct positive or negative feedback are supporting Ca 2+ -transporting systems transition between different states, are Ca 2+ cations, since the activity of majority of Ca 2+ -transporting systems depends on cytosol concentration of Ca 2+ . Endoplasmic Ca 2+ -functional unit of investigated secretory cells combines Ca 2+ -pump of endoplasmic reticulum, lnsP 3 Rs and RyRs. As a result of 1) ryanodine adding to incubatory medium of glands in submicromolar concentration causes Ca 2+ content increasing in their tissue; 2) lnsP 3 Rs stimulation prevents simultaneous RyRs stimulation or contrariwise; 3) heparin causes Ca 2+ content increasing in gland tissue, treated with saponin, but only in ryanodine presence in medium in concentration activating RyRs. Ca 2+ -functional unit of plasma mambrane are formed by voltage-operated Ca 2+ -channels, Na + -Ca 2+ exchanger and Ca 2+ -pump of plasma membrane. That assumption is based on the fact that between the voltage-operated Ca 2+ -channel and Na + -Ca 2+ exchanger, from one side, and Na + -Ca 2+ exchanger and Ca 2+ -pump of plasma membrane, from the other side, tight functional links are existing even in case of intracellular perfusion. To some extent, condition of this Ca 2+ -functional unit are defined by Na + -Ca 2+ exchange dependence on Na + -K + pump activity. Its peculiar feature is also a dependence on membrane potential level, not only on cytosolic [Ca 2+ ]. Distinct Ca 2+ -transporting systems may be a part of several Ca 2+ -functional units. Endoplasmic-mitochondrial Ca 2+ -functional unit consists of Ca 2+ -release channels of endoplasmic reticulum and mitochondrial Ca 2+ -uniporter, so far as influence of ryanodine and ruthenium red, and also lnsP 3 and ruthenium red under the condition of their combination in incubation medium with Ca 2+ content of salivary glands tissue is not additive. Postulated conception could be positioned as a working hypothesis for identification of the role of different Ca 2+ -transporting systems in coordination of Ca 2+ -signalling in different cells other than secretory cells of exocrine glands. Keywords: Ca 2+ -functional unit, Na + -Ca 2+ exchanger, Ca 2+ -pump, voltage-operated Ca 2+ -channels, InsP 3 R, RyR, Ca 2+ - uniporter, secretory cells.

Active Vibration Control of a Micro-Actuator for Hard Disk Drives using Self-Sensing Actuator

In this article, active vibration control of a micro-actuator for hard disk drives using self-sensing actuation is presented. The micro-actuators used in this article are a slider type and a suspension type. The self-sensing performance of the installing position is compared and evaluated. An assembly including these micro-actuators may not be able to sense some vibration of suspension modes. Feedback control results of direct velocity feedback and positive position feedback are presented. The feasibility of these self-sensing approaches as a vibration suppression control on the micro-actuator was verified. Using the slider type micro-actuator, the sway mode spike signal in power spectrum density was suppressed by 76% using the direct velocity feedback control, and by 60% using the positive position feedback control. Using the suspension type micro-actuator, the suspension second bending mode spike signal in power spectrum density was reduced by 74% using the direct velocity feedback control, and by 96% using the positive position feedback control. The control scheme using self-sensing signals can partially dampen the suspension modes.

Modeling direct positive feedback between predators and prey

Predators can have positive impacts on their prey through such mechanisms as nutrient mineralization and prey transport. These positive feedbacks have the potential to change predictions based on food web theory, such as the assertion that enrichment is destabilizing. We present a model of a simple food web, consisting of a resource, a consumer, and its predator. We assume that the predator has a direct positive effect on the consumer, by increasing the rate at which the consumer acquires resources. We consider two cases: the feedback strength is a saturating function of predator density, or it is proportional to the encounter rate between predators and prey. In both cases, the positive feedback is stabilizing, delaying or preventing the onset of oscillations due to enrichment. Positive feedback can introduce an Allee effect for the predator population, yielding multiple stable equilibria. Strong positive feedback can yield counterintuitive results such as a transient increase in consumer density following the introduction of predators, and a decrease in the resource pool following enrichment.

Central corticotropin-releasing hormone receptors modulate hypothalamic–pituitary–adrenocortical and sympathoadrenal activity during stress

The role of brain corticotropin-releasing hormone receptors in modulating hypothalamic–pituitary–adrenal and sympathoadrenal responses to acute immobilization stress was studied in conscious rats under central corticotropin-releasing hormone receptor blockade by intracerebroventicular injection of a peptide corticotropin-releasing hormone receptor antagonist. Blood for catecholamines, adrenocorticotropic hormone and corticosterone levels was collected through vascular catheters, and brains were removed at 3 h for in situ hybridization for tyrosine hydroxylase messenger RNA in the locus coeruleus, and corticotropin-releasing hormone and corticotropin-releasing hormone receptor messenger RNA in the hypothalamic paraventricular nucleus. Central corticotropin-releasing hormone receptor blockade reduced the early increases in plasma epinephrine and dopamine, but not norepinephrine, during stress. Immobilization stress increased tyrosine hydroxylase messenger RNA levels in the locus coeruleus by 36% in controls, but not in corticotropin-releasing hormone antagonist-injected rats. In control rats, corticotropin-releasing hormone messenger RNA and type 1 corticotropin-releasing hormone receptor messenger RNA in the paraventricular nucleus increased after stress ( P<0.01), and these responses were attenuated by central corticotropin-releasing hormone receptor blockade. In contrast, central corticotropin-releasing hormone antagonist potentiated plasma adrenocorticotropic hormone responses, but slightly attenuated plasma corticosterone responses to stress. The inhibition of plasma catecholamine and locus coeruleus tyrosine hydroxylase messenger RNA responses to stress by central corticotropin-releasing hormone receptor blockade supports the notion that central corticotropin-releasing hormone regulates sympathoadrenal responses during stress. The attenuation of stress-induced corticotropin-releasing hormone and corticotropin-releasing hormone receptor messenger RNA responses by central corticotropin-releasing hormone receptor blockade suggests direct or indirect positive feedback effects of corticotropin-releasing hormone receptor ligands on corticotropin-releasing hormone expression, whereas additional mechanisms potentiate adrenocorticotropic hormone responses at the pituitary level. In addition, changes in neural activity by central corticotropin-releasing hormone are likely to modulate adrenocortical responsiveness during stress.

Enhancement of interleukin-6 production by fibrinogen degradation product D in human peripheral monocytes and perfused murine liver.

The effect of fibrinogen degradation products D and E (FDP-D, FDP-E) on IL-6 production in perfused mouse livers and peripheral monocytes is studied. Similarly to bacterial endotoxin FDP-D is highly potent to augment the IL-6 production measured in perfused mouse livers, while FDP-E is not stimulatory. FDP-D but not FDP-E is able to stimulate the in vitro IL-6 production of human peripheral monocytes, as well. Plasmin alone is almost ineffective on IL-6 production both in perfused livers and monocytes. Our findings suggest a direct positive feedback circuit, among fibrinogen, FDP and IL-6.

Direct homeodomain-DNA interaction in the autoregulation of the fushi tarazu gene.

A major problem in the elucidation of the molecular mechanisms governing development is the distinction between direct and indirect regulatory interactions among developmental control genes. In vivo studies have indicated that the Drosophila segmentation gene fushi tarazu (ftz) directly or indirectly autoregulates its expression. Here we describe a generally applicable experimental approach which establishes a direct in vivo interaction of the homeodomain protein ftz with the ftz cis-autoregulatory control region. In vitro studies have shown that the DNA-binding specificity of the ftz homeodomain can be changed by a single amino-acid substitution in the recognition helix (Gln 50----Lys). Whereas wild-type ftz homeodomain binds preferentially to a CCATTA motif, the mutant homeodomain (ftzQ50K) recognizes a GGATTA motif. We now find that the in vivo activity of an ftz autoregulatory enhancer element is reduced by mutations of putative ftz-binding sites to GGATTA. This down-regulatory effect is specifically suppressed in vivo by the DNA-binding specificity mutant ftzQ50K. These results establish a direct positive autoregulatory feedback mechanism in the regulation of this homeobox gene.

The qualitative approach in investigating the role of species interactions on stability of natural communities

Community models with competition and mutualism are qualitatively analyzed using the methodology of loop analysis combined with computer stochastic simulation. The concept of “moving equilibrium” in the growth rate of the species is discussed in 14 “tables of predictions”, presented as analytical tools that can help to shed light on controversial ecological issues such as direct versus indirect interaction and positive feedback effects on stability. While the stochastic simulation shows that only little or no difference exists in probability of stability between models with competition and models with mutualism, the related tables of predictions show that the networks among links are able to activate indirect interactions, with both negative and positive effects, between any pair of species. This phenomenon makes it difficult to determine how much stability is related to the direct interactions.

Juvenile hormone esterase activity from Manduca sexta corpora allata in vitro

AbstractJuvenile hormone esterase (JHE) activity released by the corpora allata (CA) into incubation media (CA‐JHE) was titered daily during the course of the last (fifth [V]) larval stadium of Manduca sexta. This CA‐JHE activity was relatively low during the early last stadium up to the time of commitment (V4), then rose rapidly to a peak on V6. Activity declined sharply almost to precommitment levels by V8, before rising to a second peak on the first day of the pupal phase (P0). This pattern of activity is distinct from that of hemolymph JHE activity, which peaks just prior to wandering on V4 and again just prior to pupation (V9). Although the CA‐JHE and hemolymph‐JHE possess different temporal patterns of activity, isoelectric focusing, gel electrophoresis, and initial studies with selected inhibitors suggest that the enzymes responsible for the CA‐JHE and hemolymph‐JHE activities are similar, but not identical, in nature.Exposure of the V6 CA in vitro to JH II (0.1 μM) or fluoromevalonolactone (FMev; 0.1 mM) produced an approximate fivefold increase and 60% decrease in JH acid synthesis, respectively. Conversely, the same treatments resulted in an inhibition (JH II) and stimulation (FMev) of CA‐JHE activity. These observations suggest that JH may be involved in the direct positive feedback regulation of postwandering larval CA and that the CA‐JHE may also be integrally related to this positive feedback mechanism.

The effect of thyroid hormones on rat pineal indoleamine metabolism in vitro.

The effect of TSH, triiodothyronine (T3) and thyroxine (T4) on basic and noradrenaline (NA)-induced indoleamine metabolism was investigated in rat pineal culture based on the observation that, under the experimental system used, melatonin is formed from its amino acid precursor tryptophan. When added to the culture medium, alone or in the presence of NA, TSH in dosages of 5 and 20 mU had no significant effect on pineal tryptophan metabolism.T4 and 2.5 microgram increased the melatonin concentration and, in the presence of NA 10(-4) M, also induced an increase in N-acetylserotonin (NAS). T3, already at a dosage as low as 0.25 microgram enhanced the melatonin concentration, while 2.5 microgram produced significant increases in concentrations of all pineal indoleamines measured. The latter dosage of T3 also enhanced the NA-stimulated NAS. On adding larger quantities of T4 or T3 to the medium none of the changes encountered with the lower dosages could be seen. The results obtained may suggest a direct positive feedback between the thyroid and pineal glands.