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PubMed2006

Control of neuronal synchrony by nonlinear delayed feedback.

We present nonlinear delayed feedback stimulation as a technique for effective desynchronization. This method is intriguingly robust with respect to system and stimulation parameter variations. We demonstrate its broad applicability by applying it to different generic oscillator networks as well as to a population of bursting neurons. Nonlinear delayed feedback specifically counteracts abnormal interactions and, thus, restores the natural frequencies of the individual oscillatory units. Nevertheless, nonlinear delayed feedback enables to strongly detune the macroscopic frequency of the collective oscillation. We propose nonlinear delayed feedback stimulation for the therapy of neurological diseases characterized by abnormal synchrony.

Action Potentials↗
PubMed2006

Stimulation of the epithelial sodium channel (ENaC) by the serum- and glucocorticoid-inducible kinase (Sgk) involves the PY motifs of the channel but is independent of sodium feedback inhibition.

The epithelial sodium channel (ENaC) is the major mediator of sodium transport across the apical membranes of the distal nephron, the distal colon, the respiratory tract and the ducts of exocrine glands. It is subject to feedback inhibition by increased intracellular Na+, a regulatory system wherein the ubiquitin protein ligases, Nedd4 and Nedd4-2, bind to conserved PY motifs in the C-termini of ENaC and inactivate the channel. It has been proposed recently that the kinase Sgk activates the channel as a consequence of phosphorylating Nedd4-2, thus preventing it from inhibiting the channels. This proposal predicts that Sgk should interfere with Na+ feedback regulation of ENaC. We have tested this prediction in Xenopus laevis oocytes and in mouse salivary duct cells and found that in neither system did increased activity of Sgk interrupt Na+ feedback inhibition of ENaC. We found, however, that Sgk stimulation was largely abolished in oocytes expressing ENaC channels with C-terminal truncations or mutated PY motifs. We were also unable to confirm that Sgk directly interacts with Nedd4-2 in vitro. We conclude that the stimulatory effect of Sgk on ENaC requires the presence of the channel's PY motifs, but it is not due to the interruption of Na+ feedback regulation.

Amino Acid Motifs↗
PubMed2001

Feedback control of intracellular pH by means of iontophoretic H+/OH- injection.

A new method for controlling intracellular pH (pH(i)) within a single cell has been developed that is based on the iontophoretic injection of the pH-affecting ions H+ and OH-. The H+/OH- injection currents are governed by an electronic feedback system, which compares the actual pH(i), monitored by pH-sensitive microelectrodes, with a command value. To avoid membrane potential (Em) alterations caused by the H+/OH- currents, the pH(i) control is performed under voltage-clamp conditions, using a two-electrode voltage-clamp design. This feedback-controlled iontophoretic injection system was capable of adjusting pH(i) between pH 6.8 and 8.0 with a precision of 0.031+/-0.026 pH units (n=51) and without affecting Em. We illustrate the application of this system by investigating the pH(i) dependence of glutamate receptors in identified leech Retzius neurons. Stimulation of these receptors with the glutamatergic agonist kainate (50 microM) under control conditions induced an intracellular acidification of 0.14+/-0.07 pH units (n=13). The feedback control system for pH(i) reduced this intracellular acidification to 0.02+/-0.01 pH units (n=15). The kainate-induced inward current was not affected by pH(i) alterations. This result demonstrates that the feedback system for pH(i) control was feasible for investigating the pH(i) dependence of physiological processes and suggests that the glutamate receptors are not modulated by pH(i).

Animals↗
PubMed2006

Early exposure to haptic feedback enhances performance in surgical simulator training: a prospective randomized crossover study in surgical residents.

BACKGROUND: In the literature of skill acquisition and transfer of skills, it often is assumed that the rate of skill acquisition depends on what has been learned in a similar context (i.e., surgical simulators providing haptic feedback). This study aimed to analyze whether the addition of haptic feedback early in the training phase for image-guided surgical simulation improves performance. METHODS: A randomized crossover study design was used, in which 38 surgical residents were randomized to begin a 2-h simulator training session with either haptic or nonhaptic training followed by crossover after 1 h. The graphic context was a virtual upper abdomen. The residents performed two diathermy tasks. Two validated tests were used to control for differences in visual-spatial ability: the BasIQ general cognitive ability test and Mental Rotation Test A (MRT-A). RESULTS: After 2 h of training, the group that had started with haptic feedback performed the two diathermy tasks significantly better (p < 0.05, unpaired t-test). Only the group that had started with haptic training significantly improved during the last 1-h session (p < 0.01, paired t-test). CONCLUSION: The findings indicate that haptic feedback could be important in the early training phase of skill acquisition in image-guided surgical simulator training.

Abdomen↗
PubMed2005

Efferent-mediated fluctuations in vestibular nerve discharge: a novel, positive-feedback mechanism of efferent control.

We compared the background discharge of vestibular nerve afferents in barbiturate-anesthetized and unanesthetized, decerebrate chinchillas. Based on their interspike-interval statistics, units were categorized as regular, intermediate, or irregular. Background discharge rates were higher in irregular units from decerebrates compared to anesthetized preparations; no such difference was observed for regular or intermediate units. Large fluctuations in discharge rate were confined to intermediate and irregular units in decerebrates, but were not seen at all in anesthetized animals. The most prominent examples of fluctuations consisted of oscillations with periods exceeding 500 s and peak-to-peak amplitudes as large as 300 spikes/s. Several observations show that the fluctuations are mediated by the efferent vestibular system (EVS): (1) they are abolished when the vestibular nerve is cut proximal to the recording electrode; (2) their amplitude is correlated with the size of efferent-mediated rotational responses in individual units; and (3) they occur even when vital signs are stable. Previous studies had provided evidence that the EVS involves positive feedback: vestibular nerve afferents and EVS neurons excite one another. To study how oscillations could be produced, we developed a nonlinear model of positive feedback in which afferent feed-forward discharge was nonlinearly related to its inputs from hair cells and the EVS, while these inputs declined (adapted) as discharge was prolonged. Provided that the gain of the efferent feedback loop was sufficiently large, the model showed oscillations similar to those observed experimentally. Although large fluctuations in afferent discharge are unlikely to occur under physiological circumstances, positive feedback may be a normal feature that can amplify the influence of the EVS.

Animals↗
PubMed2006

Reciprocal, longitudinal associations among adolescents' negative feedback-seeking, depressive symptoms, and peer relations.

This study examined reciprocal associations among adolescents' negative feedback-seeking, depressive symptoms, perceptions of friendship quality, and peer-reported social preference over an 11-month period. A total of 478 adolescents in grades 6-8 completed measures of negative feedback-seeking, depressive symptoms, friendship quality, global-self-esteem, and social anxiety at two time points. Peer-reported measures of peer status were collected using a sociometric procedure. Consistent with hypotheses, path analyses results suggested that negative feedback-seeking was associated longitudinally with depressive symptoms and perceptions of friendship criticism in girls and with lower social preference scores in boys; however, depressive symptoms were not associated longitudinally with negative feedback-seeking. Implications for interpersonal models of adolescent depression are discussed.

Adolescent↗
PubMed2006

Effects of a proximity-sensing feedback chair on head, shoulder, and trunk postures when working at a visual display terminal.

INTRODUCTION: This study was designed to identify the effects of feedback from a proximity-sensing chair on head, shoulder, and trunk postures when working at a visual display terminal (VDT). METHODS: Twenty healthy adults were asked to perform VDT work, and their forward head, forward shoulder, and trunk flexion angles were analyzed using a 3-D motion analysis system. The statistical significance of differences between without and with an auditory feedback device was tested by paired t-tests, with the significance cutoff set at alpha=0.05. RESULTS: The forward head, forward shoulder, and trunk flexion angles significantly decreased during VDT work when using the proximity sensor with auditory feedback. CONCLUSION: We suggest that a feedback device promotes the adoption of beneficial postures, which may be effective in preventing VDT-work-related neck and upper-limb disorders.

Adult↗
PubMed2005

Miranda comprehension in adults with mental retardation and the effects of feedback style on suggestibility.

Interrogations present several major challenges to persons with mental retardation (MR). Sixty adults with mild MR completed measures of Miranda comprehension and tendency to yield to leading questions. In addition, suggestibility was assessed based on whether participants revised answers to questions in response to unfriendly, friendly, or neutral feedback to original responses. Furthermore, we examined how expressed confidence in answers to repeated questions varied with the type of feedback received. Results revealed that participants demonstrated marked difficulties understanding their Miranda rights and greater likelihood of changing answers to questions for which they received friendly feedback than for questions for which they received unfriendly or neutral feedback. Most participants who received positive reinforcement for their answers on a second trial expressed confidence about improvement from trial 1 to trial 2, although accuracy did not improve. Implications of these results are reviewed.

Adult↗
PubMed1989

The nonvalue of retrospective peer comparison feedback in containing hospital antibiotic costs.

UNLABELLED: Antibiotics have accounted for an increasing percentage of hospital pharmacy charges. Recently, an inexpensive method, automated peer comparison feedback, has been developed to influence physician use of resources. The documented success of several implementations of this strategy led to a one-year experiment to influence hospital antibiotic utilization. Each month, attending physicians in the top 50 percentiles for expenditure were notified of their status in relation to their peers. Expenditures by feedback and control groups were compared to determine whether feedback would result in reduced expenditures by individuals, or whether there would be a generalized reduction in expenditure by the entire group (Hawthorne effect). Over the year, no significant reduction in expenditure was noted. However, some important utilization patterns were identified. Although more surgical patients received antibiotics than did nonsurgical patients, surgical antibiotic costs were less. Surgical therapy was typically of shorter duration and involved the use of less expensive antibiotics. Multiple-antibiotic prescribing was less frequent on surgical services. Thirty percent of attending physicians were responsible for 80 percent of all antibiotic costs; 60 percent of those in this top group were members of the medical cohort. IN CONCLUSION: (1) As implemented in the current study, automated peer comparison feedback was not an effective method for reducing antibiotic utilization; (2) Differences in prescribing patterns between services may dictate the best strategies for improving antibiotic utilization; (3) More attention should be directed toward the relatively small "reference group" of physicians responsible for most hospital antibiotic prescribing.

Anti-Bacterial Agents↗
PubMed1990

Feedback by early and late primary antisera on the primary and secondary adoptive immune responses of mice to burro erythrocytes.

Experiments on antibody feedback inhibition of the immune response have confirmed that control is more effective against a primary response than against a secondary response. The cells producing antibodies in primary and secondary responses are different both in terms of number of IgFC and amount of antibody produced by individual IgFC (plaque size). Late primary anti-burro RBC sera (greater than 200 days), despite low titers, are, on a volume for volume basis, feedback inhibitors at least as good as early (8-12 days) primary antisera on primary responses but are more effective in suppressing secondary responses (B memory cells). Late primary antisera, due to the process of affinity maturation, have a high affinity for antigen. The suppressive effect of early and late antisera is equally removable by absorption with burro erythrocytes: a result which it is thought, decreases the likelihood of feedback by anti-idiotype being involved in the observed suppression. It is suggested that feedback antibody acts (a) in competition with receptors, inter alia removing antigen into immunologically irrelevant pathways, (b) by a process involving the linking of antigen to Fc receptors, and (c) as a blocking antibody coating B cells (Bm) or APC which are already binding epitopes, thus preventing their cooperation with specific helper or other accessory cells.

Animals↗
PubMed1994

Roles of gut hormones in negative-feedback regulation of pancreatic exocrine secretion in humans.

BACKGROUND/AIMS: Secretin has been shown to mediate feedback control of pancreatic secretion of fluid and bicarbonate in rats, guinea pigs, and dogs. However, little is known about secretin in the feedback regulation in humans. We investigated the roles of secretin, cholecystokinin, neurotensin, and pancreatic polypeptide on feedback regulation of pancreatic secretion in 10 human volunteers. METHODS: A 5-lumen tube was positioned in the proximal jejunum of fasting subjects under fluoroscopy so that gastric juice via lumen 1 and duodenal contents via lumen 3 were collected separately in 15-minute samples while polyethylene glycol solution was infused into duodenum via lumen 2. An acidified (pH 2.0) 4.25% amino acid mixed with phenol red was infused into proximal jejunum via lumen 4, which was alternated with NaHCO3 (control solution) or trypsin (test solution) via lumen 5 intermittently every 15 minutes during separate test periods. RESULTS: Infusion of control solution significantly increased both bicarbonate (total change [delta], 7799 +/- 1400 mumol/h) and chymotrypsin (delta 5500 +/- 762 mumol/h) outputs and levels of all four plasma hormones. The test solution significantly inhibited both bicarbonate (delta 2999 +/- 700 mumol/h; P < 0.01) and chymotrypsin output (delta 1000 +/- 120 U/h, P < 0.01), which coincided with a significant suppression of plasma concentration of secretin and cholecystokinin but not pancreatic peptide and neurotensin. CONCLUSIONS: A negative-feedback regulation of pancreatic secretion of bicarbonate and enzyme occurs in humans and is mediated via both secretin and cholecystokinin.

Adolescent↗
PubMed1991

The problem of feedback in hearing aids.

One of the factors that limits hearing-aid performance is feedback. This paper discusses the problem of feedback in hearing aids, illustrated with examples based on a computer simulation of hearing-aid behavior. The available technology for dealing with the problem of feedback is then reviewed, and new digital signal-processing approaches are described that may finally solve the feedback problem.

Equipment Design↗
PubMed1991

Properties of the feedback loops controlling eye growth and refractive state in the chicken.

Recent experiments in chickens provide evidence that axial eye growth and refractive state are guided by mechanisms sensitive to refractive error. To determine whether or not the sign of refractive error is derived from longitudinal chromatic aberration we raised chicks with spectacle lenses in monochromatic light. The eyes showed an appropriate growth response to correct for the defocus imposed by the lenses no different than in previous experiments in white light. Thus, in normally accommodating chicks chromatic cues are not necessary for emmetropization to occur. We examined the linearity of feedback loops controlling axial eye growth: positive spectacle lenses were found to inhibit axial growth very efficiently making the eyes shorter than normal whereas negative lenses had little effect on axial elongation: feedback loops for regulation of axial growth are highly nonlinear and act most efficiently on the myopic side. We found that, subsequent to a period of binocular deprivation of form vision, the refractive errors acquired are highly correlated in both eyes. Since both eyes grew without visual feedback we conclude that the gains in the feedback loops that control axial growth must be similar in both eyes. We suggest that the gains are genetically determined and are typical for each individual. Chicks made near-sighted in both eyes by "deprivation of form vision" were corrected by appropriate negative lenses. Three out of five chicks recovered from myopia despite the correction. Also two chicks that were made near-sighted in one eye recovered with no regard to the correcting lens. Three chicks remained more myopic than the correcting lens required and finally started to recover while the lens was still in place. Two out of three chicks that were made far-sighted showed recovery despite appropriate correction by positive lenses. We conclude that there must be a nonvisual mechanism highly sensitive to abnormal eye shape. During expt (4) we found unexpectedly that the development of form deprivation myopia is inhibited if no part of the retina in an animal is exposed to normal visual experience. The result indicates that some communication between both eyes exists, although form deprivation myopia itself has been shown to develop independently in both eyes.

Animals↗
PubMed1990

Completion of DNA replication is monitored by a feedback system that controls the initiation of mitosis in vitro: studies in Xenopus.

During cell division complete DNA replication must occur before mitosis is initiated. Using a cell-free extract derived from Xenopus eggs that oscillates between S phase and mitosis, we have investigated how completion of DNA synthesis is coupled to the initiation of mitosis. We find that Xenopus eggs contain a feedback pathway which suppresses mitosis until replication is completed and that activation of this inhibitory system is dependent on the presence of a threshold concentration of unreplicated DNA. We demonstrate that in the presence of unreplicated DNA the active feedback system inhibits initiation of mitosis by blocking the activation of MPF, a regulator of mitosis found in all eukaryotic cells. Our results demonstrate that the feedback system does not inhibit MPF activation by blocking the synthesis or accumulation of cyclin protein, a subunit of MPF, or by blocking association of cyclin with the cdc2 subunit of MPF. We propose that the feedback system blocks mitosis by maintaining MPF in an inactive state by modulating posttranslational modifications critical for MPF activation.

Animals↗
PubMed1991

Using bisensory feedback displays for space teleoperation.

This paper investigates the use of tactile and auditory displays to present feedback to the pilot of a spacecraft or the operator of a space teleoperated system. Force feedback is given particular attention for teleoperator scenarios in the presence of a time delay. The motivation for and potential benefits of developing bisensory feedback displays are identified. Pioneering research in developing auditory and tactile displays is discussed. Several models of the human operator concerning the processing of bisensory information are outlined, along with a discussion of presenting redundant information across sensory modalities. Preliminary experimental results concerning sensory substitution of force feedback with a vibrotactile display are presented along with future research plans.

Acoustic Stimulation↗
PubMed1991

Interaction of recurrent inhibitory and muscle spindle afferent feedback during muscle fatigue.

Mammalian skeletal motor units have differing properties including their different susceptibility to fatigue. The question discussed in this paper is whether and to what extent proprioceptive feedback via muscle spindles can contribute to shape the firing patterns of motor units so as to minimize their loss of force during fatiguing contraction. The firing of a skeleto-motoneuron dispatches signals which are fed back to the same and homonymous as well as synergistic motoneuron. Two feedback pathways are of concern here: one via the related muscle unit and muscle spindle afferents (proprioceptive path), and one via recurrent motor axon collaterals and Renshaw cells (recurrent inhibitory path). It is suggested that the contraction of a motor unit or a small group of adjacent ones is signalled to the homonymous alpha-motoneurons via proprioceptive afferents, the signal being filtered and enhanced by spinal recurrent inhibition. This is effected by timed correlation of the signals which are propagated through the two feedback loops. The effects of the correlation can be strengthened by (i) topographical order of the feedback connections, (ii) heterosynaptic interaction, and (iii) tendencies towards synchronous discharge between motoneurons. These mechanisms render the possibility more likely that information about the unfused contractions of a muscle unit (or a small group of them), mediated via proprioceptive afferents, play a role in shaping the precise discharge pattern of the innervating motoneuron(s). These mechanisms could be used to optimize the force output of large fatiguing motor units during long activation, during which their activation rates normally decrease (adapt) over time. Our results show that during adapting motoneuron firing Renshaw cells and muscle spindle afferents may show discharge patterns which at least in part are in keeping with such an hypothesis.

Animals↗
PubMed1992

Feedback connections and operation of the outer plexiform layer of the retina.

The primary feedback control apparatus in the outer retina is the sign-inverting feedback synapse between horizontal cells and cones. In many lower vertebrates horizontal cells release GABA in darkness, which opens Cl- channels in cones. Input-output relations of the feedback synapse reveal that the synaptic gain is light-dependent with the highest negative gain near the dark horizontal cell potential. The horizontal cell-cone feedback synapse improves the reliability of the photoreceptor output synapses. It also modulates the dynamic range and mediates color opponency and surround responses in second-order retinal neurons.

Animals↗
PubMed1995

Walking when utilizing a sensory feedback system and an electrical muscle stimulation gait orthosis.

Electrical muscle stimulators (EMS) have been combined with a reciprocating gait orthosis (RGO) to produce an EMS-RGO system for constant velocity ambulation exercise in a spinal cord injured (SCI) individual. The objective of this study is to evaluate an auditory feedback system (AFS) used by the SCI subject when ambulating with the EMS-RGO. Three different types of auditory signals (M = metronome alone, MSL = metronome plus stride length information, and NONE = no auditory feedback) were examined at three different constant walking velocities (WV1 = 0.64 kph, WV2 = 1.22 kph, and WV3 = 1.80 kph). The experimental design was 3 x 3 full factorial with repeated measures, and the dependent variable was the absolute error (AE) of walking distance (absolute value of the distance the subject walked in one minute subtracted from the target distance). A block diagram and circuit schematic of the AFS is provided. The results indicate that at WV1 there is no significant difference of AE among the three auditory conditions (M, MSL and NONE). At WV2, the AE for the NONE auditory condition is significantly greater than the AE for M and MSL (p < 0.05). At WV3, the AE for the NONE auditory condition is significantly less than the AE for M and MSL (p < 0.05). Finally, there was no significant difference in AE between both the M and MSL auditory conditions at any of the three walking velocities. This study indicates that an adequate sensory feedback system for constant velocity control of ambulation in this SCI subject consists of metronome only auditory feedback.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗