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PubMed2001

Performance feedback deficit in geriatric depression.

BACKGROUND: The orbital frontal cortex is involved with processing of performance feedback. This study tests the hypothesis that older depressed subjects, compared with elderly control subjects, commit more subsequent errors after receiving feedback from an initial error. METHODS: We administered 116 older depressed patients and 139 control subjects the Trail Making Test Part B (TRAILS-B). Subjects who committed an error on TRAILS-B were immediately given feedback on performance. We then measured the frequency of making an error on the subsequent three tries. The likelihood of making any subsequent error was examined. RESULTS: After controlling for the overall initial error rate, more depressed patients than control subjects made subsequent errors. This association remained significant in later regression models. When the depressed group was examined in additional models, severity of depression was not associated with increased subsequent errors. CONCLUSIONS: These results extend previous findings suggesting a performance feedback deficit in geriatric depression. The findings support previous studies linking the orbital frontal cortex and depression.

Aged↗
PubMed1996

The importance of endogenous feedback for monofollicular growth in low-dose step-up ovulation induction with follicle-stimulating hormone in polycystic ovary syndrome: a randomized study.

OBJECTIVE: To evaluate the role of endogenous feedback in monofollicular growth during low-dose gonadotrophin therapy in polycystic ovary syndrome (PCOS) by measuring FSH levels in a group of patients cotreated with a GnRH agonist (GnRH-a) (group B) compared with patients not cotreated with an agonist (group A). DESIGN: Prospective randomized study. SETTING: University tertiary care Reproductive Endocrinology Unit. PATIENTS: Women with clomiphene citrate-resistant PCOS. MAIN OUTCOME MEASURES: Follicle-stimulating hormone, E2, and inhibin levels, follicular growth. RESULTS: In group A, FSH levels decreased significantly from 7.3 mIU/mL (conversion factor to SI unit, 1.00) at day -5 to 5.9 mIU/mL at day 0 (day that hCG was administered) despite a constant dose, whereas they remained at a level of 7.4 mIU/mL in group B. The rate of monofollicular growth was significantly higher in group A (80%) than in group B (22%). No significant differences in E2 levels or inhibin levels were found between the groups. CONCLUSIONS: The absence of a decrease of FSH during GnRH-a treatment in association with a lower rate of monofollicular growth suggests that endogenous feedback during low-dose step-up ovulation induction in PCOS plays an important role. The absence of this feedback mechanism in the presence of normal inhibin levels suggests that negative feedback control by inhibin during follicular stimulation is minimal.

Adult↗
PubMed2003

Optimal choice between feedforward and feedback control in gene expression to cope with unpredictable danger.

All organisms face risks of unpredictable danger caused by harmful physical environments, pathogens, parasites or predators. Organisms may have several alternative ways of coping with such dangers. These differ in cost, effectiveness and activation time. We study the conditions under which it is optimal to use different alternatives for damage control. As an example we consider a microbe (such as E. coli), which may experience heat shocks that cause denaturation of proteins in the cell. To restore the denatured proteins the organism produces heat-shock proteins (HSP). There are two different pathways for production of HSP. Some HSP are produced immediately after a heat shock (feedforward control), but additional HSP may be produced thereafter, stimulated by the presence of denatured proteins (feedback control). Feedforward is based solely on heat-shock intensity without accurate information on the resulting amount of denatured proteins. We examine the optimal combination of the two pathways that minimizes the sum of the damage caused by the presence of untreated denatured proteins and the production cost of HSP. The optimal response depends on the time delay for feedback control, the effectiveness of HSP in processing denatured proteins, the production cost of HSP, the severity of damage by denatured proteins and the probability distribution of the abundance of denatured protein conditional on heat-shock intensity. We find that feedforward control should always be used. Additional HSP may be produced by feedback control when the abundance of denatured protein is large whilst no feedback control should be used when it is small. All the HSP are produced by feedforward control when the maximum is close to the mean of denatured protein abundance conditional on the heat-shock intensity.

Defense Mechanisms↗
PubMedDate not supplied

Does exercise affect female hamster gonadotropins by reducing estradiol negative feedback?

Exercise stimulates reproductive function in hamsters exposed to short-day photoperiod (SDP) in contrast to its inhibitory effects in women and rats. SDP inhibits hamster reproduction in part by increasing the sensitivity of the hypothalamo-pituitary-gonadal axis (HPGA) to the negative feedback of gonadal steroids. To determine whether EX facilitates reproduction in female hamsters by affecting this mechanism, we examined the influence of estradiol (E2) on basal LH and FSH concentrations in exercising and sedentary hamsters maintained on long-day photoperiod (LD 14:10, LDP) or SDP (LD 8:16). In the LDP, serum LH and FSH were unaffected or reduced by exercise in ovariectomized (OVX) nonhormone-replaced hamsters, and LH was increased after tonic E2 replacement compared to sedentary controls. In the SDP, serum LH and FSH were significantly higher in OVX exercising than in sedentary hamsters, whether the exercisers were injected with a high dose of E2 or not. Thus, the effects of exercise on basal gonadotropin secretion in female hamsters appear to depend on the level of estradiol negative feedback (ENF). When this feedback is low (LDP OVX condition), exercise is either ineffective or inhibitory. When the ENF is increased by exposure to SDP and/or by treatment with E2, exercise has a stimulatory effect on basal gonadotropin secretion. Exercise may stimulate hamster gonadotropin secretion by reducing the ENF either by lowering the sensitivity of the HPGA to steroid negative feedback or by other means.

Animals↗
PubMed2002

GABAc feedback pathway modulates the amplitude and kinetics of ERG b-wave in a mammalian retina in vivo.

The electroretinogram b-wave is generally believed to reflect mainly light-induced activity of ON-center bipolar cells and Muller cells. Recently, there is increasing evidence that third-order retinal neurons can also contribute significantly to the b-wave. In a previous study (Vis. Res. 40 (2000) 579) we proposed that the GABAc feedback from amacrine cells to bipolar cells can affect both the amplitude and kinetics of the b-wave. Here we show that blocking this feedback has profound effects on b-wave amplitude and kinetics. These results demonstrate that feedback to bipolar cells is an important mechanism through which amacrine cells contribute to b-wave generation. Our results also provide functional evidence that the feedback may be involved in temporal processing in the mammalian retina.

Amacrine Cells↗
PubMed2006

Effect of enhanced feedback and brief educational reminder messages on laboratory test requesting in primary care: a cluster randomised trial.

BACKGROUND: Laboratory services play an important part in screening, diagnosis, and management of patients within primary care. However, unnecessary use of laboratory tests is increasing. Our aim was to assess the effect of two interventions on the number of laboratory tests requested by primary-care physicians. METHODS: We did a cluster randomised controlled trial using a 2x2 factorial design, involving 85 primary-care practices (370 family practitioners) that request all laboratory tests from one regional centre. The interventions were quarterly feedback of practice requesting rates for nine laboratory tests, enhanced with educational messages, and brief educational reminder messages added to the test result reports for nine laboratory tests. The primary outcome was the number of targeted tests requested by primary-care practices during the 12 months of the intervention. This study is registered as an International Standard Randomised Controlled Trial, number ISRCTN06490422. FINDINGS: Practices that received either or both the enhanced feedback and the reminder messages were significantly less likely than the control group to request the targeted tests in total (enhanced feedback odds ratio 0.87, 95% CI 0.81-0.94; reminder messages 0.89, 0.83-0.93). The effect of the interventions varied across the targeted tests individually, although the number of tests requested for both interventions was generally reduced. Neither intervention was consistently better than the other. INTERPRETATION: Enhanced feedback of requesting rates and brief educational reminder messages, alone and in combination, are effective strategies for reducing test requesting in primary care. Both strategies are feasible within most laboratory settings.

Clinical Laboratory Techniques↗
PubMed2003

Effects of visual center of pressure feedback on postural control in young and elderly healthy adults and in stroke patients.

The goal of this study was to compare young and elderly healthy individuals and elderly stroke patients in their capacity to use visual CP feedback (VF) in controlling both quiet standing and weight shifting and to assess their sensory re-weighing when this VF is withdrawn. A total of 40 participants were involved in this study. Participants were asked to either quietly stand on a force platform for a period of 45 s with eyes open (EO), using visual feedback (VF) or without visual feedback (No VF) or to perform a dynamic weight shifting task while using VF or No VF. During the quiet standing trials with VF, only the young (YO) were able to decrease the amplitude and increase the frequency of their sway in either plane. Removal of the VF resulted in a 'destabilizing' effect in both healthy elderly (EL) and stroke patients (ST) in the sagittal plane. With regard to the dynamic task, both the YO and EL were generally more successful at weight shifting in terms of speed and control when compared to the ST. Yet, when VF was removed, only the YO were able to largely maintain speed and precision of control. Hence, providing or removing visual CP feedback during quiet standing or removing VF during visually controlled weight shifting can discriminate healthy young participants from healthy elderly, but does not clearly discriminate healthy elderly from stroke patients in the same age group. Results revealed that sagittal plane imbalance in healthy elderly and stroke patients may be largely due to the effects of aging, whereas frontal plane imbalance is much more specific for the postural problems associated with stroke.

Adult↗
PubMed2001

Operation of the follicle-stimulating hormone (FSH)-inhibin B feedback loop in the control of primate spermatogenesis.

This paper reviews our current understanding of the function and operation of the follicle-stimulating hormone (FSH)-inhibin feedback loop in the male rhesus monkey (Macaca mulatta). Inhibin B is the major testicular inhibin in the monkey, and the pattern of secretion of this hormone during postnatal development is temporally coupled to that of gonadotropin. Inhibin B secretion by the Sertoli cell is stimulated by FSH and inhibited by luteinizing hormone (LH), the latter presumably acting via Leydig cell production of testosterone (T). The dynamics of the FSH-inhibin B feedback loop in the adult monkey is revealed following unilateral orchidectomy (UO). Interestingly, a sustained, 50% deficit in inhibin B secretion occurs after UO and this persistent error signal, in turn, results in elevated concentrations of FSH in the circulation. The elevated secretion of FSH appears to be the principal drive for the increased sperm output by the remaining testis. Available data for the functioning of the FSH-inhibin B feedback loop in the human male are placed in perspective, and a model for the negative feedback regulation of sperm number in primates is proposed.

Animals↗
PubMed2003

Chronic stress attenuates glucocorticoid negative feedback: involvement of the prefrontal cortex and hippocampus.

Disruption of the glucocorticoid negative feedback system is observed in approximate one half of human depressives, and a similar condition is induced in animals by chronic stress. This disruption is thought to involve down-regulation of glucocorticoid receptors (GRs) in the feedback sites of the brain. However, the responsible site of the brain has not been well elucidated. Here we examined the effects of chronic stress induced by water immersion and restraint (2 h/day) for 4 weeks followed by recovery for 10 days on the GR levels in the prefrontal cortex (PFC), hippocampus, and hypothalamus of rats using a Western immunoblot technique. In the PFC, the cytosolic GR levels were decreased, but the nuclear GR levels were not changed. In the hippocampus, the levels of cytosolic and nuclear GRs were increased. However, there were no marked changes in the GR levels in the hypothalamus. The changes in the cytosolic GR levels were confirmed at the mRNA level by an in situ hybridization technique. We next examined the suppressive effects of dexamethasone (DEX) infusions into these regions on the circulating corticosterone levels. When DEX was infused into the PFC or hippocampus of the chronically stressed rats, the suppressive response to DEX was abolished, but the response was normal in the hypothalamus. In addition, when DEX was injected systemically to the chronically stressed rats, the suppressive response to DEX was significantly attenuated. These results suggest that the abnormal changes in GRs in the higher centers of the hypothalamo-pituitary-adrenal axis are involved in the chronic stress-induced attenuation of the feedback. Since dysfunction of the PFC or hippocampus is implicated in the pathogenesis of depression, the present findings would help to understand the mechanisms underlying the disrupted feedback system and its relation to brain dysfunction in depression.

Animals↗
PubMed2001

Chronic stress differentially regulates glucocorticoid negative feedback response in rats.

Exposure to chronic stress is thought to play an important role in the etiology of depression. In this disorder, a disrupted negative feedback response to exogenous glucocorticoids on cortisol secretion has been indicated. However, the regulation of glucocorticoid negative feedback by chronic stress is not fully understood. In the present study, we investigated the effects of chronic stress administered by water immersion and restraint (2 h/day) for four weeks on the glucocorticoid feedback in rats. In the acutely (one-time) stressed rats, the basal plasma corticosterone (CORT) level was markedly elevated, remained at high levels for 5 h after the termination of stress, and then decreased. In the chronically stressed rats, the CORT level was initially elevated similarly, but rapidly decreased at 2 h. In the dexamethasone (DEX) suppression test, the peak CORT level in response to stress was not suppressed by DEX in the acutely stressed rats, but was significantly suppressed in the chronically stressed rats. In contrast, the suppressive effects of DEX on the basal CORT secretion in naive rats were attenuated in the chronically stressed rats. In the chronically stressed hippocampus, which plays an important role in the regulation of the glucocorticoid feedback response, the binding of [3H]DEX was decreased and the increased response of activator protein-1 induced by acute stress was abolished. These results suggest that chronic stress induces a hypersuppressive state for induced CORT secretion in response to acute stress, which is caused by partial habituation, coping, and adaptation to the stressor, whereas it induces a hyposuppressive state for the basal CORT secretion, which is caused by glucocorticoid receptor downregulation. These mechanisms may be involved in the stress-induced neural abnormalities observed in depression.

Adrenal Glands↗
PubMed2000

The question of feedback at the somadendritic region and antidepressant drug action.

Presynaptic receptor theory has been expanded to encompass the regulation of the firing rate of serotonergic neurons through negative feedback mediated by the somadendritic release of transmitter. This has encouraged hypotheses as to the mechanisms of action of several classes of antidepressants and anxiolytics. One conspicuous example is the attribution of the clinical efficacy of 5-HT uptake inhibitors, such as fluoxetine and paroxetine, to desensitization of somadendritic 5-HT autoreceptors. An examination of the available evidence, mainly observations made with agonists, antagonists, monoamine oxidase inhibitors and uptake blockers, taken along with the theoretical expectations for a negative feedback loop, and the operational characteristics of inactivation pathways, indicates that negative feedback does not function at somadendritic sites to set firing rate or transmitter density, and suggests that the process may not function at all physiologically. The attribution of the effectiveness of neuroactive drugs to desensitization of raphe 5-HT inhibitory receptors, or to other interactions with feedback, is highly speculative and unlikely.

Animals↗
PubMedDate not supplied

Effect of prenatal melatonin on the gonadotropin and prolactin response to the feedback effect of testosterone in male offspring.

The purpose of this study was to investigate the effects of prenatal melatonin administration on the sensitivity of the androgens negative feedback effect on gonadotropin and prolactin secretion in male offspring. Male offspring of control (control-offspring) and melatonin treated (MEL-treated) (150 microg/100 g BW) mother rats during pregnancy (MEL-offspring), at infantile, prepubertal, and pubertal periods were studied. LH secretion in response to testosterone propionate (TP) in control-offspring showed the classical negative feedback effect at all ages studied. In MEL-offspring a negative response after TP was also observed in all ages studied although the magnitude of this response was altered in this group as compared to controls. FSH values were significantly lower at most ages and time points studied in MEL-offspring than in control-offspring. FSH secretion in MEL-offspring showed a delayed negative feedback action of TP injection as compared to control-offspring. This response was observed at 21 days of age in control-offspring and delayed until day 30 of life in MEL-offspring. Parallely it remain at later age in MEL-offspring than in control-offspring. Prolactin secretion in control-offspring showed increased values after TP injections from infantile to pubertal periods. This increase was blunted in MEL-offspring at 17 and 35 days of age showing significantly reduced (p<0.01; p<0.05) plasma prolactin levels. During pubertal period a prolactin positive response to TP administration was observed in MEL-offspring but with significantly lower magnitude than in control-offspring. These results indicate that prenatal melatonin exposure induced changes in the sensitivity of gonadotropin and prolactin feedback response to testosterone, indicating a delayed sexual maturation of the neuroendocrine-reproductive axis in male offspring.

Aging↗
PubMed2002

An unexpected role for visual feedback in vehicle steering control.

Some motor tasks can be completed, quite literally, with our eyes shut. Most people can touch their nose without looking or reach for an object after only a brief glance at its location. This distinction leads to one of the defining questions of movement control: is information gleaned prior to starting the movement sufficient to complete the task (open loop), or is feedback about the progress of the movement required (closed loop)? One task that has commanded considerable interest in the literature over the years is that of steering a vehicle, in particular lane-correction and lane-changing tasks. Recent work has suggested that this type of task can proceed in a fundamentally open loop manner, with feedback mainly serving to correct minor, accumulating errors. This paper reevaluates the conclusions of these studies by conducting a new set of experiments in a driving simulator. We demonstrate that, in fact, drivers rely on regular visual feedback, even during the well-practiced steering task of lane changing. Without feedback, drivers fail to initiate the return phase of the maneuver, resulting in systematic errors in final heading. The results provide new insight into the control of vehicle heading, suggesting that drivers employ a simple policy of "turn and see," with only limited understanding of the relationship between steering angle and vehicle heading.

Automobile Driving↗
PubMed1997

A peer review feedback method of promoting compliance with preventive care guidelines in a resident ambulatory care clinic.

BACKGROUND: Simple distribution of clinical practice guidelines to physicians does not change practice behavior. A low-cost, continuous peer review feedback method was used to promote resident physicians' compliance with nine preventive care guidelines at the ambulatory care clinic at the Marshall University School of Medicine (Huntington, West Virginia). METHODS: Preventive care guidelines were distributed and a peer review feedback program was instituted in the resident physician primary care practice. The frequency of resident physician use of nine preventive care services was assessed and compared during three periods: preguideline (September 1, 1993, to March 1, 1994; 148 patients), guideline (September 1, 1994, to March 1, 1995; 148 patients), and one-year follow-up (September 1, 1995, to March 1, 1996; 150 patients). The patients in the three periods were similar in age, gender, and risk for influenza and pneumococcal infection. RESULTS: During the guideline period, resident physicians offered patients four preventive care services-tetanus toxoid immunization, clinical breast examination, Papanicolaou smear testing, and hemoccult testing significantly more often than during the preguideline period. All services were offered significantly more often during the one-year follow-up period compared with the preguideline period and as often as in the guideline period. CONCLUSION: A low-cost, continuous peer review feedback program significantly and durably improves resident physician compliance with clinical practice guidelines on preventive care services. However, the effectiveness of the poor review feedback method may not generalize to private practice or other settings. Research on other methods to promote compliance with clinical practice guidelines and to influence physician behavior in general should continue.

Adolescent↗
PubMedDate not supplied

Force-feedback grasper helps restore sense of touch in minimally invasive surgery.

The age of minimally invasive surgery has brought forth astounding changes in the health care field. Less pain and quicker patient recovery have been demonstrated with several types of operations that were once performed by an open technique. With these changes have come reports of complications. The decreased sense of touch is just one of several limitations inherent to current techniques of minimally invasive surgery that limit detection of subtle or unapparent lesions on palpation, such as common duct stones and liver lesions. The purpose of this study is to demonstrate the ability of a force-feedback-equipped grasper to restore some of the sense of touch that is lost in minimally invasive surgery. To demonstrate this ability, we created six silicone phantoms of identical dimensions but graded compliance, and asked 10 subjects to place them in increasing/decreasing order of compliance. They used three tools (their dominant gloved hand, a standard laparoscopic Babcock grasper, and our force-feedback device fitted with the identical Babcock grasper) to rate the compliance of the samples in a blinded fashion. These conditions thus approximated the conditions of open surgery, minimally invasive surgery, and minimally invasive surgery fitted with a force-sensing device, in terms of palpating tissues. Five surgeons skilled in minimally invasive surgery and five nonsurgeons participated in the study. The results indicate that the force-feedback device is significantly (P <0.05) better than a standard Babcock grasper at rating tissue compliance, but was not as successful as a gloved hand (mean of squared errors = 1.06, 3. 15, and 0.25, respectively). There was no significant difference between surgeons and nonsurgeons in rating compliance. We conclude that this force-feedback instrument is able to partially restore the sense of touch in minimally invasive surgery. This restored ability may thus potentially result in more efficient operations with improved diagnostic capabilities and fewer complications during minimally invasive surgery.

Biocompatible Materials↗
PubMed2003

Imaging of enzyme activity by scanning electrochemical microscope equipped with a feedback control for substrate-probe distance.

The enzymatic activity of diaphorase (Dp) immobilized on a solid substrate was characterized using a scanning electrochemical microscope (SECM) with shear force feedback to control the substrate-probe distance. The shear force between the substrate and the probe was monitored with a tuning fork-type quartz crystal and used as the feedback control to set the microelectrode probe close to the substrate surface. The sensitivity and the contrast of the SECM image were improved in the constant distance mode (distance, 50 nm) with the shear force feedback compared to the image in the constant height mode without the feedback. By using this system, the SECM and topographic images of the immobilized diaphorase were simultaneously measured. The microelectrode tip used in this study was ground aslant like a syringe needle in order to obtain the shaper topographic images. This shape was also effective for avoiding the interference during the diffusion of the enzyme substrates.

Electrochemistry↗
PubMed1988

Retinal bipolar cells receive negative feedback input from GABAergic amacrine cells.

Bipolar cells make reciprocal synapses with amacrine cells in the inner plexiform layer; both feedforward connections and feedback connections are present. The physiological properties of the feedback synapse have not been well described. Since some amacrine cells are thought to be GABAergic, we examined bipolar cells for feedback input from gamma-aminobtyric acid (GABA)ergic amacrine cells. Solitary bipolar cells were dissociated enzymatically from the goldfish retina. Cells were voltage clamped with a patch pipette and their GABA sensitivity was examined. GABA evoked responses in all bipolar cells with a large axon terminal, which were identified to be the rod dominant ON type, and in some bipolar cells with a small axon terminal. The highest GABA sensitivity was located at the axon terminal. The least effective dose was as low as 100 nM. A small insignificant response of high threshold was evoked when GABA was applied to the dendrite and soma. GABA increased the Cl conductance and caused membrane hyperpolarization. The bipolar cells had the GABAA receptor coupled with a benzodiazepine receptor. The GABA-evoked response was not susceptible to Co ions, which suppressed the GABA-induced responses in turtle cones by 50% at 5 microM concentration. Incomplete desensitization was observed, suggesting that the GABAergic pathway seems capable of transmitting signals tonically. The present results strongly indicate that the rod-dominant ON-type bipolar cells and some bipolar cells with a small axon terminal receive negative feedback inputs from GABAergic amacrine cells.

Action Potentials↗
PubMed2000

Improving discussion of surgical treatment options for patients with breast cancer: local medical opinion leaders versus audit and performance feedback.

We studied whether a hospital intervention utilizing medical opinion leaders and performance feedback reduced the proportion of women who reported that surgeons did not discuss options prior to surgery for early stage breast cancer. Opinion leaders provided clinical education to their peers using a variety of strategies and were selected for their ability to influence their peers. Performance feedback involved distributing performance reports that contained data on the outcomes of interest as well as on other treatment patterns. Twenty-eight hospitals in Minnesota were randomized to the intervention or to a control group that received performance feedback only. The proportion of patients at intervention hospitals who said that their surgeon did not discuss options decreased significantly (p < 0.001) from 33% to 17%, but a similar decrease was observed among control hospitals. Using medical opinion leaders to intervene in hospitals appeared as effective as performance feedback.

Adult↗