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PubMed2003

Contribution of connexin26 to electrical feedback inhibition in the turtle retina.

The first synaptic integration in the neuronal cascade of vision in vertebrates includes a feedback from horizontal cells to cones by a mechanism yet not fully understood. Recent observations in teleosts suggested an electrical feedback mechanism mediated by connexin26 (Cx26) hemichannels at the terminal dendrites of horizontal cells. By using reverse transcription-polymerase chain reaction and immunoblotting from retinal homogenate, we detected Cx26 mRNA transcripts in the turtle retina and demonstrated that they were translated into protein. Cx26 immunoreactivity was especially prominent in the outer plexiform layer. Subcellularly, immunoreactivity was located mainly between horizontal cell axon terminals and in horizontal cell dendrites forming the lateral elements at the ribbon synaptic complex of the cone pedicle. The label was confined to the horizontal cell membrane flanking the ribbon and was not found on the opposing photoreceptor membrane. No gap junctions at this location are known, so immunosignaling suggested the presence of hemichannels. Their relevance to the feedback mechanism was investigated by intracellular recordings from horizontal cells during application of the hemichannel blocker carbenoxolone. Carbenoxolone hyperpolarized the dark membrane potential by about 25 mV, decreased the amplitudes of responses to full-field light flashes, and suppressed the feedback-induced depolarizing inflexion in the response profile. These physiological findings are compatible with the involvement of hemichannels in the feedback between horizontal cells and cones and support the anatomical findings. Together, these data suggest the presence of an electrical feedback mechanism in the turtle retina, which therefore might be a common mechanism at the first visual synapse in vertebrates.

Animals↗
PubMed1992

The role of hypoglossal sensory feedback during feeding in the marine toad, Bufo marinus.

Behavioral observations demonstrate that bilateral deafferentation of the hypoglossal nerves in the marine toad (Bufo marinus) prevents mouth opening during feeding. In the present study, we used high-speed videography, electromyography (EMG), deafferentation, muscle stimulation, and extracellular recordings from the trigeminal nerve to investigate the mechanism by which sensory feedback from the tongue controls the jaw muscles of toads. Our results show that sensory feedback from the tongue enters the brain through the hypoglossal nerve during normal feeding. This feedback appears to inhibit both tonic and phasic activity of the jaw levators. Hypoglossal feedback apparently functions to coordinate tongue protraction and mouth opening during feeding. Among anurans, the primitive condition is the absence of a highly protrusible tongue and the absence of a hypoglossal sensory feedback system. The hypoglossal feedback system evolved in parallel with the acquisition of a highly protrusible tongue in toads and their relatives.

Animals↗
PubMed2000

Effects of teacher feedback on the reputations and peer perceptions of children with behavior problems.

We explored whether teacher feedback modified children's preferences and perceptions of a target child with behavior problems. First- and second-grade children (M age = 7.8 years) viewed a videotape of a target actor presented as having a liked, average, or disliked reputation. A second videotape depicted a teacher's verbal responses to the target's behavior as (a) positive, (b) neutral-salient, or (c) corrective. Both salience and valence of teacher feedback were assessed. Main effects of feedback and reputation indicated that feedback had at least minimal effects at each level of the target's reputation. Teacher feedback is discussed with respect to its effects on perceptions of behavior versus affective responses toward behavior-problem children. A significant interaction showed that when combined with a liked reputation, positive and neutral-salient feedback conditions increased the salience and positive evaluation of the target child, thus illustrating the importance of considering nonevaluative teacher attention in combination with children's reputational status.

Child↗
PubMed2000

The effect of verbal feedback on motor learning--a PET study. Positron emission tomography.

The purpose of this study was to investigate brain mechanisms underlying feedback effects on motor learning. We measured human brain activity using positron emission tomography (PET) during length-of-line drawing tasks in the presence or absence of verbal feedback, i.e., information on the precision of motor performance. The average error in responses was significantly lower and the percentage of correct responses was significantly higher in the case of tasks with feedback than those in the absence of feedback. The contralateral sensorimotor, premotor, supplementary motor, the right prefrontal, bilateral parietal and temporal, and anterior cingulate cortices, and the left basal ganglia were activated during all the line-drawing tasks. The right lateral prefrontal and occipital cortices and the left basal ganglia exhibited marked increase in activity after learning. The right inferior parietal and the anterior cingulate cortices were activated in the presence of feedback which provided information on how the subjects should correct their performances. The results indicate that these brain areas may play an important role in representing knowledge of results during motor learning and that appropriate feedback may facilitate motor learning.

Adult↗
PubMed2002

The role of proprioceptive feedback in the regulation and adaptation of locomotor activity.

Feedback from muscle afferents is essential for locomotion to be functional under changing external conditions. In this article, we review the role of afferent feedback in adapting locomotor activity to transient and more sustained changes in sensory input in reduced and walking cat preparations. Much of the work on muscle afferent regulation of locomotion has focused on the regulation of stance phase activity. Proprioceptive feedback from extensor muscles during the stance phase ensures that the leg does not go into swing when loaded and that the magnitude of extensor activity is adequate for support. Proprioceptive feedback from flexor muscles towards the end of the stance phase facilitates the initiation of the swing phase of walking. Evidence that muscle afferent feedback also contributes to the magnitude and duration of flexor activity during the swing phase has been demonstrated recently. The regulation of the magnitude and duration of extensor and flexor activity during locomotion is mediated by monosynaptic, disynaptic, and polysynaptic muscle afferent pathways in the spinal cord. In addition to allowing for rapid adaptation in motor output during walking, afferent feedback from muscle proprioceptors is also involved in longer-term adaptations in response to changes in the biomechanical or neuromuscular properties of the walking system.

Adaptation, Physiological↗
PubMed1976

[Controlled EEG alpha feedback training in normals and headache patients (author's transl)].

Headache patients and healthy controls underwent alpha-EEG feedback training in 12 sessions. The present study does not support the literature which reports alpha increase by feedback training. The study included a patient group receiving feedback, a patient control group receiving pseudofeedback, and a volunteer group receiving feedback. Increase of alpha EEG was observed under feedback and pseudofeedback. However, there was always more alpha during baseline times than during training times. Alpha increase over time is suggested to be a habituation effect. Headache pain decreased with training (within the boundaries of a placebo effect), and there was no difference in headache decrease between feedback and pseudofeedback patients.

Adult↗
PubMed1976

Activation of tubulo-glomerular feedback by chloride transport.

To define the luminal agent(s) responsible for the reduction of nephron filtration rate following increases of loop of Henle flow rate early proximal flow rate (EPFR) during loop perfusion with 17 different salt solutions were compared to the non-perfused tubules. During orthograde microperfusions a reduction of EPFR as indication of a feedback response was noted with a number of monovalent Cl- and Br- salts (LiCl, KCl, NaCl, RbCl, CsCl, NH4Cl, choline Cl, NaBr, KBr), with Na+ salts except Na acetate (NaHCO3, NaNO3, NaF, NaI, NaSCN), and with CaCl2 and MgCl2. These latter 2 solutions where used in a concentration of 70 mM while all other solutions had a concentration of 140 mM. During retrograde perfusion from the distal to the proximal end of the loop of Henle EPFR fell significantly with Cl- and Br- salts with percentage changes of EPFR ranging from -8.0 to -44.3%. In contrast, Cl- free salts and Cl- salts of divalent cations were associated with percentage changes of EPFR ranging from +7.1 to -6.2%, significance being reached only during perfusion with NaSCN. When furosemide (5 x 10(-4) M) was added to NaBr or KBr a feedback response was not observed. During orthograde perfusion with NaNO3 distal Cl- concentrations were 44.2 +/- 5.08, mM (mean +/- S.E.) at a perfusion rate of 10 nl/min and 59.1 +/- 3.93 mM at a rate of 40 nl/min. CaCl2 perfusion induced a marked elevation of distal Cl- concentrations to levels higher than 140 mM. Loop chloride handling was normal during RbCl perfusion. The magnitude of the feedback response during retrograde perfusion was not changed by lowering NaCl concentration from 140 to 60 mM, but fell when NaCl concentration was further reduced. In contrast to orthograde perfusions it was insensitive to changes in flow rate. Our results are compatible with the thesis that feedback responses depend critically upon the rate of Cl- transport probably across the macula densa cells. Br- ions can replace Cl- because they appear to share a common transport pathway which can be inhibited with furosemide. Unspecificity of feedback responses during orthograde microperfusions is due to presence of Cl- ions in the macula densa region even when solutions are initially Cl- free. Cl- salts of divalent cations do not elicit a feedback response because Cl- transport is severely curtailed.

Animals↗
PubMed1981

The existence of a tubulo-glomerular feedback mechanism in the Amphiuma nephron.

A single nephron tubulo-glomerular feedback control of the glomerular filtration rate, which is known in mammalian animals, could be one way by which amphibians regulate the glomerular filtration rate (GFR). To investigate whether the Amphiuma means shows any sign of a tubulo-glomerular feedback control, micropuncture experiments were carried out. Six different series of experiments were performed. In the first series, tubular stop-flow pressure (SFP) was measured during distal tubular perfusion with amphibian Ringer solution at a rate of 10, 25 and 50 nl/min. A significant decrease of SFP was found at the three perfusion rates compared to the controls. In the second group, single nephron glomerular filtration rate (SNGFR) was measured, while the distal tubule was perfused at 10, 25 and 50 nl/min. At a perfusion rate of 10 nl/min the SNGFR did not decrease, whereas at 25 and 50 nl/min it decreased significantly. In the third group the perfusion pipette was located in the proximal tubule and the nephron was perfused at 10, 25 and 50 nl/min, while at the same time the proximal tubular stop-flow pressure was measured. No reduction of SFP was found at a perfusion rate of 10 nl/min, while significant reductions were noted at rates of 25 and 50 nl/min. In the fourth group the SNGFR was measured in the distal tubule beyond the macula densa and in Bowman's space of the same nephron. No significant difference was found. In the fifth group, the glomerular capillary pressure (GCP) was measured before and after blockade of the tubular fluid flow. No significant difference was found between these two measurements. The sixth series deals with the changes occurring at the single nephron level by the tubulo-glomerular feedback control. The single nephron filtration fraction (FF) was determined from efferent arteriolar protein concentration with and without a feedback-induced reduction of the SNGFR. The FF values were not significantly different from one another. From these results and data from the other series, the afferent (Raff) and efferent (Reff) arteriolar resistances were calculated. Reff did not change, while Raff increased significantly when a feedback stimulus was applied. These experiments indicate the existence of a tubulo-glomerular feedback control which depresses the SNGFR and SFP by contracting the afferent arteriole.

Animals↗
PubMed1983

Feedback and incentive effects on the decrease of interbeat interval.

Johnston and Lethem (1981) have hypothesized that when subjects attempt to decrease their interbeat interval (i.e., increase their heart rate) maximally, then interbeat interval feedback has a purely motivational role, but when they attempt to decrease their interbeat interval by a precise amount, such feedback has a primarily informational role. This was tested by comparing the performance of 16 subjects on both types of task. It was predicted that additional monetary incentives would reduce the difference between feedback and no-feedback conditions when subjects were attempting to reduce interbeat interval maximally but not when attempting to reduce it by a specific amount. This prediction was not supported. Incentive was found to aid performance on the maximal interbeat interval decrease task, but this was independent of the effects of feedback. Only feedback effects were detected on the specific interbeat interval decrease task.

Adult↗
PubMed1990

The effect of feedback-assisted reduction in heart rate reactivity on videogame performance.

In 67 male volunteers, we examined the reduction of cardiovascular responsivity to a psychomotor challenge (videogame) achieved by use of heart rate (HR) feedback and effects of these procedures on concomitant behavioral performance. Each subject participated in a pretraining assessment of his cardiovascular responses to the videogame, a training condition, and a posttraining assessment identical to the initial evaluation. During training, subjects were assigned to one of four conditions: (a) a habituation control group receiving no instructions to alter HR (HC); (b) an instructions-only control group receiving instructions to maintain a low or unchanged HR during videogame presentations (IC); (c) a feedback group receiving instructions to reduce HR using ongoing HR feedback (FB-); or (d) a feedback group receiving instructions to lower HR and given HR feedback plus a score contingency in which total game score was jointly determined by subjects' game performance and success at HR control (FB+). Subjects receiving feedback (FB+, FB-) exhibited greater reductions in HR response to the videogame in the posttraining assessment than control (HC, IC) subjects; FB+ subjects showed greater HR reductions than subjects in any other group. FB+ and FB- subjects showed a lower SBP at posttraining relative to the two control groups, but no reduction in task-induced blood pressure reactivity. There were no group differences in videogame performance, either before or following training.

Adolescent↗
PubMed1997

Interlimb coordination in patients with Parkinson's disease: motor learning deficits and the importance of augmented information feedback.

The basal ganglia have traditionally been associated with motor control functions and this view has prevailed since the late nineteenth century. Recent experimental studies suggest that this neuroanatomical system is also critically involved in motor learning. In the present study, motor learning/transfer capabilities were compared between patients with Parkinson's disease and a group of normal elderly people. Subjects practiced a bimanual coordination task that required continuous flexion-extension movements in the transverse plane with a 90 degrees phase offset between the forearms. During acquisition, augmented visual feedback of the relative motions was provided in real time. The findings revealed improvements in the bimanual coordination pattern across practice in both groups when the augmented concurrent feedback was present. However, when transferred to performance conditions in which the augmented information was withheld, performance deteriorated (relative to the augmented condition) and this effect was more prevalent in the Parkinson patients. More specifically, no improvement in interlimb coordination was observed under nonaugmented feedback conditions across practice. Instead, a drift toward the preferred in-phase and antiphase coordination patterns was evident. The present findings suggest that Parkinson patients can improve their performance on a new motor task, but they remain strongly dependent on augmented visual information to guide these newly acquired movements. The apparent adoption of a closed-loop control mode is accompanied with decreases in movement speed in order to use the feedback to ensure accuracy. When the augmented feedback is withheld and the movement pattern is to be controlled by means of intrinsic information feedback sources, performance is severely hampered. The findings are hypothesized to indicate that learning/transfer is affected in Parkinson patients who apparently prefer some constancy in the environmental contingencies under which practice takes place. The present findings are consistent with the notion that the basal ganglia form a critical neuroanatomical substrate for motor learning.

Aged↗
PubMed2002

Adaptation of movement endpoints to perturbations of visual feedback.

We investigated the extent to which humans can quickly adapt their goal-directed arm movements to perturbed feedback. We predicted that the magnitude of adaptation to a changed relationship between vision and kinesthesia would depend on the type of perturbation, being largest when the perturbation can be generalized within egocentric frames of reference. To test this prediction we asked subjects to align a real 5-cm cube so that they could feel, but not see, with a simulation that they saw via a mirror. Subjects made successive movements between target locations in a sequence of adaptation and test phases. During adaptation phases, subjects received continuous visual feedback about the position of the real cube. The feedback was either veridical or perturbed. The perturbations were consistent with either a uniform translation, a scaling or a rotation. The latter two were relative to a central position between all the targets. During test phases, subjects received no visual feedback. We compared test movement endpoints after perturbed feedback with ones after veridical feedback. We found about 40% adaptation to translation, 20% to scaling and 10% to rotation. This difference in magnitude is consistent with the ease with which the transformation can be generalized within egocentric frames of reference. Changing the task so that it required different arm postures did not change the magnitude of adaptation, so postural configuration of the arm does not appear to be critical. Nevertheless, transfer to the unexposed arm was incomplete for translations and rotations, though it was complete for scaling, suggesting that at least part of the adaptation is posture based. We conclude that the adaptation to different kinds of perturbations not only differs in extent but also involves different (egocentric) mechanisms.

Adaptation, Physiological↗
PubMed2005

The use of visual feedback is independent of visual awareness: evidence from visual extinction.

Milner and Goodale (The visual brain in action, Oxford Press, 1995) made a distinction between vision for perception and vision for action. In contrast to perception, many action tasks have strict temporal constraints, which can only be met if the visual information is relayed directly to the motor system without first passing through a conscious decision making process. Milner and Goodale therefore predict that visual stimuli do not have to reach visual awareness in order to guide rapid motor responses. Online visual feedback provides a good example of visual information that is used under tight temporal constraints to guide rapid motor responses. Online visual feedback provides information about the position of the moving limb. This information can be used to improve the accuracy of our movements. If vision for action operates independently of visual awareness, visual feedback should be beneficial even if the subject is unaware of this information. We tested this prediction in a patient (V.E.) with left-sided visual extinction, a condition in which a visual stimulus typically fails to reach awareness if a second stimulus is presented simultaneously at a more rightward location. V.E. was asked to point towards a central target with his left hand. In some trials a light-emitting diode (LED) provided brief visual feedback from the moving hand. However, in the majority of trials, V.E. was unaware of this LED, due to his extinction. His performance was nevertheless significantly better when visual feedback was present, regardless of whether or not the information was available for verbal report. We conclude that visual awareness is not essential for the effective use of online visual feedback.

Aged↗
PubMed1999

The role of visual feedback of hand position in the control of manual prehension.

Although it is obvious that vision plays a primary role in reaching and grasping objects, the sources of the visual information used in programming and controlling various aspects of these movements is still being investigated. One source of visual information is feedback relating to the characteristics of the reach itself for example, the speed and trajectory of the moving limb and the change in the posture of the hand and fingers. The present study selectively eliminated this source of visual information by blocking the subject's view of the reaching limb with an opaque barrier while still enabling subjects to view the goal object. Thus, a direct comparison was made between standard (closed-loop) and object-only (open-loop) visual-feedback conditions in a situation in which the light levels and contrast between an object and its surroundings were equivalent in both viewing conditions. Reach duration was longer with proportionate increases in both the acceleration and deceleration phases when visual feedback of the reaching limb was prevented. Maximum grip aperture and the proportion of movement time at which it occurred were the same in both conditions. Thus, in contrast to previous studies that did not employ constant light levels across closed- and open-loop reaching conditions, a dissociation was found between the spatial and temporal dimensions of grip formation. It appears that the posture of the hand can be programmed without visual feedback of the hand--presumably via a combination of visual information about the goal object and proprioceptive feedback (and/or efference copy). Nevertheless, maximum grip aperture (like the kinematic markers examined in the transport component) was also delayed when visual feedback of the reaching limb was selectively prevented. In other words, the relative timing of kinematic events was essentially unchanged, reflecting perhaps a tight coupling between the transport and grip components.

Acceleration↗
PubMed2006

Methods and mechanisms for contact feedback in a robot-assisted minimally invasive environment.

Providing a surgeon with information regarding contacts made between instruments and tissue during robot-assisted interventions can improve task efficiency and reliability. In this report, different methods for feedback of such information to the surgeon are discussed. It is hypothesized that various methods of contact feedback have the potential to enhance performance in a robot-assisted minimally invasive environment. To verify the hypothesis, novel mechanisms needed for incorporating contact feedback were designed, including a surgeon-robot interface with full force feedback capabilities and a surgical end-effector with full force sensing capabilities, that are suitable for minimally invasive applications. These two mechanisms were used to form a robotic "master-slave" test bed for studying the effect of contact feedback on the system and user performance. Using the master-slave system, experiments for surgical tasks involving soft tissue palpation were conducted. The performance of the master-slave system was validated in terms of criteria that assess the accurate transmission of task-related information to the surgeon, which is critical in the context of soft tissue surgical applications. Moreover, using a set of experiments involving human subjects, the performance of several users in carrying out the task was compared among different methods of contact feedback.

Adult↗
PubMed2006

Designing feedback-based contrast enhancement for in vivo imaging.

OBJECTIVE: Nonlinear feedback interactions induced by the spins themselves have recently been introduced as novel MRI contrast enhancement mechanisms sensitive to small differences in MR parameters. Developing feedback-based contrast enhancement into a useful tool for in vivo imaging requires improved techniques that are robust to inhomogeneity and sensitive to subtle anatomical/physiological variations. MATERIALS AND METHODS: Three different imaging methods combining the radiation damping feedback field with the distant dipolar field, applied radio-frequency (RF) fields, and local dipole fields, respectively, were designed and tested through numerical simulations on simple phantoms. These methods were demonstrated experimentally on live guppy fish, developing frog embryos, and blood in in vitro tissue samples by microimaging at 14.1 T. RESULTS: The developed feedback-based methods yielded images that identified distinct morphological features with superior contrast compared with conventional MR images and those acquired under radiation damping only. Positive contrast due to evolution under radiation damping and local dipole fields was also observed in SPIOs and blood. CONCLUSION: Approaches to enhancing feedback-based contrast were successfully designed and demonstrated in vitro and in vivo. The newly devised methods were less sensitive to field inhomogeneity and prolonged evolution under the feedback fields, allowing for better visualization of contrast in vivo.

Algorithms↗
PubMed2006

Feedback for general practitioners in training: quality, styles, and preferences.

A General Practitioner (GP) is no longer a loner, but a team player in either a group practice or a care centre. This change has led to a concomitant growth in curricular interest in skills essential for successful collaboration and for enhancing critical reflection towards colleagues' performance. Giving and receiving constructive feedback are examples of these skills. The aim of this study was to gain insight in the style and quality of feedback reports on consultation skills written by GPs-in-Training (GPiTs) and by their GP-trainers. Furthermore, the preferences of the GPiTs concerning feedback style were examined. Results show significant differences between GP-trainers and GPiTs in feedback style and quality. A ranking task indicated that GPiTs have a preference for reports characterised by a large number of reflective remarks. Questionnaire results indicate the added value of the use of peer feedback. Implications for the integration of peer feedback activities in the curriculum of GPiTs are discussed.

Clinical Competence↗
PubMed1985

Photoperiod-dependent negative feedback effects of thyroid hormones in Fundulus heteroclitus.

In Fundulus heteroclitus, an annual cycle in the response of the thyroid to ovine thyroid-stimulating hormone (oTSH) is characterized by maximal thyroxin (T4) secretion in mid-winter and minimal T4 secretion in summer. Four daily injections of oTSH, given in winter caused serum T4 to plateau at elevated levels for several days, while in summer fish similar treatment resulted in far more fluctuating titers of serum T4; maximum levels were similar in both groups. The difference in sustenance rather than magnitude of Peak T4 led to an examination of the negative feedback effects of thyroid hormones as they might relate to these seasonal changes. Radioiodine uptake by thyroid follicles served as a simple, but effective bioassay for endogenous TSH. Fish collected in summer were more sensitive to negative feedback of T3 than those collected in winter; feedback effects of T4 in the two groups were not significantly different. The effects of specific photoperiods on negative feedback sensitivity to T3 and T4 were also tested. Exposure of winter fish for one month to long days (LD 14:10) enhanced the degree of reduction of iodine uptake caused by T4 in the aquarium water (10 micrograms/100 ml). Negative feedback in short-day (LD 8:16) winter fish was not demonstrated. It is concluded that long days increase and short days diminish the negative feedback sensitivity of the hypothalamus-pituitary axis to thyroid hormones in F. heteroclitus. Such photoperiodically induced changes may act to aid in the year-round maintenance of T4 levels necessary for seasonal adaptation and survival.

Animals↗