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W Schultz

Publications and source records attributed to W Schultz.

At least 19 recordsLinked to original sources
PubMed2001

[Hemialloarthroplasty of the knee joint. Results of 2 different gliding prosthesis models].

The outcome of 2 different unicompartimental knee arthroplasty procedures (St. Georg, Link AG, and Wessinghage, Sulzer Medica AG) is presented. The clinical results were evaluated by use of the Insall Score (Knee Society Rating System). According to this system, the subjective opinion of the patients are presented as a "Function Score" and the clinical evaluations is shown as a "Knee Score". In this study, the median follow-up for the St. Georg implant was 7 years and 6 months with good results reported by both scores. The median follow-up for the Wessinghage implant was 3 years and 2 months and it also showed good results. Despite the high average age of the patients in this study as well as the high percentage of female patients, both types of prostheses produced good results. If any, partial or complete radioluciencies were mainly observed in the tibial component. However, they had no clinical consequence. It should be noted, however, that arthritis in the compartment not receiving arthroplasty surgery progressed in almost 2/3 of the patients. By implantation of both implants a physiological axis of the leg could be achieved. The survivorship of the St. Georg implant was 88.92% (10 years survivorship). For the Wessinghage implant it was 98.35% (5 years survivorship).

Aged↗
PubMed2001

Temporal difference model reproduces anticipatory neural activity.

Anticipatory neural activity preceding behaviorally important events has been reported in cortex, striatum, and midbrain dopamine neurons. Whereas dopamine neurons are phasically activated by reward-predictive stimuli, anticipatory activity of cortical and striatal neurons is increased during delay periods before important events. Characteristics of dopamine neuron activity resemble those of the prediction error signal of the temporal difference (TD) model of Pavlovian learning (Sutton & Barto, 1990). This study demonstrates that the prediction signal of the TD model reproduces characteristics of cortical and striatal anticipatory neural activity. This finding suggests that tonic anticipatory activities may reflect prediction signals that are involved in the processing of dopamine neuron activity.

Algorithms↗
PubMed2000

Reduced reward processing in the brains of Parkinsonian patients.

Regional cerebral blood flow (rCBF) in healthy controls and non-demented, non-depressed Parkinsonian patients was measured using H2(15)O PET while subjects performed a prelearned pattern recognition task with delayed response. To investigate differences between the two groups in response to reward, the experimental design consisted of three reinforcement conditions: no reinforcement consisting of nonsense feedback, positive symbolic reinforcement and monetary reward. In the controls, monetary reward activated bilaterally the striatum and anterior cingulate gyrus, as well as unilaterally the left cerebellum, midbrain and medial frontal gyrus. Symbolic reinforcement revealed a similar pattern of activation, except that the striatum and left midbrain showed no activation. The Parkinsonian patients responded to monetary reward with increased activation bilaterally in the cerebellum, medial frontal gyrus, and anterior cingulate gyrus as well as unilaterally in the right fusiform gyrus and midbrain and left caudate nucleus and precentral gyrus. Symbolic reinforcement induced significantly increased rCBF in the right cerebellum only. Compared with symbolic reinforcement, monetary reward produced extended activation of temporoparietal association cortex. The pattern observed in the controls demonstrates the role in reward processing of dopaminergic mesolimbic pathways in the healthy human brain, whereas the pattern in the Parkinsonian patients suggests the involvement of compensatory cortical loops in the diseased brain.

Arousal↗
PubMed2000

Involvement of basal ganglia and orbitofrontal cortex in goal-directed behavior.

An impressive array of neural processing appears to be dedicated to the extraction of reward-related information from environmental stimuli and use of this information in the generation of goal-directed behaviors. While other structures are certainly involved in these processes, the characteristics of activations seen in mesencephalic dopamine neurons, striatal neurons and neurons of the orbitofrontal cortex provide distinct examples of the different ways in which reward-related information is processed. In addition, the differences in activations seen in these three regions demonstrate the different roles they may play in goal-directed behavior. A principal role played by dopamine neurons is that of a detector of an error in reward prediction. The homogeneity of responsiveness across the population of dopamine neurons indicates that this error signal is widely broadcast to dopamine terminal regions where it could provide a teaching signal for synaptic modifications underlying the learning of goal-directed appetitive behaviors. The responses of these same neurons to conditioned stimuli associated with reward could also serve as a signal of prediction error useful for the learning of sequences of environmental stimuli leading to reward. Dopamine neuron responses to both rewards and conditioned stimuli are not contingent on the behavior executed to obtain the reward and thus appear to reflect a relatively pure signal of a reward prediction error. It is not yet clear whether these activations, and responses to novel stimuli, have an additional function in engaging neural systems involved in the representation and execution of goal-directed behaviors. This representation of goal-directed behaviors may involve the striatal regions studied, where processing of reward-related information appears to be much more heterogeneous. Different subpopulations of striatal neurons are activated at different stages in the course of goal-directed behaviors, with largely separate populations activated following presentation of conditioned stimuli, preceding reinforcers, and following reinforcers. Neurons exhibiting each of these types of activation appear to differentiate between rewarding and non-rewarding outcomes of behavioral acts and, as a population, appear to be biased towards processing reward vs. non-reward. These activations observed in the striatum were often contingent on the behavioral act associated with obtaining reward, reflecting an integration of information not observed in dopamine neurons. Another difference between reward processing in striatal neurons and dopamine neurons is the influence of predictability on neuronal responsiveness. Unlike dopamine neurons, many striatal neurons respond to predicted rewards, although at least some may reflect the relative degree of predictability in the magnitude of the responses to reward. Thus, striatal processing of reward-related information is in some ways more complex than that observed in dopamine neurons, incorporating information on behavior and potentially providing more detailed information regarding predictability. These activations could serve as a component of the neural representation of the goal, and/or the behavioral aspects of goal-directed behaviors. As such they would be of use for the execution of appropriate goal-directed behaviors in response to known environmental stimuli, as well as for generating behaviors in response to novel stimuli that may be associated with desirable goals. Neuronal activations in the orbitofrontal cortex appear to involve less integration of behavioral and reward-related information, but rather incorporate another aspect of reward, the relative motivational significance of different rewards. These activations would serve a function similar to those striatal neurons that encode exclusively reward-related information in situations in which only a single outcome is obtainable. (ABSTRACT TRUNCATED)

Animals↗
PubMed2000

Multiple reward signals in the brain.

The fundamental biological importance of rewards has created an increasing interest in the neuronal processing of reward information. The suggestion that the mechanisms underlying drug addiction might involve natural reward systems has also stimulated interest. This article focuses on recent neurophysiological studies in primates that have revealed that neurons in a limited number of brain structures carry specific signals about past and future rewards. This research provides the first step towards an understanding of how rewards influence behaviour before they are received and how the brain might use reward information to control learning and goal-directed behaviour.

Animals↗
PubMed2000

Massive intraosseous ganglion of the talus: reconstruction of the articular surface of the ankle joint.

We report on the outcome after autologous chondrocyte and spongiosal bone transplantation in a case of a massive intraosseous ganglion of the talus in a young patient. A 24-year-old man suffered from decreased ankle joint motion, recurrent swelling, and pain. Diagnostic evaluation by plain radiographs, computed tomography, and magnetic resonance imaging revealed cystic lesions in the head and the body of the talus with additional involvement of the cartilage surface. Operative treatment consisted primarily of an initial diagnostic arthroscopy, which established grade VI articular damage according to the arthroscopic classification of Bauer and Jackson. Pathological examination of intralesional biopsy tissue revealed the existence of an intraosseous ganglion. Additionally, healthy cartilage biopsy specimens were obtained and sent for chondrocyte extraction and cultivation with 60 mL of autologous serum. To retain the function of the ankle joint and to minimize the number of necessary operative interventions, 3 weeks after the initial arthroscopic operation, we performed a simultaneous curettage of the cystic lesion followed by autologous spongiosal bone and cultivated chondrocytes transplantation of the talus. Continuous passive motion was applied postoperatively and full weight bearing was allowed after 8 weeks. There were no complications. The clinical result after 18 months was excellent, with a fully functional, pain-free, and weight-bearing ankle joint. The postoperative evaluation score of Finsen (modified Weber score) of 2/6 = 0.3 showed an improvement comparison with the preoperative value of of 21/6 = 3.5 (0 = normal, 4 = pathologic). We encountered no complications postoperatively. Clinical success was achieved by this method of treatment on a patient too young to be treated through arthrodesis.

Adult↗
PubMed2000

Reward processing in primate orbitofrontal cortex and basal ganglia.

This article reviews and interprets neuronal activities related to the expectation and delivery of reward in the primate orbitofrontal cortex, in comparison with slowly discharging neurons in the striatum (caudate, putamen and ventral striatum, including nucleus accumbens) and midbrain dopamine neurons. Orbitofrontal neurons showed three principal forms of reward-related activity during the performance of delayed response tasks, namely responses to reward-predicting instructions, activations during the expectation period immediately preceding reward and responses following reward. These activations discriminated between different rewards, often on the basis of the animals' preferences. Neurons in the striatum were also activated in relation to the expectation and detection of reward but in addition showed activities related to the preparation, initiation and execution of movements which reflected the expected reward. Dopamine neurons responded to rewards and reward-predicting stimuli, and coded an error in the prediction of reward. Thus, the investigated cortical and basal ganglia structures showed multiple, heterogeneous, partly simultaneous activations which were related to specific aspects of rewards. These activations may represent the neuronal substrates of rewards during learning and established behavioral performance. The processing of reward expectations suggests an access to central representations of rewards which may be used for the neuronal control of goaldirected behavior.

Animals↗
PubMed2000

Neuronal coding of prediction errors.

Associative learning enables animals to anticipate the occurrence of important outcomes. Learning occurs when the actual outcome differs from the predicted outcome, resulting in a prediction error. Neurons in several brain structures appear to code prediction errors in relation to rewards, punishments, external stimuli, and behavioral reactions. In one form, dopamine neurons, norepinephrine neurons, and nucleus basalis neurons broadcast prediction errors as global reinforcement or teaching signals to large postsynaptic structures. In other cases, error signals are coded by selected neurons in the cerebellum, superior colliculus, frontal eye fields, parietal cortex, striatum, and visual system, where they influence specific subgroups of neurons. Prediction errors can be used in postsynaptic structures for the immediate selection of behavior or for synaptic changes underlying behavioral learning. The coding of prediction errors may represent a basic mode of brain function that may also contribute to the processing of sensory information and the short-term control of behavior.

Animals↗
PubMed2000

Reward-related neuronal activity during go-nogo task performance in primate orbitofrontal cortex.

The orbitofrontal cortex appears to be involved in the control of voluntary, goal-directed behavior by motivational outcomes. This study investigated how orbitofrontal neurons process information about rewards in a task that depends on intact orbitofrontal functions. In a delayed go-nogo task, animals executed or withheld a reaching movement and obtained liquid or a conditioned sound as reinforcement. An initial instruction picture indicated the behavioral reaction to be performed (movement vs. nonmovement) and the reinforcer to be obtained (liquid vs. sound) after a subsequent trigger stimulus. We found task-related activations in 188 of 505 neurons in rostral orbitofrontal area 13, entire area 11, and lateral area 14. The principal task-related activations consisted of responses to instructions, activations preceding reinforcers, or responses to reinforcers. Most activations reflected the reinforcing event rather than other task components. Instruction responses occurred either in liquid- or sound-reinforced trials but rarely distinguished between movement and nonmovement reactions. These instruction responses reflected the predicted motivational outcome rather than the behavioral reaction necessary for obtaining that outcome. Activations preceding the reinforcer began slowly and terminated immediately after the reinforcer, even when the reinforcer occurred earlier or later than usually. These activations preceded usually the liquid reward but rarely the conditioned auditory reinforcer. The activations also preceded expected drops of liquid delivered outside the task, suggesting a primary appetitive rather than a task-reinforcing relationship that apparently was related to the expectation of reward. Responses after the reinforcer occurred in liquid- but rarely in sound-reinforced trials. Reward-preceding activations and reward responses were unrelated temporally to licking movements. Several neurons showed reward responses outside the task but instruction responses during the task, indicating a response transfer from primary reward to the reward-predicting instruction, possibly reflecting the temporal unpredictability of reward. In conclusion, orbitofrontal neurons report stimuli associated with reinforcers are concerned with the expectation of reward and detect reward delivery at trial end. These activities may contribute to the processing of reward information for the motivational control of goal-directed behavior.

Animals↗
PubMed2000

Modifications of reward expectation-related neuronal activity during learning in primate orbitofrontal cortex.

This study investigated how neuronal activity in orbitofrontal cortex related to the expectation of reward changed while monkeys repeatedly learned to associate new instruction pictures with known behavioral reactions and reinforcers. In a delayed go-nogo task with several trial types, an initial picture instructed the animal to execute or withhold a reaching movement and to expect a liquid reward or a conditioned auditory reinforcer. When novel instruction pictures were presented, animals learned according to a trial-and-error strategy. After experience with a large number of novel pictures, learning occurred in a few trials, and correct performance usually exceeded 70% in the first 60-90 trials. About 150 task-related neurons in orbitofrontal cortex were studied in both familiar and learning conditions and showed two major forms of changes during learning. Quantitative changes of responses to the initial instruction were seen as appearance of new responses, increase of existing responses, or decrease or complete disappearance of responses. The changes usually outlasted initial learning trials and persisted during subsequent consolidation. They often modified the trial selectivities of activations. Increases might reflect the increased attention during learning and induce neuronal changes underlying the behavioral adaptations. Decreases might be related to the unreliable reward-predicting value of frequently changing learning instructions. The second form of changes reflected the adaptation of reward expectations during learning. In initial learning trials, animals reacted as if they expected liquid reward in every trial type, although only two of the three trial types were rewarded with liquid. In close correspondence, neuronal activations related to the expectation of reward occurred initially in every trial type. The behavioral indices for reward expectation and their neuronal correlates adapted in parallel during the course of learning and became restricted to rewarded trials. In conclusion, these data support the notion that neurons in orbitofrontal cortex code reward information in a flexible and adaptive manner during behavioral changes after novel stimuli.

Adaptation, Psychological↗
PubMed2000

[Para-articular knee osteotomies].

Osteotomy close to the knee is an established method to treat degenerative osteoarthritis of the knee with varus or valgus deformity. However, indications, surgical techniques and results are discussed controversially. This article gives an overview of those surgical procedures most commonly used for correcting valgus and varus deformities. Supported by our results it is shown that osteotomy of the tibia for degenerative osteoarthritis together with operative arthroscopy in the same operative session gives better results compared to osteotomy alone. Despite the success of arthroplasty of the knee, osteotomy has it's place in the treatment of osteoarthritis.

Arthroscopy↗
PubMed1999

Relative reward preference in primate orbitofrontal cortex.

The orbital part of prefrontal cortex appears to be crucially involved in the motivational control of goal-directed behaviour. Patients with lesions of orbitofrontal cortex show impairments in making decisions about the expected outcome of actions. Monkeys with orbitofrontal lesions respond abnormally to changes in reward expectations and show altered reward preferences. As rewards constitute basic goals of behaviour, we investigated here how neurons in the orbitofrontal cortex of monkeys process information about liquid and food rewards in a typical frontal task, spatial delayed responding. The activity of orbitofrontal neurons increases in response to reward-predicting signals, during the expectation of rewards, and after the receipt of rewards. Neurons discriminate between different rewards, mainly irrespective of the spatial and visual features of reward-predicting stimuli and behavioural reactions. Most reward discriminations reflect the animals' relative preference among the available rewards, as expressed by their choice behaviour, rather than physical reward properties. Thus, neurons in the orbitofrontal cortex appear to process the motivational value of rewarding outcomes of voluntary action.

Animals↗
PubMed1999

Articular cartilage regeneration of the knee joint after proximal tibial valgus osteotomy: a prospective study of different intra- and extra-articular operative techniques.

In this prospective study high tibial osteotomy for medial gonarthrosis was performed in 95 patients (105 knee joints). The patients underwent simultaneously diagnostic and operative arthroscopic surgery of the knee joint. A follow-up arthroscopic examination could be performed in 75 patients (85 knee joints) at the time of implant removal. In group 1 (20 knee joints), the osteotomy was performed after diagnostic arthroscopy without arthroscopic operation of the knee joint. The fixation of the osteotomy was accomplished by staples, postoperative plaster fixation and physiotherapy. In group 2 (20 knee joints), osteotomy was performed without additional operative arthroscopy after diagnostic arthroscopy, internal fixation by AOT-plate, no external fixation postoperatively and physiotherapy. In group 3 (22 knee joints), osteotomy was performed with additional operative arthroscopy (Pridie drilling), internal fixation by AOT-plate no external fixation postoperatively no external fixation, physiotherapy and continuous passive motion. In group 4 (23 knee joints), osteotomy was performed with additional operative arthroscopy (abrasio-arthroplasty), internal fixation by AOT-plate, no external fixation postoperatively, physiotherapy and continuous passive motion. All patients underwent arthroscopic examination of the knee with cartilage biopsies taken from three different regions of the femoral condyle during the same operative session as the osteotomy. At follow-up arthroscopy cartilage biopsies were taken from the same regions. There was no great difference in clinical outcome after 1 year between all groups. Arthroscopy as well as routine and electron microscopy showed better cartilage regeneration in groups 3 and 4. Groups 1 and 2 showed only regeneration isles, sometimes not well fixed to the underlying bone, while in groups 3 and 4 cartilage regeneration was thicker and more stable, sometimes covering all of the pre-existing erosions. Therefore, we recommend osteotomy of the tibia for osteoarthritis together with operative arthroscopy in the same operative session.

Adult↗
PubMed1999

A neural network model with dopamine-like reinforcement signal that learns a spatial delayed response task.

This study investigated how the simulated response of dopamine neurons to reward-related stimuli could be used as reinforcement signal for learning a spatial delayed response task. Spatial delayed response tasks assess the functions of frontal cortex and basal ganglia in short-term memory, movement preparation and expectation of environmental events. In these tasks, a stimulus appears for a short period at a particular location, and after a delay the subject moves to the location indicated. Dopamine neurons are activated by unpredicted rewards and reward-predicting stimuli, are not influenced by fully predicted rewards, and are depressed by omitted rewards. Thus, they appear to report an error in the prediction of reward, which is the crucial reinforcement term in formal learning theories. Theoretical studies on reinforcement learning have shown that signals similar to dopamine responses can be used as effective teaching signals for learning. A neural network model implementing the temporal difference algorithm was trained to perform a simulated spatial delayed response task. The reinforcement signal was modeled according to the basic characteristics of dopamine responses to novel stimuli, primary rewards and reward-predicting stimuli. A Critic component analogous to dopamine neurons computed a temporal error in the prediction of reinforcement and emitted this signal to an Actor component which mediated the behavioral output. The spatial delayed response task was learned via two subtasks introducing spatial choices and temporal delays, in the same manner as monkeys in the laboratory. In all three tasks, the reinforcement signal of the Critic developed in a similar manner to the responses of natural dopamine neurons in comparable learning situations, and the learning curves of the Actor replicated the progress of learning observed in the animals. Several manipulations demonstrated further the efficacy of the particular characteristics of the dopamine-like reinforcement signal. Omission of reward induced a phasic reduction of the reinforcement signal at the time of the reward and led to extinction of learned actions. A reinforcement signal without prediction error resulted in impaired learning because of perseverative errors. Loss of learned behavior was seen with sustained reductions of the reinforcement signal, a situation in general comparable to the loss of dopamine innervation in Parkinsonian patients and experimentally lesioned animals. The striking similarities in teaching signals and learning behavior between the computational and biological results suggest that dopamine-like reward responses may serve as effective teaching signals for learning behavioral tasks that are typical for primate cognitive behavior, such as spatial delayed responding.

Animals↗
PubMed1998

Learning of sequential movements by neural network model with dopamine-like reinforcement signal.

Dopamine neurons appear to code an error in the prediction of reward. They are activated by unpredicted rewards, are not influenced by predicted rewards, and are depressed when a predicted reward is omitted. After conditioning, they respond to reward-predicting stimuli in a similar manner. With these characteristics, the dopamine response strongly resembles the predictive reinforcement teaching signal of neural network models implementing the temporal difference learning algorithm. This study explored a neural network model that used a reward-prediction error signal strongly resembling dopamine responses for learning movement sequences. A different stimulus was presented in each step of the sequence and required a different movement reaction, and reward occurred at the end of the correctly performed sequence. The dopamine-like predictive reinforcement signal efficiently allowed the model to learn long sequences. By contrast, learning with an unconditional reinforcement signal required synaptic eligibility traces of longer and biologically less-plausible durations for obtaining satisfactory performance. Thus, dopamine-like neuronal signals constitute excellent teaching signals for learning sequential behavior.

Algorithms↗
PubMed1998

Dopamine neurons report an error in the temporal prediction of reward during learning.

Many behaviors are affected by rewards, undergoing long-term changes when rewards are different than predicted but remaining unchanged when rewards occur exactly as predicted. The discrepancy between reward occurrence and reward prediction is termed an 'error in reward prediction'. Dopamine neurons in the substantia nigra and the ventral tegmental area are believed to be involved in reward-dependent behaviors. Consistent with this role, they are activated by rewards, and because they are activated more strongly by unpredicted than by predicted rewards they may play a role in learning. The present study investigated whether monkey dopamine neurons code an error in reward prediction during the course of learning. Dopamine neuron responses reflected the changes in reward prediction during individual learning episodes; dopamine neurons were activated by rewards during early trials, when errors were frequent and rewards unpredictable, but activation was progressively reduced as performance was consolidated and rewards became more predictable. These neurons were also activated when rewards occurred at unpredicted times and were depressed when rewards were omitted at the predicted times. Thus, dopamine neurons code errors in the prediction of both the occurrence and the time of rewards. In this respect, their responses resemble the teaching signals that have been employed in particularly efficient computational learning models.

Animals↗