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At least 1,279 records · Page 71Linked to original sources
PubMed2002

Bayesian probabilistic network modeling of remifentanil and propofol interaction on wakeup time after closed-loop controlled anesthesia.

OBJECTIVE: Until now, the knowledge of combining anesthetics to obtain an adequate level of anesthesia and to economize wakeup time has been empirical and difficult to represent in quantitative models. Since there is no reason to expect that the effect of non-opioid and opioid anesthetics can be modeled in a simple linear manner, the use of a new computational approach with Bayesian belief network software is demonstrated. METHODS: A data set from a pharmacodynamic study was used where remifentanil was randomly given in three fixed target concentrations (2, 4, and 8 ng/ml) to 62 subjects. Target concentrations of propofol were controlled according to the closed-loop system feedback of the auditory evoked potential index to render modeling unbiased by the level of anesthesia. Time to open eyes was measured to represent wakeup time after surgery. The NETICA version 1.37 software was used on a personal computer for network building, validation, and prediction. RESULTS: After the learning phase, the network was used to generate a series of random cases whose probability distribution matches that of the compiled network. The sampling algorithms used are precise, so that the frequencies of the simulated cases will exactly approach the probabilities of the network and that of the data learned. The graphical display of the predicted wakeup time shows less variability but a more complex interaction pattern than with the unadjusted original data. CONCLUSIONS: Model building and evaluation with Bayesian networks does not depend on underlying linear relationships. Bayesian relationships represent true features of the represented data sample. Data may be sparse, uncertain, stochastic, or imprecise. Multiple platform software that is easy to use is increasingly available. Bayesian networks promise to be versatile tools for building valid, nonlinear, predictive instruments to further gain insight into the complex interaction of anesthetics.

Anesthesia Recovery Period↗
PubMedDate not supplied

Lead-induced changes in learning: evidence for behavioral mechanisms from experimental animal studies.

Lead is probably the most studied of the neurotoxic agents, both in humans and in animal models. Research has focused on learning impairment and other behavioral consequences produced by developmental exposure. In children, lead exposure results in deficits in such global measures as IQ, as well as more specific deficits that are suggestive of attentional deficit disorder. Research in animals has also clearly demonstrated learning and memory deficits as a consequence of developmental lead exposure. Experiments performed in monkeys implicate the same behavioral problems as those observed in children: increased distractibility, inability to inhibit inappropriate responding, and perseveration in behaviors that are no longer appropriate. For example, lead-treated monkeys were impaired in their ability to perform discrimination reversal task, but not on the initial visual discrimination task. Deficits were more severe in the presence of distracting irrelevant stimuli. Lead-treated monkeys displayed severe perseveration on one button on a task which required them to alternate responding between two buttons. Lead-treated monkeys displayed memory impairment on a task requiring them to remember a previously observed stimulus or position, which was at least in part the result of interference from responses from previous trials. Lead-treated monkeys exhibited a higher rate of response on an intermittent schedule of reinforcement, and had difficulty inhibiting responding when required. Thus, for many of the tasks on which monkeys have been found to display learning and/or memory impairment, the deficit can be attributed at least in part to an attentional deficit and/or perseverative behavior.

Animals↗
PubMed2005

Bleeding remains a major complication during laparoscopic surgery: analysis of the SALTS database.

BACKGROUND AND AIMS: The aim of this study was to determine the incidence of bleeding complications from various laparoscopic procedures in a nationwide prospective multicentre study in Switzerland from 1995 to 2001 following an initial learning curve. PATIENTS AND METHODS: Since 1989, the Swiss Association of Laparoscopic and Thoracoscopic Surgery (SALTS) has prospectively collected data from patients undergoing laparoscopic or thoracoscopic surgery at 114 surgical institutions (university, county and district hospitals, private practice). More than 130 items of data, including indication for surgery, intraoperative course, local as well as general postoperative complications, mortality and follow-up were recorded on a computerised data sheet. RESULTS: Some 43,028 procedures were assessed and analysed. Local morbidity (e.g. wound infections) occurred in 0.05% of the whole patient group, whereas 3.3% developed general postoperative complications. The overall mortality rate was 0.2%. In 1.7% of the cases, the intraoperative course was complicated by internal bleeding or haematoma of the abdominal wall. In the postoperative course, 1.5% of the patients presented with internal bleeding or bleeding of the abdominal wall. Major vascular injury occurred in 0.09%. This patient group with bleeding complications was analysed in the context of the operator's experience, instrumental lesions (Veress needle or trocar) and conversion incidence. Furthermore, a trend analysis of the complication rate from 1995 to 2001 was performed. CONCLUSION: Although the initial learning curve of laparoscopic procedures is probably finished, the rate of bleeding complications is still substantial. These results demonstrate that the collection of data in the form of multicentre studies is essential for quality control. It permits recognition and understanding of the current problems in laparoscopic surgery in order to improve the quality of daily surgical practice. The fact that the operator's experience seems to play an important role shows that improvement in learning and teaching programmes is still necessary and should be coordinated on a national basis.

Adolescent↗
PubMed2004

Bidirectional parallel fiber plasticity in the cerebellum under climbing fiber control.

Cerebellar parallel fiber (PF)-Purkinje cell (PC) synapses can undergo postsynaptically expressed long-term depression (LTD) or long-term potentiation (LTP) depending on whether or not the climbing fiber (CF) input is coactivated during tetanization. Here, we show that modifications of the postsynaptic calcium load using the calcium chelator BAPTA or photolytic calcium uncaging result in a reversal of the expected polarity of synaptic gain change. At higher concentrations, BAPTA blocks PF-LTP. These data indicate that PF-LTD requires a higher calcium threshold amplitude than PF-LTP induction and suggest that CF activity acts as a polarity switch by providing dendritic calcium transients. Moreover, previous CF-LTD induction changes the relative PF-LTD versus -LTP induction probability. These findings suggest that bidirectional cerebellar learning is governed by a calcium threshold rule operating "inverse" to the mechanism previously described at other glutamatergic synapses (BCM rule) and that the LTD/LTP induction probability is under heterosynaptic climbing fiber control.

Animals↗
PubMed2002

Enriched early experiences of mice underexpressing the beta-amyloid precursor protein restore spatial learning capabilities but not normal openfield behavior of adult animals.

We have previously reported severely impaired spatial learning in mutant mice underexpressing a shortened variant of the beta-amyloid precursor protein (beta-APPtheta/theta). This targeted mutation is functionally equivalent to a null mutation. It also disturbs behavioral and neurological maturation with deficits emerging mainly between postnatal day (pd) 11 and 19. Such early tested mice exhibited almost no genotype-related difference in Morris water maze learning, raising the possibility that early handling might have compensated for genetic deficits. To verify this effect, we compared watermaze learning and open field behavior of 66 adult mutant and wildtype mice having been handled during pd 3-27 with that of 70 non-handled mutant and wildtype mice. Neurological testing during pd 3-27 markedly reduced time near wall and improved spatial retention of adult mutants, restoring their learning capabilities to wildtype levels. Early handling did not cure the mutation associated activity deficit in the open field, but mainly increased center field exploration in both mutants and wildtypes. In a follow-up experiment we analyzed whether an early (pd 3-10, n = 22) or middle (pd 11-19, n = 24) period of handling in form of neurological testing had differential effects on adult behavior. Mice handled during pd 11-19 had slightly shorter escape times than mice handled during pd 3-10 but were not significantly different in other behavioral measures. There were no sex related differences. Correlational and factor analysis showed that both the mutation and early handling had pleiotropic behavioral effects, resulting in differentially impaired mutants depending on the test situation. Likewise, early handling affected not only thigmotactic tendencies but also, more subtly, other behavioral components underlying water maze learning. We conclude that early postnatal stimulation can prevent mutation induced learning deficits in adult mice, but probably through other developmental mechanisms than those affected by the mutation. This implies that some behavioral impairments related to beta-APP malfunction may be corrected through simple treatments.

Amyloid beta-Protein Precursor↗
PubMedDate not supplied

Goal-directed instrumental action: contingency and incentive learning and their cortical substrates.

Instrumental behaviour is controlled by two systems: a stimulus-response habit mechanism and a goal-directed process that involves two forms of learning. The first is learning about the instrumental contingency between the response and reward, whereas the second consists of the acquisition of incentive value by the reward. Evidence for contingency learning comes from studies of reward devaluation and from demonstrations that instrumental performance is sensitive not only the probability of contiguous reward but also to the probability of unpaired rewards. The process of incentive learning is evident in the acquisition of control over performance by primary motivational states. Preliminary lesion studies of the rat suggest that the prelimbic area of prefrontal cortex plays a role in the contingency learning, whereas the incentive learning for food rewards involves the insular cortex.

Adaptation, Psychological↗
PubMedDate not supplied

A growth curve model of learning acquisition among cognitively normal older adults.

The objective of this study was to model recall and learning on the Auditory Verbal Learning Test using latent growth curve techniques. Participants were older adults recruited for the ACTIVE cognitive intervention pilot. A series of nested models revealed that an approximately logarithmic growth curve model provided optimal fit to the data. Although recall and learning factors were statistically uncorrelated, a fitted multivariate model suggested that initial recall was significantly associated with demographic characteristics but unrelated to health factors and cognitive abilities. Individual differences in learning were related to race/ethnicity, speed of processing, verbal knowledge, and global cognitive function level. These results suggest that failing to recognize initial recall and learning as distinct constructs clouds the interpretation of supraspan memory tasks.

Aged↗
PubMed2002

Occam factors and model independent Bayesian learning of continuous distributions.

Learning of a smooth but nonparametric probability density can be regularized using methods of quantum field theory. We implement a field theoretic prior numerically, test its efficacy, and show that the data and the phase space factors arising from the integration over the model space determine the free parameter of the theory ("smoothness scale") self-consistently. This persists even for distributions that are atypical in the prior and is a step towards a model independent theory for learning continuous distributions. Finally, we point out that a wrong parametrization of a model family may sometimes be advantageous for small data sets.

Journal Article↗
PubMed2003

Another look at the effect of a surprising intervening event on negative priming.

Tipper et al. (1991) reported that negative priming is eliminated when a low-probability event separates presentation of the prime display from the probe display. This finding is perfectly consistent with at least three of the major accounts of negative priming. However, each of these accounts can reasonably be argued to make different predictions regarding the effect of a surprising intervening event on attended repetition effects. The purpose of the experiment reported here was to determine which of these three predictions was correct. The results obtained were consistent with none of the three predictions. The low-probability intervening event did eliminate negative priming, but did so by slowing performance in the baseline condition relative to all other conditions. The results are discussed with respect to the role of surprise in responding to novel events.

Affect↗
PubMed2005

Functional neuroanatomy of successful paired associate learning in Alzheimer's disease.

OBJECTIVE: The purpose of the study was to develop a strategy for functional imaging of neurodegenerative disorders that overcomes confounds associated with differential performance between patient and comparison groups. METHOD: Functional magnetic resonance imaging was used to examine responses to increasing difficulty of visuospatial paired associate learning in 12 patients with mild probable Alzheimer's disease and 12 age-matched healthy comparison subjects. Performance was matched across groups by only examining successful encoding and retrieval attempts. Adjustment for task difficulty was made on an individual basis so that the patients with Alzheimer's disease and the comparison subjects performed at the same relative levels of difficulty. RESULTS: A network of lateral and medial frontoparietal and occipital regions was engaged in all subjects during successful associative learning. As task difficulty increased, blood-oxygen-level-dependent responses increased linearly in occipitoparietal regions during encoding and retrieval. Differential activations in patients with Alzheimer's disease and comparison subjects were small and were found only when an uncorrected statistical threshold was used. CONCLUSIONS: By controlling for confounds of varying task difficulty and subsequent performance, remarkably similar brain activations were identified during successful paired associate learning in patients with Alzheimer's disease and in healthy comparison subjects. The study methods provide a useful model for further applications of functional imaging involving cognitive activation paradigms in the study of neuropsychiatric disorders.

Aged↗
PubMed2002

High-probability stimulus control topographies with delayed S+ onset in a simultaneous discrimination procedure.

Experimenters and teachers use discrimination learning procedures to encourage reliable attending to stimulus differences defined as relevant for their purposes. Put another way, the goal of discrimination training is to establish high-probability stimulus control topographies that are coherent with experimenter or teacher specifications. The present research was conducted to investigate a novel procedure for encouraging stimulus control topography coherence. Participants were 13 adolescents with severe intellectual handicaps. During an initial Condition A, all were exposed to a simultaneous discrimination procedure. Participants could select a form alternating with a black field (S+) or an identical form that did not alternate (S-). Accuracy scores were typically low, and there was little evidence of coherent stimulus control topographies. Subsequently, the procedure was changed. During Condition B, every trial initially presented two identical nonalternating S- forms (Trial State 1). If the participant made no selection for 5 s, one of the forms began to alternate with the black field, and he or she could make the S+/S- discrimination (Trial State 2). Selections during Trial State I prolonged the delay to Trial State 2 until there had been no response for 5 s. During Condition B, S+/S- discrimination accuracy scores improved rapidly and markedly for most participants. Reinstating Condition A often resulted in diminished accuracy scores. This study thus (a) demonstrated a novel procedure for encouraging stimulus control topography coherence and (b) provided support for the interpretation that intermediate accuracy scores may be due to different topographies of stimulus control that co-occur in the same discriminative baseline.

Adolescent↗
PubMed1988

The N2 component elicited by stimulus matches and multiple targets.

This paper examines two methodological issues concerning the N2 component of human event-related potentials. The first issue concerns the circumstance that the most common way to obtain N2 in discrimination tasks is with an infrequent deviant stimulus that mismatches a frequent, standard stimulus. In these studies it is not possible to disentangle the effects of stimulus probability and stimulus mismatch on N2. In the present study it was found that, if two stimuli regularly alternate, N2 is elicited by infrequent repetitions of either stimulus. Thus, N2 is elicited by infrequent stimulus matches as well as infrequent stimulus mismatches. The second issue concerns the effect of stimulus probability on N2. Whereas previous research has established that the amplitude of N2 is inversely related to stimulus probability, the present study found that the number of possible targets in a visual discrimination task also has effects on N2 amplitude, with the overall probability of targets kept constant. Increasing the number of targets was associated with an increase in the duration of N2 and a differential enhancement of N2 at fronto-central as opposed to posterior-lateral recording sites. The latter results provide further evidence for the existence of two visual N2 components and tentative grounds for differentiating N2 from N400.

Adult↗
PubMed2001

[Evaluation of a leadership education at the Rigshospitalet. How an evaluation design can support organizational learning].

INTRODUCTION: The aim of the present study was to evaluate a Management & Leadership Education and Training Programme at the hospital before, during, and after implementation, allowing stakeholders to qualify alteration of the Programme as a process by using for instance formative evaluation. MATERIAL AND METHODS: The Delphi method is used for pre-evaluation of the concept of the Programme. Pre- and post-questionnaires were employed to measure the participants' adaptation of the hospital's "Management Fundamentals" before and after the Programme. RESULTS: The Expert panel stated that the Programme concept was pertinent and applicable. One hundred per cent recommended the Programme to be interdisciplinary. Eighty-two per cent stated that it would probably be difficult to acquire organisational learning. The results of the pre- and post-questionnaires showed that the participants and their superiors found that they adapted the hospital's "Management Fundamentals" better after having followed the Programme. DISCUSSION: With the use of the Delphi method (formative evaluation), the Programme concept could be altered already before implementation. The experts stated that they were not sure that the Programme would support organisational learning. Having this knowledge, it has been possible to work with activities supporting organisational learning already during implementation. In future, the experience with pre- and post-measurements will be used in a concrete way to support the learning environment in the organisation.

Decision Making↗
PubMed1984

Express-saccades of the monkey: effect of daily training on probability of occurrence and reaction time.

Two monkeys learned to make saccadic eye movements from a central fixation point to a peripheral target, when there was a temporal gap between fixation point offset and target onset. Under these conditions the animals made saccades after extremely short reaction times (less than 100 ms), so called express-saccades. With ongoing training the rate of occurrence increased (10 to 1005) and the reaction time of the express-saccades decreased (95 to 75 ms). The training effects were mediated by the amount of previously executed express-saccades and they were also spatially selective for express-saccades to that target position that had been used during training. The training effects on the express-saccades can be saturated after less than 7 days of daily training and are reversible after another 7 days of no training. The results indicate the existence of a fast-operating visuo-to-oculomotor pathway which can be quickly and reversibly modified by daily exercise.

Animals↗
PubMed1985

Physician tolerance for uncertainty. Use of liver-spleen scans to detect metastases.

To gain insight into diagnostic test use, we interviewed 42 physicians who ordered 62 liver-spleen scans to detect possible metastases. Before receiving the actual scan results, physicians gave (1) pretest probability estimates for liver metastasis; (2) probability estimates and management plans given the most common scan results; and (3) probabilities above and below which they would stop the diagnostic workup (their decision thresholds). After learning the actual scan results, physicians gave their posttest probabilities and management plans. Thirteen physicians (31%) desired absolute certainty to rule in metastasis. Fifty percent planned further evaluations even when probability estimates of metastasis reached one of their probability targets for ending the workup. Greater attention to decision thresholds may improve physicians' understanding of their tolerance for diagnostic uncertainty and the ability of diagnostic tests to reduce it.

Attitude of Health Personnel↗
PubMed2002

Memory for animal tracks: a possible cognitive artifact of human evolution.

Although many human behaviors are held to have adaptive significance, specific examples of behaviors that represent direct holdovers from the ancient world have been few, particularly in the cognitive realm. In the present research, the authors tested the hypothesis that such cognitive examples might in fact exist and be experimentally verifiable. They suggested that human predispositions to learn basic aspects of hunting with relative ease might be "left over" from human evolution in the pre-agricultural past. This hypothesis was tested in 3 experiments with reference to the learning and recall of animal tracks, an activity of probable high adaptive significance within the area of visual memory. Undergraduate students selected at random learned and recalled animal tracks with significantly greater ease than they recalled other animate and inanimate items. A single exception lay in relatively unfamiliar kitchen implements, which were recalled with greater facility than were animal tracks, consistent with current theoretical considerations. Results indicate that direct behavioral holdovers from the ancient world may exist in the cognitive realm and that these may be accessed experimentally and predictably under appropriate conditions.

Adult↗
PubMedDate not supplied

Service learning. Resource allocation.

Service learning has the potential to increase student learning, assist communities, and provide faculty members with one focus area that brings teaching, service, scholarship, and practice together As nursing programs revise curricula to include community based service learning opportunities, the impact of these projects on material and human resources must be assessed. Planning can increase the probability of adequate resources, faculty productivity, and student learning. When planning service learning activities, addressing the following questions will assist in evaluating projects: Is there a the match between academic mission and community needs? What commitment will be made to the community? Will the project promote faculty productivity? Will it offer students superior learning opportunities? What resources will the project require?

Clinical Competence↗
PubMed2005

Causal and noncausal conditionals: an integrated model of interpretation and reasoning.

We present an integrated model for the understanding of and the reasoning from conditional statements. Central assumptions from several approaches are integrated into a causal path model. According to the model, the cognitive availability of exceptions to a conditional reduces the subjective conditional probability of the consequent, given the antecedent. This conditional probability determines people's degree of belief in the conditional, which in turn affects their willingness to accept logically valid inferences. In addition to this indirect pathway, the model contains a direct pathway: Availability of exceptional situations directly reduces the endorsement of valid inferences. We tested the integrated model with three experiments using conditional statements embedded in pseudonaturalistic cover stories. An explicitly mentioned causal link between antecedent and consequent was either present (causal conditionals) or absent (arbitrary conditionals). The model was supported for the causal but not for the arbitrary conditional statements.

Adult↗