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At least 1,801 records · Page 100Linked to original sources
PubMed1996

Infrapopliteal percutaneous transluminal angioplasty: what we know.

We believe that a substantial experience demonstrating the effectiveness and safety of infrapopliteal artery PTA has been accumulated. It is clear that the results of tibial PTA and femoropopliteal PTA are closely associated for most patients undergoing limb salvage procedures. Anatomic selection is most important; patients with focal disease and restorable runoff will generally benefit, and interventional radiologists should concentrate on treating this group of patients. PTA and surgery for limb salvage patients are indeed complementary procedures, and patients will benefit most by a methodical team approach to treatment. Problems with reporting of data in the literature have obscured the true effectiveness of distal PTA, with such deficiencies leading to both overestimation and underestimation of clinical utility. Nevertheless, the preponderance of evidence (as we see it) suggests a clinical effectiveness of about 80% at 2 years in appropriately selected patients. Like Dr. Fraser and his co-authors, we would welcome randomized trials of tibial PTA versus surgery, but even in the absence of these, the reporting of indications and results needs to be standardized: severity of symptoms at presentation and the extent of conservative treatments employed before intervention; life-table methodology on an intent-to-treat basis with clear delineation of end points; stratification by important variables such as lesion length, runoff status, extent of preexisting tissue loss, presence of diabetes and ESRD, and ideally, functional outcome and quality-of-life measures. Finally, we should learn from our surgical colleagues that close surveillance and early reintervention will probably increase the effectiveness of our percutaneous treatment methods.

Angioplasty, Balloon↗
PubMed1998

A computational role for dopamine delivery in human decision-making.

Recent work suggests that fluctuations in dopamine delivery at target structures represent an evaluation of future events that can be used to direct learning and decision-making. To examine the behavioral consequences of this interpretation, we gave simple decision-making tasks to 66 human subjects and to a network based on a predictive model of mesencephalic dopamine systems. The human subjects displayed behavior similar to the network behavior in terms of choice allocation and the character of deliberation times. The agreement between human and model performances suggests a direct relationship between biases in human decision strategies and fluctuating dopamine delivery. We also show that the model offers a new interpretation of deficits that result when dopamine levels are increased or decreased through disease or pharmacological interventions. The bottom-up approach presented here also suggests that a variety of behavioral strategies may result from the expression of relatively simple neural mechanisms in different behavioral contexts.

Cerebral Cortex↗
PubMed2002

Notes on Bell-Sejnowski PDF-matching neuron.

This article investigated the behavior of a single-input, single-unit neuron model of the Bell-Sejnowski class, which learn through the maximum-entropy principle, in order to understand its probability density function and matching ability.

Journal Article↗
PubMed1986

Do learning handicaps and headache cluster?

Children who are brought to medical attention because of frequently recurring or disabling headaches appear to have an increased prevalence of learning handicaps. Some of this increase might reflect Berkson's principle--the selection bias of an overrepresentation of patients with two disorders. Consideration is given to five models that show a relationship between learning handicap and headache. Two of the models are dismissed as too simple. Studies are needed to determine whether learning handicap and headache are indeed associated, and, if so, how. Clinicians are advised not to wait until these studies have been completed before implementing therapeutic programs that might prove helpful to those children with both headache and learning handicap.

Child↗
PubMed2003

Glutamate-mediated plasticity in corticostriatal networks: role in adaptive motor learning.

Little is known about how memories of new voluntary motor actions, also known as procedural memory, are formed at the molecular level. Our work examining acquisition of lever-pressing for food in rats has shown that activation of glutamate NMDA receptors, within broadly distributed but interconnected regions (e.g., nucleus accumbens core, prefrontal cortex, basolateral amygdala), is critical for such learning to occur. This receptor stimulation triggers intracellular cascades that involve protein phosphorylation and new protein synthesis. In support of this idea, we have found that posttrial inhibition of protein synthesis in the ventral striatum impairs learning, whereas posttrial NMDA receptor blockade does not. More recent data show extension of this network to the central amygdala, where infusions of NMDA antagonists also impair learning. We hypothesize that activity in this distributed network (including dopaminergic activity and perhaps muscarinic cholinergic activity) computes coincident events and thus enhances the probability that temporally related actions and events (e.g., lever pressing and delivery of reward) become associated. Such basic mechanisms of plasticity within this reinforcement learning network also appear to be profoundly affected in addiction.

Adaptation, Psychological↗
PubMed1997

Predicting the extension of equivalence classes from primary generalization gradients: the merger of equivalence classes and perceptual classes.

In Experiment 1, 6 college students were given generalization tests using 25 line lengths as samples with a long line, a short line, and a "neither" option as comparisons. The neither option was to be used if a sample did not go with the other comparisons. Then, four-member equivalence classes were formed. Class 1 included three nonsense words and the short line. Class 2 included three other nonsense words and the long line. After repeating the generalization test for line length, additional tests were conducted using members of the equivalence classes (i.e., nonsense words and lines) as comparisons and intermediate-length lines as samples. All Class 2 comparisons were selected in the presence of the test lines that also evoked the selection of the long line in the generalization test that had been given before equivalence class formation. Class 1 yielded complementary findings. Thus, the preclass primary generalization gradient predicted which test lines acted as members of each equivalence class. Regardless of using comparisons that were nonsense words or lines, the post-class-formation gradients overlapped, showing the substitutability of class members. Experiment 2 assessed the discriminability of the intermediate-length test lines from the Class 1 (shortest) and Class 2 (longest) lines. The test lines that functioned as members of an equivalence class were discriminable from the line that was a member of the same class by training. Thus, these test lines also acted as members of a dimensionally defined class of "long" or "short" lines. Extension of an equivalence class, then, involved its merger with a dimensionally defined class, which converted a close-ended class to an open-ended class. These data suggest a means of predicting class membership in naturally occurring categories.

Conditioning, Operant↗
PubMed1995

Figure-ground organization in different phases of the perceptual alternation phenomenon.

Two experiments on figure-ground organization were designed to examine whether the regions of an ambiguous stimulus perceived as "figure" vary as a function of regional area and experience with the stimulus. In Exp. 1 the perceived duration of each interpretation was recorded during continuous viewing for 10 subjects who had been trained until both percepts appeared with statistical regularity (stationary phase). In Exp. 2 the first interpretation reported by 172 naive observers after a few seconds of pattern exposure was recorded. The well-known tendency to interpret smaller regions as figure was noted in Exp. 2 whereas the results of Exp. 1 suggested equal probability of the percepts. Over-all results suggest that alternation is learned during the transient or "early" phase of perception, with some stimulus features and cultural factors influencing the figure-ground organization. During the stationary or late phase of perception the subject is well practiced and the alternating of interpretations becomes largely automatic.

Adult↗
PubMed2005

Pauses and durations exhibit a serial position effect.

This article reports evidence of two kinds of serial position effects in immediate serial recall: One involves interresponse pauses, and the other response durations. In forward and backward recall, responding was faster at initial and final positions than at center positions, exhibitinga bow-shaped function relative to serial position. These data were obtained in a spoken recall study in which ungrouped lists of four to six words and postcuing of recall direction were used. The pause pattern is consistent with several models of serial memory, including a distinctiveness model (Brown, Neath, & Chater, 2002) and a version of the ACT-R model augmented with a spontaneous grouping strategy (Maybery, Parmentier, & Jones, 2002). The duration pattern suggests that response articulation depends on the processing context, rather than being modular.

Attention↗
PubMed1999

The deletions of 22q11--the Portuguese experience.

The patients with a chromosome 22q11 deletion have a variable phenotype which includes DiGeorge (DG) and Velocardiofacial (VCF) syndromes. The aim of the present study is to characterize the phenotype of DG and VCF using facial biometry in 12 portuguese patients. We found 4/12 patients with the DG phenotype: 3/4 had telecanthus, small mouth and retrognathia; 1/4 had telecanthus, short nose with bulbous tip and a normal mouth. These patients had major cardiac defects associated with hypoplastic or absent thymus and monosomy 22q11. We did not find velopharyngeal insufficiency in patients with the so called DG phenotype 8/12 patients had the VCF phenotype: typical facies with variable features. Four of these had velopharyngeal insufficiency and learning disabilities. Four patients had cardiac defects and 5/8 had monosomy 22q11. Probably this clinical variability is due to mutations in critical genes involved in embryonic development.

Adolescent↗
PubMed2006

A machine learning approach to predicting peptide fragmentation spectra.

Accurate peptide identification from tandem mass spectrometry experiments is the cornerstone of proteomics. Although various approaches for matching database sequences with experimental spectra have been developed to date (e.g. Sequest, Mascot) the sensitivity and specificity of peptide identification have not yet reached their full potential. This is in part due to the tradeoffs between robustness and accuracy of the existing methods with respect to the non-uniform nature of peptide fragmentation and bond cleavages induced by different mass spectrometers. Accordingly, it is expected that new approaches to de novo predicting peptide fragmentation spectra will enable more accurate peptide identification. To address this problem, here we used a data-driven approach to learn peptide fragmentation rules in mass spectrometry, in the form of posterior probabilities, for various fragment-ion types of doubly and triply charged precursor ions. We show that the accuracy of our neural-network based methodology is useful for subsequent peptide database searches and that the most useful rules of fragmentation significantly differ across ion and precursor types.

Amino Acids↗
PubMed2006

[Behavioral phenotypes and cognitive characteristics in mental retardation].

The authors in a review article deal with characteristic cognitive and behavioral features appearing in mental retardations, which later are referred as behavioral phenotypes. Nyhan (1972) introduced the term "behavioral phenotype" to describe outwardly observable behavior so characteristic of children with genetic disorders that its presence suggests the underlying genetic condition. The behavioral phenotype is a characteristic pattern of motor, cognitive, linguistic and social abnormalities that is consistently associated with a biological/neurodevelopmental disorder. This does not mean that the behavior is present in all instances but that the probability of its occurrence is increased. In the future, more may be learned about brain mechanisms and gene-brain interactions by comparing those with behavioral involvement with others with the same syndrome but without the behavioral features.

Abnormalities, Multiple↗
PubMed1979

Outline literature retrieval in poison control.

As for the systems to choose, we would advocate to start with only one, in order to learn perfectly a first retrieval language. TOXLINE, at the time being, is probably the best choice. EXCERPTA MEDICA, on the other hand, if it can be made more up-to-date, could become a very important competitor. As for the most recent literature, SCISEARCH is likely to remain unbeatable.

Humans↗
PubMed1982

The pathophysiology of hemorrhagic shock.

It is difficult to summarize such a complex series of problems. Both the pathophysiology of hemorrhage and the details of its treatment are far from being fully defined in spite of the inherent simplicity of the challenge involved. The questions how much, what kind, and when still apply to such fundamental issues as the fluids given for resuscitation, red cells necessary for extensive hemorrhage and the hemostatic components. We are not clear as to what, if anything, can be done to improve antibacterial and antimicrobial defense mechanisms after a major hemorrhage. There are tantalizing leads as to specific measures that can be taken to prevent other potential complications but some maneuvers that may minimize the change for one complication may worsen the chance for others. We must, of course, continue to strive to try to reduce the complications of treatment itself, which are probably small but still significant. There is certainly much yet to be learned in both the fundamental and practical spheres.

Acidosis↗
PubMed1995

Aberrant GAP-43 gene expression in Alzheimer's disease.

GAP-43 is a growth-associated phosphoprotein expressed at high levels in neurons during development, axonal regeneration, and neuritic sprouting. GAP-43 gene expression in mature neurons is probably functionally important for the structural remodeling of synapses as required for learning and establishing new memory. The widespread aberrant neuritic growth accompanied by impaired synaptic plasticity in Alzheimer's disease (AD) suggests that abnormal GAP-43 gene expression may contribute to the cascade of neurodegeneration. In the present study, end-stage AD brains exhibited reduced neuronal expression but increased glial cell levels of GAP-43 mRNA and protein. Glial cell localization of GAP-43 gene expression was confirmed by in situ hybridization of cerebral tissue, Northern blot analysis of microdissected cerebral white matter, and independent analysis of astrocytoma cell lines and primary malignant astrocytomas. In addition, in AD, GAP-43 immunoreactivity was translocated from the cytosol to membranes of swollen neuritic (dendritic) and glial cell processes throughout cerebral cortex and white matter. Downregulated and aberrant neuronal GAP-43 gene expression appears to reflect an important molecular lesion that precedes and progresses with the widespread synaptic disconnection and dementia in AD. At the same time, the presence of similar neuronal abnormalities in Pick's disease, diffuse Lewy body disease, Parkinson's disease, and Down syndrome suggests common mechanisms in the respective cascades of neurodegeneration. Finally, the finding of aberrantly increased glial cell GAP-43 gene expression in AD exposes a previously unrecognized neurodegenerative change that may account for the axonal loss and white matter atrophy detected early in the course of disease.

Aged↗
PubMed1993

An evaluation of factors influencing Bayesian learning systems.

This paper examines the influences of situational and model factors upon the accuracy of Bayesian learning systems. In particular, it is concerned with the impact of variations in training sample size, number of attributes, choice of Bayesian model, and criteria for excluding model attributes upon the overall accuracy of the simple and proper Bayes models.

Artificial Intelligence↗

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