Biomedical subjects

J Sum

Publications and source records attributed to J Sum.

8 recordsLinked to original sources

PubMed2004

Selective recovery of striatal 125I-alpha-conotoxinmii nicotinic receptors after nigrostriatal damage in monkeys.

Evidence suggests that nicotinic receptors play a role in nigrostriatal function, a finding that may be relevant to Parkinson's disease. Knowledge of the conditions that regulate nicotinic receptor expression is therefore important. Previous studies showed that several different nicotinic receptors, including alpha-conotoxinMII (alpha-CtxMII)-sensitive receptors, are decreased after nigrostriatal damage. Nigrostriatal dopaminergic terminals also demonstrate a capacity for recovery after lesioning. The present experiments were therefore done to determine whether there were changes in striatal nicotinic receptors with recovery. To address this, we used two well-characterized animal models of nigrostriatal damage produced using the selective dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Studies in mice showed that striatal 125I-alpha-CtxMII, as well as 125I-epibatidine and 125I-A85380 binding sites significantly recovered 1 month after lesioning, suggesting that alpha6* and most likely alpha4* receptors are increased. Experiments were next done in monkeys since striatal 125I-alpha-CtxMII receptors constitute a large percentage of nicotinic receptors and are more vulnerable to nigrostriatal damage in this model that closely mirrors Parkinson's disease. In monkeys allowed to recover from the toxic effects of MPTP for a 1-2 year period, there was a significant improvement in the Parkinson disability score. There was also a reversal in lesion-induced declines in striatal alpha-CtxMII-sensitive receptors, but no significant change in 125I-epibatidine and 125I-A85380 receptors. These findings suggest that alpha3*/alpha6* sites are selectively increased in monkey striatum with recovery. The present data show that recovery of 125I-alpha-CtxMII receptors occurs in parallel with the dopamine transporter, indicating that these nicotinic receptors sites are localized to presynaptic dopamine terminals in both species.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed2000

A local training and pruning approach for neural networks.

The training of neural networks using the extended Kalman filter (EKF) algorithm is plagued by the drawback of high computational complexity and storage requirement that may become prohibitive even for networks of moderate size. In this paper, we present a local EKF training and pruning approach that can solve this problem. In particular, the by-products obtained along with the local EKF training can be utilized to measure the importance of the network weights. Comparing with the original global approach, the proposed local EKF training and pruning approach results in a much lower computational complexity and storage requirement. Hence, it is more practical in solving real world problems. The performance of the proposed algorithm is demonstrated on one medium- and one large-scale problems, namely, sunspot data prediction and handwritten digit recognition.

Algorithms↗

PubMed1999

An adaptive Bayesian pruning for neural networks in a non-stationary environment.

Pruning a neural network to a reasonable smaller size, and if possible to give a better generalization, has long been investigated. Conventionally the common technique of pruning is based on considering error sensitivity measure, and the nature of the problem being solved is usually stationary. In this article, we present an adaptive pruning algorithm for use in a nonstationary environment. The idea relies on the use of the extended Kalman filter (EKF) training method. Since EKF is a recursive Bayesian algorithm, we define a weight-importance measure in term of the sensitivity of a posteriori probability. Making use of this new measure and the adaptive nature of EKF, we devise an adaptive pruning algorithm called adaptive Bayesian pruning. Simulation results indicate that in a noisy nonstationary environment, the proposed pruning algorithm is able to remove network redundancy adaptively and yet preserve the same generalization ability.

Bayes Theorem↗

PubMed1998

Extended Kalman Filter-Based Pruning Method for Recurrent Neural Networks.

Pruning is one of the effective techniques for improving the generalization error of neural networks. Existing pruning techniques are derived mainly from the viewpoint of energy minimization, which is commonly used in gradient-based learning methods. In recurrent networks, extended Kalman filter (EKF)-based training has been shown to be superior to gradient-based learning methods in terms of speed. This article explains a pruning procedure for recurrent neural networks using EKF training. The sensitivity of a posterior probability is used as a measure of the importance of a weight instead of error sensitivity since posterior probability density is readily obtained from this training method. The pruning procedure is tested using three problems: (1) the prediction of a simple linear time series, (2) the identification of a nonlinear system, and (3) the prediction of an exchange-rate time series. Simulation results demonstrate that the proposed pruning method is able to reduce the number of parameters and improve the generalization ability of a recurrent network.

Journal Article↗

PubMed1998

A point cluster method for in vivo motion analysis: applied to a study of knee kinematics.

A new method for deriving limb segment motion from markers placed on the skin is described. The method provides a basis for determining the artifact associated with nonrigid body movement of points placed on the skin. The method is based on a cluster of points uniformly distributed on the limb segment. Each point is assigned an arbitrary mass. The center of mass and the inertia tensor of this cluster of points are calculated. The eigenvalues and eigenvectors of the inertia tensor are used to define a coordinate system in the cluster as well as to provide a basis for evaluating non-rigid body movement. The eigenvalues of the inertia tensor remain invariant if the segment is behaving as a rigid body, thereby providing a basis for determining variations for nonrigid body movement. The method was tested in a simulation model where systematic and random errors were introduced into a fixed cluster of points. The simulation demonstrated that the error due to nonrigid body movement could be substantially reduced. The method was also evaluated in a group of ten normal subjects during walking. The results for knee rotation and translation obtained from the point cluster method compared favorably to results previously obtained from normal subjects with intra-cortical pins placed into the femur and tibia. The resulting methodology described in this paper provides a unique approach to the measurement of in vivo motion using skin-based marker systems.

Adult↗

PubMed1997

Patellofemoral design influences function following total knee arthroplasty.

The functional influence of patellofemoral design was evaluated by testing two cohorts of patients with total knee arthroplasty while walking, climbing stairs, and rising from a chair. The two cohorts received one of two different designs of total knee arthroplasty. The designs differed primarily in the curvature of the femoral trochlea. These differences in curvature have been shown in in vitro studies to influence the tracking of the patella. One design had a smaller radius on the patellar flange, which caused the patella to articulate more anteriorly and distally than the second design, which had a larger radius in this region. The second design more closely replicated the curvature of the femoral trochlear anatomy. There was a significant functional difference during stairclimbing between the patient groups, whereas there was no difference during walking or chair rising. The group with the design that had nonanatomic tracking of the patella had a higher than normal moment tending to flex the knee (net quadriceps moment) during late stance phase. The increased net quadriceps moment during late stance was concurrent with an increased knee flexion. The abnormal function occurred when the patellar was tracking over the nonanatomic portion of the trochlea. Patients in the group with the anatomic trochlea did not have abnormal function. These results suggest a relationship between a nonanatomic trochlea and abnormal function during stair-climbing.

Aged↗

PubMed1996

Attraction basin of bidirectional association memories.

In this paper, we investigate the attraction basin of the bidirectional associative memory (BAM) model. The BAM is a two-layer heteroassociator that stores a prescribed set of bipolar library pairs. It consists of two layers of neurons. One layer has n neurons and the other has p neurons. We will first point out why the conventional energy approach cannot tell us about the attraction basin of each library pair. We then rigorously derive the statistical dynamics of the BAM, which shows how the upper bound on the number of errors changes during recalling for an arbitrary error pattern in the initial state. From the dynamics, we can estimate the attraction basin for the worst case errors, as well as the memory capacity and the number of errors in the retrieved pairs. The memory capacity is alpha rn, where alpha r (0 < alpha r < 1) depends on the ratio [formula: see text]. The number of errors in the retrieved pairs is [formula: see text] when the number of library pairs is alpha n. When r = 1, the lower bound on the attraction basin for the worst case errors is about 0.0068n.

Algorithms↗

PubMed1995

Intracerebral involvement in scleroderma en coup de sabre: report of a case with neuropathologic findings.

Linear scleroderma en coup de sabre (LScs) is a rare disorder not infrequently associated with neurologic symptoms, notably epilepsy. However, histopathologic documentation of intracerebral lesions in LScs is very limited and the etiology of the central nervous system symptoms has therefore never been convincingly established. We describe a 27-year-old woman with LScs and a longstanding history of epilepsy. Radiographic studies demonstrated a focal, intraparenchymal lesion in the left frontal lobe directly subjacent to the area of scleroderma on the forehead and scalp. The resected cerebral lesion revealed localized band-like sclerosis of the leptomeninges and associated vessels, as well as intraparenchymal calcifications and anomalous, ectatic vessels. These findings suggest that LScs may represent a neurocutaneous syndrome of vascular dysplasia similar to the Sturge-Weber syndrome, rather than a localized form of collagen vascular disease, as suggested by some.

Adult↗