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Biomedical subjects

A Lörincz

Publications and source records attributed to A Lörincz.

At least 19 recordsLinked to original sources
PubMed2005

Evaluation of visual inspection with acetic acid (VIA), Lugol's iodine (VILI), cervical cytology and HPV testing as cervical screening tools in Latin America. This report refers to partial results from the LAMS (Latin AMerican Screening) study.

OBJECTIVES: To assess the performance indicators of visual inspection with acetic acid (VIA) and visual inspection with Lugol's iodine (VILI) in four Latin American centres participating in the ongoing Latin AMerican Screening (LAMS) study, in settings with moderate incidence of cervical disease and with poorly to moderately well-organized cervical cancer screening. SETTING: Three Brazilian centres (São Paulo, Campinas and Porto Alegre) and one Argentine centre (Buenos Aires) recruited a total of 11,834 healthy women to undergo VIA, VILI, conventional Pap smear and Hybrid Capture II (HCII). METHODS: Women who had a positive result from any of these tests were subjected to colposcopy and biopsies (if necessary), and women with high-grade cervical intraepithelial neoplasia (CIN) were properly treated. To control for verification bias, 5% of women with normal tests were referred for colposcopy, as were 20% of HCII-negative women. RESULTS: Data on VIA (n=11,834), VILI (n=2994), conventional Pap smear (n=10,138) and HCII (n=4195) were available for test comparisons, calculating sensitivity, specificity, and positive and negative predictive values. Overall test positivity was 11.6% for VIA, 23.0% for VILI, 2.2% for Pap smear (LSIL threshold), 1.1% for Pap smear (HSIL threshold) and 17.1% for HCII. VIA was positive in 61.8% of the women with CIN 1, 57.0% of those with CIN 2, 35.0% of women with CIN 3 and in 21 of 28 (75%) of women with cancer. Approximately 10% of women with no detectable disease had an abnormal VIA. Regarding VILI, 83.3% of women diagnosed with CIN 1 and 62.5% of those with CIN 3 had an abnormal test. VILI failed to detect one of three cases of cancer. Both the sensitivity, specificity and positive predictive value of VIA and VILI in detecting CIN 2 or CIN 3 could be significantly improved depending on the combination with Pap smear or HCII (sensitivity up to 100.0% and specificity up to 99.8%). CONCLUSIONS: The LAMS study failed to reproduce the performance figures obtained with VIA and VILI (as stand-alone tests) in some other settings, where the prevalence of cervical disease was higher. However, a combined use of VIA or VILI with the Pap test or HCII allowed specific detection of cervical abnormalities.

Acetic Acid↗
PubMed2001

Ockham's razor modeling of the matrisome channels of the basal ganglia thalamocortical loops.

A functional model of the basal ganglia-thalamocortical (BTC) loops is described. In our modeling effort, we try to minimize the complexity of our starting hypotheses. For that reason, we call this type of modeling Ockham's razor modeling. We have the additional constraint that the starting assumptions should not contradict experimental findings about the brain. First assumption: The brain lacks direct representation of paths but represents directions (called speed fields in control theory). Then control should be concerned with speed-field tracking (SFT). Second assumption: Control signals are delivered upon differencing in competing parallel channels of the BTC loops. This is modeled by extending SFT with differencing that gives rise to the robust Static and Dynamic State (SDS) feedback-controlling scheme. Third assumption: Control signals are expressed in terms of a gelatinous medium surrounding the limbs. This is modeled by expressing parameters of motion in parameters of the external space. We show that corollaries of the model fit properties of the BTC loops. The SDS provides proper identification of motion related neuronal groups of the putamen. Local minima arise during the controlling process that works in external space. The model explains the presence of parallel channels as the means to avoiding such local minima. Stability conditions of the SDS predict that the initial phase of learning is mostly concerned with selection of sign for the inverse dynamics. The model provides a scalable controller. State description in external space instead of configurational space reduces the dimensionality problem. Falsifying experiment is suggested. Computer experiments demonstrate the feasibility of the approach. We argue that the resulting scheme has a straightforward connectionist representation exhibiting population coding and Hebbian learning properties.

Basal Ganglia↗
PubMed2000

Physiological patterns in the hippocampo-entorhinal cortex system.

The anatomical connectivity and intrinsic properties of entorhinal cortical neurons give rise to ordered patterns of ensemble activity. How entorhinal ensembles form, interact, and accomplish emergent processes such as memory formation is not well-understood. We lack sufficient understanding of how neuronal ensembles in general can function transiently and distinctively from other neuronal ensembles. Ensemble interactions are bound, foremost, by anatomical connectivity and temporal constraints on neuronal discharge. We present an overview of the structure of neuronal interactions within the entorhinal cortex and the rest of the hippocampal formation. We wish to highlight two principle features of entorhinal-hippocampal interactions. First, large numbers of entorhinal neurons are organized into at least two distinct high-frequency population patterns: gamma (40-100 Hz) frequency volleys and ripple (140-200 Hz) frequency volleys. These patterns occur coincident with other well-defined electrophysiological patterns. Gamma frequency volleys are modulated by the theta cycle. Ripple frequency volleys occur on each sharp wave event. Second, these patterns occur dominantly in specific layers of the entorhinal cortex. Theta/gamma frequency volleys are the principle pattern observed in layers I-III, in the neurons that receive cortical inputs and project to the hippocampus. Ripple frequency volleys are the principle population pattern observed in layers V-VI, in the neurons that receive hippocampal output and project primarily to the neocortex. Further, we will highlight how these ensemble patterns organize interactions within distributed forebrain structures and support memory formation.

Afferent Pathways↗
PubMed2000

Proximally targeted GABAergic synapses and gap junctions synchronize cortical interneurons.

Networks of GABAergic interneurons are implicated in synchronizing cortical activity at gamma frequencies (30-70 Hz). Here we demonstrate that the combined electrical and GABAergic synaptic coupling of basket cells instantaneously entrained gamma-frequency postsynaptic firing in layers 2/3 of rat somatosensory cortex. This entrainment was mediated by rapid curtailment of gap junctional coupling potentials by GABAA receptor-mediated IPSPs. Electron microscopy revealed spatial proximity of gap junctions and GABAergic synapses on somata and dendrites. Electrical coupling alone entrained postsynaptic firing with a phase lag, whereas unitary GABAergic connections were ineffective in gamma-frequency phasing. These observations demonstrate precise spatiotemporal mechanisms underlying action potential timing in oscillating interneuronal networks.

Action Potentials↗
PubMed2000

Two-phase computational model training long-term memories in the entorhinal-hippocampal region.

The computational model described here is driven by the hypothesis that a major function of the entorhinal cortex (EC)-hippocampal system is to alter synaptic connections in the neocortex. It is based on the following postulates: (1) The EC compares the difference between neocortical representations (primary input) and feedback information conveyed by the hippocampus (the "reconstructed input"). The difference between the primary input and the reconstructed input (termed "error") initiates plastic changes in the hippocampal networks (error compensation). (2) Comparison of the primary input and reconstructed input requires that these representations are available simultaneously in the EC network. We suggest that compensation of time delays is achieved by predictive structures, such as the CA3 recurrent network and EC-CA1 connections. (3) Alteration of intrahippocampal connections gives rise to a new hippocampal output. The hippocampus generates separated (independent) outputs, which, in turn, train long-term memory traces in the EC (independent components, IC). The ICs of the long-term memory trace are generated in a two-step manner, the operations of which we attribute to the activities of the CA3 (whitening) and CA1 (separation) fields. (4) The different hippocampal fields can perform both nonlinear and linear operations, albeit at different times (theta and sharp phases). We suggest that long-term memory is represented in a distributed and hierarchical reconstruction network, which is under the supervision of the hippocampal output. Several of these model predictions can be tested experimentally.

Computer Simulation↗
PubMed1998

Human papillomavirus detection in cervical intraepithelial neoplasia by the second-generation hybrid capture microplate test, comparing two different cervical specimen collection methods.

BACKGROUND: The second generation Hybrid Capture microplate-based human papillomavirus (HPV) test (HC II) was examined to determine its sensitivity for identification of cervical intraepithelial neoplasia (CIN) by two different cervical specimen collection methods. OBJECTIVES: A cohort of 115 women with a mean age of 34.6 years (SD 9.1), referred to colposcopy with a history of abnormal cytology, was studied to compare HPV prevalence and viral load in low grade CIN vs. high grade CIN. STUDY DESIGN: Prior to the application of acetic acid, cervical specimens were obtained by either method 1 or 2, as follows: method 1: A cotton-tipped swab was applied to the ectocervix and endocervix for a Papanicolaou (Pap) smear. Next, a special cone-shaped cervical brush was applied to the endocervix, the ectocervix, and to the posterior vaginal vault and suspended in 1.0 ml of transport medium for HPV testing. Method 2: a Pap smear was taken with a cyto standard cylindrical cytology brush from the endocervix, and ectocervix, and the remaining cells were suspended in 3 ml phosphate-buffered saline (PBS) for HPV testing. Next, a Dacron-tipped swab was used to take a specimen from the ectocervix and posterior fornix and suspended in the same PBS solution.

Adult↗
PubMed1998

Forming independent components via temporal locking of reconstruction architectures: a functional model of the hippocampus.

The assumption is made that the formulation of relations as independent components (IC) is a main feature of computations accomplished by the brain. Further, it is assumed that memory traces made of non-orthonormal ICs make use of feedback architectures to form internal representations. Feedback then leads to delays, and delays in cortical processing form an obstacle to this relational processing. The problem of delay compensation is formulated as a speed-field tracking task and is solved by a novel control architecture. It is shown that in addition to delay compensation the control architecture can also shape long-term memories to hold independent components if a two-phase operation mode is assumed. Features such as a trisynaptic loop and a recurrent collateral structure at the second stage of that loop emerge in a natural fashion. Based on these properties a functional model of the hippocampal loop is constructed.

Animals↗
PubMed1998

Hybrid capture.

Explore the source record for details and available documents.

DNA↗
PubMed1997

Static and dynamic state feedback control model of basal ganglia-thalamocortical loops.

It is argued that a novel control architecture, the Static and Dynamic State (SDS) feedback scheme, which utilizes speed-field tracking, exhibits global stability, and allows on-line tuning by any adaptation mechanism without canceling stability if certain structural conditions are met, can be viewed as a model of basal ganglia-thalamocortical loops since (1) the SDS scheme predicts the neuronal groups that fit neuronal classification in the supplementary motor area, the motor cortex and the putamen, (2) the structural stability conditions require parallel channels, a feature that these loops provide, and (3) the SDS scheme predicts two major disorders that can be identified as Parkinson's and Huntington's diseases. Simulations suggests that the basal ganglia work outside the realm of the stability condition allowed by the robustness of the scheme and required for increased computation speeds.

Basal Ganglia↗
PubMed1996

Human papillomavirus DNA detection in cervical specimens by hybrid capture: correlation with cytologic and histologic diagnoses of squamous intraepithelial lesions of the cervix.

Human papillomavirus (HPV) DNA detection in cervical specimens was correlated with cytologic and histologic diagnoses for 151 women who were referred to the Johns Hopkins Hospital colposcopy clinic for evaluation of an abnormal Pap smear. HPVs were identified as "high-risk" or "low-risk" by Hybrid Capture. The final disease status was categorized as high-grade squamous intraepithelial lesion (HSIL) by histology (n = 26), low-grade squamous intra-epithelial lesion (LSIL) by histology (n = 43), equivocal [histology negative, cytology atypical squamous cells of undetermined significance (ASCUS) or higher, n = 42], and negative (both histology and cytology negative, n = 40). Thirty-five percent of disease-negative women and 84% of the women with biopsy-proven or equivocal disease were HPV-positive. Ninety-two percent of the HPV-positive women harbored high-risk HPVs, either high-risk HPVs alone (77%) or high-risk HPVs along with low-risk HPVs (15%). High-risk HPVs predominated in disease-negative as well as disease-positive women. Collection of specimens with a cytobrush was more efficient for HPV DNA detection than collection by cervicovaginal lavage. Large amounts of HPV DNA correlated with presence of HSIL or LSIL. For detection of HSIL, considering only brush samples, the sensitivities of abnormal cytology (ASCUS or higher), of high-risk HPVs, and of the two combined were, respectively, 87, 93, and 100%; the corresponding specificities were 30, 30, and 20%. HPV DNA detection may be most beneficial in populations with low HPV prevalence.

Adult↗
PubMed1996

Self-organizing multi-resolution grid for motion planning and control.

A fully self-organizing neural network approach to low-dimensional control problems is described. We consider the problem of learning to control an object and solving the path planning problem at the same time. Control is based on the path planning model that follows the gradient of the stationary solution of a diffusion process working in the state space. Previous works are extended by introducing a self-organizing multigrid-like discretizing structure to represent the external world. Diffusion is simulated within a recurrent neural network built on this multigrid system. The novelty of the approach is that the diffusion on the multigrid is fast. Moreover, the diffusion process on the multigrid fits well the requirements of the path planning: it accelerates the diffusion in large free space regions while still keeps the resolution in small bottleneck-like labyrinths along the path. Control is achieved in the usual way: associative learning identifies the inverse dynamics of the system in a direct fashion. To this end there are introduced interneurons between neighboring discretizing units that detect the strength of the steady-state diffusion and forward control commands to the control neurons via modifiable connections. This architecture forms the Multigrid Position-and-Direction-to-Action (MPDA) map. The architecture integrates reactive path planning and continuous motion control. It is also shown that the scheme leads to population coding for the actual command vector.

Algorithms↗
PubMed1994

Photoacoustic characterization of different food samples.

Photoacoustic spectroscopy in the 350-700 nm range proved a useful tool for discriminating between a variety of opaque, light-scattering samples. Spectral features originating from powdered food specimens of different colour and grain size were observed. These results suggest the feasibility of photoacoustics for quality control in the food-processing industry.

Acoustics↗
PubMed1992

Detection of human papillomavirus DNA without amplification: prospects for clinical utility.

Certain HPV types are major risk factors for the development of cervical and other human cancers. This chapter describes some of the problems which have precluded accurate diagnosis of HPV-related conditions in many studies. Despite the confusion, a multitude of reports demonstrate that HPV DNA testing has clinical utility, and future investigations should be directed at more accurately delineating its role in human health care.

DNA, Viral↗