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Results for “correlation”

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At least 289 records · Page 16Linked to original sources

PubMed2000

Two-dimensional fluorescence correlation in capillary electrophoresis for peak resolution and species identification.

A new spectroscopic dimension-fluorescence intensity correlation--is introduced to enhance peak resolution and species identification in capillary electrophoresis. In two-dimensional correlation CE, a conventional electropherogram is spread into two dimensions through cross-correlation analysis of fluorescence time response. A laser that is sinusoidally modulated in intensity is used as the excitation source. Three channels of information are collected during a CE run: the steady-state intensity, the ac amplitude, and the phase-resolved fluorescence intensity. The correlation between two chosen channels is then evaluated. A two-dimensional correlation electropherogram consists of a plot of the correlation intensity versus two axes of migration time. Through correlation analysis, species discrimination and peak resolution are significantly enhanced without having to physically separate the solutes. Two-dimensional correlation CE showed complete resolution between two overlapping sample peaks with a resolution of 0.28 in the conventional one-dimensional electropherogram. In separations of polycyclic aromatic hydrocarbons by micellar electrokinetic chromatography (MEKC), two-dimensional correlation analysis resolved all overlapping elution peaks unseparable by one-dimensional MEKC, demonstrating the utility of 2D correlation in separation method development. The capability of 2D correlation CE in species identification is demonstrated with a sequence of 39 consecutively injected peaks containing four fluorescent dyes. Species identification in sequencing is achieved without complex data treatment in two-dimensional correlation CE.

Electrophoresis, Capillary↗

PubMed2005

Correlation coefficient mapping in fluorescence spectroscopy: tissue classification for cancer detection.

Correlation coefficient mapping has been applied to intrinsic fluorescence spectra of colonic tissue for the purpose of cancer diagnosis. Fluorescence emission spectra were collected of 57 colonic tissue sites in a range of 4 physiological conditions: normal (29), hyperplastic (2), adenomatous (5), and cancerous tissues (21). The sample-sample correlation was used to examine the ability of correlation coefficient mapping to determine tissue disease state. The correlation coefficient map indicates two main categories of samples. These categories were found to relate to disease states of the tissue. Sensitivity, selectivity, predictive value positive, and predictive value negative for differentiation between normal tissue and all other categories were all above 92%. This was found to be similar to, or higher than, tissue classification using existing methods of data reduction. Wavelength-wavelength correlation among the samples highlights areas of importance for tissue classification. The two-dimensional correlation map reveals absorption by NADH and hemoglobin in the samples as negative correlation, an effect not obvious from the one-dimensional fluorescence spectra alone. The integrity of tissue was examined in a time series of spectra of a single tissue sample taken after tissue resection. The wavelength-wavelength correlation coefficient map shows the areas of significance for each fluorophore and their relation to each other. NADH displays negative correlation to collagen and FAD, from the absorption of emission or fluorescence resonance energy transfer. The wavelength-wavelength correlation map for the decay set also clearly shows that there are only three fluorophores of importance in the samples, by the well-defined pattern of the map. The sample-sample correlation coefficient map reveals the changes over time and their impact on tissue classification. Correlation coefficient mapping proves to be an effective method for sample classification and cancer detection.

Adenomatous Polyposis Coli↗

PubMed2006

Experimental evolution of phenotypic plasticity: how predictive are cross-environment genetic correlations?

Genetic correlations are often predictive of correlated responses of one trait to selection on another trait. There are examples, however, in which genetic correlations are not predictive of correlated responses. We examine how well a cross-environment genetic correlation predicts correlated responses to selection and the evolution of phenotypic plasticity in the seed beetle Stator limbatus. This beetle exhibits adaptive plasticity in egg size by laying large eggs on a resistant host and small eggs on a high-quality host. From a half-sib analysis, the cross-environment genetic correlation estimate was large and positive (rA=0.99). However, an artificial-selection experiment on egg size found that the realized genetic correlations were positive but asymmetrical; that is, they depended on both the host on which selection was imposed and the direction of selection. The half-sib estimate poorly predicted the evolution of egg size plasticity; plasticity evolved when selection was imposed on one host but did not evolve when selection was imposed on the other host. We use a simple two-locus additive genetic model to explore the conditions that can generate the observed realized genetic correlation and the observed pattern of plasticity evolution. Our model and experimental results indicate that the ability of genetic correlations to predict correlated responses to selection depends on the underlying genetic architecture producing the genetic correlation.

Animals↗

PubMed1999

Superadditive correlation.

The fact that correlation does not imply causation is well known. Correlation between variables at two sites does not imply that the two sites directly interact, because, e.g., correlation between distant sites may be induced by chaining of correlation between a set of intervening, directly interacting sites. Such "noncausal correlation" is well understood in statistical physics: an example is long-range order in spin systems, where spins which have only short-range direct interactions, e.g., the Ising model, display correlation at a distance. It is less well recognized that such long-range "noncausal" correlations can in fact be stronger than the magnitude of any causal correlation induced by direct interactions. We call this phenomenon superadditive correlation (SAC). We demonstrate this counterintuitive phenomenon by explicit examples in (i) a model spin system and (ii) a model continuous variable system, where both models are such that two variables have multiple intervening pathways of indirect interaction. We apply the technique known as decimation to explain SAC as an additive, constructive interference phenomenon between the multiple pathways of indirect interaction. We also explain the effect using a definition of the collective mode describing the intervening spin variables. Finally, we show that the SAC effect is mirrored in information theory, and is true for mutual information measures in addition to correlation measures. Generic complex systems typically exhibit multiple pathways of indirect interaction, making SAC a potentially widespread phenomenon. This affects, e.g., attempts to deduce interactions by examination of correlations, as well as, e.g., hierarchical approximation methods for multivariate probability distributions, which introduce parameters based on successive orders of correlation.

Journal Article↗

PubMed2000

Correlations between corticomotoneuronal (CM) cell postspike effects and cell-target muscle covariation.

The presence of postspike facilitation (PSpF) in spike-triggered averages of electromyographic (EMG) activity provides a useful means of identifying cortical neurons with excitatory synaptic linkages to motoneurons. Similarly the presence of postspike suppression (PSpS) suggests the presence of underlying inhibitory synaptic linkages. The question we have addressed in this study concerns the extent to which the presence and strength of PSpF and PSpS from corticomotoneuronal (CM) cells correlates with the magnitude of covariation in activity of the CM cell and its target muscles. For this purpose, we have isolated cells during a reach and prehension task during which the activity of 24 individual proximal and distal forelimb muscles was recorded. These muscles show broad coactivation but with a highly fractionated and muscle specific fine structure of peaks and valleys. Covariation was assessed by computing long-term (2 s) cross-correlations between CM cells and forelimb muscles. The magnitude of cross-correlations was greater for muscles with facilitation effects than muscles lacking effects in spike-triggered averages. The results also demonstrate a significant relationship between the sign of the postspike effect (facilitation or suppression) and the presence of a peak or trough in the cross-correlation. Of all the target muscles with facilitation effects in spike-triggered averages (PSpF, PSpF with synchrony, or synchrony facilitation alone), 89.5% were associated with significant cross-correlation peaks, indicating positively covarying muscle and CM cell activity. Seven percent of facilitation effects were not associated with a significant effect in the cross-correlation, whereas only 3.4% of effects were associated with correlation troughs. In contrast, of all the muscles with suppression effects in spike-triggered averages, 38.9% were associated with significant troughs in the cross-correlation, indicating an inverse relation between CM cell and muscle activity consistent with the presence of suppression. Fifty-five percent of suppression effects was associated with correlation peaks, whereas 5.6% was not associated with a significant effect in the cross-correlation. Limiting the analysis to moderate and strong facilitation effects, the magnitude of PSpF was correlated weakly with the magnitude of the cell-muscle cross-correlation peak. Nevertheless, the results show that although many CM cell-target muscle pairs covary during the reach and prehension task in a way consistent with the sign and strength of the CM cell's synaptic effects on target motoneurons, many exceptions exist. The results are compatible with a model in which control of particular motoneuron pools reflects not only the summation of signals from many CM cells but also signals from additional descending, sensory afferent, and intrinsic spinal cord neurons. Any one neuron will make only a small contribution to the overall activity of the motoneuron pool. In view of this, it is not surprising that relationships between postspike effects and CM cell-target muscle covariation are relatively weak with many apparent incongruities.

Animals↗

PubMed1999

Clinicopathologic correlations in lupus nephritis in Lima, Peru.

BACKGROUND: We assessed whether immunohistologic markers for glomerular or tubulointerstitial injury might provide better correlations with ongoing renal function and disease activity as compared with the WHO classification or the NIH activity and chronicity indices in lupus nephritis. METHODS: Thirty-three patients with clinically defined systemic lupus underwent renal biopsy over a 1-year period at Hospital Loayza in Lima, Peru. Biopsy specimens were evaluated for macrophages, proliferating cells, alpha-actin expression, and type IV collagen deposition in both glomeruli and the tubulointerstitium and the results compared with the current WHO and NIH classifications in relation to the clinical presentation. RESULTS: Patients with WHO class IV lupus nephritis were more likely to have lower serum complements, greater proteinuria and hematuria, and worse renal function. An elevated NIH activity index correlated with microhematuria, proteinuria, and impaired renal function, whereas an elevated chronicity index correlated with renal function, hypertension, and microhematuria, but not with proteinuria. The presence of glomerular macrophages correlated with both glomerular alpha-actin expression and type IV collagen deposition, but did not correlate with renal function or proteinuria. In contrast, interstitial macrophages correlated not only with interstitial collagen deposition and myofibroblast accumulation, but also correlated with both renal function and the presence of nephrotic syndrome. CONCLUSIONS: Both the WHO classification and the NIH activity/chronicity indices correlate with clinical manifestations of lupus nephritis. While glomerular macrophage accumulation correlates with mesangial cell activation (alpha-actin expression) and collagen deposition, and interstitial macrophage accumulation correlates with interstitial fibroblast activation and collagen deposition, only interstitial macrophages correlate with renal function. Of particular interest will be future studies to determine whether these markers correlate with the prognosis.

Actins↗

PubMed2006

Correlation of symptom clusters of schizophrenia with absolute powers of main frequency bands in quantitative EEG.

BACKGROUND: Research of QEEG activity power spectra has shown intriguing results in patients with schizophrenia. Different symptom clusters have been correlated to QEEG frequency bands. The findings have been to some extent inconsistent. Replication of the findings of previous research is thus an important task. In the current study we investigated the correlations between the absolute powers of delta, theta, alpha, and beta frequency bands over the fronto-central scalp area (FC) with the PANSS subscales and the Liddle's factors in 16 patients with schizophrenia.The authors hypothesised a priori the correlations reported by Harris et al (1999) of PANSS negative subscale with delta power, Liddle's psychomotor poverty with delta and beta powers, disorganisation with delta power and reality distortion with alpha power on the midline FC. METHODS: The sample consisted of 16 patients with chronic schizophrenia considered as having insufficient clinical response to conventional antipsychotic treatment and evidencing a relapse. The correlations between quantitative electroencephalography (QEEG) absolute powers of delta (1.5-3.0 Hz), theta (3.0-7.5 Hz), alpha (7.5-12.5 Hz), and beta (12.5-20.0 Hz) frequency bands over the fronto-central scalp area (FC) with PANSS subscales and Liddle's factors (reality distortion, disorganisation, psychomotor poverty) were investigated. RESULTS: Significant positive correlations were found between the beta and psychomotor poverty (p < 0.05). Trends towards positive correlations (p < 0.1) were observed between delta and PANSS negative subscale and psychomotor poverty. Alpha did not correlate with reality distortion and delta did not correlate with disorganisation.Post hoc analysis revealed correlations of the same magnitude between beta and psychopathology generally over FC. CONCLUSION: The a priori hypothesis was partly supported by the correlation of the beta and psychomotor poverty. Liddle's factors showed correlations of the same magnitude with PANSS subscales. Supplementary analysis showed beta frequency correlating non-specifically over FC with a wide range of psychiatric symptomatology in patients with schizophrenia having a relapse.

Journal Article↗

PubMed2004

Avoiding pitfalls of correlation coefficients in the assessment of measurement instruments in rehabilitation research.

OBJECTIVE: To provide a practical guide on how to avoid the pitfalls of correlated correlation coefficients when comparing multiple instruments in rehabilitation research. DESIGN: An observational study comparing a number of instruments measuring quality of life (QoL) compared with an external criterion. SUBJECTS: Sixty-eight patients admitted to a rheumatology ward for intensive treatment of rheumatoid arthritis. METHODS: Patients completed three new (QoL) instruments and an established instrument before and after intensive treatment for rheumatoid arthritis. MAIN OUTCOME MEASURES: Correlation coefficients together with their confidence intervals and a test for the difference between a set of correlated correlation coefficients for the change in the EuroQoL Quality of Life scale (EuroQoL), the World Health Organization Quality Of Life-Abbreviated version (WHOQoL-BREF) and the Quality of Life Profile (QLP) against the Stanford Health Assessment Questionnaire (HAQ). RESULTS: Although the range of correlation between the new instruments and the external criterion was between -0.37 and -0.59 and suggested that one new instrument was far more responsive than the others,; an omnibus test for an overall difference could find no difference in responsiveness. CONCLUSIONS: It is conceptually simple to use correlation coefficients to assess the properties of multiple instruments measured on the same subjects to find a 'best' instrument. However, proper interpretation of results when correlated correlation coefficients are calculated is complex. We recommend analysis includes: (a) that simple plots of the pairs of analysed variables are shown, (b) that simple linear model-fitting statistics, e.g., the R-squared statistic, accompany the plots, (c) that confidence intervals are presented for correlation coefficients, (d) that an omnibus statistical test for the difference between correlated correlation coefficients is presented, and (e) that normal model assumptions are tested.

Arthritis, Rheumatoid↗

PubMed2004

Expression of vascular endothelial growth factor in hepatocellular carcinoma and the surrounding liver: correlation with angiographically assisted CT.

OBJECTIVE: The purpose of our study was to assess the correlation between the intensity and characteristics of contrast enhancement on angiographically assisted CT and the intensity of vascular endothelial growth factor (VEGF) expression in hepatocellular carcinoma (HCC) and in the surrounding nontumorous liver. MATERIALS AND METHODS: The intensity of VEGF expression in HCC and in the surrounding liver was expressed as a VEGF expression index by Western blot analysis in 20 surgical specimens resected in 20 patients between March 2000 and August 2002. Findings on CT during arterial portography (n = 20) and CT hepatic arteriography (n = 17) were retrospectively evaluated to determine contrast enhancement indexes and the enhancement characteristics of HCCs and of the surrounding liver. Contrast enhancement indexes and VEGF expression indexes were correlated using a simple regression test, and enhancement characteristics and VEGF expression indexes were correlated using the Spearman's rank correlation test. RESULTS: On CT hepatic arteriography, the contrast enhancement indexes of HCCs showed moderate inverse correlation with the VEGF expression indexes of HCCs (r = -0.57, p = 0.017) and high inverse correlation with the differences between the VEGF expression indexes of HCCs and those of livers (difference in the VEGF expression index, -0.80; p = 0.0001). The contrast enhancement index of the liver showed marginal moderate direct correlation with the VEGF expression index of the liver (0.44, p = 0.076) and high inverse correlation with the difference in the VEGF expression index (-0.71, p = 0.0013). On CT during arterial portography, the contrast enhancement indexes of HCCs showed moderate inverse correlation with the difference in the VEGF expression index (-0.51, p = 0.023). The qualitative degree of heterogeneity of hepatic artery enhancement in HCC on CT hepatic arteriography showed moderate direct correlation with the VEGF expression indexes of HCCs (0.55, p = 0.033) and high direct correlation with the difference in the VEGF expression indexes (0.73, p = 0.004). CONCLUSION: Our results indicated that the intensity and heterogeneity of hepatic artery enhancement of HCCs on CT hepatic arteriography correlated with the degree of VEGF expression in HCCs.

Adult↗

PubMed1999

"Quasi-REML" correlation estimates between production and health traits in the presence of selection and confounding: a simulation study.

Performance of the "quasi-REML" method for estimating correlations between a continuous trait and a categorical trait, and between two categorical traits, was studied with Monte Carlo simulations. Three continuous, correlated traits were simulated for identical populations and three scenarios with either no selection, selection for one moderately heritable trait (Trait 1, h2 = .25), and selection for the same trait plus confounding between sires and management groups. The "true" environmental correlations between Traits 2 (h2 = .10) and 3 (h2 = .05) were always of the same absolute size (.20), but further data scenarios were generated by setting the sign of environmental correlation to either positive or negative. Observations for Traits 2 and 3 were then reassigned to binomial categories to simulate health or reproductive traits with incidences of 15 and 5%, respectively. Genetic correlations (r(g12), r(g13), and r(g23) and environmental correlations (r(e12), r(e13), and r(e23)) were estimated for the underlying continuous scale (REML) and the visible categorical scales ("quasi-REML") with linear multiple-trait sire and animal models. Contrary to theory, practically all "quasi-REML" genetic correlations were underestimated to some extent with the sire and animal models. Selection inflated this negative bias for sire model estimates, and the sign of r(e23) noticeably affected r(g23) estimates for the animal model, with greater bias and SD for estimates when the "true" r(e23) was positive. Transformed "quasi-REML" environmental correlations between a continuous and a categorical trait were estimated with good efficiency and little bias, and corresponding correlations between two categorical traits were systematically overestimated. Confounding between sires and contemporary groups negatively affected all correlation estimates on the underlying and the visible scales, especially for sire model "quasi-REML" estimates of genetic correlation. Selection, data structure, and the (co)variance structure influences how well correlations involving categorical traits are estimated with "quasi-REML" methods.

Animal Husbandry↗

PubMed2005

[Correlations of clinical symptoms and treatment efficacy in patients with rheumatoid arthritis treated with Chinese herbal drugs or Western medicine].

OBJECTIVE: To evaluate the correlations between clinical symptoms and treatment efficacy in patients with rheumatoid arthritis (RA). METHODS: Four hundred and thirteen patients were included in the clinical trial from 9 clinical centers. They were randomly divided into Western medicine-treated group with 204 cases and Chinese herbal drug-treated group with 209 cases. Eighteen clinical symptoms were evaluated before and after treatment. The Western medicine therapy included voltaren extended release tablets, methotrexate and sulfasalazine. The Chinese herbal drug therapy included glucosidorum Tripterygii totorum tablets and Yishen Juanbi Tablets combined with treatment based on syndrome differentiation. The American College of Rheumatology 20 (ACR20) was used as efficacy evaluation criteria. RESULTS: In the Chinese herbal drug-treated group, clinical symptoms such as arthralgia and tenderness of joints were positively correlated with the efficacy after 12-week treatment, while frequent urination at night was negatively correlated. In the same group, tenderness of joints and fever were positively correlated with the efficacy after 24-week treatment, while deep-colored and turbid urine was negatively correlated. In the Western medicine-treated group, tenderness of joints and thirst were positively correlated with the efficacy after 12-week treatment, while vertigo was negatively correlated. And in the same group, tenderness of joints was positively correlated with the efficacy after 24-week treatment, while heaviness of limbs was negatively correlated to the efficacy. The statistical results showed that the treatment efficacy was improved when the correlated symptoms were included in the indications. CONCLUSION: The treatment efficacy of RA is correlated with some symptoms, so further studies should proceed on these correlations in order to achieve better treatment outcome.

Adult↗

PubMed2005

Correlational selection leads to genetic integration of body size and an attractive plumage trait in dark-eyed juncos.

When a trait's effect on fitness depends on its interaction with other traits, the resultant selection is correlational and may lead to the integration of functionally related traits. In relation to sexual selection, when an ornamental trait interacts with phenotypic quality to determine mating success, correlational sexual selection should generate genetic correlations between the ornament and quality, leading to the evolution of honest signals. Despite its potential importance in the evolution of signal honesty, correlational sexual selection has rarely been measured in natural populations. In the dark-eyed junco (Junco hyemalis), males with experimentally elevated values of a plumage trait (whiteness in the tail or "tail white") are more attractive to females and dominant in aggressive encounters over resources. We used restricted maximum-likelihood analysis of a long-term dataset to measure the heritability of tail white and two components of body size (wing length and tail length), as well as genetic correlations between pairs of these traits. We then used multiple regression to assess directional, quadratic, and correlational selection as they acted on tail white and body size via four components of lifetime fitness (juvenile and adult survival, mating success, and fecundity). We found a positive genetic correlation between tail white and body size (as measured by wing length), which indicates past correlational selection. Correlational selection, which was largely due to sexual selection on males, was also found to be currently acting on the same pair of traits. Larger males with whiter tails sired young with more females, most likely due to a combination of female choice, which favors males with whiter tails, and male-male competition, which favors both tail white and larger body size. To our knowledge, this is the first study to show both genetic correlations between sexually selected traits and currently acting correlational sexual selection, and we suggest that correlational sexual selection frequently may be an important mechanism for maintaining the honesty of sexual signals.

Animals↗

PubMed1993

[Correlation of the grade of nuclear and cortical cataract, visual acuity, and contrast sensitivity].

A correlative investigation of 125 eyes with senile cataractous lenses was conducted to determine the relationships between cortical (CC) and nuclear cataracts (NC), corrected visual acuity (VA), and contrast sensitivity (CS). The CS for the spatial frequency of 1.5 cycles/degree (c/d) and 12.0 c/d was analyzed in particular detail. The results were as follows: (1) CC and CS for both 1.5 and 12.0 c/d showed statistically significant negative correlations with a coefficient (CE) of -0.250 and -0.288 respectively. No correlation was found between CC and VA. (2) NC and VA showed a significant negative correlation with CE of -2.29. No correlation was found between NC and CS for at 1.5 and 12.0 c/d. (3) VA and CS showed a significant positive correlation with a CE of +0.436 at 1.5 c/d and +0.270 at 12.0 c/d. The CS at 1.5 and the CS at 12.0 c/d also showed a significant negative correlation with a CE of +0.477. (4) NC and CC showed a significantly negative correlation (r = -0.224, p < 0.01), suggesting that scattered light from the nucleus may be interfered with by cortical opacities during slitlamp examinations. (5) In 29 cases of no cortical opacity, nuclear opacity showed significant negative correlation with VA (r = 0.556 p < 0.01) but no significant correlation with CS of both 1.5 and 12 c/d. (6) In 30 cases with less than 0.085 of nuclear opacity, cortical opacity showed significant negative correlation with CS at 12.0 c/d (r = 0.364 p < 0.01) but showed no significant correlation with VA and CS at 1.5 c/d.

Aged↗

PubMed1998

The correlation of urodynamic findings with cranial magnetic resonance imaging findings in multiple sclerosis.

PURPOSE: To our knowledge there are no studies of the correlation between urinary complaints or urodynamic findings in multiple sclerosis and magnetic resonance imaging (MRI) findings. We investigated the correlation of urodynamic results in multiple sclerosis patients with voiding complaints to the cranial MRI findings. We also sought to correlate urodynamic results in these patients with International Prostate Symptom Scores (IPSS). MATERIALS AND METHODS: We retrospectively reviewed urodynamic results and cranial MRI findings in 90 multiple sclerosis patients (64 women, 26 men, mean age 44.5 years) with voiding complaints. The most recent urodynamic study and cranial MRI for each patient were reviewed. The interval between the 2 studies and MRI was no more than 6 months. Detrusor contractions were categorized as areflexic, hyporeflexic, hyperreflexic or hyperreflexic with impaired contractility. The presence of impaired compliance or detrusor-external sphincter dyssynergia was recorded. The cranial MRI findings were categorized on the basis of the presence of atrophy or enhancing lesions, total number of lesions and size of largest lesion. The urodynamic and MRI findings were correlated. Of the patients 40 who had urodynamic studies done within the last 6 months completed the IPSS, and severity of cranial MRI findings in these patients was correlated with the IPSS results. In addition, the presence of irritative findings of detrusor hyperreflexia or detrusor hyperreflexia with impaired contractility was correlated with the irritative score (sum of questions 1, 2, 4, 7), and the presence of detrusor-external sphincter dyssynergia was correlated with the obstructive score (sum of questions 3, 5, 6). RESULTS: There was no correlation between urodynamic category, presence of impaired compliance or presence of detrusor-external sphincter dyssynergia and any of the MRI findings of atrophy or enhancing lesions, total number of lesions or size of the largest lesions. In the patients who completed the IPSS there was no correlation between total number of lesions and IPSS score. There was no correlation between the presence of detrusor-external sphincter dyssynergia and obstructive score on the IPSS or between the presence of detrusor hyperreflexia and irritative score. CONCLUSIONS: Although patients with multiple sclerosis often are followed closely with urodynamic studies and cranial MRI, there appears to be no correlation between these 2 studies. Symptom scores also do not appear to correlate with urodynamic findings. Therefore, urodynamic studies appear to be warranted and irreplaceable in the evaluation of voiding dysfunction in multiple sclerosis patients.

Adolescent↗

PubMed1998

Correlation-based development of ocularly matched orientation and ocular dominance maps: determination of required input activities.

We extend previous models for separate development of ocular dominance and orientation selectivity in cortical layer 4 by exploring conditions permitting combined organization of both properties. These conditions are expressed in terms of functions describing the degree of correlation in the firing of two inputs from the lateral geniculate nucleus (LGN), as a function of their retinotopic separation and their "type" (ON center or OFF center and left eye or right eye). The development of ocular dominance requires that the correlations of an input with other inputs of the same eye be stronger than or equal to its correlations with inputs of the opposite eye and strictly stronger at small retinotopic separations. This must be true after summing correlations with inputs of both center types. The development of orientation-selective simple cells requires that (1) an input's correlations with other inputs of the same center type be stronger than its correlations with inputs of the opposite center type at small retinotopic separation; and (2) this relationship reverse at larger retinotopic separations within an arbor radius (the radius over which LGN cells can project to a common cortical point). This must be true after summing correlations with inputs serving both eyes. For orientations to become matched in the two eyes, correlated activity within the receptive fields must be maximized by specific between-eye alignments of ON and OFF subregions. Thus the correlations between the eyes must differ depending on center type, and this difference must vary with retinotopic separation within an arbor radius. These principles are satisfied by a wide class of correlation functions. Combined development of ocularly matched orientation maps and ocular dominance maps can be achieved either simultaneously or sequentially. In the latter case, the model can produce a correlation between the locations of orientation map singularities and local ocular dominance peaks similar to that observed physiologically. The model's main prediction is that the above correlations should exist among inputs to cortical layer 4 simple cells before vision. In addition, mature simple cells are predicted to have certain relationships between the locations of the ON and OFF subregions of the left and right eyes' receptive fields.

Animals↗

PubMed1999

Estimation of the average correlation coefficient for stratified bivariate data.

If the relationship between two ordered categorical variables X and Y is influenced by a third categorical variable with K levels, the Cochran-Mantel-Haenszel (CMH) correlation statistic QC is a useful stratum-adjusted summary statistic for testing the null hypothesis of no association between X and Y. Although motivated by and developed for the case of K I x J contingency tables, the correlation statistic QC is also applicable when X and Y are continuous variables. In this paper we derive a corresponding estimator of the average correlation coefficient for K I x J tables. We also study two estimates of the variance of the average correlation coefficient. The first is a restricted variance based on the variances of the observed cell frequencies under the null hypothesis of no association. The second is an unrestricted variance based on an asymptotic variance derived by Brown and Benedetti. The estimator of the average correlation coefficient works well in tables with balanced and unbalanced margins, for equal and unequal stratum-specific sample sizes, when correlation coefficients are constant over strata, and when correlation coefficients vary across strata. When the correlation coefficients are zero, close to zero, or the cell frequencies are small, the confidence intervals based on the restricted variance are preferred. For larger correlations and larger cell frequencies, the unrestricted confidence intervals give superior performance. We also apply the CMH statistic and proposed estimators to continuous non-normal data sampled from bivariate gamma distributions. We compare our methods to statistics for data sampled from normal distributions. The size and power of the CMH and normal theory statistics are comparable. When the stratum-specific sample sizes are small and the distributions are skewed, the proposed estimator is superior to the normal theory estimator. When the correlation coefficient is zero or close to zero, the restricted confidence intervals provide the best performance. None of the confidence intervals studied provides acceptable performances across all correlation coefficients, sample sizes and non-normal distributions.

Aged↗

PubMed2006

Correlation between the bone marrow blood perfusion and lipid water content on the lumbar spine in female subjects.

PURPOSE: To assess the marrow lipid water ratio (LWR) and spectral line width (LW) of lumbar vertebra by proton MR spectroscopy ((1)H MRS) and correlate with the marrow blood perfusion (MBP) by contrast-enhanced dynamic MRI (dMRI) in female subjects. MATERIALS AND METHODS: A total of 50 female subjects were included. Single-voxel (1)H MRS was measured at the L3 vertebrae. In the dMRI study, the maximum enhancement percentage (E(max)) and enhancement slope were calculated from time-intensity curves. Pearson's correlation was calculated to explore the association of (1)H MRS, age, and perfusion parameters. Partial correlation was then used to control confounder effect. RESULTS: LWR was negatively correlated with E(max) (r = -0.72; P < 0.0001), but positively correlated with age (r = 0.63; P < 0.0001). Lipid LW was negatively correlated with age (r = -0.33; P <0.05), but positively correlated with E(max) (r = 0.4; P < 0.05). After adjusting for the age effect by partial correlation, marrow LWR still negatively correlated with E(max) (r = -0.63; P < 0.0001). After adjusting for the E(max) effect, marrow LWR still positively correlated with age (r = 0.37; P < 0.05). CONCLUSION: After controlling the age factor, the LWR and water LW has significant negative correlation with vertebral BMP. Further investigation is needed to explore the relationship between bone marrow fat metabolism and angiogenesis.

Adult↗

PubMed1997

Parallel processing by a homogeneous group of coupled model neurons can enhance, reduce and generate signal correlations.

Correlated activities have been proposed as correlates of flexible association and assembly coding. We addressed the basic question of how signal correlations on parallel pathways are enhanced, reduced and generated by homogeneous groups of coupled neurons, and how this depends on the input activities and their interactions with internal coupling processes. For this we simulated a fully connected group of identical impulse-coded neurons with dynamic input and threshold processes and additive or multiplicative lateral coupling. Input signals were Gaussian white noise (GWN), completely independent or partially correlated on a subgroup of the parallel inputs. We show that in states of high average spike rates input-output correlations were weak while the network could generate correlated activities of stochastic, oscillatory and rhythmic bursting types depending exclusively on lateral coupling strength. In states of low average spike rates input-output correlations were high and the network could effectively enhance or reduce differences in spatial correlation applied to its parallel inputs. The correlation differences were more pronounced with multiplicative lateral coupling than with the additive interactions commonly used. As the different modes of correlation processing emerged already by global changes in the average spike rate and lateral coupling strength, we assume that in real cortical circuits changes in correlational processing may also be induced by unspecific modulations of activation and lateral coupling.

Action Potentials↗