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PubMed1997

Correlation between maximum bite force and facial morphology in children.

The correlation between maximum bite force and facial morphology was studied in 54 boys, 8 to 16 years old, and 66 girls, 7 to 17 years old. Bite force was measured at the first molars with a miniature bite force recorder. Facial morphology was evaluated on profile cephalograms. In addition, the number of teeth in contact in the intercuspal position was recorded with occlusal foils. In the girls, maximum bite force was correlated with the inclination of the mandible, the size of the gonial angle, and the ratio between posterior and anterior face heights. The correlations implied a large bite force with a small mandibular inclination and gonial angle, a large posterior face height in relation to the anterior face height, and a small bite force with the opposite facial characteristics. These correlations were nonexistent or weaker in boys. In both sexes, bite force was correlated with the number of occlusal contacts. Elimination of the influence of age and occlusal contact in the group of girls by the use of partial correlations reduced the correlation between bite force and facial morphology. A significant correlation with the size of the gonial angle remained, however, and the correlation with mandibular inclination was close to significance. In addition to the correlations found with facial morphology, the study clearly demonstrated the need to take gender and occlusal contacts into consideration in future studies of masticatory muscle function and strength in relation to facial morphology.

Adolescent↗

PubMed1990

[Measuring the optic papilla with planimetry and the optic nerve head analyzer in glaucoma and suspected glaucoma. II. Correlations of the results of both methods with changes in the visual field, studied with the Octopus automatic perimeter].

Sixty-seven optic nerve heads of 40 patients with proven or suspected glaucoma were measured by planimetry and with the Rodenstock Optic Nerve Head Analyser (ONHA). The results were compared to visual field indices obtained with the Octopus program G-1. Good correlation of the results obtained by the two measurement procedures has been shown (Stürmer et al. 1989), between values for the disk area, the excavation area, and the cup/disk ratio. However, there is only weak correlation of values for the neuroretinal rim. The planimetrically measured neuroretinal rim area in the total population examined proved to be significantly correlated only with the visual field index for mean retinal sensitivity (MS; r2 = 0.106; P = 0.007) and short-term fluctuations (SF; r2 = 0.066; P = 0.036). After division of the population examined into different diagnostic groups, further statistically significant correlations between optic nerve head parameters and the various visual field indices were shown; here, the cup/disk ratio of both measurement procedures in two subgroups showed the best correlation with the visual field indices MS and mean defect (MD). Neither in the total population nor in any of the subgroups was a statistically significant correlation found between the volume of the excavation and one of the visual field indices. Comparing only the data for the temporal quadrant of the optic nerve head with the visual field did not improve the correlations. The best, i.e. highly significant, correlations were between optic nerve head parameters and the age of the patient. The correlation factors are much lower than other published data. A variety of factors could be responsible for these weak correlations: different optic nerve head configurations on the one hand, and localized or diffuse visual field defects on the other. In unselected cases it appears impossible to predict the visual field of a given optic nerve head. Both methods are suitable for follow-up, but not all anatomical configuration of the optic nerve head permit this.

Adolescent↗

PubMed1997

Potentially predictive and manipulable blood serum correlates of aging in the healthy human male: progressive decreases in bioavailable testosterone, dehydroepiandrosterone sulfate, and the ratio of insulin-like growth factor 1 to growth hormone.

A cross-sectional survey was made in 56 exceptionally healthy males, ranging in age from 20 to 84 years. Measurements were made of selected steroidal components and peptidic hormones in blood serum, and cognitive and physical tests were performed. Of those blood serum variables that gave highly significant negative correlations with age (r > -0.6), bioavailable testosterone (BT), dehydroepiandrosterone sulfate (DHEAS), and the ratio of insulin-like growth factor 1 (IGF-1) to growth hormone (GH) showed a stepwise pattern of age-related changes most closely resembling those of the age steps themselves. Of these, BT correlated best with significantly age-correlated cognitive and physical measures. Because DHEAS correlated well with BT and considerably less well than BT with the cognitive and physical measures, it seems likely that BT and/or substances to which BT gives rise in tissues play a more direct role in whatever processes are rate-limiting in the functions measured and that DHEAS relates more indirectly to these functions. The high correlation of IGF-1/GH with age, its relatively low correlation with BT, and the patterns of correlations of IGF-1/GH and BT with significantly age-correlated cognitive and physical measures suggest that the GH-IGF-1 axis and BT play independent roles in affecting these functions. Serial determinations made after oral ingestion of pregnenolone and data from the literature suggest there is interdependence of steroid metabolic systems with those operational in control of interrelations in the GH-IGF-1 axis. Longitudinal concurrent measurements of serum levels of BT, DHEAS, and IGF-1/GH together with detailed studies of their correlations with age-correlated functional measures may be useful in detecting early age-related dysregulations and may be helpful in devising ameliorative approaches.

Adult↗

PubMed1983

Alcohol consumption and ischemic heart disease mortality: are time-series correlations meaningful?

Recently, time-series correlations of aggregated data have been used to demonstrate the length of latency periods for environmental factors, such as economic conditions and alcohol consumption, in influencing heart disease mortality. Latency periods were specified by lagging mortality rates relative to the economic indicators or rates of alcohol consumption until the highest correlations were achieved. The tendency has been to interpret these correlations without regard to whether the latency periods described are biologically plausible. The authors have identified four models which represent all the possible outcomes of correlational studies of time-series data. Using United States and Canadian mortality rates in relationship to alcohol consumption, they have demonstrated the application of each of these models. For three of the four models, the time-series (lag) correlations are uniform regardless of the number of years mortality is lagged relative to alcohol consumption, and this uniformity does not permit a latency period to be identified. Only the lag correlations between two nonlinear variables show variations over time, depending on the degree of correspondence between the increasing and decreasing line segments of the two curves. Correlations ranging from high positive to high negative are possible, and several peak correlations (positive and negative) can occur. However, the biologic interpretation of multiple peaks with the same or different signs is problematic. The authors conclude that time-series correlations of aggregated data are not useful for the study of latency periods, and that analysis of time-series correlations for this purpose can be at best ambiguous, and at worst, completely misleading.

Adolescent↗

PubMed2002

Continuous cerebral autoregulation monitoring by cross-correlation analysis: evaluation in healthy volunteers.

OBJECTIVE: In a former study, we applied cross-correlation (CC) analysis to recordings of arterial blood pressure (BP), intracranial pressure (ICP), and intracranial blood flow velocity (FV). A lack of significant time delay and a positive correlation coefficient of slow oscillations between these parameters was interpreted as indicative of impaired cerebral autoregulation, whereas a significant time delay and a negative correlation was regarded as preserved autoregulation. To test this hypothesis, cross-correlation was applied on recordings of BP and FV (CC [BP --> FV]) in healthy volunteers with a presumably preserved cerebral autoregulation. DESIGN: Study of a diagnostic test. SUBJECTS: A total of 17 healthy volunteers. MEASUREMENTS AND MAIN RESULTS: BP was recorded by using a tonometric device, and bilateral FV in the middle cerebral arteries (MCA) was measured by transcranial Doppler sonography. Signals were sampled at a resting horizontal position for 29 mins. Cluster analysis showed a mean +/- sd time delay for CC [BP --> FV(MCA right)] of 6.45 +/- 2.1 secs, and for CC [BP --> FV(MCA left) ] of 6.09 +/- 1.8 secs. The mean correlation coefficient was -.33 +/-.17 for the left and -.36 +/-.09 for the right side. In about 30%, differing results with a correlation coefficient between -.2 and.2 and a time delay near zero were found. Cross-correlation between left and right FV showed a mean time delay of 0.09 +/- 0.18 secs, with a mean correlation coefficient of.82 +/-.16. CONCLUSION Spontaneous slow oscillations of BP and FV were detected, and cross-correlation analysis showed a negative correlation and a positive time delay in about 70% of the examinations. These findings corroborate the hypothesis that CC [BP --> FV] might be able to assess the status of cerebral autoregulation continuously. The observed time delay between BP and FV oscillations is in good agreement with former studies on the dynamic properties of cerebral autoregulation.

Adult↗

PubMed2003

Correlation between hearing loss and scala media area in guinea pigs with long-standing endolymphatic hydrops.

HYPOTHESIS: Histologic analysis of the hydropic and normal guinea pig cochleae was undertaken to assess a potential correlation between the magnitude of endolymphatic hydrops and hearing loss. It was hypothesized that a greater correlation than previously reported might be found by looking at long-standing endolymphatic hydrops and high-frequency range hearing. BACKGROUND: Surgically induced endolymphatic hydrops in guinea pigs is the most widely used animal model for the study of human Ménière's Disease and recapitulates both endolymphatic hydrops and progressive sensorineural hearing loss. A strong correlation between the magnitude of hydrops and severity of hearing loss has been reported in the human condition, but not in the animal model. METHODS: Nine albino guinea pigs were each subjected to surgical obstruction of the endolymphatic sac and duct of the right ear. The left ears remained as internal histologic controls. Hearing was assessed from 2 kHz to 32 kHz by auditory brain stem response testing for 16 to 25 weeks after surgery. Histologic morphometry after the animals were killed was used to quantify both turn-specific and weighted overall hydrops. These measures were correlated with hearing loss in each animal at all tested frequencies. RESULTS: A statistically significant correlation between the magnitude of hydrops and the severity of hearing loss was observed for 2 kHz and 16 kHz. These frequencies correlated with both turn-specific hydrops and overall hydrops. However, turn-specific hydrops did not reliably correlate with the magnitude of hearing loss at anatomically appropriate frequency ranges. Where such a correlation did exist, it might well have been simply part of an expression of an overall correlation between hydrops and hearing loss. CONCLUSIONS: There may be a greater correlation between hydrops and hearing loss in guinea pigs with long-standing surgically induced hydrops than has previously been reported in animals with less advanced disease. These findings help to validate continued use of the model for hearing loss related to Ménière's Disease, verify the rationale of treatment modalities aimed at reducing hydrops in the human condition, and may indicate that efforts at reducing hydrops in such patients has benefits toward long-term hearing preservation.

Animals↗

PubMed2006

Correlations between the activities of 19 anti-tumor agents and the intracellular glutathione concentrations in a panel of 14 human cancer cell lines: comparisons with the National Cancer Institute data.

The aim of this work was 2-fold: (i) to identify correlations between the activities of pairs of 19 anti-tumor agents in a mini-panel of 14 human cancer cell lines of diverse origins with the goal of validating the panel, and (ii) to look for correlations between the activities of 19 standard anti-tumor agents and the intracellular concentrations of glutathione (GSH). Validation with analogous data from the National Cancer Institute (NCI) Developmental Therapeutics Program was made. The cell growth inhibition potencies of the anti-tumor agents [cisplatin, carboplatin, oxaliplatin, DACH-Pt, melphalan, chlorambucil, thiotepa, busulfan, doxorubicin, etoposide, camptothecin, vinblastine, podophyllotoxin, colchicine, taxol, hydroxyurea, methotrexate, 5-azacytidine and 5-fluorouracil (5-FU)] were estimated in 14 cancer cell lines by their GI50 values. An enzymatic assay based on the method of Tietze was employed to measure intracellular total GSH concentrations. The Delta method was used to compare pairs of anti-tumor agents; similarities and differences in activity profiles (mean graphs) were evaluated by regression analysis. Most, but not all, of the correlations could be explained based on similarities in the mechanisms of action and many correlations/non-correlations were also observed in the NCI data. Some correlations were unexpected however, and not seen in the NCI data. For example, strong positive correlations (P < 0.01) were found between the GI50 values of melphalan/chlorambucil and the anti-mitotic agents. Similarly unexpected, a strong positive correlation was observed between methotrexate and cisplatin (P < 0.01). Interestingly, moderate to strong negative correlations (P < 0.01-0.05) were found between the GI50 values of 5-FU and the anti-mitotic agents/melphalan/chlorambucil. Significant positive correlations between intracellular GSH concentrations and GI50 values were found only for thiotepa (P < 0.05) and doxorubicin (P < 0.01). Data from a NCI panel of 34 cancer cell lines showed no correlations between GSH levels and the GI50 values of the same 19 compounds. In conclusion, a panel of 14 human cancer cell lines of diverse origin was used to identify similarities and differences in the activities of standard anti-tumor agents. The level of significance was stronger with the 34 cell lines of the NCI, however. Our results indicate that GSH intracellular concentrations correlate with resistance only with doxorubicin and thiotepa in these cell lines.

Antineoplastic Agents↗

PubMed2001

Population coding in neuronal systems with correlated noise.

Neuronal representations of external events are often distributed across large populations of cells. We study the effect of correlated noise on the accuracy of these neuronal population codes. Our main question is whether the inherent error in the population code can be suppressed by increasing the size of the population N in the presence of correlated noise. We address this issue using a model of a population of neurons that are broadly tuned to an angular variable in two dimensions. The fluctuations in the neuronal activities are modeled as Gaussian noises with pairwise correlations that decay exponentially with the difference between the preferred angles of the correlated cells. We assume that the system is broadly tuned, which means that both the correlation length and the width of the tuning curves of the mean responses span a substantial fraction of the entire system length. The performance of the system is measured by the Fisher information (FI), which bounds its estimation error. By calculating the FI in the limit of a large N, we show that positive correlations decrease the estimation capability of the network, relative to the uncorrelated population. The information capacity saturates to a finite value as the number of cells in the population grows. In contrast, negative correlations substantially increase the information capacity of the neuronal population. These results are supplemented by the effect of correlations on the mutual information of the system. Our analysis provides an estimate of the effective number of statistically independent degrees of freedom, denoted N(eff), that a large correlated system can have. According to our theory N(eff) remains finite in the limit of a large N. Estimating the parameters of the correlations and tuning curves from experimental data in some cortical areas that code for angles, we predict that the number of effective degrees of freedom embedded in localized populations in these areas is less than or of the order of approximately 10(2).

Animals↗

PubMed2005

Finite-size scaling analysis of percolation in three-dimensional correlated binary Markov chain random fields.

Percolation and finite-size scaling properties in three-dimensional binary correlated Markov-chain random fields on a cubic lattice are computed by extensive Monte Carlo simulation. At short correlation scales, the percolation threshold in correlated random fields decreases as the correlation scale increases. The rate of decrease rapidly diminishes for correlation lengths larger than 2-3 lattice sites. At correlation scales of 4-6 lattice sites, the percolation threshold is found to be 0.126 +/- 0.001 for the Markov chain random fields, similar to that for sequential Gaussian and indicator random fields, which are evaluated for comparison. The average percolation threshold in finite-size lattices is a function of both, the correlation length and the finite lattice size. The universal scaling constants for mean cluster size and backbone fraction are found to be consistent with results on uncorrelated lattices. But prefactors of scaling relationships vary with correlation length. The squared radius of gyration of non-percolating clusters is found to scale with gamma/nu and its scaling prefactors are independent of the correlation scale. Prefactors are similar between the three random field generators evaluated. The percolation properties derived here are useful to account for finite-size effects on percolation in natural or man-made correlated systems.

Journal Article↗

PubMed1993

The correlation of running ability and physiological variables in thoroughbred racehorses.

The running abilities of 25 Thoroughbred racehorses were measured at distances of 1200, 1600 and 20000 m. Various physiological variables were measured subsequently on the treadmill and correlated with running speed. There was a negative correlation for running speed with the velocity (VLa4) and work rate (WLa4) at which blood lactate reaches a steady-state concentration of 4 mmol/litre and a positive correlation with peak plasma lactate, suggesting that plasma lactate concentrations of faster horses rise more rapidly and to higher levels than do those of slower horses. The correlation between running speeds and heart rates (HR) was stronger for unfit than fit horses, suggesting that cardiovascular effects of training are more beneficial to slower horses. The significant correlation between running speeds and V200 suggests that the HR of faster horses increases more rapidly than in slower horses performing similar exercise. The correlation of running speeds and VO2max suggests that the HR of faster horses increases more rapidly than in slower horses performing similar exercise. The correlation of running speeds and VO2max suggests that faster horses utilise more oxygen during maximal intensity exercise. The correlation of running speeds with minimum pH and minimum HCO3- suggests that faster horses maintain speed at higher hydrogen ion (H+) concentrations. Correlations between running speeds and the measured variables were consistently stronger for the longer distance runs. Because VLa4 and WLa4 were obtained during sub-maximal exercise, these variables were determined to be the best correlates of running performance.

Animals↗

PubMed1991

Fringed correlation discrimination and binaural detection.

Results are reported from a series of binaural detection and interaural correlation discrimination experiments at 500 Hz. The experiments include fringed correlation discrimination in which the correlation change is restricted to a narrow (38 Hz) target band of frequencies and the reference correlation is maintained in a fringe band of frequencies. This experiment is designed to be analogous to a detection experiment with a narrow-band target; in both cases the correlation changes only inside the target band. A simplified theoretical framework is used to compare the results of the detection and correlation discrimination experiments. Results are consistent with the notion that binaural detection and interaural correlation discrimination are effected by a common mechanism when the reference correlation is unity (as in the NoS pi case). When the reference correlation is zero (as in the NuSo case), detection performance is significantly better than predicted from the measured ability to discriminate interaural correlation.

Attention↗

PubMed2004

Diffusion-weighted MR imaging in closed head injury: high correlation with initial glasgow coma scale score and score on modified Rankin scale at discharge.

PURPOSE: To determine whether diffusion-weighted magnetic resonance (MR) imaging findings and conventional MR imaging findings correlate with initial Glasgow Coma Scale score and score on modified Rankin scale at discharge. MATERIALS AND METHODS: Twenty-six patients (18 male and eight female patients; mean age, 25.2 years; age range, 4-72 years) with diffuse axonal injury were examined with diffusion-weighted MR imaging and with fluid-attenuated inversion recovery, T2-weighted fast spin-echo, and T2*-weighted gradient-echo sequences. All images were evaluated by two neuroradiologists in consensus. Tissue volume with trauma-related signal-intensity abnormality on images from each sequence, number of lesions for each sequence, number of lesions for all sequences, and number of lesions with reduced apparent diffusion coefficient were correlated with scores on Glasgow Coma Scale and modified Rankin scale. Involvement of brainstem, deep gray matter, and corpus callosum were also correlated with clinical scores. Spearman rank correlation coefficients (r) were calculated. RESULTS: The strongest correlation was between signal-intensity abnormality volume on diffusion-weighted images and modified Rankin score (r = 0.772, P <.001). The strength of this correlation did not improve when only volume of lesions with decreased apparent diffusion coefficient was considered. For lesion number, the strongest correlation was between lesion number on images acquired with all sequences and modified Rankin score (r = 0.662, P <.001). For lesion location, the strongest correlation was between lesion location in the corpus callosum and modified Rankin score (r = 0.513, P =.007). CONCLUSION: Volume of lesions on diffusion-weighted MR images provides the strongest correlation with a score of subacute on modified Rankin scale at discharge. Total lesion number also correlates well with modified Rankin score. In future, diffusion-weighted images may be useful in determining treatment strategies for acute head injury.

Adolescent↗

PubMed1989

Cross-correlation analysis of taste neuron pairs in rat solitary tract nucleus.

1. Experiments were conducted to examine the possibility that the taste-sensitive neurons with similar taste-selectivity are preferentially innervated by common driving neurons whose taste-selectivity is also similar. 2. Multiple microelectrodes, in most cases a pair of glued electrodes, were inserted into the unilateral solitary tract nucleus (NTS) of the rat, and simultaneous recordings were made in neuron pairs responding to the four basic taste stimuli. The spike response density (RD) of each neuron during tastant stimulation was determined. Correlation coefficients of spike occurrence were calculated for each neuron pair during application of tastants and distilled water and also during spontaneous background activity. The frequency of correlated discharge (FC) of a neuron pair was measured as the area of the peak appearing on the cross-correlogram (CC). The FC value was divided by the RD value to calculate the weight of the correlated discharges in the output of each neuron (WC value). 3. Eleven pairs showed peaks in the CC constructed during tastant stimulation, whereas in other 11 pairs no peaks were found. The cross-correlation-positive group with peaks was composed of 18 NaCl-best (responding most vigorously to NaCl) and 4 HCl-best neurons, whereas the negative group without peaks included 9 NaCl-best, 9 HCl-best, and 4 sucrose-best neurons. 4. In the cross-correlation-positive pairs the taste quality most effective for one of the component neurons was often (13 NaCl-best and 2 HCl-best, 15/22 = 0.681) identical to the taste quality giving the highest probability of correlated discharge, i.e., highest FC value, in the neuron pair. 5. There were five cross-correlation-positive pairs (5/11 = 0.455) in which both of the component neurons were NaCl-best and the FC value was highest during NaCl stimulation. 6. The CCs constructed during water application exhibited peaks for all the pairs which gave positive cross-correlation in response to stimulation with tastants, whereas all pairs with negative cross-correlation during tastant stimulation never gave a detectable peak during water application. 7. In three pairs of the cross-correlation-positive group, the CCs constructed during spontaneous background activity without application of any liquid showed a small peak. 8. During NaCl stimulation some neurons exhibited relatively high FC values, but the WC values were always low. In contrast, during sucrose stimulation, the FC value was always low, but the WC value was quite high in some neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1994

Receptive-field maps of correlated discharge between pairs of neurons in the cat's visual cortex.

1. To investigate the functional significance of temporally correlated discharge between nearby cells in the visual cortex, we obtained receptive-field maps of correlated discharge for 68 cell pairs in kittens and cats. Discharge from cell pairs was measured by a single extracellular electrode. A reverse correlation procedure was used to relate neural discharge to particular stimuli within a random sequence of briefly flashed bright and dark bars. Bicellular receptive fields (BRFs) were mapped by applying reverse correlation to approximately synchronous discharge from two cells. Unicellular receptive fields (URFs) were simultaneously mapped by separately applying reverse correlation to the discharge of each cell. 2. The receptive fields of the two neurons within each pair were initially studied by varying the orientation and spatial frequency of drifting sinusoidal gratings. After these tests a random sequence of appropriately oriented bars was used to evoke discharge suitable for reverse correlation analysis. For most cell pairs, the temporal pattern or strength of correlated discharge produced by such stimulation is different from that observed with stimulation by sinusoidal gratings. This indicates that visually evoked correlated discharge between nearby cells is stimulus dependent. 3. BRFs were classified according to their pattern of spatial sensitivity into three groups that roughly correspond to the single-cell receptive-field types of the lateral geniculate nucleus (LGN; center-surround) and visual cortex (simple and complex). These classifications were compared with the receptive-field types of the single cells within each pair. LGN-type and simple-type BRFs were only seen for pairs in which at least one of the cells was simple. Conversely, complex-type BRFs were only seen for pairs in which at least one of the cells was complex. 4. Because the reverse correlation procedure can be used to characterize the spatiotemporal receptive-field structure of simple cells, we were able to compare both the spatial and temporal properties associated with the URFs and BRFs of simple cell pairs. The spatiotemporal structure of the BRF of a simple-cell pair can largely be predicted on the basis of the two URFs. Although this prediction suggests the possibility that BRFs are stimulus artifacts, a shuffle procedure, in which multiple repetitions of random sequences were presented, verifies the neural origin of BRFs. BRFs emerge from specific neural pathways and are not simply a consequence of unicellular response preferences. 5. Five measures were derived from the reverse correlation analysis of simple-cell receptive fields: width, duration, optimal spatial and temporal frequency, and optimal velocity.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1999

Occurrence of widespread motor-unit firing correlations in muscle contractions: their role in the generation of tremor and time-varying voluntary force.

The firing behavior of motor units (MUs) of the first dorsal interrosseus muscle of the hand was examined during both constant-force and varying-force (sinusoidal or broadband random variations) isometric contractions in healthy adults. The emphasis was on the analysis of MU synchrony with an efficient and sensitive method. In static contractions, widespread and strong MU firing correlations, with the MUs in phase, were present at the frequency of muscle tremor, when the tremor was regular (narrowband) and large. MU correlations could also exist in contractions where the tremor of a subject was irregular (broadband) overall, but they were generally weak. These correlations were at the frequency of the subject's regular tremor, and the corresponding distinct tremor component was sometimes discernible within the broad tremor-band. In contrast, the MUs did not show any such correlations in the case of purely irregular and small tremor. On the basis of these observations, it is concluded that the rhythms in the force contributions of the last- recruited, large MUs, which fire near their threshold rate, compose the broadband frequency content of physiological muscle tremor in every contraction. Within this band, there is an additional distinct tremor component when MU correlations are present. For widespread and strong MU correlations, this component dominates and constitutes the observed regular tremor. In dynamic contractions, the firing of all MUs was modulated in the frequency band of both the sinusoidal and the complex variations of the force. The MU modulations showed a time-lead over the force variations and were strongly correlated both to these variations and among themselves. Thus widespread and strong correlations of MU firing modulations seem to provide a mechanism for generation of time-varying voluntary force, under general dynamic conditions. Finally, when regular tremor was present in dynamic contractions, widespread and fairly strong MU correlations also existed at the tremor frequency. It is concluded that at least two mechanisms can cause widespread MU synchrony, and they can act in parallel. They involve two types of correlated inputs to the alpha-motoneurons (presumably from the muscle spindles and the cortex), whose effects combine at the level of the membrane potential of the cells.

Adult↗

PubMed1993

Correlation of aminoglycoside and vancomycin pharmacokinetic parameters.

OBJECTIVE: To investigate a correlation between the elimination rate constants (Ke) of aminoglycosides (AG) and vancomycin; to investigate the correlation between actual Ke and creatinine clearance (Clcr) for AG versus vancomycin; to investigate the calculated versus actual Ke for AG and vancomycin; and to investigate a correlation between volumes of distribution (Vd) between AG and vancomycin. DESIGN: Retrospective data collection. METHODS: Patients in our institution who received AGs or vancomycin concomitantly or within six weeks of each other were identified retrospectively. Patient subpopulations were identified and analyzed collectively as well as individually. Steady-state serum concentrations of AG and vancomycin (more than four half-lives) were obtained and kinetic parameters (Ke, Vd) were calculated using first-order pharmacokinetic equations. Linear regression was used to determine correlation coefficients. RESULTS: In the total population and all subpopulations, the correlation between Ke of AG and vancomycin was superior to the correlation between Ke and Clcr. The correlations (r2) between Ke for AG and vancomycin in the total, general medicine, oncology, and intensive care units (ICU) populations were 0.572, 0.878, 0.349, and 0.561, respectively. The correlations (r2) between Ke and Clcr for AG in the total, general medicine, oncology, and ICU populations were 0.235, 0.430, 0.005, and 0.238, respectively. The correlations (r2) between Ke and Clcr for vancomycin in the total, general medicine, oncology, and ICU populations were 0.300, 0.407, 0.055, and 0.309, respectively. CONCLUSIONS: The correlation between Ke of AG and vancomycin may be beneficial for predicting Ke of vancomycin when AG concentrations have already been obtained or vice versa, and may give more accurate estimations of dosing intervals and require less time adjusting, ordering, and interpreting concentrations and dosages.

Adult↗

PubMed2005

The effects of normalization on the correlation structure of microarray data.

BACKGROUND: Stochastic dependence between gene expression levels in microarray data is of critical importance for the methods of statistical inference that resort to pooling test-statistics across genes. It is frequently assumed that dependence between genes (or tests) is sufficiently weak to justify the proposed methods of testing for differentially expressed genes. A potential impact of between-gene correlations on the performance of such methods has yet to be explored. RESULTS: The paper presents a systematic study of correlation between the t-statistics associated with different genes. We report the effects of four different normalization methods using a large set of microarray data on childhood leukemia in addition to several sets of simulated data. Our findings help decipher the correlation structure of microarray data before and after the application of normalization procedures. CONCLUSION: A long-range correlation in microarray data manifests itself in thousands of genes that are heavily correlated with a given gene in terms of the associated t-statistics. By using normalization methods it is possible to significantly reduce correlation between the t-statistics computed for different genes. Normalization procedures affect both the true correlation, stemming from gene interactions, and the spurious correlation induced by random noise. When analyzing real world biological data sets, normalization procedures are unable to completely remove correlation between the test statistics. The long-range correlation structure also persists in normalized data.

Algorithms↗

PubMed2006

Complex amplitude correlation for compensation of large in-plane motion in digital speckle pattern interferometry.

The use of complex amplitude correlation to compensate for large in-plane motion in digital speckle pattern interferometry is investigated. The result is compared with experiments where digital speckle photography (DSP) is used for compensation. An advantage of using complex amplitude correlation instead of intensity correlation (as in DSP) is that the phase change describing the deformation is retrieved directly from the correlation peak, and there is no need to compensate for the large movement and then use the interferometric algorithms. A discovered drawback of this method is that the correlation values drop quickly if a phase gradient larger than pi is present in the subimages used for cross correlation. This means that, for the complex amplitude correlation to be used, the size of the subimages must be well chosen or a third parämeter in the cross-correlation algorithm that compensates for the phase variation is needed. Correlation values and wrapped phase maps from the two techniques (intensity and complex amplitude correlation) are presented.

Journal Article↗