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PubMed2002

Correlation between retinal abnormalities and intracranial abnormalities in the shaken baby syndrome.

PURPOSE: To report correlation between retinal and intracranial abnormalities and to evaluate pathogenesis of retinal hemorrhages in the shaken baby syndrome (SBS). DESIGN: Observational case series. METHODS: Seventy-five children with apparent nonaccidental head trauma consistent with SBS had complete physical examination, complete ophthalmologic examination, neuroimaging by CT or MRI, or both, and skeletal radiographic survey. In this retrospective review, ophthalmoscopic and intracranial abnormalities were correlated. RESULTS: The age of patients ranged from 2 to 48 months (mean - SD, 10.6 +/- 10.4 months). Neuroimaging was abnormal in all 75 cases. Findings included subdural hematoma (70 children, 93%), cerebral edema (33 children, 44%), subarachnoid hemorrhage (12 children, 16%), vascular infarction (nine children, 12%), intraparenchymal blood (six children, 8%), parenchymal contusion (six children, 8%), and epidural hemorrhage (one child, 1%). Sixty-four (64/75, 85%) children had retinal abnormalities, mostly (53/64, 82%) confluent multiple hemorrhages that were subretinal, intraretinal, and preretinal in 47/64 (74%) and bilateral in 52/64 (81%). No association was found between anatomic site (left, right, or bilateral) of intracranial and retinal findings (McNemar test kappa = -0.026-0.106) or between any of the intracranial findings mentioned above and the following retinal findings: normal or abnormal retinal examination, multiple (>10) or few retinal hemorrhages (< or =10), symmetric or asymmetric retinal findings, or retinoschisis (kappa = -0.127-0.104). Signs of possible increased intracranial pressure were not correlated with any retinal abnormality (kappa = -0.03-0.073). There was no correlation between evidence of impact trauma to the head and retinal hemorrhages (kappa = 0.058). Total Cranial Trauma Score and Total Retinal Hemorrhage Score, both indicating the severity of injury, were correlated (P =.032). CONCLUSIONS: Our study supports previous observations that the severity of retinal and intracranial injury is correlated in SBS. We cannot support the suggestions that in most children with SBS retinal bleeding is caused by sustained elevated intracranial, elevated intrathoracic pressure, direct tracking of blood from the intracranial space, or direct impact trauma. The correlation in severity of both eye and head findings may suggest, however, that retinal abnormalities are the result of mechanical shaking forces.

Battered Child Syndrome↗

PubMed1994

Scanning concentration correlation spectroscopy using the confocal laser microscope.

Concentration correlation spectroscopy allows the assessment of molecular motions in complex systems. The technique generally monitors concentration fluctuations by means of some method such as the intensity of fluorescent molecules (fluorescence correlation spectroscopy). We describe here the use of scanning confocal laser microscopy to measure correlation functions in both space and time. This methodology offers two major advantages over conventional methods. First, collecting data from different regions of the sample significantly increases the signal-to-noise ratio. Second, molecular motions of colloidal gold can be analyzed by correlation methods with high temporal and spatial resolution. Using a MRC 600 laser scanning system, we collect data from an ensemble of 768 independent subvolumes and determine the space-time correlation function. We demonstrate the technique using two different types of samples, fluorescently labeled DNA molecules in solution and colloidal gold-tagged lipids in a planar bilayer. This approach, which we term "scanning concentration correlation spectroscopy," provides a straightforward means of performing high resolution correlation analysis of molecular motions with available instrumentation.

Biophysical Phenomena↗

PubMed2001

Comparison of spinal myotatic reflexes in human adults investigated with cross-correlation and signal averaging methods.

A cross-correlation method for recording spinal myotatic reflexes has been developed to meet the need for brief test periods in babies and children and subjects with central neurological pathology. In normal adult subjects the method has been validated by comparing excitatory and inhibitory reflexes obtained with cross-correlation with those obtained with conventional signal averaging. In the cross-correlation method a pseudo-random binary sequence of 64 brief tendon taps was delivered in <1.5 s, and in the averaging method 20-150 taps at one per second. The reflexes were expressed as unit impulse responses to enable direct, quantitative comparisons to be made. With cross-correlation the responses were slightly expanded in time, had lower peak amplitudes, and onset latencies advanced by 10 ms, the clock period of the pseudo-random binary sequence. The amplitude of biceps phasic stretch reflex increased with muscle contraction in a similar manner with both methods. In tests for stationarity the amplitude of biceps phasic stretch reflex varied <10% in the first six repeats of the pseudo-random binary sequence. The tap force required at threshold for cross-correlation was approximately half that for averaging, but with both methods the magnitude of biceps phasic stretch reflex varied linearly with tap force over the range of one to two times threshold. The validity of responses obtained with cross-correlation was assessed by a statistical procedure. In conclusion, the cross-correlation method is robust and gives similar results to those obtained with averaging.

Adult↗

PubMed2003

Locations and morphologies of sympathetically correlated neurons in the T(10) spinal segment of the rat.

We precisely localized and morphologically characterized sympathetically correlated neurons in the acutely transected spinal cord of the rat. We have shown that these neurons are likely members of the spinal networks that generate sympathetic activity after spinal cord transection. In humans with injured spinal cords, these networks are responsible for hypertensive crises that occur in response to ordinarily innocuous stimuli. We recorded from neurons in the dorsal horn of the T(10) spinal segment of anesthetized rats after acute spinal cord transection at C(2). Neurons with activities closely correlated to renal sympathetic nerve activity (RSNA) were considered to be putative components of spinal sympathetic systems. These neurons had receptive fields on the left flank and abdomen. After characterizing their ongoing activities, receptive fields, and degrees of correlation with RSNA, we juxtacellularly labeled neurons with biotinamide and subsequently reconstructed their somas and dendrites histologically. Confirming our earlier studies, sympathetically correlated neurons were found in dorsal horn laminae III, IV, and V. For the first time, we also identified sympathetically correlated neurons in laminae I and II. The dendrites of all sympathetically correlated neurons projected to multiple lamina. By virtue of the positions of their somas and the broad projections of their dendrites, we concluded that sympathetically correlated neurons may receive direct input both from supraspinal systems and from nociceptive and non-nociceptive primary afferents.

Animals↗

PubMed1997

Serum leptin levels are independently correlated with two measures of HDL.

Leptin is the peptide product of the OB gene, which is associated with obesity in some strains of mice. Because dyslipidemias are frequently associated with obesity, we have begun to characterize the pathways connecting these related traits. In this investigation we tested for correlation of HDL phenotype measures with leptin concentrations using data from 1159 participants in the San Antonio Family Heart Study, a study of risk factors for cardiovascular disease in Mexican Americans living in and around San Antonio, Texas. In a subset of 288 unrelated individuals, we tested for correlation of leptin with nine different measures of HDL phenotype and found that only three were significantly related. However, stepwise regression analysis suggested that only two measures, HDL triglyceride concentrations (HDL-TG) and the proportion of apo A-I on HDL particles larger than HDL3 (Large HDL-apo A-I), were independently correlated with leptin. Because obesity and HDL phenotypes are both under strong genetic control, we conducted a trivariate genetic analysis, using the entire data set, to test the hypothesis that the phenotypic correlations were due to the effects of shared genes (i.e., pleiotropy). Heritabilities for the three traits were estimated to be 0.47 for leptin, 0.46 for HDL-TG, and 0.46 for Large HDL-apo A-I. Results from the genetic analyses revealed that the phenotypic correlation of leptin with HDL-TG was nongenetic (i.e., shared environment), while the phenotypic correlation with Large HDL-apo A-I was due to pleiotropy (i.e., shared genes). These results confirmed the result derived from the subset of unrelated individuals that the two measures of HDL are independently correlated with leptin. To our knowledge, this is the first report of a relationship between leptin and any aspect of lipoprotein phenotype. A better understanding of the genes responsible for this relationship may provide a molecular explanation for the aggregation of atherogenic phenotypes, such as diabetes, obesity, and dyslipoproteinemia.

Adult↗

PubMed1992

Slope filtered pointwise correlation dimension algorithm and its evaluation with prefibrillation heart rate data.

Various studies have shown that a low variability in heart rate is associated with increased risk of ventricular fibrillation. Low chaotic (correlation) dimension in the heart rate also appears to predict fibrillation risk. However, these results have been based on intergroup comparisons and have not been found useful for predicting when a patient may fibrillate with any degree of sensitivity, specificity, or temporal accuracy. There are two primary limitations in using dimensional analysis to predict imminent fibrillation. The first is that the standard algorithms (for correlation dimension) assume stationarity of the system. The second limitation is that these algorithms require 10,000-50,000 data points to achieve good accuracy. Thus, even if stationarity were not an issue, there would be a lag of 2.4-12 hours to warn of impending fibrillation. An algorithm has been developed to calculate an accurate pointwise correlation dimension of heart rate data. The slope filtered pointwise correlation dimension algorithm requires as few as 1,000 points of data. Using this algorithm, it was found that the correlation dimension dropped from 2.50 +/- 0.81 to 1.07 +/- 0.18 in the minute before fibrillation in conscious pigs with an occluded coronary artery. In clinical studies, Holter tapes from patients that had suffered fatal fibrillation were also analyzed along with healthy controls and nonfibrillation ventricular patients. The fibrillation patients all had excursions of low dimension (less than 1.5), while the majority of the others did not. In the minutes before fibrillation, the correlation dimension dropped to a steady range of 0.8-1.3. Drops in the slope filtered pointwise correlation dimension appear to predict fibrillation in animals and patients.

Algorithms↗

PubMed1988

Cell cycle models and mother-daughter correlation.

Among the different experimental features that are usually used to measure the variability of cell cycle duration (Tc), the mother-daughter correlation is a special case since apparently contradictory results have been reported from different experimental systems. Indeed, positive, null and negative experimental values have been found, raising problems in cell cycle modeling in as much as one would like a general, unified view of the control of the cell cycle. Such views are provided by mathematical models. We present a method to derive the value(s) of the correlation between mother and daughter Tcs predicted from any such model, provided Tc can be analytically expressed. An exact calculation is proposed for the case when Tc can be expressed as a linear combination of the parameters involved. Otherwise, using Taylor series expansion, an approximate expression for the correlation can be derived. In both cases, the predicted values can be compared with experimental ones. The proposed method is illustrated using the Growth Controlled model of Koch (1980, Nature 286: 80) and the Continuum model of Cooper (1982, J. theor. Biol. 94: 783). Whereas Koch's model leads to inflexible negative values of the correlation between mother and daughter Tcs, our results demonstrate that differences in the mean duration of the G1 phase may account for differences in the sign of this correlation in Cooper's model. Furthermore, the proposed method can also be applied to other correlations such as the correlation between sibling cell Tcs.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Cycle↗

PubMed2006

Correlation between serum prostate specific antigen and prostate volume in Taiwanese men with biopsy proven benign prostatic hyperplasia.

PURPOSE: We studied the correlation between serum prostate specific antigen and the volume of different zones of the prostate in Taiwanese men with biopsy proven benign prostatic hyperplasia. MATERIALS AND METHODS: A total of 233 patients with a mean age of 71.4 years (range 42 to 89), serum prostate specific antigen less than 10 ng/ml and pathologically confirmed benign prostatic hyperplasia were enrolled in this study. Total prostate and transitional zone volumes were measured with transrectal ultrasonography. Peripheral zone volume was determined by subtracting transitional zone volume from total prostate volume. Correlations between patient age, total serum prostate specific antigen and the volume of each prostate zone were analyzed with the Pearson correlation coefficient. A linear regression model was used to determine the relationship between prostate specific antigen and prostate volume. The prostate specific antigen-prostate volume relationship in our patients was compared with published data on white and Japanese men. RESULTS: Age did not significantly correlate with serum prostate specific antigen and prostate volume. Serum prostate specific antigen significantly correlated with the volume of each prostate zone. After log transformation the Pearson correlation coefficient between total prostate specific antigen and the volume of the whole prostate gland, the transitional zone and the peripheral zone were 0.369, 0.377 and 0.272, respectively (p <0.001). Taiwanese men had lower prostate volume per unit prostate specific antigen comparing with white men, while the prostate specific antigen-total prostate volume relationship between Taiwanese and Japanese men was similar. CONCLUSIONS: In Taiwanese men with biopsy proven benign prostatic hyperplasia the volume of each prostate zone has significantly correlates with serum prostate specific antigen. The prostate specific antigen-total prostate volume relationship in Taiwanese men is different from that in white men. However, the prostate specific antigen-total prostate volume relationship between Taiwanese and Japanese men is similar.

Adult↗

PubMed1986

Clinical evaluation of patients with prostatic obstruction: correlation of flow rates with voided, residual or total bladder volume.

Previous investigators reported that accurate estimation of average or maximum urinary flow rates required correlation with total bladder volume (voided plus residual volumes). To test this requirement we performed uroflowmetry studies on 124 patients before and 77 patients after prostatectomy. Of the patients 20 were tested on multiple preoperative and postoperative occasions to comprise paired observations. Observations were made on age, voided and residual volumes, voiding duration, and average, maximum and adjusted maximum flow rates. Prostatectomy resulted in significant increases in all flow rates and significant decreases in voiding duration. The procedure had significant effects on reducing residual volume but voided volumes increased and total volume decreased only slightly postoperatively. Preoperative average, maximum and adjusted peak urinary flow rates correlated negatively with residual volume (increasing residual volume correlates with decreasing flow rate). Maximum flow rates correlated positively with voided volume. Whether measured preoperatively or postoperatively no significant correlation was found among average, peak or adjusted flow rates and total bladder volume. The only consistent significant correlation found among voided, residual and total volumes, and other measurements was voiding duration, which increased as any of the aforementioned volumes increased. Comparison of the random total and paired populations revealed no significant difference. Use of voided rather than total volume seems preferred in correlations with maximum urinary flow rates. Determination of residual urine remains necessary as an estimation of emptying failure but it is not required information for determination of flow rates.

Aged↗

PubMed1997

Computed axial tomographic scan measurement of abdominal fat distribution and its correlation with anthropometry and insulin secretion in healthy Asian Indians.

Asian Indians have high insulin resistance, hyperinsulinemia, a high prevalence of diabetes, and a high waist to hip ratio (WHR), although the rate of obesity is low. WHR and visceral fat (VF) are highly correlated, and both are associated with insulin resistance. This study was performed to determine the normal ranges of abdominal fat distribution (subcutaneous [SF] and VF) in nondiabetic South Indians and also to study its correlations with WHR, plasma insulin, and metabolic profiles. Fat areas were measured by computed axial tomographic scan at the L4 to L5 level. Mean areas of SF and VF in men and women in this study were similar to the values in white populations. Women had significantly less VF than men. Gender differences were observed in the contribution of fat areas to anthropometric, hormonal, and metabolic variables. In general, in men, total fat (TF) area showed significant independent correlation with body mass index (BMI), WHR, and total cholesterol, and VF correlated with insulin secretion. In women, TF and BMI were correlated and SF showed a correlation with total cholesterol. Insulin secretion in women did not show a correlation with fat areas.

Abdomen↗

PubMed2003

Immunomodulatory cytokines in human seminal plasma correlate with immunomodulatory steroids.

7alpha-Hydroxy-dehydroepiandrosterone and its 7beta-hydroxyepimer, which act as local immunomodulatory agents, dehydroepiandrosterone, cortisol, and major androgens, together with four cytokines-interleukins 2, 4, 10, and IFN-gamma, reflecting the activity of TH1 or TH2 cells present in semen, were measured in seminal plasma from 35 male donors. Cortisol, dehydroepiandrosterone, its sulfate, 7-hydroxy-dehydroepiandrosterone epimers, testosterone, and estradiol were also measured in their blood serum. Steroids and interleukins in semen as well as serum steroids and seminal interleukins were mutually correlated to find out whether a relationship between immunomodulatory steroids and cytokines influencing the immune environment does exist. A highly significant (P<0.001) positive correlation was found between seminal 7beta-hydroxy-dehydroepiandrosterone and IFN-gamma, while a negative correlation was found between cortisol and IL-10. Highly significant positive correlations were also found between serum 7alpha-hydroxy-dehydroepiandrosterone and seminal IFN-gamma and between serum 7beta-hydroxy-dehydroepiandrosterone and seminal IL-2, while a negative correlation was found between serum dehydroepiandrosterone and seminal IL-10. Different and in some instances, even contradictory findings concerning the influence of dehydroepiandrosterone and cortisol on TH1 and TH2 cytokines were observed in seminal plasma as compared to those found by others in serum. The differences can be ascribed to the different environments of mucosal and systemic immunity. Correlations between the levels of steroids and cytokines in seminal plasma did not always correspond to the correlations between given cytokines and hormones in sera. The results, however, are in agreement with our recent finding of an autonomous production of these steroids in the male reproductive tract.

Adult↗

PubMed2003

Correlations between cadmium and mineral nutrients in absorption and accumulation in various genotypes of rice under cadmium stress.

The absorption and accumulation of Cd2+, Fe3+, Zn2+, Mn2+, Cu2+ and Mg2+ in the roots and leaves of 20 rice cultivars (Oryza sativa L.) with different genotypes under cadmium (Cd) stress were investigated with pot experiments. The results showed that there existed significant differences among the rice cultivars in the contents of six mineral elements in both roots and leaves at both heading and ripening periods. The statistical analysis showed that, for their contents in roots, significant and positive correlations between Cd2+ and Fe3+, Cd2+ and Zn2+, Cd2+ and Mn2+, Cd2+ and Cu2+ existed, but no significant correlation between Cd2+ and Mg2+, at the two periods. In the leaves, Cd also showed significant and positive correlations with Fe3+, Zn2+ and Cu2+ at the both periods, but a significant and negative correlation with Mn2+ and no significant correlation with Mg2+ at heading, a significant and positive correlation with Mg2+ and no significant correlation with Mn2+ at ripening. These results suggested that there were cooperative absorption between Cd2+ and Fe3+, Mn2+, Cu2+, Mn2+ in rice plants. Genotypic differences in Cd uptake and translocation among the rice cultivars suggested that paddy field of some rice cultivars may be irrigated with partially treated sewage water.

Absorption↗

PubMed1998

Correlation of transrectal ultrasound measurements of prostate and transition zone size with symptom score, bother score, urinary flow rate, and post-void residual volume.

OBJECTIVES: To assess the correlation of total prostatic size and prostate transition zone dimensions with various measurements of the severity of bladder outlet obstruction secondary to benign prostatic hyperplasia. METHODS: Prostate-specific antigen, creatinine, American Urological Association symptom score, bother score, urinary history, uroflowmetry, and post-void residual urine volume determination was followed by measurement of the prostate gland and transition zone on transrectal ultrasound images in 136 men undergoing systematic prostate biopsies. Patients were divided into five groups based on past urinary tract treatment history and the presence of prostate cancer on the biopsies. The total prostate and transition zone dimensions, as well as calculated prostate and transition zone volumes, were compared by Pearson correlation with both the subjective and objective voiding parameters in each patient group. RESULTS: The transition zone dimensions correlated positively with American Urological Association symptom score, bother score, and post-void residual urine volume and correlated negatively with maximum and mean flow rates, particularly in patients with no history of prostate surgery, alpha-blocker administration, urinary infections, irritative voiding symptoms, or prostate cancer. CONCLUSIONS: Transrectal ultrasound measurements of transition zone dimensions correlate better than total prostatic dimensions or calculated prostatic or transition zone volumes with the severity of benign prostatic hyperplasia. Of these, the transverse transition zone dimension demonstrated the best correlation; however, this correlation is probably not adequate for clinical utility.

Aged↗

PubMed2003

Correlation between intraocular pressure level and optic disc changes in high-tension glaucoma suspects.

PURPOSE: To assess the correlation between intraocular pressure (IOP) and future optic disc changes in eyes of patients suspected of having high-tension glaucoma and to determine the target pressure in eyes of patients suspected of having high-tension glaucoma. DESIGN: Prospective, comparative, observational case series. PARTICIPANTS: Fifty-seven eyes of 57 patients suspected of having high-tension glaucoma selected from 226 consecutive patients with glaucoma or suspected glaucoma. INTERVENTION: The status of the optic disc and visual fields was evaluated during an initial examination by confocal laser ophthalmoscopy and automatic perimetry, respectively. Fifty-seven eyes were followed up for at least 2.5 years and then underwent a final examination. IOP was measured every 3 months. MAIN OUTCOME MEASURES: The correlation between changes in optic disc status and IOP control during follow-up was determined. Changes in the optic disc were evaluated by using the percentage change in total contour area, neuroretinal rim area, and cup-to-disc ratio. The control IOPs were evaluated on the basis of the percentage of time during which IOP was <18 mmHg (%<18 mmHg control) and <21 mmHg (%<21 mmHg control) during follow-up in each eye. The correlation between visual field changes and IOP control was also analyzed. RESULTS: Results from 48 (84.2%) of 57 participants were included. Patients were followed up for a mean 4.4 years. The %<21 mmHg control was significantly correlated with changes in neuroretinal rim area (r = 0.40; P = 0.0055) and in cup-to-disc ratio (r = -0.40; P = 0.0051) by linear regression analysis. The correlations were also significant if the difference in the length of follow-up was adjusted by multivariate regression analysis. There was no significant correlation between %<18 mmHg control and changes in disc parameters. Seven (14.6%) of 48 eyes had glaucomatous visual field defects at the final examination. The %<21 mmHg control was significantly lower in eyes with visual field changes compared with eyes with no changes (P = 0.0153; unpaired t test). In contrast, %<18 mmHg control was not significantly different between eyes with and without visual field changes (P = 0.3886). CONCLUSIONS: The IOP level correlates with topographic changes in the optic disc in eyes of patients suspected of having high-tension glaucoma. The target pressure for such eyes may need to be between 18 and 21 mmHg, and <18 mmHg is a safe target level in the treatment of patients suspected of having high-tension glaucoma to delay topographic optic disc changes.

Adult↗

PubMed1999

Correlation of tear fluorescein clearance and Schirmer test scores with ocular irritation symptoms.

OBJECTIVE: To correlate and compare the Schirmer 1 test and a new method of measuring tear fluorescein clearance with the CytoFluor II fluorometer with the severity of ocular irritation symptoms, clinical signs of meibomian gland disease, corneal fluorescein staining scores, and corneal and conjunctival sensitivity. DESIGN: Case-control study. PARTICIPANTS: Forty patients presenting with a chief complaint of ocular irritation, and 40 asymptomatic control subjects of similar age distribution. INTERVENTION: All subjects completed a symptom questionnaire, a baseline ocular examination, fluorescein clearance test (FCT), and Schirmer 1 test. MAIN OUTCOME MEASURES: The FCT was performed with a CytoFluor II fluorophotometer by measuring the fluorescein concentration in minimally stimulated tear samples collected from the inferior tear meniscus 15 minutes after instillation of 5 microl of 2% sodium fluorescein. Severity of ocular irritation was assessed with a symptom questionnaire. Schirmer 1 test, biomicroscopic meibomian gland evaluation, corneal fluorescein staining score, and corneal and conjunctival sensation scores were assessed with the Cachet-Bonnet anesthesiometer in all subjects. RESULTS: Irritation symptoms correlated with higher log tear fluorescein concentration (symptomatic 3.08 +/- 0.62 units/,microl, normal control 1.89 +/- 0.7 units/microl, P < 0.005) and lower Schirmer 1 test scores (symptomatic 12.6 mm, normal control 22.3 mm, P < 0.005). The FCT showed greater predictive value for identifying ocular irritation than the Schirmer 1 test. A fluorescein concentration of 274 units//microl eliminated 80% of the normal subjects (specificity) and identified 85% of the abnormal subjects (sensitivity). Log of tear fluorescein concentration and the Schirmer 1 test correlated with meibomian gland orifice metaplasia (2.81 +/- 0.78 units/microl and 14.47 +/- 9.53 mm in those with metaplasia vs. 1.83 +/- 0.71 units/microl and 23.14 +/- 7.67 mm in those without metaplasia, P < 0.001) and with the percentage of acinar dropout. Both log of tear fluorescein concentration and the Schirmer 1 test correlated with corneal fluorescein staining (Pearson correlation of 0.394 P < 0.0001 for Schirmer 1 test and 0.312 P < 0.005 for log of tear fluorescein). In addition, log of tear fluorescein and Schirmer 1 test scores correlated with corneal and conjunctival sensation scores (Spearman's rho for corneal sensation: log of tear fluorescein -0.38, P < 0.003, Schirmer 1 test -0.39, P < 0.002, and for conjunctival sensation: log of tear fluorescein -0.391, P < 0.001, Schirmer 1 test -0.23, P < 0.061). CONCLUSIONS: The FCT shows a greater predictive value for ocular irritation than the Schirmer 1 test. It correlates better with age, meibomian gland dysfunction, and decreased corneal and conjunctival sensation. Decreased tear clearance was identified as a risk factor for ocular irritation, even in subjects with normal Schirmer scores. This simple technique may provide new clues into the mechanism and therapy of ocular irritation.

Adult↗

PubMed1997

Phase correlation among rhythms present at different frequencies: spectral methods, application to microelectrode recordings from visual cortex and functional implications.

In classical EEG analysis rhythms with different frequencies occurring at separable regions and states of the brain are analysed. Rhythms in different frequency bands have often been assumed to be independent and their occurrence was interpreted as a sign of different functional operations. Independence has scarcely been proved because of conceptual and computational difficulties. It is, on the other hand, probable that different rhythmic brain processes are coupled because of the broad recurrent connectivity among brain structures. We, therefore, set out to find interactions among rhythmic signals at different frequencies. We were particularly interested in interactions between lower frequency bands and gamma-activities (30-90 Hz), because the latter have been analysed in our laboratory in great detail and had properties suggesting their involvement in perceptual feature linking. Fast oscillations occurred synchronized in a stimulus-specific way in the visual cortex of cat and monkey. Their presence was often accompanied by lower frequency components at considerable power. Such multiple spectral peaks are known from many cortical and subcortical structures. Despite their well known occurrence, coupling among different frequencies has not been established, apart from harmonic components. For the present investigation we extended existing analytical tools to detect non-linear correlations among signal pairs at any frequency (including incommensurate ones). These methods were applied to multiple microelectrode recordings from visual cortical areas 17 and 18 of anesthetized cats and V1 of awake monkeys. In particular, we assessed non-linear correlations by means of higher order spectral analysis of multi-unit spike activities (MUA) and local slow wave field potentials (LFP, 1-120 Hz) recorded with microelectrodes. Non-linear correlations among signal components at different frequencies were investigated in the following steps. First, the frequency content of short (approximately 250 ms) sliding window signal epochs was analyzed for simultaneously occurring rhythms of significant power at different frequencies. This was done by a newly developed method derived from the trispectrum using separate averaging of the products of short-epoch power spectra for any possible combination of frequency pairs. Second, non-linear (quadratic) phase coupling between different frequencies was assessed by the methods of bispectrum and bicoherence. We found phase correlations at different frequencies in the visual cortex of the cat and monkey. These couplings were significant in about 60% of the investigated MUA and LFP recordings, including several cases of coupling among incommensurate (i.e. non-harmonic) frequencies. Significant phase correlations were present: (1) within the gamma-frequency range; (2) between gamma- and low frequency ranges (1-30 Hz, including alpha- and beta-rhythms); and (3) within the low frequency range. Phase correlations depended, in most cases, on specific visual stimulation. We discuss the possible functional significance of phase correlations among high and low frequencies by including proposals from previous work about potential roles of single-frequency rhythms of the EEG. Our suggestions include: (1) visual feature linking across different temporal and spatial scales provided by coherent oscillations at high and low frequencies; (2) linking of visual cortical representations (high frequencies) to subcortical centers (low frequencies) like the thalamus and hippocampus; and (3) temporal segmentation of the sustained stream of incoming visual information into separate frames at different temporal resolutions in order to prevent perceptual smearing due to shifting retinal images. These proposals are, at present, merely speculative. However, they can, in principle, be proved by microelectrode recordings from trained behaving animals.

Animals↗

PubMed1999

Peripheral blood mitochondrial DNA content correlates with lipid oxidation rate during euglycemic clamps in healthy young men.

Both qualitative and quantitative changes in mitochondrial DNA (mtDNA) have been implicated in the pathogenesis of diabetes mellitus. It was previously found that decreased mtDNA content preceded the development of diabetes and mtDNA content correlated with the clinical parameters of insulin resistance syndrome, including diastolic blood pressure and waist-hip ratio. These results prompted one to look whether there are correlations between mtDNA content and the biochemical parameters of insulin resistance in non-diabetic subjects. MtDNA content of peripheral blood leukocytes was measured in Korean healthy young men, and this was correlated with various parameters of fuel metabolism at baseline and during euglycemic hyperinsulinemic clamps with indirect calorimetry. MtDNA content in peripheral blood leukocytes did not correlate with insulin sensitivity index or other metabolic variables such as body mass index (BMI), waist-to-hip ratio (WHR) and blood pressure. However, mtDNA content showed a positive significant correlation with fat oxidation rate during euglycemic clamps (r = 0.61, P < 0.05). Changes in fat oxidation rate and carbohydrate oxidation rate during the clamps were significantly correlated with mtDNA content (r = 0.65, P < 0.05, r = -0.65, P < 0.05, respectively). These results suggest that mtDNA content in peripheral blood may not correlate with insulin resistance per se but with some aspect of insulin resistance in healthy young men.

Adult↗

PubMed1997

Are there social correlates to suicide?

A structural-sociological approach to suicide research holds that an aggregate-level cause of suicide should correlate with the suicide rates in a population. In 1980, Sainsbury, Jenkins, and Levey published the article "The Social Correlates of Suicide in Europe" which related the suicide rates in 1961-63 and the changes in them in the following 11 years to 15 social variables in 18 European countries. Its main findings were that the changes in suicide rates could be attributed to specific changes in the social environment. Complementary discriminant analyses showed that it was possible accurately to divide the countries into low- and high-change suicide rate groups on the basis of a combination of the social variables. Although criticized for its method, the study has been widely quoted and sometimes presented as the most definitive current study on the subject. In order to see whether its results held for similar data 16 years later it was replicated for 1977-79 and the ensuing 11 years, with data and method as similar as possible to the original. The results agreed with those of the original study on only one point: the correlations between the levels of the social variables and those of the suicide rates were similar in both periods. However, changes in the suicide rates were unrelated to either the levels of the social variables or the changes in them: correlations found in the original study tended to change profoundly or disappear. Moreover, the results of the original discriminant analyses were a property of the method employed and thus independent of the data. Statistical artefacts or social processes such as changing expectations are unlikely to explain the suddenly changing or vanishing correlations. The original correlations seem to have been largely spurious and dependent on the fact that the more modern countries in Europe experienced a "suicide boom" in the 1960s. As the boom waned in these, it was beginning in the less modern countries: the correlations between the processes indicated by the social variables and the suicide rates were reversed or disappeared. The results call the existence of clear relations between these "suicidogenic" social circumstances and the suicide rates into question. Since many of the variables used are traditional "Durkheimian" indicators of the integration of society, a critique of this still-dominant view of the relationship between society and suicide mortality, or its common operationalization, is implied.

Adolescent↗