PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “interaction frequencies”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35Linked to original sources
PubMedDate not supplied

Effects of arecoline and scopolamine on open field behavior of adult monkeys treated with lead during the first year postpartum.

Nursery-reared rhesus monkeys were treated with no or moderate levels of lead during the first year postpartum. Previously, the lead-treated monkeys exhibited behaviors in the nonhuman primate version of the open field (10) resembling those caused by hippocampal lesions. The current study investigated the mechanism(s) underlying these lead-related effects using a cholinergic agonist (arecoline) and antagonist (scopolamine) as pharmacological probes that were administered prior to open field testing at 5 and 6 years of age, respectively. Arecoline decreased locomotion and number of sectors entered. Scopolamine decreased defecation frequency. Neither drug interacted with prior lead treatment, indicating limited cholinergic involvement in the expression of these alterations. The lead-treated subjects continued to exhibit alterations as previously reported (10); specifically, a longer latency to enter the open field, increased frequency and duration of environmental exploration and, at 5 years of age, decreased duration of inactivity in the open field. These effects were seen four and five years after lead treatment ended and nearly three and four years after blood lead levels had declined to less than or equal to 5 micrograms/dL. Although latency to enter and duration of inactivity seem to be approaching control levels, the increased exploration does not.

Animals↗
PubMed1997

An examination of word frequency and neighborhood density in the development of spoken-word recognition.

In this study, the effects of word-frequency and phonological similarity relations in the development of spoken-word recognition were examined. Seven-, 9-, and 11-year-olds and adults listened to increasingly longer segments of high- and low-frequency monosyllabic words with many or few word neighbors that sounded similar (neighborhood density). Older children and adults required less of the acoustic-phonetic information to recognize words with few neighbors and low-frequency words than did younger children. Adults recognized high-frequency words with few neighbors on the basis of less input than did all three of the children's groups. All subjects showed a higher proportion of different-word guesses for words with many versus few neighbors. A frequency x neighborhood density interaction revealed that recognition is facilitated for high-frequency words with few versus many neighbors; the opposite was found for low-frequency words. Results are placed within a developmental framework on the emergence of the phoneme as a unit in perceptual processing.

Adult↗
PubMed1988

Frequency-dependent selection and competition: empirical approaches.

When Darwin and Wallace first formulated the theory of evolution by natural selection, they were greatly influenced by the idea that populations tend to increase geometrically and rapidly outgrow the resources available to them. They argued that the ensuing competition among individuals would be a major agent of natural selection. Since their day, competition has become almost synonymous with the idea of natural selection or survival of the fittest. In this paper we examine the relation between competition and selection by using simple competition models, consider the interaction of density and frequency in determining competitive outcome, and review the literature on frequency-dependent competitive interactions among genotypes within populations.

Animals↗
PubMed2005

[Location and frequency of visual field defects as measured by SITA (Swedish Interactive Threshold Algorithm) strategy in primary open angle glaucoma].

PURPOSE: To evaluate the frequency, location and pattern of visual field defects as measured by SITA strategy in primary open angle glaucoma (POAG). METHODS: Six thousand and two-hundred charts were reviewed. One hundred and fifty two patients who fulfilled the inclusion criteria were included. They were stratified according to severity into early, moderate and severe. The following visual field defects were defined: nasal step, paracentral scotomata, arcuate defect, Seidel scotomata, temporal defect, general reduction of sensitivity, annular scotomata and central island. Each examination was divided into sectors corresponding to optic disc regions. Student's t test was used to compare differences in frequency. RESULTS: In the early glaucoma group, the nasal superior step was the most frequent visual field defect, followed by paracentral scotoma and inferior nasal step. General reduction of sensitivity was noted in 7.8%. Defects were more common in the superior hemifield (p<0.05). CONCLUSION: The superior nasal step and paracentral scotoma were the most commun visual field defects in early primary open angle glaucoma as evaluated by SITA strategy, and the superior hemifield comprises most of the defects. General reduction of sensitivity was an early and rare visual field defect.

Adult↗
PubMed2000

A model of the Parkinsonian visual system: support for the dark adaptation hypothesis.

Considerable evidence suggests that some visual abnormalities in Parkinson's disease are mediated by disruption of dopaminergic processes in the retina. Since dopamine is thought to be involved in the process of dark adaptation, and some of these abnormalities are similar to the changes which accompany dark adaptation in normal subjects, it has been proposed that the parkinsonian retina behaves as though inappropriately dark-adapted. In Parkinson's disease, the apparent contrast of peripherally viewed medium and high spatial frequency gratings is reduced. In our first experiment, normal subjects were dark-adapted, and were required to match the apparent contrast of a peripherally viewed grating to that of a foveally viewed grating. The results showed an interaction between spatial frequency and dark adaptation, reflecting a greater reduction in the apparent contrast of peripheral high spatial frequency gratings. In a second experiment, no effect of dark adaptation was found on the apparent spatial frequency of a peripherally viewed grating required to match that of a foveally viewed grating. The first experiment supports the dark adaptation hypothesis of parkinsonian vision, and the second suggests that the changes in apparent contrast are mediated by different amounts of change in contrast gain in central and peripheral vision, rather than by differential changes in receptive field size.

Adaptation, Ocular↗
PubMed2001

Rate and timing cues associated with the cochlear amplifier: level discrimination based on monaural cross-frequency coincidence detection.

The perceptual significance of the cochlear amplifier was evaluated by predicting level-discrimination performance based on stochastic auditory-nerve (AN) activity. Performance was calculated for three models of processing: the optimal all-information processor (based on discharge times), the optimal rate-place processor (based on discharge counts), and a monaural coincidence-based processor that uses a non-optimal combination of rate and temporal information. An analytical AN model included compressive magnitude and level-dependent-phase responses associated with the cochlear amplifier, and high-, medium-, and low-spontaneous-rate (SR) fibers with characteristic frequencies (CFs) spanning the AN population. The relative contributions of nonlinear magnitude and nonlinear phase responses to level encoding were compared by using four versions of the model, which included and excluded the nonlinear gain and phase responses in all possible combinations. Nonlinear basilar-membrane (BM) phase responses are robustly encoded in near-CF AN fibers at low frequencies. Strongly compressive BM responses at high frequencies near CF interact with the high thresholds of low-SR AN fibers to produce large dynamic ranges. Coincidence performance based on a narrow range of AN CFs was robust across a wide dynamic range at both low and high frequencies, and matched human performance levels. Coincidence performance based on all CFs demonstrated the "near-miss" to Weber's law at low frequencies and the high-frequency "mid-level bump." Monaural coincidence detection is a physiologically realistic mechanism that is extremely general in that it can utilize AN information (average-rate, synchrony, and nonlinear-phase cues) from all SR groups.

Audiometry, Pure-Tone↗
PubMed2006

Measuring cell adhesion on RGD-modified, self-assembled PEG monolayers using the quartz crystal microbalance technique.

In this study, the suitability of a flow-through quartz crystal microbalance system for the detection of the adhesion of rMSCs and 3T3-L1 fibroblasts on different surfaces is demonstrated. Frequency shifts for rMSCs of -6.7 mHz x cell(-1) and -2.0 mHz x cell(-1) for 3T3-L1 cells could be detected on non-modified gold sensors, revealing that the frequency shift per cell is comparable to that of a static setup. Modifying the sensor surface with SAMs of thioalkylated omega-amine-terminated PEG derivatives led to cell-adhesion-resistant surfaces. Total frequency shifts of only -20 +/- 7 Hz showed that protein adsorption was also significantly reduced. Attaching 35 pmol x mm(-2) of the GRGDS cell adhesion motif to the SAMs induced specific cell adhesion due to RGD-integrin interactions; the resonance frequency dropped by 3.4 mHz x cell(-1). Furthermore, the kinetics of cell detachment could be determined. The corresponding processes were completed after 10 min for trypsin, and not before 90 min with GRGDS. Moreover, the detectability of cell adhesion was shown to increase after the addition of manganese cations. The total decrease in the resonance frequency was almost 80 Hz in the presence of Mn(2+) (6.4 mHz x cell(-1)). [image: see text] Staining the cytoskeleton of the rMSCs shows that the GRGDS-modified surfaces are almost completely covered with well-spread cells.

Animals↗
PubMed1978

On reversible changes in the steady state ion-conductance of the Ranvier node membrane under low frequency sound fields.

The influence of sound waves on the stationary membrane conductivity of the axon membrane in myelinated nerve was investigated. Sound fields with frequencies within the auditory limit shift the transition voltage Vtr and correspondingly the threshold voltage of the action potential in polarisation direction. The results indicate that these changes of the electrical membrane behavior are due to a direct mechanical interaction between low frequency sound fields and membrane structure.

Action Potentials↗
PubMed1991

Heparin-polypeptide interaction. Near-i.r. spectroscopy in an anhydrous dispersant allows the involvement of polymer-associated water to be assessed.

Involvement of polymer-associated water in the interaction of heparin with poly-L-arginine and poly-L-lysine was studied by i.r. spectroscopy of complexes suspended in a non-aqueous dispersant. Movement of i.r. absorption bands due to heparin-associated water to lower frequencies upon polymer interaction indicates that hydrogen-bonding accompanies complexation. We suggest that this bonding includes water bridging between the interacting species, and that the resulting changes in water chemistry may affect the biological activity of such interacting macromolecules.

Heparin↗
PubMed1993

The role of spatial frequency in the processing of hierarchically organized stimuli.

Can spatial frequency differences between local and global forms account for differences in the way different levels of structure are analyzed? We examined this question by having subjects identify local or global forms of hierarchical stimuli that had been contrast balanced. Contrast balancing eliminates low spatial frequencies, so that both local and global forms must be identified on the basis of high spatial frequency information. Response times (RTs) to global (but not local) forms were slowed for contrast-balanced stimuli, suggesting that low spatial frequencies mediate the global RT advantage typically found. In contrast, interference between local and global forms was little affected by contrast balancing or by shifts of attention between local and global forms, suggesting that it does not result from inhibitory interactions between spatial frequency channels or from temporal precedence of low versus high spatial frequency information. Finally, shifts of attention between local and global forms were also little affected by contrast balancing, suggesting that they were not based on spatial frequency.

Adolescent↗
PubMed2003

Binaural interaction in the human auditory cortex revealed by neuromagnetic frequency tagging: no effect of stimulus intensity.

Frequency tagging of magnetoencephalographic signals was recently introduced as a new tool to study binaural interaction in the human auditory cortex [Fujiki et al., J. Neurosci. 22 (2002) RC205]. As the method has potential value for assessing brain plasticity in patients with unilateral hearing deficits, we studied binaural interaction in 10 healthy adults at different intensity levels. Cortical steady-state fields were measured with a 306-channel whole-scalp neuromagnetometer to amplitude-modulated sounds (carrier frequency 1 kHz), presented monaurally or binaurally at 45, 60 and 75 dB SL. The modulation frequencies were 39.1 Hz for the right ear and 41.1 Hz for the left. During binaural stimulation, the ipsilateral responses were suppressed more than the contralateral ones in both hemispheres, and the hemispheric balance shifted towards the contralateral hemisphere for inputs from both ears. The patterns of binaural interaction were similar at all three stimulus intensities. These data could be useful in examining patients who suffer from auditory disorders as well as in revealing basic mechanism of human auditory processing.

Acoustic Stimulation↗
PubMed2004

Atom-bond electronegativity equalization method fused into molecular mechanics. I. A seven-site fluctuating charge and flexible body water potential function for water clusters.

Recently, experimental and theoretical studies on the water system are very active and noticeable. A transferable intermolecular potential seven points approach including fluctuation charges and flexible body (ABEEM-7P) based on a combination of the atom-bond electronegativity equalization and molecular mechanics (ABEEM/MM), and its application to small water clusters are explored and tested in this paper. The consistent combination of ABEEM and molecular mechanics (MM) is to take the ABEEM charges of atoms, bonds, and lone-pair electrons into the intermolecular electrostatic interaction term in molecular mechanics. To examine the charge transfer we have used two models coming from the charge constraint types: one is a charge neutrality constraint on whole water system and the other is on each water molecule. Compared with previous water force fields, the ABEEM-7P model has two characters: (1) the ABEEM-7P model not only presents the electrostatic interaction of atoms, bonds and lone-pair electrons and their changing in respond to different ambient environment but also introduces "the hydrogen bond interaction region" in which a new parameter k(lp,H)(R(lp,H)) is used to describe the electrostatic interaction of the lone-pair electron and the hydrogen atom which can form the hydrogen bond; (2) nonrigid but flexible water body permitting the vibration of the bond length and angle is allowed due to the combination of ABEEM and molecular mechanics, and for van der Waals interaction the ABEEM-7P model takes an all atom-atom interaction, i.e., oxygen-oxygen, hydrogen-hydrogen, oxygen-hydrogen interaction into account. The ABEEM-7P model based on ABEEM/MM gives quite accurate predictions for gas-phase state properties of the small water clusters (H(2)O)(n) (n=2-6), such as optimized geometries, monomer dipole moments, vibrational frequencies, and cluster interaction energies. Due to its explicit description of charges and the hydrogen bond, the ABEEM-7P model will be applied to discuss properties of liquid water, ice, aqueous solutions, and biological systems.

Journal Article↗
PubMed1982

Dichoptic interaction of harmonically related spatial and temporal frequencies.

Steady-state visual evoked potentials were recorded in response to contrast Reprint requests: Dr. Elmar T. Schmeisser, Division of Ocular Hazards, Letterman Army complex (sum of two spatial frequencies) suprathreshold sinusoidal gratings of two and six cycles/degree in a 5 degrees field. Sine mode counterphasing enhances the second temporal harmonic component of the evoked waveform; square mode counterphasing generates a response with essentially all the power at the fundamental temporal frequency. Digital sums of observed responses to simple gratings presented alone had significantly greater amplitudes than any observed response to presented complex gratings. Response amplitudes ranked significantly by condition: binocular greater than dichoptic greater than monoptic. It is concluded that (a) sinusoidal counterphasing stimuli lead to two stimulus events per shift (an observed grating onset and offset), and (b) spatial frequency channels that are harmonically related in 1:3 ratio do not destructively interfere with each other in either monoptic or dichoptic presentation.

Adult↗
PubMed2005

[Drug interactions in an elderly population. Prospective assessment of their frequency and seriousness among 56 patients].

OBJECTIVE: To assess the nature and the number of potential adverse drug interactions by analysis of outpatient prescriptions for elderly patients, of medications taken during the week before hospitalization in a general surgery department. METHOD: The study of 56 patients older than 65 years was conducted from November 2002 through February 2003. The outpatient prescriptions corresponding to medications taken during the 7 days before admission were analyzed by a pharmacy resident, who used data-processing tools and databases. RESULTS: Most patients (83%) knew the reason for their prescription. Thirteen (28%) reported using over-the-counter medication. Only 89% of the patients reported complete compliance with the prescription. The average age of the patients was 72.1 +/- 6.3 years and the median was 71 years [65-91]; 43% were women and 57% men. The 257 lines of prescriptions analyzed averaged 5.7 +/- 2.6 drugs (range: 2-10) per prescription. The average number of possible interactions was 3.1 +/- 2.8 per prescription for a total of 89 listed potential interactions. The levels observed were 3 warnings (3%), 37 precautions (42%) and 49 possible adverse interactions (55%). No contraindication was noted. The drugs mentioned most often were benzodiazepines, diuretics, conversion enzyme inhibitors, angiotensin II inhibitors, and beta-blockers. The potential risks most often found were hypotension, depression of the central nervous system, hypoglycemia and acute renal failure. The drug interactions were mainly due to the accumulation of the effects of separate drug classes. Deterioration in renal function was often noted as plasma concentration of the second drug increased. DISCUSSION: This exploratory study shows the reality of the iatrogenic risk for elderly patients. This analysis of outpatient prescriptions is consistent with findings in the literature. Analysis of interactions is conducted on a pairwise basis. It is thus difficult to envisage the consequences of the association of 5 or more drugs in patients with complex illnesses and diminished physiological and metabolic capacity. Patient files kept by the pharmacist could provide information about individual combinations ofthe prescription and over-the-counter drugs.

Age Factors↗
PubMed2026

Intervention components, training dose, and adherence in exercise-based prevention of hamstring strain injury in football: a systematic review and meta-analysis.

OBJECTIVE: To quantify associations between exercise-based prevention programmes and hamstring strain injury (HSI) risk in football participants, and whether training dose and adherence modify effects. METHODS: Six databases were searched to 1 October 2025. Randomised and cluster-randomised trials comparing HSI prevention programmes with usual practice or warm-up in football participants were included. Random-effects meta-analysis pooled risk ratios (RRs); subgroup analyses and meta-regression assessed effect modification. RESULTS: Fifteen trials (n = 7,465) were analysed. Programmes reduced HSI risk (RR = 0.51, 95% CI 0.36-0.71), with I&#xb2;=57% and a prediction interval crossing the null (0.18-1.40). Based on a control event rate of 7.8%, absolute risk reduction was 3.8% (38 fewer HSIs per 1000 participants; 95% CI 23-50 fewer). Effects were stronger for shorter interventions (1-6 months; RR = 0.43) than longer interventions (7-10 months; RR = 0.77; P for interaction=0.04), and for elite/semi-professional players (RR = 0.38) than amateur players (RR = 0.77; P for interaction = 0.02). Training frequency and weekly volume did not modify effects, whereas adherence did. High adherence (&#x2265;75%) was associated with lower HSI risk (RR = 0.36, 95% CI 0.28-0.48), whereas low adherence (<75%) showed no clear benefit (RR = 0.92, 95% CI 0.68-1.23; P for interaction <0.00001). Each 10% increase in adherence corresponded to an RR multiplier of 0.83 (approximately 17% lower RR). Certainty of evidence was low. CONCLUSION: Exercise-based programmes reduce HSI risk in football when implementation supports sustained adherence. Effects may be stronger in shorter interventions and elite populations, but evidence remains insufficient to differentiate programme types or components.

Humans↗
PubMed2005

Maxwell-Wagner relaxation in electrical imaging.

The electric field tomography (EFT) method exploits interaction of high-frequency electric field with an inhomogeneous conductive medium without contact with the electrodes. The interaction is accompanied by a high-frequency redistribution of free charges inside the medium and leads to small and regular phase shifts of the field in the area surrounding an object. Such a kind of phenomenon is referred to as the Maxwell-Wagner relaxation. Measuring the perturbations of the field using the set of electrodes placed around the object enables us to reconstruct the internal structure of the medium, generally the spatial distribution of a nonlinear combination of permittivity and resistivity. In the case of biomedical applications the result of measurements is determined mainly by the resistivity of the tissues. Three-dimensional simulation based on the finite element method has demonstrated the feasibility of the technique.

Algorithms↗