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PubMed2006

Supraspinal fatigue does not explain the sex difference in muscle fatigue of maximal contractions.

Young women are less fatigable than young men for maximal and submaximal contractions, but the contribution of supraspinal fatigue to the sex difference is not known. This study used cortical stimulation to compare the magnitude of supraspinal fatigue during sustained isometric maximal voluntary contractions (MVCs) performed with the elbow flexor muscles of young men and women. Eight women (25.6 +/- 3.6 yr, mean +/- SD) and 9 men (25.4 +/- 3.8 yr) performed six sustained MVCs (22-s duration each, separated by 10 s). Before the fatiguing contractions, the men were stronger than the women (75.9 +/- 9.2 vs. 42.7 +/- 8.0 N.m; P < 0.05) in control MVCs. Voluntary activation measured with cortical stimulation before fatigue was similar for the men and women during the final control MVC (95.7 +/- 3.0 vs. 93.3 +/- 3.6%; P > 0.05) and at the start of the fatiguing task (P > 0.05). By the end of the six sustained fatiguing MVCs, the men exhibited greater absolute and relative reductions in torque (65 +/- 3% of initial MVC) than the women (52 +/- 9%; P < 0.05). The increments in torque (superimposed twitch) generated by motor cortex stimulation during each 22-s maximal effort increased with fatigue (P < 0.05). Superimposed twitches were similar for men and women throughout the fatiguing task (5.5 +/- 4.1 vs. 7.3 +/- 4.7%; P > 0.05), as well as in the last sustained contraction (7.8 +/- 5.9 vs. 10.5 +/- 5.5%) and in brief recovery MVCs. Voluntary activation determined using an estimated control twitch was similar for the men and women at the start of the sustained maximal contractions (91.4 +/- 7.4 vs. 90.4 +/- 6.8%, n = 13) and end of the sixth contraction (77.2 +/- 13.3% vs. 73.1 +/- 19.6%, n = 10). The increase in the area of the motor-evoked potential and duration of the silent period did not differ for men and women during the fatiguing task. However, estimated resting twitch amplitude and the peak rates of muscle relaxation showed greater relative reductions at the end of the fatiguing task for the men than the women. These results indicate that the sex difference in fatigue of the elbow flexor muscles is not explained by a difference in supraspinal fatigue in men and women but is largely due to a sex difference of mechanisms located within the elbow flexor muscles.

Adult↗

PubMed2003

Spectral cues explain illusory elevation effects with stereo sounds in cats.

Mammals localize sound sources in azimuth based on two binaural cues, interaural differences in the time of arrival and level of the sounds at the ears. In contrast, the cue for elevation is based on patterns of the broadband power spectra at each ear that result from the direction-dependent acoustic filtering properties of the head and pinnae. Although the exact form of this "spectral shape" cue is unknown, most attention has been directed toward a prominent direction-dependent energy minimum, or "notch," because its location in frequency, for both humans and cats, moves predictably from low to high as a source is moved from low to high elevations. However, there is little direct evidence that these spectral notches are important elevational cues in animals other than humans. Here we demonstrate a striking illusion in the localization of sounds in elevation by cats using stimulus configurations that elicit summing localization and the precedence effect that can be explained by spectral shape cues.

Animals↗

PubMed2006

Spectral receptive field properties explain shape selectivity in area V4.

Neurons in cortical area V4 respond selectively to complex visual patterns such as curved contours and non-Cartesian gratings. Most previous experiments in V4 have measured responses to small, idiosyncratic stimulus sets and no single functional model yet accounts for all of the disparate results. We propose that one model, the spectral receptive field (SRF), can explain many observations of selectivity in V4. The SRF describes tuning in terms of the orientation and spatial frequency spectrum and can, in principle, predict the response to any visual stimulus. We estimated SRFs for neurons in V4 of awake primates by linearized reverse correlation of responses to a large set of natural images. We find that V4 neurons have large orientation and spatial frequency bandwidth and often bimodal orientation tuning. For comparison, we estimated SRFs for neurons in primary visual cortex (V1). Consistent with previous observations, we find that V1 neurons have narrower bandwidth than that of V4. To determine whether estimated SRFs can account for previous observations of selectivity, we used them to predict responses to Cartesian gratings, non-Cartesian gratings, natural images, and curved contours. Based on these predictions, we find that the majority of neurons in V1 are selective for Cartesian gratings, whereas the majority of V4 neurons are selective for non-Cartesian gratings or natural images. The SRF describes visual tuning properties with a second-order nonlinear model. These results support the hypothesis that a second-order model is sufficient to describe the general mechanisms mediating shape selectivity in area V4.

Algorithms↗

PubMed2004

Subthreshold resonance explains the frequency-dependent integration of periodic as well as random stimuli in the entorhinal cortex.

Neurons integrate subthreshold inputs in a frequency-dependent manner. For sinusoidal stimuli, response amplitudes thus vary with stimulus frequency. Neurons in entorhinal cortex show two types of such resonance behavior: stellate cells in layer II exhibit a prominent peak in the resonance profile at stimulus frequencies of 5-16 Hz. Pyramidal cells in layer III show only a small impedance peak at low frequencies (1-5 Hz) or a maximum at 0 Hz followed by a monotonic decrease of the impedance. Whether the specific frequency selectivity for periodic stimuli also governs the integration of non-periodic stimuli has been questioned recently. Using frozen-noise stimuli with different distributions of power over frequencies, we provide experimental evidence that the integration of non-periodic subthreshold stimuli is determined by the same subthreshold frequency selectivity as that of periodic stimuli. Differences between the integration of noise stimuli in stellate and pyramidal cells can be fully explained by the resonance properties of each cell type. Response power thus reflects stimulus power in a frequency-selective way. Theoretical predictions based on linear system's theory as well as on conductance-based model neurons support this finding. We also show that the frequency selectivity in the subthreshold range extends to suprathreshold responses in terms of firing rate. Cells in entorhinal cortex are representative examples of cells with resonant or low-pass filter impedance profiles. It is therefore likely that neurons with similar frequency selectivity will process input signals according to the same simple principles.

Action Potentials↗

PubMed1997

Animal model explains the origins of the cranial dystonia benign essential blepharospasm.

The current study demonstrates that combining two mild alterations to the rat trigeminal reflex blink system reproduces the symptoms of benign essential blepharospasm, a cranial dystonia characterized by uncontrollable spasms of blinking. The first modification, a small striatal dopamine depletion, reduces the tonic inhibition of trigeminal reflex blink circuits. The second alteration, a slight weakening of the lid-closing orbicularis oculi muscle, begins an adaptive increase in the drive on trigeminal sensory-motor blink circuits that initiates blepharospasm. By themselves, neither of these modifications causes spasms of lid closure, but combined, they induce bilateral forceful blinking and spasms of lid closure. A two-factor model based on these rodent experiments may explain the development of benign essential blepharospasm in humans. The first factor, a subclinical loss of striatal dopamine, creates a permissive environment within the trigeminal blink circuits. The second factor, an external ophthalmic insult, precipitates benign essential blepharospasm. This two-factor model may also be applicable to the genesis of other cranial dystonias.

Animals↗

PubMed1998

Analysis of neural interactions explains the activation of occipital cortex by an auditory stimulus.

Analysis of neural interactions explains the activation of occipital cortex by an auditory stimulus. J. Neurophysiol. 80: 2790-2796, 1998. Large-scale neural interactions were characterized in human subjects as they learned that an auditory stimulus signaled a visual event. Once learned, activation of left dorsal occipital cortex (increased regional cerebral blood flow) was observed when the auditory stimulus was presented alone. Partial least-squares analysis of the interregional correlations (functional connectivity) between the occipital area and the rest of the brain identified a pattern of covariation with four dominant brain areas that could have mediated this activation: prefrontal cortex (near Brodmann area 10, A10), premotor cortex (A6), superior temporal cortex (A41/42), and contralateral occipital cortex (A18). Interactions among these regions and the occipital area were quantified with structural equation modeling to identify the strongest sources of the effect on left occipital activity (effective connectivity). Learning-related changes in feedback effects from A10 and A41/42 appeared to account for this change in occipital activity. Influences from these areas on the occipital area were initially suppressive, or negative, becoming facilitory, or positive, as the association between the auditory and visual stimuli was acquired. Evaluating the total effects within the functional models showed positive influences throughout the network, suggesting enhanced interactions may have primed the system for the now-expected visual discrimination. By characterizing both changes in activity and the interactions underlying sensory associative learning, we demonstrated how parts of the nervous system operate as a cohesive network in learning about and responding to the environment.

Acoustic Stimulation↗

PubMed2005

Explaining the socioeconomic variation in cancer risk in the Norwegian Women and Cancer Study.

Associations between level of education and cancer risk is well supported by scientific evidence, but previous studies could only partly adjust for relevant confounding factors. In this article, we examined how risk of cancer varies with level of education and identified factors that explain this variation using data from a prospective cohort study, including 93,638 Norwegian women who responded to an extensive questionnaire in 1991/1992 or 1996/1997. A total of 3,259 incident primary invasive cancer cases were diagnosed during follow-up, which ended in December 2001. We used Cox proportional hazards model to calculate relative risks (RR) with 95% confidence intervals (95% CI). Besides a similar overall risk of female cancers by level of education, we observed differing risks between educational groups for cancers of the lung, breast, cervix, kidney, and skin melanoma. Women with >16 years of education had an increased risk of breast cancer (RR, 1.46; 95% CI, 1.19-1.79) and a decreased risk of lung cancer (RR, 0.30; 95% CI, 0.13-0.70) and cervical cancer (RR, 0.38; 95% CI, 0.17-0.85) compared with the lowest educated women (7-9 years). The middle educated (13-16 years) had the lowest risk of kidney cancer (RR, 0.24; 95% CI, 0.08-0.71), whereas the risk of skin melanoma was highest among women with 10 to 12 years of education (RR, 1.53; 95% CI, 1.05-2.24) compared with the lowest educated women. After multivariate adjustment for potential confounders related to level of education, the variation in cancer risk according to educational levels declined into nonsignificance for all these sites.

Adult↗

PubMed2006

"Oncogenic shock": explaining oncogene addiction through differential signal attenuation.

"Oncogene addiction" describes the curious acquired dependence of tumor cells on an activated oncogene for their survival and/or proliferation, a phenomenon that has important implications for the success of targeted cancer therapies. However, the mechanisms explaining oncogene addiction remain elusive. We propose that "addiction" may be an illusion generated as a consequence of differential attenuation rates of prosurvival and proapoptotic signals emanating from an oncoprotein acutely following its inactivation. According to this model, which we call "oncogenic shock," prosurvival signals dissipate quickly on oncoprotein inactivation whereas proapoptotic signals linger sufficiently long to commit the cell to an apoptotic death. This mechanism may contribute to the rapid and dramatic clinical responses observed in some cancer patients treated with selective tyrosine kinase inhibitors and could yield additional drug targets that determine the balance of signaling outputs from activated oncoproteins.

Humans↗

PubMed2001

An integrated proposal to explain the epidemic of cardiovascular disease in a developing country. From socioeconomic factors to free radicals.

An increase of coronary artery disease has been observed in developing countries during the last years. Various factors may explain this accelerated increase. We propose that inappropriate diet and inadequate sanitary infrastructure may act as triggers to create an imbalance between nitric oxide (NO) and superoxide (O2-). An increase in the concentrations of oxidized LDL produces both decreased NO and increased O2- endothelial synthesis, by accumulation of asymmetrical NG-NG-dimethyl-L-arginine, the endogenous inhibitor of NO, and by activation of NAD(P)H oxidase. On the other hand, high rates of chronic infection-inflammation, due to inappropriate sanitary environment stimulate higher circulating levels of proinflammatory cytokines. These cytokines also contribute to reduced NO and increased O2- endothelial production through the same mechanisms of oxidized LDL. The net result of this imbalance is an increased generation of peroxynitrate that injures the endothelium in a proatherogenic, prothrombotic and vasoconstrictive manner.

Arginine↗

PubMedDate not supplied

Explaining attitudinal ratings of Dutch rising contours: morphological structure vs. the frequency code.

In this article, two hypotheses were tested to explain attitudinal ratings like SURPRISE, SUGGESTION, REMINDER etc. of four rising nuclear contours observed in a Dutch question corpus and described as (a) H*L H%, (b) H* H%, (c) L*H H% and (d) L* H%. According to one hypothesis, the middle tones in (a) and (c) should be parcelled out, such that their absence produces contours (b) and (d), respectively, predicting communality of meaning within (a, c) that excludes (b, d). That is, (b, d) could be viewed as undershot variants of (a, c), with undershoot expressing a shade of meaning different from that of the fully realised pitch accents. This hypothesis was not confirmed by the data, though. The other hypothesis was based on the concept of the 'frequency code', which associates high/rising F(0) values with non-assertive behaviour and appeared to provide a much better model to predict listeners' ratings.

Humans↗

PubMedDate not supplied

Explaining variation in affiliative relationships among male white-faced capuchins (Cebus capucinus).

Relationships among coresident male white-faced capuchins are highly variable, ranging from affiliative to aggressive. In this paper I examine the affiliative relationships of all adult and subadult males residing in four social groups in Santa Rosa National Park, Costa Rica. Relationships among males in two study groups were neutral and tolerant, while in the remaining two groups males were highly affiliative. Male-male dyadic affiliative interactions were examined to determine which variables (group size, sex ratio, age relationship, relationship duration, and rank distance) influence the quality of male relationships within the study groups. Group size explained much of the variation, with males in small groups being more affiliative. However, the duration and history of the relationship among coresident males appears to be the most important variable in understanding male-male relationships within social groups.

Aging↗

PubMed2004

Does differential selection on the 5S rDNA explain why the rainbow trout sex chromosome heteromorphism is not linked to the SEX locus?

Many but not all rainbow trout strains have morphologically distinguishable sex chromosomes. In these strains, the short arm of the X has multiple copies of 5S rDNA and a bright DAPI band near the centromere, both of which are missing from the Y chromosome, which has a very small short arm. We examined the presence of these markers using fluorescence in situ hybridization (FISH) in four different YY clonal lines derived from different strains and compared the results with sexed fish of the Donaldson strain with the normal X/Y heteromorphism. The Y chromosome in two of the YY clonal lines (Arlee and Swanson) is indistinguishable from the X chromosome and it is positive for 5S rDNA and the DAPI bright band. On the other hand, both 5S rDNA sequences and the DAPI band were not found on the Y chromosome in Hot Creek and Clearwater which have the normal Y. Thus the presence of these two cytogenetic markers may account for the size difference between the short arm of the X and Y chromosome found in most rainbow trout strains. In fishes the expression of one type of 5S rRNA is restricted to oocytes and previous work suggests that although XX males are fairly common, XY females are rare, implying a selective disadvantage for XY females. A hypothesis is presented to explain why this sex chromosome heteromorphism is not closely linked to the SEX locus, which is found on the long arm of the Y chromosome in rainbow trout.

Animals↗

PubMed2006

Lower consumption of cow milk protein A1 beta-casein at 2 years of age, rather than consumption among 11- to 14-year-old adolescents, may explain the lower incidence of type 1 diabetes in Iceland than in Scandinavia.

AIM: To compare the consumption of the cow milk proteins A1 and B beta-casein among children and adolescents in Iceland and Scandinavia (Norway, Denmark, Sweden and Finland) as this might explain the lower incidence of type 1 diabetes (per 100,000/year, 0-14 years) in Iceland. METHODS: The consumption of A1 beta-casein in each country among 2- and 11- to 14-year-old children was calculated from results on food intake and on cow milk protein concentration. The consumption values were then compared and evaluated against the incidence of type 1 diabetes. RESULTS: There was a significant difference between the consumption of A1 (p = 0.034) as well as the sum of A1 and B (p = 0.021) beta-casein in Iceland and Scandinavia for 2-year-old children. In the same age group, consumption of A1 beta-casein correlated with the incidence of type 1 diabetes in the countries (r = 0.9; p = 0.037). No significant difference in consumption of A1 or the sum of A1 and B beta-casein was found for 11- to 14-year-old adolescents. CONCLUSION: This study supports that lower consumption of A1 beta-casein might be related to the lower incidence of type 1 diabetes in Iceland than in Scandinavia. Additionally it indicates that consumption in young childhood might be of more importance for the development of the disease incidence than consumption in adolescence.

Adolescent↗

PubMed1990

Measurements of plasma colloid osmotic pressure, total protein and sodium concentration during haemodialysis: can single-pool sodium modelling explain the results?

Considering the plasma colloid osmotic pressure (COP) as a possible parameter for the monitoring of dialysis treatment compatibility, a characteristic time course was found. The COP and the total protein concentration very often do not increase significantly during the first treatment hour in spite of ultrafiltration. An increase in the plasma sodium concentration, which was higher than expected, was found to be the reason for a plasma dilution effect. This can be explained by a transcapillary sodium transfer coefficient which is not infinitely high as assumed in single-pool sodium modelling. From a 2-pool model considering the plasma volume as a separate pool and including capillary filtration time courses for plasma sodium, total protein concentration and COP could be calculated, which was very similar to the measured curves.

Blood Proteins↗

PubMed1981

Nonimmune complexes of pregnancy-specific beta 1-glycoprotein explain its heterogeneity.

Nonimmune complexes of pregnancy-specific beta 1-glycoprotein (SP1) explain its heterogeneity. Two proteins reacting with antisera specific to pregnancy-specific beta 1-glycoprotein (SP1) have previously been detected in serum from pregnant women by use of crossed immunoelectrophoresis (CIE). The major SP1-reactive protein, SP1 beta, has a molecular weight of about 90,000 and the minor, antigenically deficient protein, SP1 alpha, about 200,000. In this study, gel filtration of serum on Ultrogel AcA 34 and Sephacryl S-300 has revealed that classical radioimmunoassay (RIA) techniques of two types only measure SP1 beta. With RIAs specially designed to detect complexed SP1 two higher molecular weight, SP1-containing complexes could be identified. CIE of serum or fractions from gel filtrations revealed a loss of the anodal part of the SP1 precipitate. However, when 4% polyethylene glycol (PEG) was incorporated in the anti-SP1-containing gel an antigenically deficient precipitate developed in the alpha-region. Incorporation of antialbumin in an intermediate gel in CIE reduced the anodal loss of the SP1 precipitate in anti-SP1-containing gels without PEG which resulted in a homogeneous peak. In addition, in anti-SP1-containing gels with PEG the anodal precipitate was reduced. This SP1-albumin complex fulfills all criteria for the previously described SP1 alpha. For measuring low levels of SP1 RIAs can be used. For higher values nephelometry is preferable. Although the amount of complexed SP1 is small in comparison with the amount of native SP1 methods employing electrophoresis are not recommended. In such tests SP1 complexed to fast-moving proteins like albumin might influence the results.

Antigen-Antibody Complex↗

PubMed1997

Differences in nonspecific bronchial responsiveness between patients with asthma and patients with rhinitis are not explained by type and degree of inhalant allergy.

Patients with allergic asthma have higher levels of nonspecific bronchial responsiveness than patients with allergic rhinitis. The aim of the study was to investigate whether this is caused by differences in the degree of allergy to inhalant allergens between asthmatics and rhinitics. Therefore, bronchial responsiveness to histamine was measured in 25 allergic patients with isolated upper airways symptoms. Nonspecific bronchial responsiveness in this group was compared with nonspecific bronchial responsiveness in a group of 136 patients with allergic asthma, with allergy and % predicted FEV1 as confounding variables. In addition, a matched pair analysis was performed. Twenty-five patients with nonallergic rhinitis served as controls to evaluate the influence of an IgE-independent inflammatory reaction in the upper respiratory tract on the level of bronchial responsiveness. Furthermore, we investigated the level of nonspecific responsiveness in 18 healthy controls. In the patients with allergic asthma, a correlation was found between nonspecific bronchial responsiveness and IgE against indoor allergens (n = 136, r = 0.34, p < 0.001) and % predicted FEV1 (n = 136, r = 0.37), p < 0.001). Patients with allergic asthma and patients with allergic rhinitis differed with respect to the level of bronchial responsiveness (p < 0.001), and the amount of specific IgE antibodies against indoor allergens (p = 0.01). The difference in level of bronchial responsiveness remained (p < 0.001) after correction with % predicted FEV1 and specific IgE against indoor allergens as confounding variables. Similarly, after matching of patients with allergic rhinitis (n = 25) with patients with allergic asthma (n = 25) regarding the specific IgE, total IgE and age of the patients, the difference in level of bronchial responsiveness remained (p < 0.001). Patients with nonallergic rhinitis had higher levels of nonspecific bronchial responsiveness than healthy controls and did not differ from patients with allergic rhinitis. In conclusion, the results confirm that IgE against common indoor allergens plays an important role in the mechanism underlying nonspecific bronchial hyperresponsiveness. However, differences in bronchial responsiveness between patients with asthma and patients with rhinitis are not merely explained by differences in the IgE antibody concentrations.

Adolescent↗

PubMed1995

Explaining the dispersion of the single-vowel occurrences in an F1/F2 space.

The variability of the Finnish vowel occurrences on the F1/F2 chart was studied. Repetitions (n = 8 x 10 + 10 = 160) of two syllable types, /hVh/ and /tVt/, produced by a male speaker were analysed. The F1/F2 variability in both contexts was estimated. In the /hVh/ context, the phoneme targets were considerably more peripheral than in the /tVt/ contexts. In the /tVt/ context, the phoneme placements were nearer the upper left corner of the F1/F2 space in /u/, /o/, /a/, and /ae/. That is understandable on the basis of the alveolar tongue blade position: the tongue holds its position nearer the alveolar area during its movement from [t] to [V] and back to [t] compared to the [hVh] articulation. In the latter articulation, the tongue is free to move and the vowel reaches its ideal position. This interpretation was corroborated by means of the test items with an open syllable (/tVV/). In order to explain the variability of the repetitions in one context, the notion of auditory critical band window (CBW) was used. A CBW covers an area on the psychoacoustical F1/F2 plot that comprises 1 bark on the F1 and F2 scales. Its modification CBW-F1 implies that a critical band is presented as a circle comprising the diameter of 1 bark according to the F1 scale. Practically all single F1/F2 points occur within the CBW-F1 circle. In most cases, the variability is smaller than one CBW-F1 circle, but we can consider that a greater amount of repetitions would yield a greater dispersion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1985

Some of the most important properties of silicone oil to explain its action.

The action of silicone oil is due especially to two of its properties: density and surface tension. Its density is less than 1: for this reason, the silicone oil bubble always presses upon the upper part of the eye, i.e. most of the time at twelve o'clock; so there is a constant support upwards which closes the tears and reattaches the retina. The action of silicone oil is different on the lower part of the eye, even if the cavity is filled with silicone oil: a buckle is then required. The surface tension being weak, a vitrectomy is necessary to obtain a single bubble which gives a higher pressure than several small bubbles. The cumulative effect of the density below 1 and the low surface tension explains that the recurrences always occur in the lower part of the retina. Retinotomies or retinectomies are presently trying to counteract this ineffectiveness of silicone oil.

Humans↗