Learning to differentiate microintervals of time using verbal feedback

Reaction time (RT) and the number of correct estimations of time microintervals (10 and 180 ms) between two visual stimuli were recorded in healthy subjects. It has been shown that 10 ms interval is better estimated when the stimuli are presented in the right visual field, i.e. when they are addressed directly to the left hemisphere. At the same time the number of correct estimations of 180 ms interval is greater and their RT is less when the stimuli are addressed directly to the right hemisphere. This points to different hemispheric mechanisms of time microintervals estimation. Study of the influence of different forms of verbal reinforcement on this learning has shown that after positive reinforcement (the word "good") the number of correct estimations is on average by 10% greater than after negative reinforcement (the word "error"). This may be connected with such processes as isolation and identification of erroneous reaction.     

Effect of the duration of a reproducible interval on reaction time in man

The dependence of reaction time (RT) of reproduction of presented standard intervals on their duration (100-5000 ms) was studied on 30 subjects. The intervals were limited by two electrocutaneous stimuli or two clicks and were presented both at random and at a gradual increase or decrease, with a step of 100 ms. They were reproduced by pressing a button. The RTs duration depended on the presented interval within the range from 100 to 2000 ms. Such scatter of the upper limit is due to differences in the methods of presentation of the material and to individual features of the subjects. A presence of two mechanisms of time intervals reproduction is suggested for such experimental conditions: the image of the standard interval might be created either after its presentation or in the process of its presentation. Correspondingly, the RT dependence on the interval duration is manifest in the first case and is absent in the second.     

Effects of inhaled nicotine on instrumental learning of blood pressure responses.

The present study investigated the effects of biofeedback of arterial blood pressure on cortical, peripheral, and psychological measures and the dependence of these effects on nicotine. Four groups of subjects, nonsmokers, and habitual smokers who smoked cigarettes during the experimental sessions containing 0.3, 0.8, or 1.5 mg nicotine, respectively, participated in a feedback paradigm in which continuous feedback of mean blood pressure was provided for intervals of 8 s each. While tonic blood pressure did not differ between the groups, the ability to modulate blood pressure (under feedback conditions) was restricted in smokers as compared to nonsmoking subjects; increasing nicotine dosage was accompanied by poorer performance. Independently of habitual smoking and nicotine doses, heart rate increased during feedback and under conditions of blood pressure increase. In smokers, activity in the alpha band was reduced in a dose-dependent manner. Slow cortical potentials (SCPs) during the feedback interval varied with self-induced blood pressure changes in nonsmokers (blood pressure increase was accompanied by reduced surface-negative potential shifts and vice versa), while SCP variations during feedback conditions were small in smokers, more so under the influence of 0.3 and 0.8-mg nicotine, less so under 1.5 mg. Verbal reports suggest that awareness of performance strategies may not be a necessary variable for performance on the blood pressure regulation task.     

Effects of inhaled nicotine on instrumental learning of blood pressure responses

The present study investigated the effects of biofeedback of arterial blood pressure on cortical, peripheral, and psychological measures and the dependence of these effects on nicotine. Four groups of subjects, nonsmokers, and habitual smokers who smoked cigarettes during the experimental sessions containing 0.3, 0.8, or 1.5 mg nicotine, respectively, participated in a feedback paradigm in which continuous feedback of mean blood pressure was provided for intervals of 8 s each. While tonic blood pressure did not differ between the groups, the ability to modulate blood pressure (under feedback conditions) was restricted in smokers as compared to nonsmoking subjects; increasing nicotine dosage was accompanied by poorer performance. Independently of habitual smoking and nicotine doses, heart rate increased during feedback and under conditions of blood pressure increase. In smokers, activity in the alpha band was reduced in a dose-dependent manner. Slow cortical potentials (SCPs) during the feedback interval varied with self-induced blood pressure changes in nonsmokers (blood pressure increase was accompanied by reduced surface-negative potential shifts and vice versa), while SCP variations during feedback conditions were small in smokers, more so under the influence of 0.3 and 0.8-mg nicotine, less so under 1.5 mg. Verbal reports suggest that awareness of performance strategies may not be a necessary variable for performance on the blood pressure regulation task.This experiment was supported by Reemtsma Inc. Hamburg, which also provided the experimental cigarettes.     

Changes in the cortical electric activity in the course of set formation under conditions of increased loading of the working memory

Stability of the cognitive set to nonsense words in healthy adult subjects was compared in two experimental conditions: (1) subjects had only to recognize pseudowords/words; (2) in each trial after the pseudoword/word recognition, subjects had to press a button in response to a visual probe stimulus and only after this action to pronounce a recognized pseudoword/word. It was shown that complication of the cognitive performance in the second condition did not affect the set rigidity. However, the pattern of the cortical electric activity substantially changed: the EEG power in the theta frequency range and coherence function, in particular, interhemispheric, in the frontal cortical areas were higher in the second condition. The increase in coherence function in the frontal areas was most pronounced in the theta and alphal ranges. It was suggested that increase in activity of the frontal regions of the brain cortex facilitates shifts of visual sets under increasing load of the working memory.     

Influence of spatial and temporal heterogeneities on the estimation of demographic parameters in a continuous population using individual microsatellite data

Drift and migration disequilibrium are very common in animal and plant populations. Yet their impact on methods of estimation of demographic parameters was rarely evaluated especially in complex realistic population models. The effect of such disequilibria on the estimation of demographic parameters depends on the population model, the statistics, and the genetic markers used. Here we considered the estimation of the product Dsigma2 from individual microsatellite data, where D is the density of adults and sigma2 the average squared axial parent-offspring distance in a continuous population evolving under isolation by distance. A coalescence-based simulation algorithm was used to study the effect on Dsigma2 estimation of temporal and spatial fluctuations of demographic parameters. Estimation of present-time Dsigma2 values was found to be robust to temporal changes in dispersal, to density reduction, and to spatial expansions with constant density, even for relatively recent changes (i.e., a few tens of generations ago). By contrast, density increase in the recent past gave Dsigma2 estimations biased largely toward past demographic parameters values. The method was also robust to spatial heterogeneity in density and estimated local demographic parameters when the density is homogenous around the sampling area (e.g., on a surface that equals four times the sampling area). Hence, in the limit of the situations studied in this article, and with the exception of the case of density increase, temporal and spatial fluctuations of demographic parameters appear to have a limited influence on the estimation of local and present-time demographic parameters with the method studied.     

Modulation of intracellular Ca(2+) concentration by tedisamil,a class III antiarrhythmic agent,in isolated heart preparation

New class III antiarrhythmic/defibrillating compound tedisamil was shown to facilitate termination of atrial and ventricular fibrillation in experimental as well as clinical conditions. However, class III-related inhibition of K(+) current associated with prolongation of repolarization can not solely explain its defibrillating ability. Following recent findings it was hypothesized that defibrillating effect of tedisamil is likely due to its sympathomimetic feature linked with modulation of intracellular calcium. Results of this study obtained in isolated heart preparation showed that elevated intracellular Ca(2+) free concentration was decreased by administration of tedisamil in concentration that did not induce Q-T interval prolongation. Due to species differences the effective concentration was in rat 10(-7) M, while in guinea pig 10(-5) M. On the contrary, further dramatic increase of elevated Ca(2+) was detected upon administration of tedisamil in concentration that markedly prolonged Q-T interval (10(-5) M in rat). It is concluded that defibrillating ability of tedisamil is most likely associated with attenuation of abnormal and harmful intracellular Ca(2+) elevation (that is highly arrhythmogenic) than with prolongation of APD or Q-T interval.     

Towards Identifying and Reducing the Bias of Disease Information Extracted from Search Engine Data

The estimation of disease prevalence in online search engine data (e.g., Google Flu Trends (GFT)) has received a considerable amount of scholarly and public attention in recent years. While the utility of search engine data for disease surveillance has been demonstrated, the scientific community still seeks ways to identify and reduce biases that are embedded in search engine data. The primary goal of this study is to explore new ways of improving the accuracy of disease prevalence estimations by combining traditional disease data with search engine data. A novel method, Biased Sentinel Hospital-based Area Disease Estimation (B-SHADE), is introduced to reduce search engine data bias from a geographical perspective. To monitor search trends on Hand, Foot and Mouth Disease (HFMD) in Guangdong Province, China, we tested our approach by selecting 11 keywords from the Baidu index platform, a Chinese big data analyst similar to GFT. The correlation between the number of real cases and the composite index was 0.8. After decomposing the composite index at the city level, we found that only 10 cities presented a correlation of close to 0.8 or higher. These cities were found to be more stable with respect to search volume, and they were selected as sample cities in order to estimate the search volume of the entire province. After the estimation, the correlation improved from 0.8 to 0.864. After fitting the revised search volume with historical cases, the mean absolute error was 11.19% lower than it was when the original search volume and historical cases were combined. To our knowledge, this is the first study to reduce search engine data bias levels through the use of rigorous spatial sampling strategies.     

Dynamics of temporal parameters of sensorimotor reactions in relation to the type of human movement

The study was conducted on nine right-handed male subjects 20-24 year old and consisted of two series. In the first series one warning signal in the form of one of the digits (from 1 to 8) was successively presented to the subjects on the display and then four trigger signals which required either simple pressing of the push button (an arrow with a dot) or its holding during 0.5 s (two arrows) by the right or left hand depending on the arrow direction. The digit corresponded to one variant of signals succession. Each variant was repeated randomly among other variants 15 times. In the second series instead of arrows asterisks were presented. Reaction time and duration of push button holding were recorded. Two regularities were observed: significant decrease of RT in the series of reacting by memory and successive decrease of RT in accordance with the decrease of the number of the remaining signals observed in both series. In the first series RT successively decreased by 35-40 ms, in the second one-by 16-20 ms. It is supposed that the difference in RTs between series characterizes the time of signal structure analysis, while the difference in RTs within one block of signals in the second series-the time of extraction of selected motor program from memory.     

Changes of Hand Switching Costs during Bimanual Sequential Learning

Many tasks in our daily life demand not only the use of different fingers of one hand in a serial fashion, but also to alternate from one hand to the other. Here, we investigated performance in a bimanual serial reaction time task (SRTT) with particular emphasis on learning-related changes in reaction time (RT) for consecutive button presses for homologous index- and middle fingers. The bimanual SRTT consisted of sequential button presses either with the left or right index- and middle-finger to a series of visual letters displayed on a computer screen. Each letter was assigned a specific button press with one of four fingers. Two outcome measures were investigated: (a) global sequence learning as defined by the time needed to complete a 15-letter SRTT sequence and (b) changes in hand switch costs across learning. We found that bimanual SRTT resulted in a global decrease in RT during the time course of learning that persisted for at least two weeks. Furthermore, RT to a button press showed an increase when the previous button press was associated with another hand as opposed to the same hand. This increase in RT was defined as switch costs. Hand switch costs significantly decreased during the time course of learning, and remained stable over a time of approximately two weeks. This study provides evidence for modulations of switch costs during bimanual sequence learning, a finding that might have important implications for theories of bimanual coordination and learning.     

Selective lateral muscle activation in moderate medial knee osteoarthritis subjects does not unload medial knee condyle

There is some debate in the literature regarding the role of quadriceps-hamstrings co-contraction in the onset and progression of knee osteoarthritis. Does co-contraction during walking increase knee contact loads, thereby causing knee osteoarthritis, or might it be a compensatory mechanism to unload the medial tibial condyle? We used a detailed musculoskeletal model of the lower limb to test the hypothesis that selective activation of lateral hamstrings and quadriceps, in conjunction with inhibited medial gastrocnemius, can actually reduce the joint contact force on the medial compartment of the knee, independent of changes in kinematics or external forces. “Baseline” joint loads were computed for eight subjects with moderate medial knee osteoarthritis (OA) during level walking, using static optimization to resolve the system of muscle forces for each subject?s scaled model. Holding all external loads and kinematics constant, each subject?s model was then perturbed to represent non-optimal “OA-type” activation based on mean differences detected between electromyograms (EMG) of control and osteoarthritis subjects. Knee joint contact forces were greater for the “OA-type” than the “Baseline” distribution of muscle forces, particularly during early stance. The early-stance increase in medial contact load due to the “OA-type” perturbation could implicate this selective activation strategy as a cause of knee osteoarthritis. However, the largest increase in the contact load was found at the lateral condyle, and the “OA-type” lateral activation strategy did not increase the overall (greater of the first or second) medial peak contact load. While “OA-type” selective activation of lateral muscles does not appear to reduce the medial knee contact load, it could allow subjects to increase knee joint stiffness without any further increase to the peak medial contact load.     

Swallowing function and upper airway sensation in obstructive sleep apnea.

The objective of this study was to determine whether impaired upper airway (UA) mucosal sensation contributes to altered swallowing function in obstructive sleep apnea (OSA). We determined UA two-point discrimination threshold (2PDT) and vibratory sensation threshold (VST) in 15 men with untreated OSA and 9 nonapneic controls (CL). We then assessed swallowing responses to oropharyngeal fluid boluses delivered via a catheter. The threshold volume required to provoke swallowing and the mean latency to swallowing were determined, as was the phase of the respiratory cycle in which swallowing occurred [expressed as percentage of control cycle duration (%CCD)] and the extent of prolongation of the respiratory cycle after swallowing [inspiratory suppression time (IST)]. 2PDT and VST were significantly impaired in OSA patients compared with CL subjects. 2PDT was positively correlated with swallowing latency and threshold volume in CL subjects, but not in OSA patients. Threshold volume did not differ between the groups [median value = 0.1 ml (95% confidence interval = 0.1-0.2) for OSA and 0.15 ml (95% confidence interval = 0.1-0.16) for CL], whereas swallowing latency was shorter for OSA patients [3.3 (SD 0.7) vs. 3.9 (SD 0.8) s, P = 0.04]. %CCD and IST were similar for OSA patients and CL subjects. However, among OSA patients there was a significant inverse relation between VST and IST. These findings suggest that oropharyngeal sensory impairment in OSA is associated with an attenuation of inhibitory modulating inputs to reflex and central control of UA swallowing function.     

Regulation of Taurine Transport in Rat Skeletal Muscle

Taurine concentration of soleus muscle (SL, slow-twitch) was initially about twofold higher than that of extensor digitorum longus muscle (EDL, fast-twitch). Taurine concentration in gastrocnemius muscle (GC) was intermediate between that of EDL and SL. Four days after sciatic nerve section, taurine concentration in the EDL but not in the SL was increased by 2.5-fold. The increase was not due to the muscle atrophy and was observed 28 days after denervation. Tenotomy did not increase the total taurine content of the EDL. The increase in taurine concentration of the denervated EDL was prevented by simultaneous ingestion of guanidinoethane sulfonate, a competitive inhibitor of taurine transport. The initial and the maximal rates of [3H]taurine uptake were significantly higher in SL than in EDL. Denervation dramatically accelerated the initial and the maximal rates of the transport in EDL, whereas it significantly reduced those in SL. In contrast, the electrical stimulation of sciatic nerve accelerated the uptake of taurine by EDL and SL of the control but not of the curare-treated rats. These results suggest that transport of taurine into rat skeletal muscles is regulated differently by neural information and by muscular activity, and that the regulation is dependent on the muscle phenotype.     

Validation of a personalized curved muscle model of the lumbar spine during complex dynamic exertions

Previous curved muscle models have typically examined their robustness only under simple, single-plane static exertions. In addition, the empirical validation of curved muscle models through an entire lumbar spine has not been fully realized. The objective of this study was to empirically validate a personalized biologically-assisted curved muscle model during complex dynamic exertions. Twelve subjects performed a variety of complex lifting tasks as a function of load weight, load origin, and load height. Both a personalized curved muscle model as well as a straight-line muscle model were used to evaluate the model’s fidelity and prediction of three-dimensional spine tissue loads under different lifting conditions. The curved muscle model showed better model performance and different spinal loading patterns through an entire lumbar spine compared to the straight-line muscle model. The curved muscle model generally showed good fidelity regardless of lifting condition. The majority of the 600 lifting tasks resulted in a coefficient of determination (R²) greater than 0.8 with an average of 0.83, and the average absolute error less than 15% between measured and predicted dynamic spinal moments. As expected, increased load and asymmetry were generally found to significantly increase spinal loads, demonstrating the ability of the model to differentiate between experimental conditions. A curved muscle model would be useful to estimate precise spine tissue loads under realistic circumstances. This precise assessment tool could aid in understanding biomechanical causal pathways for low back pain.     

Subject-specific calibration of neuromuscular parameters enables neuromusculoskeletal models to estimate physiologically plausible hip joint contact forces in healthy adults

In-vivo hip joint contact forces (HJCF) can be estimated using computational neuromusculoskeletal (NMS) modelling. However, different neural solutions can result in different HJCF estimations. NMS model predictions are also influenced by the selection of neuromuscular parameters, which are either based on cadaveric data or calibrated to the individual. To date, the best combination of neural solution and parameter calibration to obtain plausible estimations of HJCF have not been identified. The aim of this study was to determine the effect of three electromyography (EMG)-informed neural solution modes (EMG-driven, EMG-hybrid, and EMG-assisted) and static optimisation, each using three different parameter calibrations (uncalibrated, minimise joint moments error, and minimise joint moments error and peak HJCF), on the estimation of HJCF in a healthy population (n = 23) during walking. When compared to existing in-vivo data, the EMG-assisted mode and static optimisation produced the most physiologically plausible HJCF when using a NMS model calibrated to minimise joint moments error and peak HJCF. EMG-assisted mode produced first and second peaks of 3.55 times body weight (BW) and 3.97 BW during walking; static optimisation produced 3.75 BW and 4.19 BW, respectively. However, compared to static optimisation, EMG-assisted mode generated muscle excitations closer to recorded EMG signals (average across hip muscles R² = 0.60 ± 0.37 versus R² = 0.12 ± 0.14). Findings suggest that the EMG-assisted mode combined with minimise joint moments error and peak HJCF calibration is preferable for the estimation of HJCF and generation of realistic load distribution across muscles.     

The emotional assessment by test subjects of short musical fragments

Emotional estimation of 96 short (2-5 s) musical fragments was studied in 6 healthy subjects. Fragments were scored on a 5-point scale. Statistically significant difference in estimations of specific musical fragments (positive, negative, or indifferent) was found.     

Baseline gamma activity EEG and induced responses to facial stimuli of the visual cognitive set

Power spectra of cortical potentials of baseline activity during interstimuli intervals (4 s; Fourier transform in the frequency band of 1-60 Hz) and short-term (0.8 s) induced responses to facial stimuli (wavelet transform in the 15-60 Hz band) were assessed in the study of the visual cognitive set to facial expression. Significant differences between groups of subjects with different set rigidity were observed only at the set-testing stage. Estimation of the short-term (0.8 s) induced responses of the wavelet spectra in the group with plastic set revealed an increase in the power (in comparison with the power of background activity) of the gamma2 band (41-60 Hz) in the left hemisphere of the temporal, central and occipital areas, whereas in the group with rigid set these power spectra decreased. At the same time the power in the gamma1 band (21-40 Hz) was significantly lower (at the same level with the rigid form), indicating a discrete nature and functional selectivity in the gamma frequency band.     

Improving Collective Estimations Using Resistance to Social Influence

Groups can make precise collective estimations in cases like the weight of an object or the number of items in a volume. However, in others tasks, for example those requiring memory or mental calculation, subjects often give estimations with large deviations from factual values. Allowing members of the group to communicate their estimations has the additional perverse effect of shifting individual estimations even closer to the biased collective estimation. Here we show that this negative effect of social interactions can be turned into a method to improve collective estimations. We first obtained a statistical model of how humans change their estimation when receiving the estimates made by other individuals. We confirmed using existing experimental data its prediction that individuals use the weighted geometric mean of private and social estimations. We then used this result and the fact that each individual uses a different value of the social weight to devise a method that extracts the subgroups resisting social influence. We found that these subgroups of individuals resisting social influence can make very large improvements in group estimations. This is in contrast to methods using the confidence that each individual declares, for which we find no improvement in group estimations. Also, our proposed method does not need to use historical data to weight individuals by performance. These results show the benefits of using the individual characteristics of the members in a group to better extract collective wisdom.     

Thyroarytenoid muscle activity during loaded and nonloaded breathing in adult humans

Previous fiber-optic studies in humans have demonstrated narrowing of the glottic aperture in expiration during application of expiratory resistive loads. Nine healthy subjects were studied to determine the effect of expiratory resistive loads on the electromyographic activity of the thyroarytenoid (TA) muscle, a vocal cord adductor. Four of the nine subjects also underwent the application of inspiratory resistive loads and voluntary prolongation of either inspiratory (TI) or expiratory (TE) time. TA activity was recorded by intramuscular hooked-wire electrodes. During quiet breathing in all subjects, the TA was phasically active on expiration and often tonically active throughout the respiratory cycle. TA expiratory activity progressively increased with increasing levels of expiratory load. Inspiratory loads resulted in increased TA "inspiratory" activity. Voluntary prolongation of TE to times similar to those reached during loaded breathing induced increases in TA expiratory activity similar to those reached during the loaded state. Voluntary prolongation of TI was associated with an increase in TA inspiratory activity. Similar increases in TI during inspiratory loading or voluntary conditions were associated with comparable increases in TA inspiratory activity in three of the four subjects. In conclusion, increased activation of TA during the application of expiratory resistive loads implies that the reported narrowing of glottic aperture during expiratory loading is an active phenomenon. Changes in activation of the TA with resistive loads appear to be related to changes in respiratory pattern.