The relationship between prepulse inhibition and perceived intensity of the blink-eliciting stimulus: Stimulus intensity and lead interval effects

The hypothesis that prepulse inhibition of the blink reflex reflects a transient process that protects preattentive processing of the prepulse was investigated. Participants were presented with pairs of blink-eliciting noises, with some noises preceded by a prepulse, and were asked to rate the intensity of the second noise relative to the first. Inhibition of blink amplitude was greater for a 110 dB(A) noise than for a 95 dB(A) noise with a 120 ms lead interval, whereas there was no difference with a 30 ms lead interval. The reduction in perceived intensity was greater for the 110 dB(A) noise than for the 95 dB(A) noise with the 120 ms lead interval, but not with the 30 ms lead interval. The parallel results support an association between prepulse inhibition and perceived intensity. However, the prepulse did not reduce intensity ratings relative to control trials in some conditions, suggesting that prepulse inhibition is not always associated with an attenuation of the impact of the blink-eliciting stimulus.

Anharmonic effects on a phonon-number measurement of a quantum-mesoscopic-mechanical oscillator

We generalize a proposal for detecting single-phonon transitions in a single nanoelectromechanical system (NEMS) to include the intrinsic anharmonicity of each mechanical oscillator. In this scheme two NEMS oscillators are coupled via a term quadratic in the amplitude of oscillation for each oscillator. One NEMS oscillator is driven and strongly damped and becomes a transducer for phonon number in the other measured oscillator. We derive the conditions for this measurement scheme to be quantum limited and find a condition on the size of the anharmonicity. We also derive the relation between the phase diffusion back-action noise due to number measurement and the localization time for the measured system to enter a phonon-number eigenstate. We relate both these time scales to the strength of the measured signal, which is an induced current proportional to the position of the read-out oscillator.

Spring-neap tide-induced beach water table fluctuations in a sloping coastal aquifer

Predictions of water table fluctuations in coastal aquifers are needed for numerous coastal and water resources engineering problems. Most previous investigations have been based on the Boussinesq equation for the case of a vertical beach. In this note an analytical solution based on shallow water expansion for the spring- neap tide- induced water table fluctuations in a coastal aquifer is presented. Unlike most previous investigations, multitidal signals are considered with a sloping coastal aquifer. The new solution is verified by comparing with field observations from Ardeer, Scotland. On the basis of the analytical approximation the influences of higher- order components on water table elevation are examined first. Then, a parametric study has been performed to investigate the effects of the amplitude ratio (lambda), frequency ratio (omega), and phases (delta(1) and delta(2)) on the tide- induced water table fluctuations in a sloping sandy beach.

5 Hz repetitive TMS increases anticipatory motor activity in the human cortex

In the present study, we analyzed how high-frequency repetitive transcranial magnetic stimulation (rTMS) of the primary motor hand area (M1-Hand) shapes anticipatory motor activity in frontal areas as indexed by the contingent negative variation (CNV). Eight right-handed volunteers received real or sham 5 Hz rTMS at an intensity of 90% resting motorthreshold (1500 stimuli per session). Real but not sham rTMS to left M1-Hand induced a site-specific increase in amplitude of the late component of the CNV at the electrode C3 overlaying the site of stimulation. The increase in pre-movement activity in the stimulated cortex may reflect an increase in facilitatory drive from connected motor areas, enhanced responsiveness of the stimulated cortex to these inputs or both. (c) 2005 Elsevier Ireland Ltd. All rights reserved.

Comparison of Quantitative T-Wave Alternans Profiles of Healthy Subjects and ICD Patients

Background: Current relevance of T-wave alternans is based on its association with electrical disorder and elevated cardiac risk. Quantitative reports would improve understanding on TWA augmentation mechanisms during mental stress or prior to tachyarrhythmias. However, little information is available about quantitative TWA values in clinical populations. This study aims to create and compare TWA profiles of healthy subjects and ICD patients, evaluated on treadmill stress protocols. Methods: Apparently healthy subjects, not in use of any medication were recruited. All eligible ICD patients were capable of performing an attenuated stress test. TWA analysis was performed during a 15-lead treadmill test. The derived comparative profile consisted of TWA amplitude and its associated heart rate, at rest (baseline) and at peak TWA value. Chi-square or Mann-Whitney tests were used with p values <= 0.05. Discriminatory performance was evaluated by a binary logistic regression model. Results: 31 healthy subjects (8F, 23M) and 32 ICD patients (10F, 22M) were different on baseline TWA (1 +/- 2 mu V; 8 +/- 9 mu V; p < 0.001) and peak TWA values (26 +/- 13 mu V; 37 +/- 20 mu V; p = 0,009) as well as on baseline TWA heart rate (79 +/- 10 bpm; 67 +/- 15 bpm; p < 0.001) and peak TWA heart rate (118 +/- 8 bpm; 90 +/- 17 bpm; p < 0.001). The logistic model yielded sensitivity and specificity values of 88.9% and 92.9%, respectively. Conclusions: Healthy subjects and ICD patients have distinct TWA profiles. The new TWA profile representation (in amplitude-heart rate pairs) may help comparison among different research protocols. Ann Noninvasive Electrocardiol 2009;14(2):108-118.

Ferromagnetism, paramagnetism, and a Curie-Weiss metal in an electron-doped Hubbard model on a triangular lattice

Motivated by the unconventional properties and rich phase diagram of NaxCoO2 we consider the electronic and magnetic properties of a two-dimensional Hubbard model on an isotropic triangular lattice doped with electrons away from half-filling. Dynamical mean-field theory (DMFT) calculations predict that for negative intersite hopping amplitudes (t < 0) and an on-site Coulomb repulsion, U, comparable to the bandwidth, the system displays properties typical of a weakly correlated metal. In contrast, for t > 0 a large enhancement of the effective mass, itinerant ferromagnetism, and a metallic phase with a Curie-Weiss magnetic susceptibility are found in a broad electron doping range. The different behavior encountered is a consequence of the larger noninteracting density of states (DOS) at the Fermi level for t > 0 than for t < 0, which effectively enhances the mass and the scattering amplitude of the quasiparticles. The shape of the DOS is crucial for the occurrence of ferromagnetism as for t > 0 the energy cost of polarizing the system is much smaller than for t < 0. Our observation of Nagaoka ferromagnetism is consistent with the A-type antiferromagnetism (i.e., ferromagnetic layers stacked antiferromagnetically) observed in neutron scattering experiments on NaxCoO2. The transport and magnetic properties measured in NaxCoO2 are consistent with DMFT predictions of a metal close to the Mott insulator and we discuss the role of Na ordering in driving the system towards the Mott transition. We propose that the Curie-Weiss metal phase observed in NaxCoO2 is a consequence of the crossover from a bad metal with incoherent quasiparticles at temperatures T > T-* and Fermi liquid behavior with enhanced parameters below T-*, where T-* is a low energy coherence scale induced by strong local Coulomb electron correlations. Our analysis also shows that the one band Hubbard model on a triangular lattice is not enough to describe the unusual properties of NaxCoO2 and is used to identify the simplest relevant model that captures the essential physics in NaxCoO2. We propose a model which allows for the Na ordering phenomena observed in the system which, we propose, drives the system close to the Mott insulating phase even at large dopings.

Phase waves in mode-locked superfluorescent lasers

We present results from both theoretical and experimental studies of the noise characteristics of mode-locked superfluorescent lasers. The results show that observed macroscopic broadband amplitude noise on the laser pulse train has its origin in quantum noise-initiated ''phase-wave'' fluctuations, and we find an associated phase transition in the noise characteristics as a function of laser cavity detuning.

Numerical modelling of tide-induced beach water table fluctuations

Field studies have shown that the elevation of the beach groundwater table varies with the tide and such variations affect significantly beach erosion or accretion. In this paper, we present a BEM (Boundary Element Method) model for simulating the tidal fluctuation of the beach groundwater table. The model solves the two-dimensional flow equation subject to free and moving boundary conditions, including the seepage dynamics at the beach face. The simulated seepage faces were found to agree with the predictions of a simple model (Turner, 1993). The advantage of the present model is, however, that it can be used with little modification to simulate more complicated cases, e.g., surface recharge from rainfall and drainage in the aquifer may be included (the latter is related to beach dewatering technique). The model also simulated well the field data of Nielsen (1990). In particular, the model replicated three distinct features of local water table fluctuations: steep rising phase versus flat falling phase, amplitude attenuation and phase lagging.

Beach water table fluctuations due to wave run-up: Capillarity effects

High-frequency beach water table fluctuations due to wave run-up and rundown have been observed in the field [Waddell, 1976]. Such fluctuations affect the infiltration/exfiltration process across the beach face and the interstitial oxygenation process in the beach ecosystem. Accurate representation of high-frequency water table fluctuations is of importance in the modeling of (1) the interaction between seawater and groundwater, more important, the effects on swash sediment transport and (2) the biological activities in the beach ecosystem. Capillarity effects provide a mechanism for high-frequency water table fluctuations. Previous modeling approaches adopted the assumption of saturated flow only and failed to predict the propagation of high-frequency fluctuations in the aquifer. In this paper we develop a modified kinematic boundary condition (kbc) for the water table which incorporates capillarity effects. The application of this kbc in a boundary element model enables the simulation of high-frequency water table fluctuations due to wave run-up. Numerical tests were carried out for a rectangular domain with small-amplitude oscillations; the behavior of water table responses was found to be similar to that predicted by an analytical solution based on the one-dimensional Boussinesq equation. The model was also applied to simulate the water table response to wave run-up on a doping beach. The results showed similar features of water table fluctuations observed in the field. In particular, these fluctuations are standing wave-like with the amplitude becoming increasingly damped inland. We conclude that the modified kbc presented here is a reasonable approximation of capillarity effects on beach water table fluctuations. However, further model validation is necessary before the model can confidently be used to simulate high-frequency water table fluctuations due to wave run-up.

Sample-induced RF perturbations in high-field, high-resolution NMR spectroscopy

Conducting dielectric samples are often used in high-resolution experiments at high held. It is shown that significant amplitude and phase distortions of the RF magnetic field may result from perturbations caused by such samples. Theoretical analyses demonstrate the spatial variation of the RF field amplitude and phase across the sample, and comparisons of the effect are made for a variety of sample properties and operating field strengths. Although the effect is highly nonlinear, it tends to increase with increasing field strength, permittivity, conductivity, and sample size. There are cases, however, in which increasing the conductivity of the sample improves the homogeneity of the amplitude of the RF field across the sample at the expense of distorted RF phase. It is important that the perturbation effects be calculated for the experimental conditions used, as they have the potential to reduce the signal-to-noise ratio of NMR experiments and may increase the generation of spurious coherences. The effect of RF-coil geometry on the coherences is also modeled, with the use of homogeneous resonators such as the birdcage design being preferred, Recommendations are made concerning methods of reducing sample-induced perturbations. Experimental high-field imaging and high-resolution studies demonstrate the effect. (C) 1997 Academic Press.

Movement-related potentials in Parkinson's disease - Motor imagery and movement preparation

Movement-related potentials (MRPs) associated with voluntary movements reflect cortical activity associated with processes Of movement preparation and movement execution. Early-stage pre-movement activity is reduced in amplitude in Parkinson's disease. However it is unclear whether this neurophysiological deficit relates to preparatory or execution-related activity, since previous studies have not been able to separate different functional components of MRPs. Motor imagery is thought to involve mainly processes of movement preparation, with reduced involvement of end-stage movement execution-related processes. Therefore, MRP components relating to movement preparation and execution may be examined separately by comparing MRPs associated with imagined and actual movements. In this study, MRPs were recorded from 14 subjects with Parkinson's disease and 10 age-matched control subjects while they performed a sequential button-pressing task, and while they imagined performance of the same task. Early-stage pre-movement activity was present in both Parkinson's disease patients and control subjects when they imagined movement, but was reduced in amplitude compared with that for actual movement. Movement execution-related components, arising predominantly from the primary motor cortex, were relatively unaffected in Parkinson's disease subjects. However motor preparatory processes, probably involving the supplementary motor area, were reduced in amplitude overall and abnormally prolonged, Indicating impaired termination following the motor response. Further this impaired termination of preparatory-phase activity was observed only in patients with more severe parkinsonian symptoms, and not in early-stage Parkinson's disease.

Influence of Cochlear Function on Auditory Temporal Resolution in Tinnitus Patients

Our aim was to analyze the influence of subtle cochlear damage on temporal auditory resolution in tinnitus patients. Forty-eight subjects (hearing threshold <= 25 dB HL) were assigned to one of two experimental groups: 28 without auditory complaints (mean age, 28.8 years) and 20 with tinnitus (mean age, 33.5 years). We analyzed distortion product otoacoustic emission growth functions (by threshold, slope, and estimated amplitude), extended high-frequency thresholds, and the Gaps-in-Noise test. There were differences between the groups, principally in the extended high-frequency thresholds and the Gaps-in-Noise test results. Our findings suggest that subtle peripheral hearing impairment affects temporal resolution in tinnitus, even when pure-tone thresholds as conventionally measured appear normal. Copyright (C) 2010 S. Karger AG, Basel

Stuttering treatment control using P300 event-related potentials

Positron emission tomography studies during speech have indicated a failure to show the normal activation of auditory cortical areas in stuttering individuals. In the present study, P300 event-related potentials were used to investigate possible effects of behavioral treatment on the pattern of signal amplitude and latency between waves. In order to compare variations in P300 measurements, a control group paired by age and gender to the group of stutterers, was included in the study. Findings suggest that the group of stutterers presented a significant decrease in stuttering severity after the fluency treatment program. Regarding P300 measurements, stutterers and their controls presented results within normal limits in all testing situations and no significant statistical variations between pre and post treatment testing. When comparing individual results between the testing situations, stutterers presented a higher average decrease in wave latency for the right ear following treatment. The results are discussed in light of previous P300 event-related potentials and functional imaging studies with stuttering adults. Educational objectives: The reader will learn about and be able to describe the: (1) use of P300 event-related potentials in the study of stuttering; (2) differences between stuttering and non-stuttering adults; and (3) effects of behavioral fluency treatment on cerebral activity in stuttering speakers. (C) 2011 Elsevier Inc. All rights reserved.

Early motor and electrophysiological changes in transgenic mouse model of amyotrophic lateral sclerosis and gender differences on clinical outcome

Amyotrophic lateral sclerosis (ALS) is a progressive degenerative disorder affecting motoneurons and the SOD1(G93A) transgenic mice are widely employed to study disease physiopathology and therapeutic strategies. Despite the cellular and biochemical evidences of an early motor system dysfunction, the conventional behavioral tests do not detect early motor impairments in SOD1 mouse model. We evaluated early changes in motor behavior of ALS mice by doing the analyses of tail elevation, footprint, automatic recording of motor activities by means of an infrared motion sensor activity system and electrophysiological measurements in male and female wild-type (WT) and SOD1(G93A) mice from postnatal day (P) 20 up to endpoint. The classical evaluations of mortality, weight loss, tremor, rotometer, hanging wire and inclined plane were also employed. There was a late onset (after P90) of the impairments of classical parameters and the outcome varied between genders of ALS mice, being tremor, cumulative survival, weight loss and neurological score about 10 days earlier in male than female ALS mice and also about 20 days earlier in ALS males regarding rotarod and hanging wire performances. While diminution of hindpaw base was 10 days earlier in ALS males (P110) compared to females, the steep length decreased 40 days earlier in ALS females (P60) than ALS males. The automatic analysis of motor impairments showed substantial late changes (after P90) of motility and locomotion in the ALS females, but not in the ALS males. It was surprising that the scores of tail elevation were already decreased in ALS males and females by P40, reaching the minimal values at the endpoint. The electrophysiological analyses showed early changes of measures in the ALS mouse sciatic nerve, i.e., decreased values of amplitude (P40) and nerve conduction velocity (P20), and also an increased latency (P20) reaching maximal level of impairments at the late disease phase. The early changes were not accompanied by reductions of neuronal protein markers of neurofilament 200 and ChAT in the ventral part of the lumbar spinal cord of P20 and P60 ALS mice by means of Western blot technique, despite remarkable decreases of those protein levels in P120 ALS mice. In conclusion, early changes of motor behavior and electrophysiological parameters in ALS mouse model must be taken into attention in the analyses of disease mechanisms and therapeutic effects. (C) 2011 Published by Elsevier B.V.

Choroidal expansion during the water drinking test

To evaluate the correlation between intraocular pressure (IOP) rise, ocular pulse amplitude (OPA), and choroidal thickness (ChT) during the water drinking test (WDT). Primary open-angle glaucoma (POAG) patients were submitted to the WDT followed by serial IOP measurements using dynamic contour tonometry (DCT), Goldman tonometry (GAT), and ChT measurements using ultrasonographic A and B-scan (USG). A control group not submitted to the test was also evaluated using DCT, GAT, and USG. Intraclass correlation coefficient (ICC) was calculated in the control group in order to assess the reproducibility of measurements. Spearman`s coefficient (rho) was used to assess the correlation between the variables. Thirty eyes were included in the study. There was a significant IOP rise during the WDT using both GAT and DCT (p < 0.001). The OPA and ChT measurements also increased significantly (p < 0.001). Spearman`s correlation between the OPA values and ChT measurements was significant and moderate (rho = 0.40, p = 0.005). The average increase of OPA and ChT measurements occurred 15 min before the IOP rise. There was a significant increase of OPA and ChT measurements followed by an IOP rise during the WDT. Increased choroidal volume due to hemodynamic forces may be enrolled in the mechanism of IOP elevation during this stress test.