Temporal properties of responses to broadband noise in the auditory nerve

Temporal information in the responses of auditory neurons to sustained sounds has been studied mostly with periodic stimuli, using measures that are based on Fourier analysis. Less information is available on temporal aspects of responses to nonperiodic wideband sounds. We recorded responses to a reference Gaussian noise and its polarity-inverted version in the auditory nerve of barbiturate-anesthetized cats and used shuffled autocorrelograms (SACs) to quantify spike timing. Two metrics were extracted from the central peak of autocorrelograms: the peak-height and the width at halfheight. Temporal information related to stimulus fine-structure was isolated from that to envelope by subtracting or adding responses to the reference and inverted noise. Peak-height and halfwidth generally behaved as expected from the existing body of data on phase-locking to pure tones and sinusoidally amplitude-modulated tones but showed some surprises as well. Compared with synchronization to low-frequency tones, SACs reveal large differences in temporal behavior between the different classes of nerve fibers (based on spontaneous rate) as well as a strong dependence on characteristic frequency (CF) throughout the phase-locking range. SACs also reveal a larger temporal consistency (i.e., tendency to discharge at the same point in time on repeated presentation of the same stimulus) in the responses to the stochastic noise stimulus than in the responses to periodic tones. Responses at high CFs reflect envelope phase-locking and are consistent with previous reports using sinusoidal AM. We conclude that the combined use of broadband noise and SAC analysis allow a more general characterization of temporal behavior than periodic stimuli and Fourier analysis.     

Neural processing of amplitude-modulated sounds

Amplitude modulation (AM) is a temporal feature of most natural acoustic signals. A long psychophysical tradition has shown that AM is important in a variety of perceptual tasks, over a range of time scales. Technical possibilities in stimulus synthesis have reinvigorated this field and brought the modulation dimension back into focus. We address the question whether specialized neural mechanisms exist to extract AM information, and thus whether consideration of the modulation domain is essential in understanding the neural architecture of the auditory system. The available evidence suggests that this is the case. Peripheral neural structures not only transmit envelope information in the form of neural activity synchronized to the modulation waveform but are often tuned so that they only respond over a limited range of modulation frequencies. Ascending the auditory neuraxis, AM tuning persists but increasingly takes the form of tuning in average firing rate, rather than synchronization, to modulation frequency. There is a decrease in the highest modulation frequencies that influence the neural response, either in average rate or synchronization, as one records at higher and higher levels along the neuraxis. In parallel, there is an increasing tolerance of modulation tuning for other stimulus parameters such as sound pressure level, modulation depth, and type of carrier. At several anatomical levels, consideration of modulation response properties assists the prediction of neural responses to complex natural stimuli. Finally, some evidence exists for a topographic ordering of neurons according to modulation tuning. The picture that emerges is that temporal modulations are a critical stimulus attribute that assists us in the detection, discrimination, identification, parsing, and localization of acoustic sources and that this wide-ranging role is reflected in dedicated physiological properties at different anatomical levels.     

Oocyte and embryo quality as well as pregnancy rate in intracytoplasmic sperm injection are not affected by high follicular phase serum progesterone

The effect of elevated serum progesterone concentrations (>1ng/1) on or before the day of human chorionic gonadotrophin(HCG) injection on the outcome of women receiving gonadotrophin-releasinghormone analogue (GnRHa)/ human menopausal gonadotrophin (HMG)for ovarian stimulation prior to intracytoplasmic sperm injection(ICSI) was evaluated. A total of 1275 ICSI cycles were analysedretrospectively. In 53 cycles (4.5%), serum progesterone concentrationswere > 1 ng/ml. Patients in the high progesterone group hadsignificantly higher oestradiol and luteinizing hormone concentrationson the day of HCG injection. The characteristics of the cumulus-coronacell complexes and the nuclear maturity of the oocytes weresimilar in the groups of patients with high and low serum progesteronelevels. Fertilization and cleavage rates as well as embryo qualitywere not different in the two groups. No difference in implantationor clinical pregnancy rates was observed between the high progesteroneand low progesterone groups. Moreover, the cumulative exposureto progesterone during the follicular phase, as expressed bythe area under the curve (AUC), and the duration of exposureto high serum progesterone levels (>1 ng/ml) were not significantlydifferent between pregnant and non-pregnant women in the highprogesterone group. We conclude that in ICSI cycles pretreatedwith GnRHa, increased serum progesterone concentrations on orbefore the day of HCG injection do not affect ICSI outcome.     

A Novel Iterative Penalty Method to Enforce Boundary Conditions in Finite Volume POD-Galerkin Reduced Order Models for Fluid Dynamics Problems

A Finite-Volume based POD-Galerkin reduced order model is developed for fluid dynamics problems where the (time-dependent) boundary conditions are controlled using two different boundary control strategies: the lifting function method, whose aim is to obtain homogeneous basis functions for the reduced basis space and the penalty method where the boundary conditions are enforced in the reduced order model using a penalty factor. The penalty method is improved by using an iterative solver for the determination of the penalty factor rather than tuning the factor with a sensitivity analysis or numerical experimentation.The boundary control methods are compared and tested for two cases: the classical lid driven cavity benchmark problem and a Y-junction flow case with two inlet channels and one outlet channel. The results show that the boundaries of the reduced order model can be controlled with the boundary control methods and the same order of accuracy is achieved for the velocity and pressure fields. Finally, the reduced order models are 270-308 times faster than the full order models for the lid driven cavity test case and 13-24 times for the Y-junction test case.     

Intracytoplasmic sperm injection in the mouse

Intracytoplasmic sperm injection (ICSI) into mouse oocytes involvesa very low survival rate. This study was designed to determinewhy ICSI frequently fails in mice. Metaphase II oocytes wereobtained from superovulated 4–6 week old F₁ hybrid mice.Spermatozoa were retrieved from the epididymis of 12–14week old F₁ hybrid mice. The spiked microinjection pipette usedto inject a spermatozoon into the ooplasm had outer and innerdiameters of 10 and 8 µm respectively. The oocytes usedin the first part of the study were not activated (group 1).Some oocytes were incubated with calcium ionophore for 5 min(group 2). The injected oocytes were evaluated 6, 20, 48 and72 h after injection. A total of 143 eggs in each group underwentICSI. In group 1, sperm heads escaped into the perivitellinespace. In all, 63 (47%) of the remaining oocytes were damagedduring the injection or had degenerated by the first evaluation.The survival rate was 53%, but fertilization did not occur.In group 2, 31 oocytes (22%) were damaged during microinjectionor soon degenerated. Two oocytes underwent accidental subzonalinsemination. Six oocytes were fertilized (4.2%) among the 78%of survivors. After injection, the sperm tail was found in thecytoplasm (27 and 31% in groups 1 and 2 respectively), the perivitellinespace (45% in both groups) or protruding through the zona pellucida(28 and 23% respectively). More oocytes degenerated when thetail remained in the cytoplasm, i.e. 78% in group 1 and 36%in group 2.     

Quantitative nephelometric assay for determining myoglobin evaluated

A recently introduced automated nephelometric immunoassay involving shell/core particles for determination of myoglobin (Behringwerke) was evaluated with the BNA Nephelometer. Method precision was good: the intra-assay CV varied between 1.5% and 6.1%; with daily calibration, the interassay CV ranged between 1.5% and 7.5%. For usual sample dilutions, the assay response varied linearly with myoglobin concentrations up to 23.1 nmol/L. After automatic dilution by the instrument, concentrations up to 2310 nmol/L could be measured without high-dose "hook" effect. Further manual dilution allowed measurement of myoglobin concentrations up to 26,000 nmol/L. Calibration was stable for at least seven days. We detected no significant interferences from hemoglobin, haptoglobin, bilirubin, iodine-containing contrast media, and rheumatoid factors. Treating lipemic samples with Lipoclean (Behringwerke) decreased test results. Simultaneously drawn serum and plasma samples from the same subject showed no consistent differences in myoglobin concentrations. The mean reference myoglobin concentration was 1.380 (SD 0.82) nmol/L for men and 0.878 (SD 0.45) nmol/L for women. In patients with renal insufficiency, serum creatinine values were moderately related to serum myoglobin values (r = 0.465). Although a commercial radioimmunoassay (Byk-Sangtec) and the nephelometric assay intercorrelated well (r = 0.929), values obtained by nephelometry were significantly lower (P less than 0.05). By both assays, results for heart and skeletal muscle tissue extracts showed no correlation, a finding that suggests the existence of multiple forms of myoglobin in human tissues. We conclude that immunonephelometry is a rapid, practical, and reliable method for measuring myoglobin in serum.     

Hypnosedation, a new method of anesthesia for cervical endocrine surgery. Prospective randomized study

Retrospective studies have confirmed the feasibility and safety of thyroid and parathyroid procedures performed under hypnoanesthesia (hypnosis, local anesthesia and minimal conscious sedation) as sole method of anesthesia. This very effective technique seems to provide physiological, psychological and economic benefits for the patient. STUDY AIM: To assess, by means of a prospective randomized study, the advantages of hypnosedation as an alternative to general anesthesia in terms of clinical and laboratory parameters. PATIENTS AND METHODS: Twenty patients operated under hypnoanesthesia were compared to 20 patients operated under conventional anesthesia. The two groups were compared in terms of inflammatory, neuroendocrine, hemodynamic and immunologic parameters and postoperative course (pain, fatigue, muscle strength and stress). RESULTS: No clinical or demographic differences were observed between the two groups. Operative times, bleeding, weight of specimens, and surgical comfort were similar. Significant differences in terms of inflammatory response and hemodynamic parameters were observed in favor of hypnoanesthesia. Neuroendocrine and immunological parameters were similar. Patients of the hypnoanesthesia group had significantly less postoperative pain. Postoperative fatigue syndrome and convalescence were significantly improved in these patients. CONCLUSION: This study confirms that, in our hands, hypnosedation presents real advantages over general anesthesia, in patients undergoing thyroid surgery.