The neuronal basis of attention: rate versus synchronization modulation

Extensive theoretical and experimental work on the neuronal correlates of visual attention raises two hypotheses about the underlying mechanisms. The first hypothesis, named biased competition, originates from experimental single-cell recordings that have shown that attention upmodulates the firing rates of the neurons encoding the attended features and downregulates the firing rates of the neurons encoding the unattended features. Furthermore, attentional modulation of firing rates increases along the visual pathway. The other, newer hypothesis assigns synchronization a crucial role in the attentional process. It stems from experiments that have shown that attention modulates gamma-frequency synchronization. In this paper, we study the coexistence of the two phenomena using a theoretical framework. We find that the two effects can vary independently of each other and across layers. Therefore, the two phenomena are not concomitant. However, we show that there is an advantage in the processing of information if rate modulation is accompanied by gamma modulation, namely that reaction times are shorter, implying behavioral relevance for gamma synchronization.

Measured and predicted resting metabolic rate in obese and nonobese adolescents.

OBJECTIVES: The validity of equations for the calculation of resting metabolic rate (RMR) were studied and new predictive equations were developed. STUDY DESIGN: The RMR was measured in a sample of 371 10- to 16-year-old prepubertal and postpubertal children. The study group included 193 male (116 nonobese and 77 obese) and 178 female (119 nonobese and 59 obese) subjects; for each group the RMRs predicted from five equations recommended for this age group were compared. The RMR was assessed by indirect calorimetry with a ventilated hood system for 45 minutes after an overnight fast. Body composition was estimated from skin-fold measurements. RESULTS: The mean +/- SD RMR was found to be 5600 +/- 972 kJ/24 hr and 7223 +/- 1220 kJ/24 hr in nonobese and obese boys, and 5112 +/- 632 kJ/24 hr and 6665 +/- 1106 kJ/24 hr in nonobese and obese girls, respectively. All five equations applicable to 10- to 16-year-old children overestimated RMR by 7.5% to 18.1% (p < 0.001 for each equation). Stepwise regression analysis, with independent variables such as age, weight, height, and gender, allowed development of new predictive equations for the calculation of RMR in 10- to 16-year-old boys (RMR = 50.9 Weight (kg) + 25.3 Height (cm) -50.3 Age (yr) + 26.9; R2 = 0.884, p < 0.0001) and girls (RMR = 51.2 Weight (kg) + 24.5 Height (cm) - 207.5 Age (yr) + 1629.8; R2 = 0.824, p < 0.0001). These predictive equations were tested in a second, independent cohort of children (80 male and 61 female subject) and were found to give a reliable estimate of RMR in 10- to 16-year-old obese and nonobese adolescents. CONCLUSIONS: The currently used predictive equations overestimate RMR in 10- to 16-year-old children. The use of the newly developed equations is recommended.

On high-rate full-diversity 2x2 space-time codes with low-complexity optimum detection

The 2×2 MIMO profiles included in Mobile WiMAX specifications are Alamouti’s space-time code (STC) fortransmit diversity and spatial multiplexing (SM). The former hasfull diversity and the latter has full rate, but neither of them hasboth of these desired features. An alternative 2×2 STC, which is both full rate and full diversity, is the Golden code. It is the best known 2×2 STC, but it has a high decoding complexity. Recently, the attention was turned to the decoder complexity, this issue wasincluded in the STC design criteria, and different STCs wereproposed. In this paper, we first present a full-rate full-diversity2×2 STC design leading to substantially lower complexity ofthe optimum detector compared to the Golden code with only a slight performance loss. We provide the general optimized form of this STC and show that this scheme achieves the diversitymultiplexing frontier for square QAM signal constellations. Then, we present a variant of the proposed STC, which provides a further decrease in the detection complexity with a rate reduction of 25% and show that this provides an interesting trade-off between the Alamouti scheme and SM.

Per-antenna rate and power control for MIMO layered architectures in the low- and high-power regimes

In a MIMO layered architecture, several codewordsare transmitted from a multiplicity of antennas. Although thespectral efficiency is maximized if the rates of these codewordsare separately controlled, the feedback rate within the linkadaptation loop is reduced if they are constrained to be identical.This poses a direct tradeoff between performance andfeedback overhead. This paper provides analytical expressionsthat quantify the difference in spectral efficiency between bothapproaches for arbitrary numbers of antennas. Specifically, thecharacterization takes place in the realm of the low- and highpowerregimes via expansions that are shown to have a widerange of validity.In addition, the possibility of adjusting the transmit powerof each codeword individually is considered as an alternative tothe separate control of their rates. Power allocation, however,turns out to be inferior to rate control within the context of thisproblem.

Capacity to within one bit of a class of Gaussian multicast channels with interference

This paper studies the fundamental operational limits of a class of Gaussian multicast channels with an interference setting. In particular, the paper considers two base stations multicasting separate messages to distinct sets of users. In the presence of channel state information at the transmitters and at the respective receivers, the capacity region of the Gaussian multicast channel with interference is characterized to within one bit. At the crux of this result is an extension to the multicast channel with interference of the Han-Kobayashi or the Chong-Motani-Garg achievable region for the interference channel.

A comparison of full-rate full-diversity 2x2 space-time codes for WiMAX systems

Multiple-input multiple-output (MIMO) techniques have become an essential part of broadband wireless communications systems. For example, the recently developed IEEE 802.16e specifications for broadband wireless access include three MIMOprofiles employing 2×2 space-time codes (STCs), and two of these MIMO schemes are mandatory on the downlink of Mobile WiMAX systems. One of these has full rate, and the other has full diversity, but neither of them has both of the desired features. The third profile, namely, Matrix C, which is not mandatory, is both a full rate and a full diversity code, but it has a high decoder complexity. Recently, the attention was turned to the decodercomplexity issue and including this in the design criteria, several full-rate STCs were proposed as alternatives to Matrix C. In this paper, we review these different alternatives and compare them to Matrix C in terms of performances and the correspondingreceiver complexities.

Rates of cultural change and patterns of cultural accumulation in stochastic models of social transmission.

Cultural variation in a population is affected by the rate of occurrence of cultural innovations, whether such innovations are preferred or eschewed, how they are transmitted between individuals in the population, and the size of the population. An innovation, such as a modification in an attribute of a handaxe, may be lost or may become a property of all handaxes, which we call "fixation of the innovation." Alternatively, several innovations may attain appreciable frequencies, in which case properties of the frequency distribution-for example, of handaxe measurements-is important. Here we apply the Moran model from the stochastic theory of population genetics to study the evolution of cultural innovations. We obtain the probability that an initially rare innovation becomes fixed, and the expected time this takes. When variation in cultural traits is due to recurrent innovation, copy error, and sampling from generation to generation, we describe properties of this variation, such as the level of heterogeneity expected in the population. For all of these, we determine the effect of the mode of social transmission: conformist, where there is a tendency for each naïve newborn to copy the most popular variant; pro-novelty bias, where the newborn prefers a specific variant if it exists among those it samples; one-to-many transmission, where the variant one individual carries is copied by all newborns while that individual remains alive. We compare our findings with those predicted by prevailing theories for rates of cultural change and the distribution of cultural variation.

Trophic specialization influences the rate of environmental niche evolution in damselfishes (Pomacentridae).

The rate of environmental niche evolution describes the capability of species to explore the available environmental space and is known to vary among species owing to lineage-specific factors. Trophic specialization is a main force driving species evolution and is responsible for classical examples of adaptive radiations in fishes. We investigate the effect of trophic specialization on the rate of environmental niche evolution in the damselfish, Pomacentridae, which is an important family of tropical reef fishes. First, phylogenetic niche conservatism is not detected in the family using a standard test of phylogenetic signal, and we demonstrate that the environmental niches of damselfishes that differ in trophic specialization are not equivalent while they still overlap at their mean values. Second, we estimate the relative rates of niche evolution on the phylogenetic tree and show the heterogeneity among rates of environmental niche evolution of the three trophic groups. We suggest that behavioural characteristics related to trophic specialization can constrain the evolution of the environmental niche and lead to conserved niches in specialist lineages. Our results show the extent of influence of several traits on the evolution of the environmental niche and shed new light on the evolution of damselfishes, which is a key lineage in current efforts to conserve biodiversity in coral reefs.

Deep sclerectomy combined with trabeculectomy in pediatric glaucoma

Résumé : Ce travail porte sur l'étude rétrospective d'une série de jeunes patients opérés de glaucomes pédiatriques. Le but est d'évaluer le résultat au long cours d'une intervention chirurgicale combinant une sclérectomie profonde et une trabéculectomie (sclérectomie profonde pénétrante). Durant la période de mars 1997 à octobre 2006, 28 patients on été suivis pour évaluer le résultat de cette chirurgie effectuées sur 35 yeux. Un examen ophtalmologique complet a été pratiqué avant la chirurgie, 1 et 7 jours, puis 1, 2, 3, 4, 6, 9, 12 mois, enfin tous les 6 mois après l'opération. Les critères d'évaluation du résultat postopératoire sont : les changements de pression intraoculaire, le traitement antiglaucomateux adjuvant, le taux de complication, le nombre de reprises chirurgicales,- l'erreur de réfraction, la meilleure acuité visuelle corrigée, l'état et le diamètre de la cornée. L'âge moyen est de 3.6 ± 4.5 ans et le suivi moyen de 3.6 ± 2.9 ans. La pression intraoculaire préopératoire de 31.9 ± 11.5 mmHg baisse de 58.3% (p<0.005) à la fin du suivi. Sur les 14 patients dont l'acuité visuelle a pu être mesurée, 8 (57.1 %) ont une acuité égale ou supérieure à 5/10e, 3 (21.4%) une acuité de 2/10e après intervention. Le taux de succès cumulatif complet à 9 ans est de 52.3%, le succès relatif 70.6%. Les complications menaçant la vision (8.6%) ont été plus fréquentes dans les cas de glaucome réfractaire. Pour conclure la sclérectomie profonde combinée à une trabéculectomie est une technique chirurgicale développée afin de contrôler la pression intraoculaire dans les cas de glaucomes congénitaux, juvéniles et secondaires. Les résultats intermédiaires sont encourageants et prometteurs. Les cas préalablement opérés avant cette nouvelle technique ont cependant un pronostic moins favorable. Le nombre de complications menaçant la vision est essentiellement lié à la sévérité du glaucome et au nombre d'interventions préalables. Abstract : Purpose : To evaluate the outcomes of combined deep sclerectomy and trabeculectomy (penetrating deep sclerectomy) in pediatric glaucoma. Design : Retrospective, non-consecutive, non-comparative, interventional case series. Participants : Children suffering from pediatric glaucoma who underwent surgery between March 1997 and October 2006 were included in this study. Methods : A primary combined deep sclerectomy and trabeculectomy was performed in 35 eyes of 28 patients. Complete examinations were performed before surgery, postoperatively at 1 and 7 days, at 1, 2, 3, 4, 6, 9, 12 months and then every 6 months after surgery. Main Outcome Measures : Surgical outcome was assessed in terms of intraocular pressure (IOP) change, additional glaucoma medication, complication rate, need for surgical revision, as well as refractive errors, best corrected visual acuity (BCVA), and corneal clarity and diameters. Results : The mean age before surgery was 3.6 ± 4.5 years, and the mean follow-up was 3.5 ± 2.9 years. The mean preoperative IOP was 31.9 ± 11.5 mmHg. At the end of follow-up, the mean IOP decreased by 58.3% (p<0.005), and from 14 patients with available BCVA 8 patients (57.1 %) achieved. 0.5 (20/40) or better, 3 (21.4%) 0.2 (20/100), and 2 (14.3%) 0.1 (20/200) in their better eye. The mean refractive error (spherical equivalent) at final follow-up visits was +0.83 ± 5.4. Six patients (43%) were affected by myopia. The complete and qualified success rates, based on a cumulative survival curve, after- 9 years were 52.3% and 70.6%, respectively (p<0.05). Sight threatening complications were more common (8.6%) in refractory glaucomas. Conclusions : Combined deep sclerectomy and trabeculectomy is a surgical technique developed to control IOP in congenital, secondary and juvenile glaucomas. The intermediate results are satisfactory and promising. Previous classic glaucoma surgeries performed before this new technique had less favourable results. The number of sight threatening complications is related to the severity of glaucoma and number of previous surgeries.

A lower fistula rate in hypospadias surgery.

OBJECTIVE: To determine whether specific steps taken after a critical quality control of our results in hypospadias surgery lead to a decrease in fistula rate. PATIENTS AND METHODS: Retrospective review of prospectively collected data. Between 1994 and 2001, our series of 85 tubularized plate urethroplasties (modified Duplay or Duplay-Snodgrass procedure) had a fistula rate of 25.9%. In 2001, we modified our approach by systematically padding the urethral suture with a layer of vascularized subcutaneous preputial tissue, as described by Snodgrass. Scrotal hypospadias were excluded. Surgical outcome was assessed at 1 and 12months. In both groups, all repairs were performed by or under direct supervision of the senior author (BJM). RESULTS: After 2001, 57 hypospadias repairs were performed in 57 patients aged 8months to 14years (median 1.4years). Fistula occurred in two cases, one of which closed spontaneously within 6months. Our fistula rate had dropped to 3.5%, with a minimum follow up of 12months. CONCLUSION: Covering the urethral suture with a padding flap of vascularized preputial tissue helps avoid fistula formation. Technique modification after critical appraisal of our own series led to a much better outcome in this demanding surgery.

Age over 40 years increases the failure rate of non-operative management of blunt splenic injuries

Objective: Non-operative management (NOM) of blunt splenic injuries (BSI) is nowadays considered the standard treatment. The study aimed to determine the criteria applied for NOM and to identify risk factors for its failure. Methods: Review of all adult patients with BSI treated at the University Hospital Bern, Switzerland, between 2000 and 2008. Results: There were 206 patients (146 men, 70·9%) with a mean age of 38·2 ± 19·1 years and an Injury Severity Score of 30·9 ± 11·6. The American Association for the Surgery of Trauma classification of the splenic injury was: grade I, n=43 (20·9%); grade II, n=52 (25·2%); grade III, n=60 (29·1%); grade IV, n=42 (20·4%) and grade V, n=9 (4·4%). 47 patients (22·8%) required immediate surgery. Five or more units of red cell transfusions (P<0·001), Glasgow Coma Scale<11 (P=0·009) and age ≥55 years (P=0·038) were associated with primary operative management (OM). 159 patients (77·2%) qualified for NOM, which was successful in 89·9% (143/159). The overall splenic salvage rate was 69·4% (143/206). Multivariate analysis found age ≥40 years to be the only factor independently related to the failure of NOM (P=0·001). Conclusion: Advanced age is associated with an increased failure rate ofNOM in patients with BSI.

The circadian rhythm of the perinatal mortality rate in Switzerland.

The authors examine the relation between the perinatal mortality rate (PMR), birth weight in four categories, and hour of birth throughout the week in Switzerland, using data on 672,013 births and 5,764 perinatal deaths recorded between 1979 and 1987. From Monday to Friday, the PMR follows a circadian rhythm with a regular increase from early morning to evening, with a peak for babies born between 7 and 8 p.m. This pattern of variation has two main components: The circadian rhythms for the proportion of births in the four weight categories and the PMR circadian rhythm for babies weighing more than 2.5 kg. According to a cosinor model, which describes about 40% of the total variation in the PMR, the most important determinants are changes in the proportions of births: Low birth weight increases toward the afternoon and night. Mechanisms underlying the weight-specific timing of birth are discussed, including time selection of birth according to obstetric risks, the direct effect of neonatal and obstetric care, and chronobiologic behavior.

Imaging for clarification of accusation of treatment error

In the assessment of medical malpractice imaging methods can be used for the documentation of crucial morphological findings which are indicative for or against an iatrogenically caused injury. The clarification of deaths in this context can be usefully supported by postmortem imaging (primarily native computed tomography, angiography, magnetic resonance imaging). Postmortem imaging offers significant additional information compared to an autopsy in the detection of iatrogenic air embolisms and documentation of misplaced medical aids before dissection with an inherent danger of relocation. Additional information is supplied by postmortem imaging in the search for sources of bleeding as well as the documentation of perfusion after cardiovascular surgery. Key criteria for the decision to perform postmortem imaging can be obtained from the necessary preliminary inspection of clinical documentation.

Breeding rate is associated with pheomelanism in male and with eumelanism in female barn owls

Melanin-based coloration exists in 2 types: black eumelanism and reddish-brown pheomelanism, which both have a strong heritable component. To test whether these 2 types of melanism are associated with alternative adaptations, we carried out a correlative study over 8 years and an experiment in a Swiss population of barn owls, Tyto alba. This species varies in coloration from reddish-brown to white and from lightly to heavily marked with black spots. Based on the fact that plumage coloration and spottiness are male- and female-specific secondary sexual characters, respectively, we examined whether the probability of breeding is associated with the degree of pheomelanism in males and of eumelanism in females. In males, recruited nestlings were significantly less reddish-brown than their nonrecruited nest mates. In females, individuals displaying larger black spots started to breed at a younger age and had a higher survival, and females with experimentally reduced plumage spottiness bred less often than control females. Therefore, in the barn owl, the degree of male pheomelanism is associated with the probability of being recruited in the local population, whereas the degree of female eumelanism correlates with age at sexual maturity, survival probability, and also the probability of skipping reproduction.

Concepts and Rationale for Regional Nitrogen Rate Guidelines for Corn, April 2006

Nitrogen (N) is typically one of the largest corn fertilization expenses. Nitrogen application is critical because it signifi cantly improves corn yield in many crop rotations. When choosing N rates, producers need to carefully consider both achieving most profi table economic return and advancing environmental stewardship. In 2004, university agronomists from the Corn Belt states began discussions regarding N rate use for corn production. The reasons for the discussions centered on apparent differences in methods for determining N rates across states, misperceptions regarding N rate guidelines, and concerns about application rates as corn yields have climbed to historic levels. An outcome of those discussions was an effort with the objectives to: ▪ develop N rate guidelines that could be applicable on a regional basis and ▪ identify the most profi table fertilizer N rates for corn production across the Corn Belt. This publication provides an overview of corn N fertilization in regard to rate of application, investigates concepts for determining economic application rates, and describes a suggested regional approach for developing corn N rate guidelines directly from recent research data.