The brainstem reticular formation is a small-world, not scale-free, network

Recently, it has been demonstrated that several complex systems may have simple graph-theoretic characterizations as so-called ‘small-world’ and ‘scale-free’ networks. These networks have also been applied to the gross neural connectivity between primate cortical areas and the nervous system of Caenorhabditis elegans. Here, we extend this work to a specific neural circuit of the vertebrate brain—the medial reticular formation (RF) of the brainstem—and, in doing so, we have made three key contributions. First, this work constitutes the first model (and quantitative review) of this important brain structure for over three decades. Second, we have developed the first graph-theoretic analysis of vertebrate brain connectivity at the neural network level. Third, we propose simple metrics to quantitatively assess the extent to which the networks studied are small-world or scale-free. We conclude that the medial RF is configured to create small-world (implying coherent rapid-processing capabilities), but not scale-free, type networks under assumptions which are amenable to quantitative measurement

The Initial Mass Function in the Nearest Strong Lenses from SNELLS: Assessing the Consistency of Lensing, Dynamical, and Spectroscopic Constraints

We present new observations of the three nearest early-type galaxy (ETG) strong lenses discovered in the SINFONI Nearby Elliptical Lens Locator Survey (SNELLS). Based on their lensing masses, these ETGs were inferred to have a stellar initial mass function (IMF) consistent with that of the Milky Way, not the bottom-heavy IMF that has been reported as typical for high-σ ETGs based on lensing, dynamical, and stellar population synthesis techniques. We use these unique systems to test the consistency of IMF estimates derived from different methods. We first estimate the stellar M */L using lensing and stellar dynamics. We then fit high-quality optical spectra of the lenses using an updated version of the stellar population synthesis models developed by Conroy & van Dokkum. When examined individually, we find good agreement among these methods for one galaxy. The other two galaxies show 2–3σ tension with lensing estimates, depending on the dark matter contribution, when considering IMFs that extend to 0.08 M ⊙. Allowing a variable low-mass cutoff or a nonparametric form of the IMF reduces the tension among the IMF estimates to <2σ. There is moderate evidence for a reduced number of low-mass stars in the SNELLS spectra, but no such evidence in a composite spectrum of matched-σ ETGs drawn from the SDSS. Such variation in the form of the IMF at low stellar masses (m lesssim 0.3 M ⊙), if present, could reconcile lensing/dynamical and spectroscopic IMF estimates for the SNELLS lenses and account for their lighter M */L relative to the mean matched-σ ETG. We provide the spectra used in this study to facilitate future comparisons

The association of osteoarthritis risk factors with localized, regional and diffuse knee pain

SummaryObjectiveTo identify determinants of different patterns of knee pain with a focus on risk factors for knee osteoarthritis (OA).DesignThe Knee Pain Map is an interviewer-administered assessment that asks subjects to characterize their knee pain as localized, regional, or diffuse. A total of 2677 participants from the Osteoarthritis Initiative were studied.We used multinomial logistic regression to examine the relationship between risk factors for OA and knee pain patterns. We examined the bivariate and multivariate relationships of knee pain pattern with age, body mass index (BMI), sex, race, family history of total joint replacement, knee injury, knee surgery, and hand OA.ResultsWe compared 2462 knees with pain to 1805 knees without pain. In the bivariate analysis, age, sex, BMI, injury, surgery, and hand OA were associated with at least one pain pattern. In the multivariate model, all of these variables remained significantly associated with at least one pattern. When compared to knees without pain, higher BMI, injury, and surgery were associated with all patterns. BMI had its strongest association with diffuse pain. Older age was less likely to be associated with localized pain while female sex was associated with regional pain.ConclusionsWe have shown that specific OA risk factors are associated with different knee pain patterns. Better understanding of the relationship between OA risk factors and knee pain patterns may help to characterize the heterogeneous subsets of knee OA

The relationship between mitochondrial function and walking performance in older adults with a wide range of physical function.

Age related declines in walking performance may be partly attributable to skeletal muscle mitochondrial dysfunction as mitochondria produce over 90% of ATP needed for movement and the capacity for oxidative phosphorylation decreases with age. Participants were from two studies: an ancillary to the Lifestyle Interventions and Independence for Elders (LIFE) Study (n=33), which recruited lower functioning participants (Short Physical Performance Battery [SPPB], 7.8±1.2), and the Study of Energy and Aging-Pilot (SEA, n=29), which enrolled higher functioning (SPPB, 10.8±1.4). Physical activity was measured objectively using the Actigraph accelerometer (LIFE) and SenseWear Pro armband (SEA). Phosphocreatine recovery following muscle contraction of the quadriceps was measured using (31)P magnetic resonance spectroscopy and ATPmax (mM ATP/s) was calculated. Walking performance was defined as time (s) to walk 400m at a usual-pace. The cross-sectional association between mitochondrial function and walking performance was assessed using multivariable linear regression. Participants were 77.6±5.3years, 64.2% female and 67.2% white. ATPmax was similar in LIFE vs. SEA (0.52±0.14 vs. 0.55±0.14, p=0.31), despite different function and activity levels (1.6±2.2 vs.77.4±73.3min of moderate activity/day, p&lt;0.01). Higher ATPmax was related to faster walk-time in SEA (r(2)=0.19, p=0.02,); but not the LIFE (r(2)&lt;0.01, p=0.74) cohort. Mitochondrial function was associated with walking performance in higher functioning, active older adults, but not lower functioning, sedentary older adults

Relationship of ankle blood pressures to cardiovascular events in older adults.

BACKGROUND AND PURPOSE - Low values of ankle-arm systolic blood pressure ratio predict mortality and cardiovascular events. High values, associated with arterial calcification, also carry risk for mortality. We focus on the extent to which low and high ankle-arm index values as well as noncompressible arteries are associated with mortality and cardiovascular events, including stroke in older adults. METHODS - We followed 2886 adults aged 70 to 79 for a mean of 6.7 years for vital status and cardiovascular events (coronary heart disease, stroke, and congestive heart failure). RESULTS - Normal ankle-arm index values of 0.91 to 1.3 were found in 80%, low values of ≤0.9 were found in 13%, high values of >1.3 were obtained in 5%, and noncompressible arteries were found in 2% of the group. Increased mortality was associated with both low and high ankle-arm index values beginning at levels of <1.0 or ≥1.4. Subjects with low ankle-arm index values or noncompressible arteries had significantly higher event rates than those with normal ankle blood pressures for all end points. For coronary heart disease, hazard ratios associated with a low ankle-arm index, high ankle-arm index, and noncompressible arteries were 1.4, 1.5, and 1.7 (P<0.05 for all) after controlling for age, gender, race, prevalent cardiovascular disease, diabetes, and major cardiovascular risk factors. Noncompressible arteries carried a particularly high risk of stroke and congestive heart failure (hazard ratio=2.1 and 2.4, respectively). CONCLUSIONS - Among older adults, low and high ankle-arm index values carry elevated risk for cardiovascular events. Noncompressible leg arteries carry elevated risk for stroke and congestive heart failure specifically. © 2008 American Heart Association, Inc

Randomly dilute Ising model: A nonperturbative approach

The N-vector cubic model relevant, among others, to the physics of the randomly dilute Ising model is analyzed in arbitrary dimension by means of an exact renormalization-group equation. This study provides a unified picture of its critical physics between two and four dimensions. We give the critical exponents for the three-dimensional randomly dilute Ising model which are in good agreement with experimental and numerical data. The relevance of the cubic anisotropy in the O(N) model is also treated.Comment: 4 pages, published versio

Glassiness and constrained dynamics of a short-range non-disordered spin model

We study the low temperature dynamics of a two dimensional short-range spin system with uniform ferromagnetic interactions, which displays glassiness at low temperatures despite the absence of disorder or frustration. The model has a dual description in terms of free defects subject to dynamical constraints, and is an explicit realization of the ``hierarchically constrained dynamics'' scenario for glassy systems. We give a number of exact results for the statics of the model, and study in detail the dynamical behaviour of one-time and two-time quantities. We also consider the role played by the configurational entropy, which can be computed exactly, in the relation between fluctuations and response.Comment: 10 pages, 9 figures; minor changes, references adde

A multistate model of health transitions in older people: a secondary analysis of ASPREE clinical trial data

Background: Understanding the nature of transitions from a healthy state to chronic diseases and death is important for planning health-care system requirements and interventions. We aimed to quantify the trajectories of disease and disability in a population of healthy older people. Methods: We conducted a secondary analysis of data from the ASPREE trial, which was done in 50 sites in Australia and the USA and recruited community-dwelling, healthy individuals who were aged 70 years or older (≥65 years for Black and Hispanic people in the USA) between March 10, 2010, and Dec 24, 2014. Participants were followed up with annual face-to-face visits, biennial assessments of cognitive function, and biannual visits for physical function until death or June 12, 2017, whichever occurred first. We used multistate models to examine transitions from a healthy state to first intermediate disease events (ie, cancer events, stroke events, cardiac events, and physical disability or dementia) and, ultimately, to death. We also examined the effects of age and sex on transition rates using Cox proportional hazards regression models. Findings: 19 114 participants with a median age of 74·0 years (IQR 71·6–77·7) were included in our analyses. During a median follow-up of 4·7 years (IQR 3·6–5·7), 1933 (10·1%) of 19 114 participants had an incident cancer event, 487 (2·5%) had an incident cardiac event, 398 (2·1%) had an incident stroke event, 924 (4·8%) developed persistent physical disability or dementia, and 1052 (5·5%) died. 15 398 (80·6%) individuals did not have any of these events during follow-up. The highest proportion of deaths followed incident cancer (501 [47·6%] of 1052) and 129 (12·3%) participants transitioned from disability or dementia to death. Among 12 postulated transitions, transitions from the intermediate states to death had much higher rates than transitions from a healthy state to death. The progression rates to death were 158 events per 1000 person-years (95% CI 144–172) from cancer, 112 events per 1000 person-years (86–145) from stroke, 88 events per 1000 person-years (68–111) from cardiac disease, 69 events per 1000 person-years (58–82) from disability or dementia, and four events per 1000 person-years (4–5) from a healthy state. Age was significantly associated with an accelerated rate for most transitions. Male sex (vs female sex) was significantly associated with an accelerate rate for five of 12 transitions. Interpretation: We describe a multistate model in a healthy older population in whom the most common transition was from a healthy state to cancer. Our findings provide unique insights into the frequency of events, their transition rates, and the impact of age and sex. These results have implications for preventive health interventions and planning for appropriate levels of residential care in healthy ageing populations. Funding: The National Institutes of Health