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There are 29 new articles in PLoS ONE today. As always, you should rate the articles, post notes and comments and send trackbacks when you blog about the papers. You can now also easily place articles on various social services (CiteULike, Mendeley, Connotea, Stumbleupon, Facebook and Digg) with just one click. Here are my own picks for the week – you go and look for your own favourites:
The Apollo Number: Space Suits, Self-Support, and the Walk-Run Transition:

How space suits affect the preferred walk-run transition is an open question with relevance to human biomechanics and planetary extravehicular activity. Walking and running energetics differ; in reduced gravity (<0.5 g), running, unlike on Earth, uses less energy per distance than walking. The walk-run transition (denoted *) correlates with the Froude Number (Fr = v2/gL, velocity v, gravitational acceleration g, leg length L). Human unsuited Fr* is relatively constant (~0.5) with gravity but increases substantially with decreasing gravity below ~0.4 g, rising to 0.9 in 1/6 g; space suits appear to lower Fr*. Because of pressure forces, space suits partially (1 g) or completely (lunar-g) support their own weight. We define the Apollo Number (Ap = Fr/M) as an expected invariant of locomotion under manipulations of M, the ratio of human-supported to total transported mass. We hypothesize that for lunar suited conditions Ap* but not Fr* will be near 0.9, because the Apollo Number captures the effect of space suit self-support. We used the Apollo Lunar Surface Journal and other sources to identify 38 gait events during lunar exploration for which we could determine gait type (walk/lope/run) and calculate Ap. We estimated the binary transition between walk/lope (0) and run (1), yielding Fr* (0.36±0.11, mean±95% CI) and Ap* (0.68±0.20). The Apollo Number explains 60% of the difference between suited and unsuited Fr*, appears to capture in large part the effects of space suits on the walk-run transition, and provides several testable predictions for space suit locomotion and, of increasing relevance here on Earth, exoskeleton locomotion. The knowledge of how space suits affect gait transitions can be used to optimize space suits for use on the Moon and Mars.

Ants, Cataglyphis cursor, Use Precisely Directed Rescue Behavior to Free Entrapped Relatives:

Although helping behavior is ubiquitous throughout the animal kingdom, actual rescue activity is particularly rare. Nonetheless, here we report the first experimental evidence that ants, Cataglyphis cursor, use precisely directed rescue behavior to free entrapped victims; equally important, they carefully discriminate between individuals in distress, offering aid only to nestmates. Our experiments simulate a natural situation, which we often observed in the field when collecting Catagyphis ants, causing sand to collapse in the process. Using a novel experimental technique that binds victims experimentally, we observed the behavior of separate, randomly chosen groups of 5 C. cursor nestmates under one of six conditions. In five of these conditions, a test stimulus (the “victim”) was ensnared with nylon thread and held partially beneath the sand. The test stimulus was either (1) an individual from the same colony; (2) an individual from a different colony of C cursor; (3) an ant from a different ant species; (4) a common prey item; or, (5) a motionless (chilled) nestmate. In the final condition, the test stimulus (6) consisted of the empty snare apparatus. Our results demonstrate that ants are able to recognize what, exactly, holds their relative in place and direct their behavior to that object, the snare, in particular. They begin by excavating sand, which exposes the nylon snare, transporting sand away from it, and then biting at the snare itself. Snare biting, a behavior never before reported in the literature, demonstrates that rescue behavior is far more sophisticated, exact and complexly organized than the simple forms of helping behavior already known, namely limb pulling and sand digging. That is, limb pulling and sand digging could be released directly by a chemical call for help and thus result from a very simple mechanism. However, it’s difficult to see how this same releasing mechanism could guide rescuers to the precise location of the nylon thread, and enable them to target their bites to the thread itself.

Illusionary Self-Motion Perception in Zebrafish:

Zebrafish mutant belladonna (bel) carries a mutation in the lhx2 gene (encoding a Lim domain homeobox transcription factor) that results in a defect in retinotectal axon pathfinding, which can lead to uncrossed optic nerves failing to form an optic chiasm. Here, we report on a novel swimming behavior of the bel mutants, best described as looping. Together with two previously reported oculomotor instabilities that have been related to achiasmatic bel mutants, reversed optokinetic response (OKR) and congenital nystagmus (CN, involuntary conjugate oscillations of both eyes), looping opens a door to study the influence of visual input and eye movements on postural balance. Our result shows that looping correlates perfectly with reversed OKR and CN and is vision-dependent and contrast sensitive. CN precedes looping and the direction of the CN slow phase is predictive of the looping direction, but is absent during looping. Therefore, looping may be triggered by CN in bel. Moreover, looping in wild-type fish can also be evoked by whole-field motion, suggesting that looping in a bel mutant larvae is a result of self-motion perception. In contrary to previous hypotheses, our findings indicate that postural control in vertebrates relies on both direct visual input (afference signal) and eye-movement-related signals (efference copy or reafference signal).

Neural Correlates of Appetite and Hunger-Related Evaluative Judgments:

How much we desire a meal depends on both the constituent foods and how hungry we are, though not every meal becomes more desirable with increasing hunger. The brain therefore needs to be able to integrate hunger and meal properties to compute the correct incentive value of a meal. The present study investigated the functional role of the amygdala and the orbitofrontal cortex in mediating hunger and dish attractiveness. Furthermore, it explored neural responses to dish descriptions particularly susceptible to value-increase following fasting. We instructed participants to rate how much they wanted food menu items while they were either hungry or sated, and compared the rating differences in these states. Our results point to the representation of food value in the amygdala, and to an integration of attractiveness with hunger level in the orbitofrontal cortex. Dishes particularly desirable during hunger activated the thalamus and the insula. Our results specify the functions of evaluative structures in the context of food attractiveness, and point to a complex neural representation of dish qualities which contribute to state-dependent value.

Do Genetic Diversity Effects Drive the Benefits Associated with Multiple Mating? A Test in a Marine Invertebrate:

Mothers that mate with multiple males often produce higher quality offspring than mothers that mate with a single male. By engaging in polyandry, mothers may increase their chances of mating with a compatible male or promote sperm competition – both of which act to increase maternal fitness via the biasing of the paternity of offspring. Surprisingly, mating with multiple males, can carry benefits without biasing paternity and may be due simply to differences in genetic diversity between monandrous and polyandrous clutches but role of genetic diversity effects in driving the benefits of polyandry remains poorly tested. Disentangling indirect, genetic benefits from genetic diversity effects is challenging but crucial if we are to understand the selection pressures acting to promote polyandry. Here, we examine the post-fertilisation benefits of accessing the sperm of multiple males in an externally fertilising polychaete worm. Accessing the sperm of multiple males increases offspring performance but this benefit was driven entirely by genetic diversity effects and not by the biasing of paternity at fertilisation. Previous studies on polyandry should be interpreted cautiously as genetic diversity effects alone can explain the benefits of polyandry yet these diversity effects may be difficult to disentangle from other mechanisms. We suggest that future studies use a modified experimental design in order to discriminate between genetic diversity effects and indirect, genetic benefits.

Brain Potentials of Conflict and Error-Likelihood Following Errorful and Errorless Learning in Obsessive-Compulsive Disorder:

The anterior cingulate cortex (ACC) is thought to be overacting in patients with Obsessive Compulsive Disorder (OCD) reflecting an enhanced action monitoring system. However, influences of conflict and error-likelihood have not been explored. Here, the error-related negativity (ERN) originating in ACC served as a measure of conflict and error-likelihood during memory recognition following different learning modes. Errorless learning prevents the generation of false memory candidates and has been shown to be superior to trial-and-error-learning. The latter, errorful learning, introduces false memory candidates which interfere with correct information in later recognition leading to enhanced conflict processing. Sixteen OCD patients according to DSM-IV criteria and 16 closely matched healthy controls participated voluntarily in the event-related potential study. Both, OCD- and control group showed enhanced memory performance following errorless compared to errorful learning. Nevertheless, response-locked data showed clear modulations of the ERN amplitude. OCD patients compared to controls showed an increased error-likelihood effect after errorless learning. However, with increased conflict after errorful learning, OCD patients showed a reduced error-likelihood effect in contrast to controls who showed an increase. The increase of the errorlikelihood effect for OCD patients within low conflict situations (recognition after errorless learning) might be conceptualized as a hyperactive monitoring system. However, within high conflict situations (recognition after EF-learning) the opposite effect was observed: whereas the control group showed an increased error-likelihood effect, the OCD group showed a reduction of the error-likelihood effect based on altered ACC learning rates in response to errors. These findings support theoretical frameworks explaining differences in ACC activity on the basis of conflict and perceived error-likelihood as influenced by individual error learning rate.

The Genome Response to Artificial Selection: A Case Study in Dairy Cattle:

Dairy cattle breeds have been subjected over the last fifty years to intense artificial selection towards improvement of milk production traits. In this study, we performed a whole genome scan for differentiation using 42,486 SNPs in the three major French dairy cattle breeds (Holstein, Normande and Montbéliarde) to identify the main physiological pathways and regions which were affected by this selection. After analyzing the population structure, we estimated FST within and across the three breeds for each SNP under a pure drift model. We further considered two different strategies to evaluate the effect of selection at the genome level. First, smoothing FST values over each chromosome with a local variable bandwidth kernel estimator allowed identifying 13 highly significant regions subjected to strong and/or recent positive selection. Some of them contained genes within which causal variants with strong effect on milk production traits (GHR) or coloration (MC1R) have already been reported. To go further in the interpretation of the observed signatures of selection we subsequently concentrated on the annotation of differentiated genes defined according to the FST value of SNPs localized close or within them. To that end we performed a comprehensive network analysis which suggested a central role of somatotropic and gonadotropic axes in the response to selection. Altogether, these observations shed light on the antagonism, at the genome level, between milk production and reproduction traits in highly producing dairy cows.

Let’s see what’s new in PLoS ONE, PLoS Biology, PLoS Medicine and PLoS Neglected Tropical Diseases today. As always, you should rate the articles, post notes and comments and send trackbacks when you blog about the papers. You can now also easily place articles on various social services (CiteULike, Mendeley, Connotea, Stumbleupon, Facebook and Digg) with just one click. Here are my own picks for the week – you go and look for your own favourites:
Long-Term Functional Side-Effects of Stimulants and Sedatives in Drosophila melanogaster:

Small invertebrate animals, such as nematodes and fruit flies, are increasingly being used to test candidate drugs both for specific therapeutic purposes and for long-term health effects. Some of the protocols used in these experiments feature such experimental design features as lifelong virginity and very low densities. By contrast, the ability of both fruit flies and nematodes to resist stress is frequently correlated with their longevity and other functional measures, suggesting that low-stress assays are not necessarily the only useful protocol for testing the long-term effects of drugs. Here we report an alternative protocol for fruit fly drug-testing that maximizes reproductive opportunities and other types of interaction, with moderately high population densities. We validate this protocol using two types of experimental tests: 1. We show that this protocol detects previously well-established genetic differences between outbred fruit fly populations. 2. We show that this protocol is able to distinguish among the long-term effects of similar types of drugs within two broad categories, stimulants and tranquilizers. Large-scale fly drug testing can be conducted using mixed-sex high-density cage assays. We find that the commonly-used stimulants caffeine and theobromine differ dramatically in their chronic functional effects, theobromine being more benign. Likewise, we find that two generic pharmaceutical tranquilizers, lithium carbonate and valproic acid, differ dramatically in their chronic effects, lithium being more benign. However, these findings do not necessarily apply to human subjects, and we thus do not recommend the use of any one substance over any other.

Distinct Parietal and Temporal Pathways to the Homologues of Broca’s Area in the Monkey:

Two distinct cortical areas in the frontal lobe of the human brain, known as Broca’s region, are involved with language production. This region has also been shown to exist in nonhuman primates. In this study, we explored the precise neural connectivity of Broca’s region in macaque monkeys using the autoradiographic method to achieve a level of detail impossible in the human brain. We identified two major streams of connections feeding into Broca’s area: a ventral stream from the temporal region, which includes areas processing auditory, multisensory, and visual information and a dorsal stream originating from the inferior parietal lobule and the adjacent superior temporal sulcus. Our detailed connectivity analysis illuminates the pathways via which posterior cortical areas can interact functionally with Broca’s region, in addition to contributing to an understanding of the evolution of language. We suggest that a fundamental function of Broca’s region is to retrieve information in a controlled strategic way from posterior cortical regions and to translate this information into action. This fundamental function was adapted during evolution of the left hemisphere of the human brain to serve language.

Motor Properties of Peripersonal Space in Humans:

A stimulus approaching the body requires fast processing and appropriate motor reactions. In monkeys, fronto-parietal networks are involved both in integrating multisensory information within a limited space surrounding the body (i.e. peripersonal space, PPS) and in action planning and execution, suggesting an overlap between sensory representations of space and motor representations of action. In the present study we investigate whether these overlapping representations also exist in the human brain. We recorded from hand muscles motor-evoked potentials (MEPs) induced by single-pulse of transcranial magnetic stimulation (TMS) after presenting an auditory stimulus either near the hand or in far space. MEPs recorded 50 ms after the near-sound onset were enhanced compared to MEPs evoked after far sounds. This near-far modulation faded at longer inter-stimulus intervals, and reversed completely for MEPs recorded 300 ms after the sound onset. At that time point, higher motor excitability was associated with far sounds. Such auditory modulation of hand motor representation was specific to a hand-centred, and not a body-centred reference frame. This pattern of corticospinal modulation highlights the relation between space and time in the PPS representation: an early facilitation for near stimuli may reflect immediate motor preparation, whereas, at later time intervals, motor preparation relates to distant stimuli potentially approaching the body.

Adaptive Lévy Walks in Foraging Fallow Deer:

Lévy flights are random walks, the step lengths of which come from probability distributions with heavy power-law tails, such that clusters of short steps are connected by rare long steps. Lévy walks maximise search efficiency of mobile foragers. Recently, several studies raised some concerns about the reliability of the statistical analysis used in previous analyses. Further, it is unclear whether Lévy walks represent adaptive strategies or emergent properties determined by the interaction between foragers and resource distribution. Thus two fundamental questions still need to be addressed: the presence of Lévy walks in the wild and whether or not they represent a form of adaptive behaviour. We studied 235 paths of solitary and clustered (i.e. foraging in group) fallow deer (Dama dama), exploiting the same pasture. We used maximum likelihood estimation for discriminating between a power-tailed distribution and the exponential alternative and rank/frequency plots to discriminate between Lévy walks and composite Brownian walks. We showed that solitary deer perform Lévy searches, while clustered animals did not adopt that strategy. Our demonstration of the presence of Lévy walks is, at our knowledge, the first available which adopts up-to-date statistical methodologies in a terrestrial mammal. Comparing solitary and clustered deer, we concluded that the Lévy walks of solitary deer represent an adaptation maximising encounter rates with forage resources and not an epiphenomenon induced by a peculiar food distribution.

Can We Systematically Review Studies That Evaluate Complex Interventions?:

The UK Medical Research Council defines complex interventions as those comprising “a number of separate elements which seem essential to the proper functioning of the interventions although the ‘active ingredient’ of the intervention that is effective is difficult to specify.” A typical example is specialist care on a stroke unit, which involves a wide range of health professionals delivering a variety of treatments. Michelle Campbell and colleagues have argued that there are “specific difficulties in defining, developing, documenting, and reproducing complex interventions that are subject to more variation than a drug” [10]. These difficulties are one of the reasons why it is challenging for researchers to systematically review complex interventions and synthesize data from separate studies. This PLoS Medicine Debate considers the challenges facing systematic reviewers and suggests several ways of addressing them.

Schizophrenia and Violence: Systematic Review and Meta-Analysis:

Schizophrenia is a lifelong, severe psychotic condition. One in 100 people will have at least one episode of schizophrenia during their lifetime. Symptoms include delusions (for example, patients believe that someone is plotting against them) and hallucinations (hearing or seeing things that are not there). In men, schizophrenia usually starts in the late teens or early 20s; women tend to develop schizophrenia a little later. The causes of schizophrenia include genetic predisposition, obstetric complications, illegal drug use (substance abuse), and experiencing traumatic life events. The condition can be treated with a combination of antipsychotic drugs and supportive therapy; hospitalization may be necessary in very serious cases to prevent self harm. Many people with schizophrenia improve sufficiently after treatment to lead satisfying lives although some patients need lifelong support and supervision.

Cross-National Analysis of the Associations among Mental Disorders and Suicidal Behavior: Findings from the WHO World Mental Health Surveys:

Suicide is a leading cause of death worldwide. Every 40 seconds, someone somewhere commits suicide. Over a year, this adds up to about 1 million self-inflicted deaths. In the USA, for example, where suicide is the 11th leading cause of death, more than 30,000 people commit suicide every year. The figures for nonfatal suicidal behavior (suicidal thoughts or ideation, suicide planning, and suicide attempts) are even more shocking. Globally, suicide attempts, for example, are estimated to be 20 times as frequent as completed suicides. Risk factors for nonfatal suicidal behaviors and for suicide include depression and other mental disorders, alcohol or drug abuse, stressful life events, a family history of suicide, and having a friend or relative commit suicide. Importantly, nonfatal suicidal behaviors are powerful predictors of subsequent suicide deaths so individuals who talk about killing themselves must always be taken seriously and given as much help as possible by friends, relatives, and mental-health professionals.

There are 19 new articles in PLoS ONE today. As always, you should rate the articles, post notes and comments and send trackbacks when you blog about the papers. You can now also easily place articles on various social services (CiteULike, Mendeley, Connotea, Stumbleupon, Facebook and Digg) with just one click. Here are my own picks for the week – you go and look for your own favourites:
What You See Is What You Get? Exclusion Performances in Ravens and Keas:

Among birds, corvids and parrots are prime candidates for advanced cognitive abilities. Still, hardly anything is known about cognitive similarities and dissimilarities between them. Recently, exclusion has gained increasing interest in comparative cognition. To select the correct option in an exclusion task, one option has to be rejected (or excluded) and the correct option may be inferred, which raises the possibility that causal understanding is involved. However, little is yet known about its evolutionary history, as only few species, and mainly mammals, have been studied. We tested ravens and keas in a choice task requiring the search for food in two differently shaped tubes. We provided the birds with partial information about the content of one of the two tubes and asked whether they could use this information to infer the location of the hidden food and adjust their searching behaviour accordingly. Additionally, this setup allowed us to investigate whether the birds would appreciate the impact of the shape of the tubes on the visibility of food. The keas chose the baited tube more often than the ravens. However, the ravens applied the more efficient strategy, choosing by exclusion more frequently than the keas. An additional experiment confirmed this, indicating that ravens and keas either differ in their cognitive skills or that they apply them differently. To our knowledge, this is the first study to demonstrate that corvids and parrots may perform differently in cognitive tasks, highlighting the potential impact of different selection pressures on the cognitive evolution of these large-brained birds.

Cognitive Processes Associated with Sequential Tool Use in New Caledonian Crows:

Using tools to act on non-food objects–for example, to make other tools–is considered to be a hallmark of human intelligence, and may have been a crucial step in our evolution. One form of this behaviour, ‘sequential tool use’, has been observed in a number of non-human primates and even in one bird, the New Caledonian crow (Corvus moneduloides). While sequential tool use has often been interpreted as evidence for advanced cognitive abilities, such as planning and analogical reasoning, the behaviour itself can be underpinned by a range of different cognitive mechanisms, which have never been explicitly examined. Here, we present experiments that not only demonstrate new tool-using capabilities in New Caledonian crows, but allow examination of the extent to which crows understand the physical interactions involved. In two experiments, we tested seven captive New Caledonian crows in six tasks requiring the use of up to three different tools in a sequence to retrieve food. Our study incorporated several novel features: (i) we tested crows on a three-tool problem (subjects were required to use a tool to retrieve a second tool, then use the second tool to retrieve a third one, and finally use the third one to reach for food); (ii) we presented tasks of different complexity in random rather than progressive order; (iii) we included a number of control conditions to test whether tool retrieval was goal-directed; and (iv) we manipulated the subjects’ pre-testing experience. Five subjects successfully used tools in a sequence (four from their first trial), and four subjects repeatedly solved the three-tool condition. Sequential tool use did not require, but was enhanced by, pre-training on each element in the sequence (‘chaining’), an explanation that could not be ruled out in earlier studies. By analyzing tool choice, tool swapping and improvement over time, we show that successful subjects did not use a random probing strategy. However, we find no firm evidence to support previous claims that sequential tool use demonstrates analogical reasoning or human-like planning. While the ability of subjects to use three tools in sequence reveals a competence beyond that observed in any other species, our study also emphasises the importance of parsimony in comparative cognitive science: seemingly intelligent behaviour can be achieved without the involvement of high-level mental faculties, and detailed analyses are necessary before accepting claims for complex cognitive abilities.

Keeping in Touch with One’s Self: Multisensory Mechanisms of Self-Consciousness:

The spatial unity between self and body can be disrupted by employing conflicting visual-somatosensory bodily input, thereby bringing neurological observations on bodily self-consciousness under scientific scrutiny. Here we designed a novel paradigm linking the study of bodily self-consciousness to the spatial representation of visuo-tactile stimuli by measuring crossmodal congruency effects (CCEs) for the full body. We measured full body CCEs by attaching four vibrator-light pairs to the trunks (backs) of subjects who viewed their bodies from behind via a camera and a head mounted display (HMD). Subjects made speeded elevation (up/down) judgments of the tactile stimuli while ignoring light stimuli. To modulate self-identification for the seen body subjects were stroked on their backs with a stick and the felt stroking was either synchronous or asynchronous with the stroking that could be seen via the HMD. We found that (1) tactile stimuli were mislocalized towards the seen body (2) CCEs were modulated systematically during visual-somatosensory conflict when subjects viewed their body but not when they viewed a body-sized object, i.e. CCEs were larger during synchronous than during asynchronous stroking of the body and (3) these changes in the mapping of tactile stimuli were induced in the same experimental condition in which predictable changes in bodily self-consciousness occurred. These data reveal that systematic alterations in the mapping of tactile stimuli occur in a full body illusion and thus establish CCE magnitude as an online performance proxy for subjective changes in global bodily self-consciousness.

Monday – time to check out PLoS Biology, PLoS Medicine and PLoS Neglected Tropical Diseases, as well as, of course, PLoS ONE.
As always, you should rate the articles, post notes and comments and send trackbacks when you blog about the papers. You can now also easily place articles on various social services (CiteULike, Mendeley, Connotea, Stumbleupon, Facebook and Digg) with just one click. Here are my own picks for the week – you go and look for your own favourites:
Equity for Open-Access Journal Publishing by Stuart M. Shieber:

Scholars write articles to be read–the more access to their articles the better–so one might think that the open-access approach to publishing, in which articles are freely available online to all without interposition of an access fee, would be an attractive competitor to traditional subscription-based journal publishing.
But open-access journal publishing is currently at a systematic disadvantage relative to the traditional model.
I propose a simple, cost-effective remedy to this inequity that would put open-access publishing on a path to become a sustainable, efficient system, allowing the two journal publishing systems to compete on a more level playing field. The issue is important, first, because academic institutions shouldn’t perpetuate barriers to an open-access business model on principle and, second, because the subscription-fee business model has manifested systemic dysfunctionalities in practice. After describing the problem with the subscription-fee model, I turn to the proposal for providing equity for open-access journal publishing–the open-access compact.

Prolonged Grief Disorder: A Problem for the Past, the Present, and the Future:

In systematically, and to me at least, persuasively establishing prolonged grief disorder (PGD) as a uniquely identifiable illness that requires specific treatments, Holly Prigerson and colleagues have separated PGD from normal grief and from other forms of pathologic grief responses [2]. Is it useful to include it in the DSM (Diagnostic and Statistical Manual of Mental Disorders)? I believe it is for several reasons. First, treatment for PGD is effective and substantially different from treatment for other forms of psychiatric illnesses that can be triggered by or arise with grief and loss.

The Validation and Assessment of Machine Learning: A Game of Prediction from High-Dimensional Data:

In applied statistics, tools from machine learning are popular for analyzing complex and high-dimensional data. However, few theoretical results are available that could guide to the appropriate machine learning tool in a new application. Initial development of an overall strategy thus often implies that multiple methods are tested and compared on the same set of data. This is particularly difficult in situations that are prone to over-fitting where the number of subjects is low compared to the number of potential predictors. The article presents a game which provides some grounds for conducting a fair model comparison. Each player selects a modeling strategy for predicting individual response from potential predictors. A strictly proper scoring rule, bootstrap cross-validation, and a set of rules are used to make the results obtained with different strategies comparable. To illustrate the ideas, the game is applied to data from the Nugenob Study where the aim is to predict the fat oxidation capacity based on conventional factors and high-dimensional metabolomics data. Three players have chosen to use support vector machines, LASSO, and random forests, respectively.