What we talk about when we talk about access deficits

Semantic impairments have been divided into storage deficits, in which the semantic representations themselves are damaged, and access deficits, in which the representations are intact but access to them is impaired. The behavioural phenomena that have been associated with access deficits include sensitivity to cueing, sensitivity to presentation rate, performance inconsistency, negative serial position effects, sensitivity to number and strength of competitors, semantic blocking effects, disordered selection between strong and weak competitors, correlation between semantic deficits and executive function deficits and reduced word frequency effects. Four general accounts have been proposed for different subsets of these phenomena: abnormal refractoriness, too much activation, impaired competitive selection and deficits of semantic control. A combination of abnormal refractoriness and impaired competitive selection can account for most of the behavioural phenomena, but there remain several open questions. In particular, it remains unclear whether access deficits represent a single syndrome, a syndrome with multiple subtypes or a variable collection of phenomena, whether the underlying deficit is domain-general or domain-specific, whether it is owing to disorders of inhibition, activation or selection, and the nature of the connection (if any) between access phenomena in aphasia and in neurologically intact controls. Computational models offer a promising approach to answering these questions.     

What we talk about when we talk with medical students

In this article, we review how we interact with medical students in our efforts to teach blood pressure regulation and systemic cardiovascular control along with related elements of respiratory and exercise physiology. Rather than provide a detailed lecture with key facts, we attempted to outline our approach to teaching integrative cardiovascular physiology to medical students, which includes five major themes. First, focus on questions versus answers and facts. We believe that this offers both the learner and teacher a number of advantages. Second, avoid teaching dogma in the name of clarity (i.e., heavy focus on teaching "facts" that have not yet been fully investigated). This is especially important because of the way knowledge evolves over time. Third, include laboratory-based experiences in human integrative physiology. Fourth, provide students with intellectual frameworks versus a list of "facts" to serve as a platform for question generation. Finally, focus on the role of integration and regulatory redundancy in physiology and the idea that physiology is a narrative that can help. In this article, we discuss the philosophy behind the themes outlined above and argue that questions, and not answers, are where the action is for both research and education.     

What we talk about when we talk about capacitance measured with the voltage-clamp step method

Capacitance is a fundamental neuronal property. One common way to measure capacitance is to deliver a small voltage-clamp step that is long enough for the clamp current to come to steady state, and then to divide the integrated transient charge by the voltage-clamp step size. In an isopotential neuron, this method is known to measure the total cell capacitance. However, in a cell that is not isopotential, this measures only a fraction of the total capacitance. This has generally been thought of as measuring the capacitance of the ??well-clamped?? part of the membrane, but the exact meaning of this has been unclear. Here, we show that the capacitance measured in this way is a weighted sum of the total capacitance, where the weight for a given small patch of membrane is determined by the voltage deflection at that patch, as a fraction of the voltage-clamp step size. This quantifies precisely what it means to measure the capacitance of the ??well-clamped?? part of the neuron. Furthermore, it reveals that the voltage-clamp step method measures a well-defined quantity, one that may be more useful than the total cell capacitance for normalizing conductances measured in voltage-clamp in nonisopotential cells.     

Sex allocation conflict in ants: when the queen rules

Insect societies are paramount examples of cooperation, yet they also harbor internal conflicts whose resolution depends on the power of the opponents. The male-haploid, female-diploid sex-determining system of ants causes workers to be more related to sisters than to brothers, whereas queens are equally related to daughters and sons. Workers should thus allocate more resources to females than to males, while queens should favor an equal investment in each sex. Female-biased sex allocation and manipulation of the sex ratio during brood development suggest that workers prevail in many ant species. Here, we show that queens of Formica selysi strongly influenced colony sex allocation by biasing the sex ratio of their eggs. Most colonies specialized in the production of a single sex. Queens in female-specialist colonies laid a high proportion of diploid eggs, whereas queens in male-specialist colonies laid almost exclusively haploid eggs, which constrains worker manipulation. However, the change in sex ratio between the egg and pupae stages suggests that workers eliminated some male brood, and the population sex-investment ratio was between the queens' and workers' equilibria. Altogether, these data provide evidence for an ongoing conflict between queens and workers, with a prominent influence of queens as a result of their control of egg sex ratio.     

Reproductive behaviour evolves rapidly when intralocus sexual conflict is removed

Background

Intralocus sexual conflict can inhibit the evolution of each sex towards its own fitness optimum. In a previous study, we confirmed this prediction through the experimental removal of female selection pressures in Drosophila melanogaster, achieved by limiting the expression of all major chromosomes to males. Compared to the control populations (C_1-4) where the genomes are exposed to selection in both sexes, the populations with male-limited genomes (ML_1-4) showed rapid increases in male fitness, whereas the fitness of females expressing ML-evolved chromosomes decreased [1].

Methodology/Principal Findings

Here we examine the behavioural phenotype underlying this sexual antagonism. We show that males expressing the ML genomes have a reduced courtship level but acquire the same number of matings. On the other hand, our data suggest that females expressing the ML genomes had reduced attractiveness, stimulating a lower rate of courtship from males. Moreover, females expressing ML genomes tend to display reduced yeast-feeding behaviour, which is probably linked to the reduction of their fecundity.

Conclusion/Significance

These results suggest that reproductive behaviour is shaped by opposing selection on males and females, and that loci influencing attractiveness and foraging were polymorphic for alleles with sexually antagonistic expression patterns prior to ML selection. Hence, intralocus sexual conflict appears to play a role in the evolution of a wide range of fitness-related traits and may be a powerful mechanism for the maintenance of genetic variation in fitness.     

The role of conformity in foraging when personal and social information conflict

There is currently considerable interest in the interplay betweenpersonal and social information in decision-making processes.Two experiments are presented exploring the relative use ofprior personal information and subsequent social informationin foraging decisions of guppies. Experiment 1 tested the assumptionthat when the use of information acquired through personal experienceis not costly, conflicting social information will be ignored.The assumption was confirmed because, when given a choice betweenfeeding at two food patches, at one of which they had previouslyseen conspecifics feed, individual fish with prior experienceof feeding at the alternative site chose the alternative, whereasfish with no prior experience chose the site at which theirconspecifics had fed. Experiment 2 tested theoretical predictionsthat when the use of information acquired through personal experienceis potentially costly, conflicting social information will beweighed more heavily than will personal information. The predictionwas confirmed because, when given a choice between feeding attwo food patches, one at which they had previously seen conspecificsfeed and one behind a visual barrier, individual fish with priorexperience of feeding behind the barrier chose the site at whichtheir conspecifics had fed. These findings suggest that conformitycan promote social learning in naïve individuals, but priorexperience can insulate individuals from conformity providedthe costs of relying on that experience are small. In addition,the experiments highlight the fact that personal and socialinformation are not always weighed equally.     

Nine-spined sticklebacks exploit the most reliable source when public and private information conflict

Social foragers can potentially use private information gained from personal experience and public information gained from observing the foraging success of others to determine the profitability of a foraging patch. We investigated how nine-spined sticklebacks use conflicting public and private information of variable reliability to make foraging decisions. In a first experiment, when private information was reliable, sticklebacks ignored public information and based their foraging decision on private information. However, when private information was less reliable, sticklebacks tended to use public rather than private information. A second experiment investigated how the time since experiencing private information affected sticklebacks' use of this information when it conflicted with recent public information. Fish based their foraging decisions on recently acquired private information, but reliance on private information diminished as the period since experiencing it increased. Fish used public information if 7 days had elapsed since updating their private information. Our findings suggest that nine-spined sticklebacks flexibly adjust their decision making to exploit the most reliable information available, be it public or private, and that animals will weight private and public information appropriately depending on circumstances.