Am I seeing my hand? Visual appearance and knowledge of controllability both contribute to the visual capture of a person's own body

When confronted with complex visual scenes in daily life, how do we know which visual information represents our own hand? We investigated the cues used to assign visual information to one''s own hand. Wrist tendon vibration elicits an illusory sensation of wrist movement. The intensity of this illusion attenuates when the actual motionless hand is visually presented. Testing what kind of visual stimuli attenuate this illusion will elucidate factors contributing to visual detection of one''s own hand. The illusion was reduced when a stationary object was shown, but only when participants knew it was controllable with their hands. In contrast, the visual image of their own hand attenuated the illusion even when participants knew that it was not controllable. We suggest that long-term knowledge about the appearance of the body and short-term knowledge about controllability of a visual object are combined to robustly extract our own body from a visual scene.     

Is the body the self? Women and body image

This paper discusses how women's body image or experience of the body influences their identity and self-image. What are the implications of this tendency to equate the body and the self? For many women, being a dieter represents not only something that they do, but also an important aspect of how they see themselves. We propose that choosing to become a chronic dieter is a means of regulating not just one's feelings, but also one's identity and self-image when those central aspects of the self feel threatened. Weight-loss dieting is often unsuccessful, however, and repeated dieting attempts may increase weight as often as they reduce it, so using body shape to determine self-worth or identity is a maladaptive strategy for most women.     

Where is my hand in space? The internal model of gravity influences proprioception

Knowing where our limbs are in space is crucial for a successful interaction with the external world. Joint position sense (JPS) relies on both cues from muscle spindles and joint mechanoreceptors, as well as the effort required to move. However, JPS may also rely on the perceived external force on the limb, such as the gravitational field. It is well known that the internal model of gravity plays a large role in perception and behaviour. Thus, we have explored whether direct vestibular-gravitational cues could influence JPS. Participants passively estimated the position of their hand while they were upright and therefore aligned with terrestrial gravity, or pitch-tilted 45° backwards from gravity. Overall participants overestimated the position of their hand in both upright and tilted postures; however, the proprioceptive bias was significantly reduced when participants were tilted. Our findings therefore suggest that the internal model of gravity may influence and update JPS in order to allow the organism to interact with the environment.     

Adaptation or exaptation? The case of the human hand

A controversy of relevance to the study of biological form involves the concept of adaptation. This controversy is illustrated by the structure and function of the human hand. A review of the principal definitions of adaptation points to two main problems: (1) they are qualitative and make reference to the whole structure (or substructural feature) and (2) they are based on the idea of natural selection as a moulding factor. The first problem would be solved by a definition that encompasses quantitative measures of the effects of selection, drawing on new advances in the comparative method. The second problem is deeper and presents greater conceptual difficulties. I will argue that the idea of natural selection as a moulding factor depends on the notion of a genetic program for development. But regarding the hand, experimental evidence on limb development challenges the idea of a genetic program for skeletal pattern formation, undermining a simple application of standard adaptationist concepts. These considerations lead to a revised definition of adaptation and interpretation of the evolutionary determinants of the hand’s form.     

Is the establishment rate and fecundity of Haemonchus contortus related to body or abomasal measurements in sheep?

The relationship among parasitological parameters, abomasal size and body size measurements was investigated in lambs following an experimental infection with Haemonchus contortus. In total, 100 lambs from five different genotypes (German Merino (GM), Texel × GM, Suffolk × GM, German Blackhead Mutton × GM and Ile de France × GM) were experimentally infected with 5000 infective third stage larvae of H. contortus at the time of weaning at 12 weeks of age. Four and six weeks after infection, individual faecal samples were collected for estimation of faecal egg counts (FECs). Furthermore, wither height, shoulder width, heart girth, loin girth and body length were taken at 18 weeks of life. Lambs were slaughtered and necropsied 7 weeks post-infection, and worm counts, abomasal volume and surface area were determined. Positive correlations were found between different body size parameters, body weight and abomasal sizes. FEC and worm counts were not significantly correlated either with body size parameters or with abomasal size. The mean worm burden was higher in GM than in crossbred lambs. There was no significant difference in abomasal size between GM and crossbred lambs. The results suggest that the variations between animals in worm burden following an experimental infection with H. contortus (worm resistance) are not influenced by body size parameters or abomasal sizes. Therefore, other factors, including genetic-based differences in resistance, must cause these findings between and within breeds.     

Is acidosis the clue to the loss of structure and functioning of the sarcolemma?

The only way for a tissue or organ to survive ischemia is by reperfusion or restoration of the blood flow. However, if the ischemic period is too long reperfusion leads to a Ca2+ overload of the myocardial cells and thereby to cell death. The question is; what are the key events during ischemia which cause this transition from reversible to irreversible injury. In this article we discuss whether acidosis may play a crucial role by inducing Ca2+ release from the sarcolemma and reorganization of membrane components especially the membrane lipids, i.e. lateral phase separation, resulting in membrane protein clustering and changes in lipid asymmetry.     

Is the effect of wounding on leaf senescence due to ethylene?

Wounding delays the loss of chlorophyll (Chl) that normally occurs when oat (Avena sativa L.) leaf segments are held in the dark. There was a continued increase in ethylene production during the senescence of the control segments; in contrast, ethylene production by the wounded segments, although it increased by a factor of 2–3 times, reached its peak in 48 h and then dropped sharply to below the basal level. Added 1-aminocyclopropane-1-carboxylic acid (ACC) caused a very large increase in ethylene production in both control and wounded segments, but it increased the rate of Chl loss, though only marginally. Aminoethoxyvinylglycine (AVG) inhibited ethylene production by both control and wounded segments and this did decrease the Chl loss, but only in the control segments. In the wounded segments, AVG antagonized the Chl-retaining action of the wound. Since wounding delayed the loss of Chl and yet caused a moderate increase in ethylene production, we conclude that the ethylene production by senescing oat leaves is not the main controlling influence in the wounding effect. The data also throw doubt on the causal participation of ethylene in normal Chl loss by these leaves in darkness.     

Does the impact of nutrients on the biological structure and function of brackish and freshwater lakes differ?

The effects of nutrients on the biological structure of brackish and freshwater lakes were compared. Quantitative analysis of late summer fish, zooplankton, mysid and macrophyte populations was undertaken in 20–36 shallow brackish lakes of various trophic states and the findings compared with a similar analysis of shallow freshwater lakes based on either sampling (fish) or existing data (zooplankton, mysids and macrophytes). Special emphasis was placed on differences in pelagic top-down control. Whereas the fish biomass (CPUE, multiple mesh-size gill nets) rose with increasing P-concentration in freshwater lakes, that of brackish lakes was markedly reduced at P-concentrations above ca. 0.4 mg P l^-1 and there was a concomitant shift to exclusive dominance by the small sticklebacks (Gasterosteus aculeatus and Pungitius pungitius); as a result, fish density remained relatively high. Mysids (Neomysis integer) were found at a salinity greater than 0.5 and increased substantially with increasing P-concentration, reaching levels as high as 13 ind. l^-1. This is in contrast to the carnivorous zooplankton of freshwater lakes, which are most abundant at intermediate P levels. The efficient algal controller, Daphnia was only found at a salinity below 2 and N. integer in lakes with a salinity above 0.5. Above 2 the filter-feeding zooplankton were usually dominated by the less efficient algal controllers Eurytemora and Acartia. In contrast to freshwater lakes, no shift to a clearwater state was found in eutrophic brackish lakes when submerged macrophytes became abundant. We conclude that predation pressure on zooplankton is higher and algal grazing capacity lower in brackish eutrophic-hypertrophic lakes than in comparable freshwater lakes, and that the differences in trophic structure of brackish and freshwater lakes have major implications for the measures available to reduce the recovery period following a reduction in nutrient loading. From the point of view of top-down control, the salinity threshold dividing freshwater and brackish lakes is much lower than the conventionally defined 5.     

The continuity of living matter and the discontinuities of its constituents: do plankton and benthos really exist?

Plankton and benthos are popular concepts identifying two ways of life of aquatic organisms. Their spatial separation led to the development of different sampling techniques and to separate conceptualizations of the principles governing these subsets of the aquatic environment. Reciprocal connections between plankton and benthos, however, are very strong both from a functional (energy fluxes) and a structural (life cycle dynamics) point of view. A full appreciation of such links is forcing marine ecology towards a more integrated approach.     

The effects of habitat on the vigilance of shorebirds: Is visibility important?

Previous studies of vigilance have concentrated on situations where the prey species has an unimpaired view of its surroundings. Here the effects of reduced visibility caused by objects adjacent to the prey are studied in two species of shorebird. A reduction in visibility causes an increase in the level of vigilance, indicating an increase in vulnerability despite the greater degree of camouflaging. This increase is due to individuals being less able to see both approaching predators and their neighbours. Turnstones, Arenaria interpres, and purple sandpipers, Calidris maritima, show very similar increases in the level of vigilance with decreasing visibility, but achieve these increases by different means: turnstones lengthen the duration of each vigilant scan, while purple sandpipers scan more often. Increasing scanning rate produces a shortened interval between scans, which reduces the risk of being caught unawares by an approaching predator. However, it may also reduce feeding efficiency, and it is suggested that this might be more serious in turnstones due to greater handling times for food items, so causing them to adopt a different strategy to increase vigilance.     

Is the C-terminal arm of lens gap junction channel protein the channel gate?

Lens gap junction channels are studied in a reconstituted system obtained by incorporating into liposomes, with or without calmodulin, the lens junction protein (MIP26) and its trypsin-cleaved product (MIP21) that lacks the C-terminal arm. Channel permeability is studied with an osmotic swelling assay. MIP26 and MIP21 liposomes swell in sucrose or polyethyleneglycol with or without Ca++ indicating the presence of large channels. Without Ca++, MIP26 and MIP21 liposomes swell in both permeants. With Ca++, MIP26-calmodulin liposomes do not swell in either permeant, indicating complete channel closure, while MIP21-calmodulin liposomes swell in sucrose but not in polyethyleneglycol. This suggests that the C-terminal arm participates in channel gating.     

Is polychaete family-level sufficient to assess impact on tropical estuarine gradients?

Regular, robust monitoring programs set up to assess the environmental conditions of aquatic systems often target different biological groups. And, of these, macroinvertebrate communities and particularly the class Polychaeta are frequently used. Identifying these organisms takes time, money and specialized expertise to ensure correct identification to the lowest possible taxonomic level. Identification errors can lead to an erroneous assessment. The concept of taxonomic sufficiency has been proposed both to minimize errors and to save time and money. This study tested the usefulness of this concept in tropical estuaries in northeast Brazil. We selected two transitional systems with different degrees of human impact due to different land uses and different conservation systems: the Mamanguape estuary, which is in an environmental conservation unit for sustainable use, and the highly impacted, urban Paraíba do Norte estuary. The results clearly showed that nutrient concentrations were markedly higher in the Paraíba do Norte estuary in the dry season and that the composition of the polychaete assemblages differed between the two estuaries as well as along the spatial gradient of each estuary. The use of either genus or family level led to equivalent representation in each system in terms of taxon richness and both the Margalef and Shannon-Wiener diversity indices. Both taxonomic levels described similar changes in the polychaete assemblage along the estuarine gradients. Based on our findings, the use of a coarser taxonomic level (i.e., family) is a good option when the aim is to implement a monitoring program in tropical estuaries with the polychaete assemblages as one of the target groups. This time-efficient taxonomic resolution can help improve sampling designs and allow long-term monitoring studies without losing much vital information.     

The impact of time of day on the gait and balance control of Alzheimer’s patients

Alzheimer’s patients suffer from circadian dysregulation. The aim of this study was to examine the evolution of balance control and gait at different times of the day (11:00, 14:00, 18:00) in order to identify whether Alzheimer’s patients were more likely to fall at certain periods of the day. Spatio-temporal parameters of centre of foot pressure displacements were measured with a force platform and spatio-temporal parameters of walking were evaluated with a gait analysis device. The results highlighted that balance control was worse in the evening and the afternoon than in the morning. Furthermore, the walking speed was faster and support duration, swing duration and cycle duration were shorter in the evening than in the morning and afternoon. The combined analysis of balance control and gait parameters revealed that balance control and walking are concomitantly altered in the evening which increases the fall risk in the evening, in comparison with the morning, for Alzheimer’s patients.     

Is virtual reality a useful tool in the teaching of physiology?

This opinion statement points out some of the considerations and pitfalls in using virtual reality computer programs in the teaching of life sciences. Emphasis is placed on the possibility of such programs leading to reductionist thinking including how reductionist thinking could foster the formation of misconceptions. Negative feedback is used as the classic example of reductionist thinking in physiological regulation, including how classic negative feedback is inconsistent with evidence of complexity in living systems. This statement concludes that virtual reality can be a useful tool in the teaching of physiology so long as the complexity of living systems is taken into account.