Path integration mediated systematic search: A Bayesian model

The systematic search behaviour is a backup system that increases the chances of desert ants finding their nest entrance after foraging when the path integrator has failed to guide them home accurately enough. Here we present a mathematical model of the systematic search that is based on extensive behavioural studies in North African desert ants . Cataglyphis fortis. First, a simple search heuristic utilising Bayesian inference and a probability density function is developed. This model, which optimises the short-term nest detection probability, is then compared to three simpler search heuristics and to recorded search patterns of . Cataglyphis ants. To compare the different searches a method to quantify search efficiency is established as well as an estimate of the error rate in the ants' path integrator. We demonstrate that the Bayesian search heuristic is able to automatically adapt to increasing levels of positional uncertainty to produce broader search patterns, just as desert ants do, and that it outperforms the three other search heuristics tested. The searches produced by it are also arguably the most similar in appearance to the ant's searches

Orientation and Search Strategies of Desert Arthropods : Path Integration Models and Experiments with Desert Ants, <i>Cataglyphis fortis</i> (Forel 1902)

Path integration enables desert arthropods to find back to their nest on the shortest track from any position. To perform path integration successfully, speeds and turning angles along the preceding outbound path have to be measured continuously and combined to determine an internal global vector leading back home at any time. A number of experiments have given an idea how arthropods might use allothetic or idiothetic signals to perceive their orientation and moving speed. When the global vector has been run off but the nest has not yet been reached, the arthropods engage in systematic search behavior. This behavior consists of a series of search loops of ever increasing size and finally leads to a search density profile peaking at the starting location. In the theoretical part of this work, the model descriptions of mathematically precise path integration that have been developed so far are reviewed, and the hitherto not used variant of egocentric cartesian coordinates is proposed and explained. Its simple and intuitive structure is demonstrated in comparison to the previous path integration models. Measuring two quantities, forward moving speed and angular turning rate, and implementing them into a linear system of differential equations provides the necessary information during foraging run, reorientation process (e.g. at a feeding site) and return path to the nest. In addition, several possible types of systematic errors that can cause deviations from the correct homeward course are easily implemented and illustrated by means of the model. Such deviations have been observed for several species of desert arthropods in different experiments, but their origin is still under debate. The two most important error mechanisms in this respect are the Müller-Wehner-error, an approximative path integration model that accumulates systematic miscalculations in path integration whenever the animal walks different from the correct inbound and outbound direction, and the leaky integrator, a mechanism that predicts a linear underestimation of the distance to the nest with an exponential rate; both error types have been shown to occur in specific experimental paradigms with desert ants Cataglyphis fortis. Using the egocentric path integration model, simple indices are proposed that might allow to rule out or corroborate certain error types by conducting experiments. Experiments were conducted with desert ants C. fortis. Those experiments, in which natural outbound runs as well as the following inbound runs and systematic search behaviors were observed and analyzed, revealed that natural outbound runs do not differ remarkably among different ants. This holds true for their spatial conformation as well as for overall path length and distance covered during foraging. Consequently, no significant correlations between all factors determining the shape of the outbound runs and the errors that were measured via different variables for inbound run as well as systematic search were found. Besides, the extension of the systematic search does not differ remarkably. However, due to the only slight differences of the natural outbound runs, such correlations cannot be totally excluded. The error postulated by Müller and Wehner seems to be of no or minor importance during natural foraging excursions; the principle of the leaky integrator, on the other hand, might be able to explain some shortcomings of the path integration mechanism with respect to distance estimation. Repeated training increases the straightness of outbound runs. In experiments, where desert ants were trained to different distances, it became obvious that the longer the distances of foraging excursions, the larger the errors occurring during path integration (again measured via home run and systematic search), and that the ants adapt their systematic search strategy to their increasing uncertainty by extending the search pattern. Additional experiments, during which the distance was kept constant, revealed that not only the characteristics of the foraging trip influence the accuracy of path integrator and systematic search behavior, but that also nest- or route specific cues have an impact on the orientation and the systematic search patterns of desert ants. If desert ants are disturbed during their outbound runs, most of them immediately set out in direction back to the nest, even without having food in their mandibles. External cues, in the respective experiment huge landmarks placed on the route between nest and feeder, increased the number of ants that continued its preceding foraging run; but still the majority headed back towards the nest. For a number of ants successive outbound and inbound runs (ontogeny-experiment) were recorded and analyzed. As a result, their outbound runs to a known feeding site get straighter over time, whereas the inbound runs are very straight from the very beginning and no increase of their straightness could be observed. For both outbound and inbound runs also no improvement in terms of accuracy of the path integrator was found; obviously the ants perform path integration in the same fashion all the time. Even if trained to a feeder for a long time in an area free of landmarks, desert ants do not develop specific paths, as they have been observed for other species of desert arthropods

Shoulder joint replacement can improve quality of life and outcome in patients with dysmelia: a case series

Background: Arthroplasty is a proven treatment option for glenohumeral osteoarthritis. Common indications include primary or posttraumatic osteoarthritis, avascular necrosis of the humeral head, rotator cuff tear arthropathy and rheumatoid osteoarthritis. Arthroplasty is rarely performed among patients with glenohumeral dysmelia. An overuse of the upper limb in patients with thalidomide-induced phocomelia and people with similar congenital deformities like dysmelia results in premature wear of the shoulder joint. This study aims to evaluate our experience with cases of glenohumeral osteoarthritis caused by dysmelia and treated with arthroplasty. To date, few reports on the outcome of shoulder arthroplasty exist on this particular patient group. Case presentation: We included four dysmelic patients (five shoulders) with substantial glenoid dysplasia in a prospective database after approval by the local ethics committee. Once conservative treatment options had been exhausted, the patients were treated with shoulder arthroplasty and assessed clinically and radiographically before and after surgery. The mean patient age at the time of surgery was 50.4 years. The minimum follow-up time was 24 months (24–91 months). All patients experienced a considerable improvement of range of motion (ROM) and a relief of pain. No intra- or postoperative complications appeared. Conclusion: Patients with dysmelia have acceptable short and mid-term results with resurfacing hemiarthroplasty. It is an effective although somewhat complicated method to relieve pain and improve movement. Long-term performance of arthroplasty in patients with dysmelia remains to be seen, particularly with regard to the remaining problem of the altered and often deficient glenoid

The Early Postnatal Nonhuman Primate Neocortex Contains Self-Renewing Multipotent Neural Progenitor Cells

The postnatal neocortex has traditionally been considered a non-neurogenic region, under non-pathological conditions. A few studies suggest, however, that a small subpopulation of neural cells born during postnatal life can differentiate into neurons that take up residence within the neocortex, implying that postnatal neurogenesis could occur in this region, albeit at a low level. Evidence to support this hypothesis remains controversial while the source of putative neural progenitors responsible for generating new neurons in the postnatal neocortex is unknown. Here we report the identification of self-renewing multipotent neural progenitor cells (NPCs) derived from the postnatal day 14 (PD14) marmoset monkey primary visual cortex (V1, striate cortex). While neuronal maturation within V1 is well advanced by PD14, we observed cells throughout this region that co-expressed Sox2 and Ki67, defining a population of resident proliferating progenitor cells. When cultured at low density in the presence of epidermal growth factor (EGF) and/or fibroblast growth factor 2 (FGF-2), dissociated V1 tissue gave rise to multipotent neurospheres that exhibited the ability to differentiate into neurons, oligodendrocytes and astrocytes. While the capacity to generate neurones and oligodendrocytes was not observed beyond the third passage, astrocyte-restricted neurospheres could be maintained for up to 6 passages. This study provides the first direct evidence for the existence of multipotent NPCs within the postnatal neocortex of the nonhuman primate. The potential contribution of neocortical NPCs to neural repair following injury raises exciting new possibilities for the field of regenerative medicine

Learning new sensorimotor contingencies:Effects of long-term use of sensory augmentation on the brain and conscious perception

Theories of embodied cognition propose that perception is shaped by sensory stimuli and by the actions of the organism. Following sensorimotor contingency theory, the mastery of lawful relations between own behavior and resulting changes in sensory signals, called sensorimotor contingencies, is constitutive of conscious perception. Sensorimotor contingency theory predicts that, after training, knowledge relating to new sensorimotor contingencies develops, leading to changes in the activation of sensorimotor systems, and concomitant changes in perception. In the present study, we spell out this hypothesis in detail and investigate whether it is possible to learn new sensorimotor contingencies by sensory augmentation. Specifically, we designed an fMRI compatible sensory augmentation device, the feelSpace belt, which gives orientation information about the direction of magnetic north via vibrotactile stimulation on the waist of participants. In a longitudinal study, participants trained with this belt for seven weeks in natural environment. Our EEG results indicate that training with the belt leads to changes in sleep architecture early in the training phase, compatible with the consolidation of procedural learning as well as increased sensorimotor processing and motor programming. The fMRI results suggest that training entails activity in sensory as well as higher motor centers and brain areas known to be involved in navigation. These neural changes are accompanied with changes in how space and the belt signal are perceived, as well as with increased trust in navigational ability. Thus, our data on physiological processes and subjective experiences are compatible with the hypothesis that new sensorimotor contingencies can be acquired using sensory augmentation