The concept of positional information is applied to a large amount of data obtained previously in experiments on developing and regenerating amphibian limbs. Only the proximo-distal axis of the limb is considered. It is shown that the concept provides a simple, unitary hypothesis which satisfactorily accounts for the experimental data, and may moreover suggest meaningful new approaches. It is suggested that the boundaries of the bipolar limb system lie in the girdle skeleton and at the distal end of the limb, (...) respectively, and that it is the apical epidermis of the growing or regenerating limb which defines the distal boundary conditions. A relatively stable gradient of positional information is assumed to be set up in the mesoderm . It is further shown that the differentiated limb retains its positional information and upon amputation imparts it to the base of the blastema. To explain an apparent discrepancy between the developing and the regenerating limb, it is proposed that dedifferentiation of mesodermal limb tissues upon amputation entails a change of positional value in the mesenchyme. Consequently, the amputation level does not once and for all specify the positional value at the proximal end of a mass of blastemal mesenchyme, particularly when the mesenchyme is transplanted in such a way that its linear size decreases or increases. (shrink)

Therapeutic strategies capable of inducing and enhancing prosthesis embodiment are a key point for better adaptation to and acceptance of prosthetic limbs. In this study, we developed a training protocol using an EMG-based human-machine interface that was applied in the preprosthetic rehabilitation phase of people with amputation. This is a case series with the objective of evaluating the induction and enhancement of the embodiment of a virtual prosthesis. Six men and a woman with unilateral transfemoral traumatic amputation without previous use (...) of prostheses participated in the study. Participants performed a training protocol with the EMG-based HMI, composed of six sessions held twice a week, each lasting 30 mins. This system consisted of myoelectric control of the movements of a virtual prosthesis immersed in a 3D virtual environment. Additionally, vibrotactile stimuli were provided on the participant’s back corresponding to the movements performed. Embodiment was investigated from the following set of measurements: skin conductance response, crossmodal congruency effect, ability to control the virtual prosthesis, and reports before and after the training. The increase in the skin conductance response in conditions where the virtual prosthesis was threatened, recalibration of the peripersonal space perception identified by the crossmodal congruency effect, ability to control the virtual prosthesis, and participant reports consistently showed the induction and enhancement of virtual prosthesis embodiment. Therefore, this protocol using EMG-based HMI was shown to be a viable option to achieve and enhance the embodiment of a virtual prosthetic limb. (shrink)

This article is concerned with the problem of the relation between the genetic information contained in the DNA and the emergence of visible structure in multicellular animals. The answer is sought in a reappraisal of the data of experimental embryology, considering molecular, cellular and organismal aspects. The presence of specific molecules only confers a tissue identity on the cells when their concentration exceeds the threshold of differentiation. When this condition is not fulfilled the activity of the genes that code for (...) the specific molecules in question only confers on them a histogenetic potency, i.e. the capacity to form the corresponding tissue in further development (or to transdifferentiate to that tissue). The progressive restriction of histogenetic potencies during development reflects the irreversible repression of more and more genes. The establishment of a given tissue identity under the influence of an inducing tissue (or a morphogenetic hormone) is only possible when the cells have acquired the competence to respond. Tissue differentiation proceeds progressively during development thanks to the cytoplasmic memory that cells retain collectively (or sometimes individually) of the items of information successively registered by their ancestors cells. The increasing complexity of visible structure emerging during development results only from the progression of tissue differentiation. This involves continual exchange of information among the cells and leads to (1) cell displacements and rearrangements, particularly during organogenesis and (2) extreme diversification of cell individualities within tissues, particularly during postembryonic growth. A mutation (just as a teratogenic factor) evokes an anomaly that is localized in both space and time because it alters a certain aspect of cell behaviour (particularly cell surface adhesiveness or mitotic activity) at the time when this is involved in the establishment of a particular structural trait. Neither the organization of the adult nor the modalities of development are encoded in the DNA. The automatic concatenation of cell interactions in the embryo and the structural amplification it entails is conditioned by the specific biochemical composition of the cytoplasm of the egg and by the heterogeneous distribution of its inclusions. (shrink)

As long-term childhood cancer survivors are at risk for late effects, ongoing medical care is crucial to detect and treat physical illnesses as early as possible. However, previous research from around the world has shown that many adult survivors did not participate in long-term medical follow-up. This study aimed to provide insight into German survivors’ care situation, with a particular focus on barriers to follow-up care. We investigated a sample of adult CCS drawn from the German Childhood Cancer Registry’s oldest (...) cohort. Our analyses included data from a standardized medical examination, a self-report questionnaire, and in-depth interviews with a subsample. Half of the participants reported participating in some kind of medical follow-up. In a logistic regression analysis, attendance of medical follow-up care was associated with higher age. Reasons for non-attendance were assigned to four categories: lack of information about medical follow-up and/or its purpose, termination by the health care provider, structural barriers, and emotional-motivational aspects. The interviews contributed to a better understanding of how these reported barriers played out in the care of individual survivors. Further, they revealed that some survivors currently in medical follow-up had had periods without follow-up care in the past—which were also in many cases related to a lack of information, both on the part of health care providers and CCS themselves. The results indicated that a large proportion of long-term CCS do not receive the recommended follow-up care. Further, there is a great need for more information regarding the aims of long-term medical follow-up and available offers. This is an important prerequisite for CCS to make informed decisions. (shrink)

Although several theoretical approaches consider general methods for dealing with shape, recent observations and experimental data show that embryos exhibit marked changes in the properties of the biological material involved in shape development and shape regulation capacity. In vivo experiments have shown that the amphibian embryo gradually develops from a situation in which it is not able to maintain its shape to one in which it can not only maintain its shape but also possesses a maximal tolerance towards deformation together (...) with a maximal shape regulation capacity. So far two especially clear conclusions have emerged: (i) the form of the embryo appears to be determined by cell activities intrinsic to each stage, and (ii) the morphogenetic programme can be executed normally within wide limits notwithstanding dramatic deformations of the embryo during quite a long period. Thus the hypothesis may be advanced that shape and morphogenesis to some extent become independent phenomena during embryonic development. (shrink)

Ludwig Boltzmann is one of the foremost responsible for the development of modern atomism in thermodynamics. His proposition was revolutionary not only because it brought a new vision for Thermodynamics, merging a statistical approach with Newtonian physics, but also because he produced an entirely new perspective on the way of thinking about and describing physical phenomena. Boltzmann dared to flirt with constructivism and realism simultaneously, by hypothesizing the reality of atoms and claiming an inherent probabilistic nature related to many particles (...) systems. Boltzmann faced criticism from the positivists, who rejected the hypothesis of the atom as a matter of principle, and also from physicists, who rejected the idea of a classical bounded system that does not follow deterministic mechanical laws. We consider that Boltzmann thermodynamics has emerged as a systemic theory that deals with macroscopic bodies using collective variables; it was reformulated to a kinetic theory of gases, and subsequently to statistical mechanics. From the theoretical physical point of view, Boltzmann advocates an approach to thermodynamics based on mechanics and was one of the founders of statistical mechanics, together with ideas by Maxwell, Clausius and Gibbs. Subsequently, statistical mechanics has also influenced the development of quantum mechanics and information theory. Using an evolutionary epistemological perspective as a metaphor to describe the physical entities claimed in Boltzmann propositions, we interpret his work as a selected theory that gained attributes of reality and “survived” during a scientific-contextual competition to be more adapted, in the sense that it was able to better explain physical phenomena, and also generated “descendants”. (shrink)

In the course of the history of science, some concepts have forged theoretical foundations, constituting paradigms that hold sway for substantial periods of time. Research on the history of explanations of the action of one body on another is a testament to the periodic revival of one theory in particular, namely, the theory of ether. Even after the foundation of modern Physics, the notion of ether has directly and indirectly withstood the test of time. Through a spontaneous physics philosophical analysis, (...) this article will explore how certain aspects of the concept of ether have appeared in different branches of the history of science. (shrink)