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21.
A goal of sensory coding is to capture features of sensory input that are behaviorally relevant. Therefore, a generic principle of sensory coding should take into account the motor capabilities of an agent. Up to now, unsupervised learning of sensory representations with respect to generic coding principles has been limited to passively received sensory input. Here we propose an algorithm that reorganizes an agent''s representation of sensory space by maximizing the predictability of sensory state transitions given a motor action. We applied the algorithm to the sensory spaces of a number of simple, simulated agents with different motor parameters, moving in two-dimensional mazes. We find that the optimization algorithm generates compact, isotropic representations of space, comparable to hippocampal place fields. As expected, the size and spatial distribution of these place fields-like representations adapt to the motor parameters of the agent as well as to its environment. The representations prove to be well suited as a basis for path planning and navigation. They not only possess a high degree of state-transition predictability, but also are temporally stable. We conclude that the coding principle of predictability is a promising candidate for understanding place field formation as the result of sensorimotor reorganization. 相似文献
22.
Summary In the initial phase of the geotropical reaction of the Chara rhizoid the growth difference postulated by Sievers (1967c) between the physically upper, slightly subapical flank and the lower one is demonstrated. In horizontal exposure the growth of the extreme cell apex is continued, while the growth of the lower flank is inhibited and that of the upper one is promoted. In the end phase the cell apex shows a damped oscillation until it finally reaches the vertical growth direction. The statoliths follow the oscillating growth of the cell tip from one flank to the opposite one until they are statistically equally redistributed in their normal position.—In vertical exposure under reduced turgor pressure the statoliths fall down into the extreme cell apex, where they inhibit the growth of this part of the cell wall, while the subapical wall grows transversally.—It is concluded that the statoliths inhibit the growth of the cell wall area which they cover.—The physical phase of the reaction chain, the susception, is the gravity-induced downward displacement of the statoliths. The physiological phase starts with the diversion of the acropetal transport of the Golgi vesicles to the upper part of the cell, which is caused by the block of statoliths (perception). The greater rate of vesicle incorporation into the upper flank in comparison to the lower one causes the subapical growth difference which results in the curvature (reaction).—In the case of the Chara rhizoid Golgi- and statolith-apparatus function as a self-regulating cellular system.
Herrn Prof. Dr. Dr. h. c. Kurt Mothes zum 70. Geburtstag. 相似文献
Herrn Prof. Dr. Dr. h. c. Kurt Mothes zum 70. Geburtstag. 相似文献
23.
Andreas Helbig 《Journal of Ornithology》1987,128(4):441-456
Zusammenfassung Im westlichen Küstenflachland Malaysias überwintern Eisvögel unbekannter Herkunft in großer Zahl vor allem an der mangrovenbewachsenen Küste (ca. 8000–10 000 Vögel auf 800 km Küstenlänge). Die Nahrung (60% Fische, 30% Garnelen) wurde stoßtauchend von einer Warte (90%), aus dem Rüttelflug (2,6%) oder aus horizontalem Flug (0,9%) erbeutet mit einer Erfolgsrate von ca. 53%. Bevorzugt wurden Beutetiere mit einer Kopf-Rumpf-Länge von 15–45 mm (Abb. 1). Die Bearbeitungsdauer nahm mit der Beutegröße zu, Fische wurden intensiver bearbeitet als Garnelen (maximal 208 Schläge in 8,5 min). Pro Tag nahm ein Vogel 50–60% seines Körpergewichts an Nahrung auf, wozu er im Mittel 38 erfolgreiche Beutestöße benötigte. Die Vögel waren 53% der hellen Tageszeit inaktiv; 37% dienten dem Nahrungserwerb, 4% der Revierverteidigung und 5% dem Komfortverhalten. Bevorzugung von schattigen Sitzwarten und erhöhte Tauchfrequenz ohne Beutefang zur heißesten Tageszeit werden als Thermoregulationsverhalten interpretiert. Eisvögel verhielten sich weitgehend territorial, besonders in nahrungsreichen Gebieten der Küste überschnitten sich aber die Aktionsräume.Alcedo atthis füllt in Malaysia eine vakante ökologische Nische und ist von zehn anderen Eisvogelarten, die wie er nicht ausschließlich an den Primärwald gebunden sind, durch Habitat- und/oder Nahrungswahl getrennt. Dies ermöglicht gelegentliches Brüten im Binnenland, wo geeignete Steilwände vorhanden sind, die jedoch an der Küste völlig fehlen.
Ecology of the European Kingfischer (Alcedo atthis) in a southeast Asian wintering area
Summary Many Kingfishes of unknown origin winter in lowland and coastal habitats of Peninsular Malaysia, where they are not present from May to August. They utilize a broad habitat spectrum and are most numerous along the mangrove coast (estimated 8000–10 000 birds on 800 km coast). Foraging techniques consisted of plunge diving from a perch (90%), from hovering flight (2.6%) and from horizontal flight (0.9%). 6.7% of dives were aborted. The overall success rate was 53%. The diet consisted mainly of fish (60%) and shrimp (ca. 30%, less inland). Prey lengths were mostly 15–45 mm, i. e. clearly smaller than food usually delivered to half-or full-grown nestlings. Fish were battered against the perch more often than shrimp of the same size and handling time increased with prey size (Fig. 3; max. 208 beats in 8.5 min). A Kingfisher consumed prey equivalent to 50–60% of its body weight per day and needed on average 38 successful dives to obtain it. Birds were inactive about 53% of the daylight hours, foraging took up 37%, comfort behaviour 5% and territorial disputes 4% (Table 5). This suggests that their energy budget was balanced or positive. Daily routines included alternating periods of foraging and inactivity. There was no well defined activity maximum at any time of the day. A preference for perches near shading vegetation and a 60% increase in the frequency of dives without prey capture during the hottest part of the day (Table 6) indicates behavioural thermoregulation. Kingfishers were territorial to a varying extent. Fights were rare but lasted up to 35 min. Home and feeding ranges of up to 5 birds overlapped in areas of high prey density, especially on the coast. Intraspecific competion appeared not to be severe. WinteringA. atthis fill a largely vacant niche in coastal Malaysia. With their small size and aquatic prey they are well segregated either through habitat choice or diet from at least ten other Alcedinidae potentially occuring in the same area. Nesting occurs at least occasionally, but seems to be limited by a lack of suitable nest sites (earth walls) along the coast and possibly competition inland.相似文献
24.
25.
Ruofan Wang Camille R. Simoneau Jessie Kulsuptrakul Mehdi Bouhaddou Katherine A. Travisano Jennifer M. Hayashi Jared Carlson-Stevermer James R. Zengel Christopher M. Richards Parinaz Fozouni Jennifer Oki Lauren Rodriguez Bastian Joehnk Keith Walcott Kevin Holden Anita Sil Jan E. Carette Nevan J. Krogan Andreas S. Puschnik 《Cell》2021,184(1):106-119.e14
26.
Cristiana Leite N. Tatiana Silva Sandrine Mendes Andreia Ribeiro Joana Paes de Faria Tania Louren?o Francisco dos Santos Pedro Z. Andrade Carla M. P. Cardoso Margarida Vieira Artur Paiva Cláudia L. da Silva Joaquim M. S. Cabral Jo?o B. Relvas Mário Gr?os 《PloS one》2014,9(10)
Mesenchymal stem cells (MSCs) are viewed as safe, readily available and promising adult stem cells, which are currently used in several clinical trials. Additionally, their soluble-factor secretion and multi-lineage differentiation capacities place MSCs in the forefront of stem cell types with expected near-future clinical applications. In the present work MSCs were isolated from the umbilical cord matrix (Wharton''s jelly) of human umbilical cord samples. The cells were thoroughly characterized and confirmed as bona-fide MSCs, presenting in vitro low generation time, high proliferative and colony-forming unit-fibroblast (CFU-F) capacity, typical MSC immunophenotype and osteogenic, chondrogenic and adipogenic differentiation capacity. The cells were additionally subjected to an oligodendroglial-oriented step-wise differentiation protocol in order to test their neural- and oligodendroglial-like differentiation capacity. The results confirmed the neural-like plasticity of MSCs, and suggested that the cells presented an oligodendroglial-like phenotype throughout the differentiation protocol, in several aspects sharing characteristics common to those of bona-fide oligodendrocyte precursor cells and differentiated oligodendrocytes. 相似文献
27.
Laura Cernat Cristina Blaj Rene Jackstadt Lydia Brandl Jutta Engel Heiko Hermeking Andreas Jung Thomas Kirchner David Horst 《PloS one》2014,9(8)
Colonic crypts are stereotypical structures with distinct stem cell, proliferating, and differentiating compartments. Colorectal cancers derive from colonic crypt epithelia but, in contrast, form morphologically disarrayed glands. In this study, we investigated to which extent colorectal cancers phenocopy colonic crypt architecture and thus preserve structural organization of the normal intestinal epithelium. A subset of colon cancers showed crypt-like compartments with high WNT activity and nuclear β-Catenin at the leading tumor edge, adjacent proliferation, and enhanced Cytokeratin 20 expression in most differentiated tumor epithelia of the tumor center. This architecture strongly depended on growth conditions, and was fully reproducible in mouse xenografts of cultured and primary colon cancer cells. Full crypt-like organization was associated with low tumor grade and was an independent prognostic marker of better survival in a collection of 221 colorectal cancers. Our findings suggest that full activation of preserved intestinal morphogenetic programs in colon cancer requires in vivo growth environments. Furthermore, crypt-like architecture was linked with less aggressive tumor biology, and may be useful to improve current colon cancer grading schemes. 相似文献
28.
29.
30.
Thea Kristiansen Jens‐Christian Svenning Wolf L. Eiserhardt Dennis Pedersen Hans Brix Søren Munch Kristiansen Maria Knadel César Grández Henrik Balslev 《Journal of Biogeography》2012,39(7):1318-1332
Aim It is a central issue in ecology and biogeography to understand what governs community assembly and the maintenance of biodiversity in tropical rain forest ecosystems. A key question is the relative importance of environmental species sorting (niche assembly) and dispersal limitation (dispersal assembly), which we investigate using a large dataset from diverse palm communities. Location Lowland rain forest, western Amazon River Basin, Peru. Methods We inventoried palm communities, registering all palm individuals and recording environmental conditions in 149 transects of 5 m × 500 m. We used ordination, Mantel tests and indicator species analysis (ISA) to assess compositional patterns, species responses to geographical location and environmental factors. Mantel tests were used to assess the relative importance of geographical distance (as a proxy for dispersal limitation) and environmental differences as possible drivers of dissimilarity in palm species composition. We repeated the Mantel tests for subsets of species that differ in traits of likely importance for habitat specialization and dispersal (height and range size). Results We found a strong relationship between compositional dissimilarity and environmental distance and a weaker but also significant relationship between compositional dissimilarity and geographical distance. Consistent with expectations, relationships with environmental and geographical distance were stronger for understorey species than for canopy species. Geographical distance had a higher correlation with compositional dissimilarity for small‐ranged species compared with large‐ranged species, whereas the opposite was true for environmental distance. The main environmental correlates were inundation and soil nutrient levels. Main conclusions The assembly of palm communities in the western Amazon appears to be driven primarily by species sorting according to hydrology and soil, but with dispersal limitation also playing an important role. The importance of environmental characteristics and geographical distance varies depending on plant height and geographical range size in agreement with functional predictions, increasing our confidence in the inferred assembly mechanisms. 相似文献