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31.
32.
Optimal Information Representation and Criticality in an Adaptive Sensory Recurrent Neuronal Network
Recurrent connections play an important role in cortical function, yet their exact contribution to the network computation remains unknown. The principles guiding the long-term evolution of these connections are poorly understood as well. Therefore, gaining insight into their computational role and into the mechanism shaping their pattern would be of great importance. To that end, we studied the learning dynamics and emergent recurrent connectivity in a sensory network model based on a first-principle information theoretic approach. As a test case, we applied this framework to a model of a hypercolumn in the visual cortex and found that the evolved connections between orientation columns have a "Mexican hat" profile, consistent with empirical data and previous modeling work. Furthermore, we found that optimal information representation is achieved when the network operates near a critical point in its dynamics. Neuronal networks working near such a phase transition are most sensitive to their inputs and are thus optimal in terms of information representation. Nevertheless, a mild change in the pattern of interactions may cause such networks to undergo a transition into a different regime of behavior in which the network activity is dominated by its internal recurrent dynamics and does not reflect the objective input. We discuss several mechanisms by which the pattern of interactions can be driven into this supercritical regime and relate them to various neurological and neuropsychiatric phenomena. 相似文献
33.
Synaesthesia is an unusual perceptual experience in which an inducer stimulus triggers a percept in a different domain in addition to its own. To explore the conditions under which synaesthesia evolves, we studied a neuronal network model that represents two recurrently connected neural systems. The interactions in the network evolve according to learning rules that optimize sensory sensitivity. We demonstrate several scenarios, such as sensory deprivation or heightened plasticity, under which synaesthesia can evolve even though the inputs to the two systems are statistically independent and the initial cross-talk interactions are zero. Sensory deprivation is the known causal mechanism for acquired synaesthesia and increased plasticity is implicated in developmental synaesthesia. The model unifies different causes of synaesthesia within a single theoretical framework and repositions synaesthesia not as some quirk of aberrant connectivity, but rather as a functional brain state that can emerge as a consequence of optimising sensory information processing. 相似文献
34.
35.
Na Wang Sari Palmroth Christopher A. Maier Jean‐Christophe Domec Ram Oren 《Plant, cell & environment》2019,42(5):1690-1704
The genus Pinus has wide geographical range and includes species that are the most economically valued among forest trees worldwide. Pine needle length varies greatly among species, but the effects of needle length on anatomy, function, and coordination and trade‐offs among traits are poorly understood. We examined variation in leaf morphological, anatomical, mechanical, chemical, and physiological characteristics among five southern pine species: Pinus echinata, Pinus elliottii, Pinus palustris, Pinus taeda, and Pinus virginiana. We found that increasing needle length contributed to a trade‐off between the relative fractions of support versus photosynthetic tissue (mesophyll) across species. From the shortest (7 cm) to the longest (36 cm) needles, mechanical tissue fraction increased by 50%, whereas needle dry density decreased by 21%, revealing multiple adjustments to a greater need for mechanical support in longer needles. We also found a fourfold increase in leaf hydraulic conductance over the range of needle length across species, associated with weaker upward trends in stomatal conductance and photosynthetic capacity. Our results suggest that the leaf size strongly influences their anatomical traits, which, in turn, are reflected in leaf mechanical support and physiological capacity. 相似文献
36.
Physical interaction with Yes-associated protein enhances p73 transcriptional activity 总被引:10,自引:0,他引:10
Strano S Munarriz E Rossi M Castagnoli L Shaul Y Sacchi A Oren M Sudol M Cesareni G Blandino G 《The Journal of biological chemistry》2001,276(18):15164-15173
37.
Belyaeva OB Griffiths WT Kovalev JV Timofeev KN Litvin FF 《Biochemistry. Biokhimii?a》2001,66(2):173-177
The primary stages of protochlorophyllide phototransformation in an artificially formed complex containing heterologously expressed photoenzyme protochlorophyllide-oxidoreductase (POR), protochlorophyllide, and NADPH were investigated by optical and ESR spectroscopy. An ESR signal (g = 2.002; H = 1 mT) appeared after illumination of the complex with intense white light at 77 K. The ESR signal appeared with simultaneous quenching of the initial protochlorophyllide fluorescence, this being due to the formation of a primary non-fluorescent intermediate. The ESR signal disappeared on raising the temperature to 253 K, and a new fluorescence maximum at 695 nm belonging to chlorophyllide simultaneously appeared. The data show that the mechanism of protochlorophyllide photoreduction in the complex is practically identical to the in vivo mechanism: this includes the formation of a short-lived non-fluorescent free radical that is transformed into chlorophyllide in a dark reaction. 相似文献
38.
Regulation of the p53 tumor suppressor protein 总被引:35,自引:0,他引:35
Oren M 《The Journal of biological chemistry》1999,274(51):36031-36034
39.
Previous research suggested that the hydraulic properties of root systems
of intact plants could be described by two parameters: the hydraulic
conductivity (Lpr) or the slope of the
flow-density/water potential gradient relationship, and the offset or
minimum water potential gradient required to induce flow. In this study
Lpr and offset were correlated with anatomical
features of the root radial path in plants with contrasting root anatomy.
Two woody and three herbaceous species were examined which exhibit a range
of root anatomical features: Asparagus densiflorus
(Kunth) Jessop (asparagus), Dendrobium superbum Rchb.
f. (dendrobium), Glycine max (L.) Merr. (soybean),
Prunus persica (L.) Batsch. (peach), Citrus
aurantium L. (sour orange). Lpr varied
about 8-fold, and the offset varied about 6-fold among the five species.
Lpr was inversely related to root diameter
(r20.39) and cortex width
(r20.55), suggesting that species with thinner
roots or roots with a thin cortex had the highest Lpr.
Further observations suggested that the cortex width was a stronger
determinant of Lpr than root diameter. However, the
offset was not correlated with root diameter, stele diameter or cortex
width, but was >2-fold higher in species having an exodermis in the
root radial path (sour orange, asparagus, and dendrobium) compared to those
lacking an exodermis (peach and soybean). The data on root
Lr obtained were similar to those given in the
literature for both intact plants and excised roots which have been
measured with different techniques. It is concluded that
Lpr and offset, which describe the flow-water
potential relationship for intact root systems, are related to differences
in the root cortex; specifically, its thickness and the presence/absence of
a suberized exodermis. Hence, these anatomical differences may, in part,
cause the variability in root hydralic properties that exists among plant
species. 相似文献
40.
Melittin, a 26 residue, non-cell-selective cytolytic peptide, is the major component of the venom of the honey bee Apis mellifera. In a previous study, a diastereomer ([D]-V(5,8),I(17),K(21)-melittin, D-amino acids at positions V(5,8),I(17),K(21)) of melittin was synthesized and its function was investigated [Oren, Z., and Shai, Y. (1997) Biochemistry 36, 1826-1835]. [D]-V(5,8),I(17),K(21)-melittin lost its cytotoxic effects on mammalian cells; however, it retained antibacterial activity. Furthermore, [D]-V(5,8),I(17),K(21)-melittin binds strongly and destabilizes only negatively charged phospholipid vesicles, in contrast to native melittin, which binds strongly also zwitterionic phospholipids. To understand the differences in the properties of melittin and its diastereomer, 2D-NMR experiments were carried out with [D]-V(5,8),I(17),K(21)-melittin, and polarized attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy experiments were done with both melittin and [D]-V(5,8), I(17),K(21)-melittin. The structure of the diastereomer was characterized by NMR in water, as well as in three different membrane-mimicking environment, 40% 2,2,2-trifluoroethanol (TFE)/water, methanol, and dodecylphosphocholine/phosphatidylglycerol (DPC/DMPG) micelles. The NMR data revealed an amphipathic alpha-helix only in the C-terminal region of the diastereomer in TFE/water and methanol solutions and in DPC/DMPG micelles. ATR-FTIR experiments revealed that melittin and [D]-V(5,8),I(17),K(21)-melittin are oriented parallel to the membrane surface. This study indicates the role of secondary structure formation in selective cytolytic activity of [D]-V(5,8), I(17),K(21)-melittin. While the N-terminal helical structure is not required for the cytolytic activity toward negatively charged membranes and bacterial cells, it appears to be a crucial structural element for binding and insertion into zwitterionic membranes and for hemolytic activity. 相似文献