It Is Not Just in the Genes

Asymmetries in the functional and structural organization of the nervous system are widespread in the animal kingdom and especially characterize the human brain. Although there is little doubt that asymmetries arise through genetic and nongenetic factors, an overarching model to explain the development of functional lateralization patterns is still lacking. Current genetic psychology collects data on genes relevant to brain lateralizations, while animal research provides information on the cellular mechanisms mediating the effects of not only genetic but also environmental factors. This review combines data from human and animal research (especially on birds) and outlines a multi-level model for asymmetry formation. The relative impact of genetic and nongenetic factors varies between different developmental phases and neuronal structures. The basic lateralized organization of a brain is already established through genetically controlled embryonic events. During ongoing development, hemispheric specialization increases for specific functions and subsystems interact to shape the final functional organization of a brain. In particular, these developmental steps are influenced by environmental experiences, which regulate the fine-tuning of neural networks via processes that are referred to as ontogenetic plasticity. The plastic potential of the nervous system could be decisive for the evolutionary success of lateralized brains.

Investigation of Lade-Kim Plastic Potential Applicability under Various Stress Paths for Rockfill Materials

The dilatancy behavior of rockfill materials shows obvious stress path dependence. Lade-Kim plastic potential equation has been proposed for a long time to model the mechanical behavior of sand and concrete materials. However, it lacks the verification of rockfill materials, especially under various stress paths. In this paper, the dilatancy performance of coarse-grained materials under various stress paths is investigated, and then the dilatancy equation description and verification method based on Lade-Kim plastic potential are given. The applicability of Lade-Kim plastic potential for different stress path tests, such as conventional triaxial tests, constant P tests, and constant stress (increment) ratio tests, are verified and evaluated. It is found that Lade-Kim plastic potential is difficult to consider the influence of stress path. Finally, the Lade-Kim plastic potential, together with nonlinear dilatancy equation, is evaluated by changing the dilatancy equation in the framework of generalized plasticity. Lade-Kim plastic potential is suitable for constant stress increment ratio loading experiments and special care should be taken when applied to other stress paths. These works are helpful to understand stress path dependence of dilatancy behavior for rockfill materials and is beneficial for the establishment of stress path constitutive model.

Visual Plasticity in Adulthood: Perspectives from Hebbian and Homeostatic Plasticity

The visual system retains profound plastic potential in adulthood. In the current review, we summarize the evidence of preserved plasticity in the adult visual system during visual perceptual learning as well as both monocular and binocular visual deprivation. In each condition, we discuss how such evidence reflects two major cellular mechanisms of plasticity: Hebbian and homeostatic processes. We focus on how these two mechanisms work together to shape plasticity in the visual system. In addition, we discuss how these two mechanisms could be further revealed in future studies investigating cross-modal plasticity in the visual system.

Non-normal flow rules affect fracture angles in sea ice viscous–plastic rheologies

The standard viscous–plastic (VP) sea ice model with an elliptical yield curve and a normal flow rule has at least two issues. First, it does not simulate fracture angles below 30∘ in uni-axial compression, in contrast with observations of linear kinematic features (LKFs) in the Arctic Ocean. Second, there is a tight, but unphysical, coupling between the fracture angle, post-fracture deformation, and the shape of the yield curve. This tight coupling was identified as the reason for the overestimation of fracture angles. In this paper, these issues are addressed by removing the normality constraint on the flow rule in the standard VP model. The new rheology is tested in numerical uni-axial loading tests. To this end, an elliptical plastic potential – which defines the post-fracture deformations, or flow rule – is introduced independently of the elliptical yield curve. As a consequence, the post-fracture deformation is decoupled from the mechanical strength properties of the ice. We adapt Roscoe's angle theory, which is based on observations of granular materials, to the context of sea ice modeling. In this framework, the fracture angles depend on both yield curve and plastic potential parameters. This new formulation predicts accurately the results of the numerical experiments with a root-mean-square error below 1.3∘. The new rheology allows for angles of fracture smaller than 30∘ in uni-axial compression. For instance, a plastic potential with an ellipse aspect ratio smaller than 2 (i.e., the default value in the standard viscous–plastic model) can lead to fracture angles as low as 22∘. Implementing an elliptical plastic potential in the standard VP sea ice model requires only small modifications to the standard VP rheology. The momentum equations with the modified rheology, however, are more difficult to solve numerically. The independent plastic potential solves the two issues with VP rheology addressed in this paper: in uni-axial loading experiments, it allows for smaller fracture angles, which fall within the range of satellite observations, and it decouples the angle of fracture and the post-fracture deformation from the shape of the yield curve. The orientation of the post-fracture deformation along the fracture lines (convergence and divergence), however, is still controlled by the shape of the plastic potential and the location of the stress state on the yield curve. A non-elliptical plastic potential would be required to change the orientation of deformation and to match deformation statistics derived from satellite measurements.

After traumatic brain injury oligodendrocytes regain a plastic phenotype and can become astrocytes

After acute brain injuries various response cascades are evoked that direct the formation of the glial scar. Here, we report that acute lesions associated with a disruption of the blood-brain barrier trigger a re-programming within the oligodendrocyte lineage. In PLP-DsRed1/GFAP-EGFP and PLP-EGFPmem/GFAP-mRFP1 transgenic mice with cortical injuries, we transiently found PLP transgene-labelled cells with activated GFAP promoter activity adjacent to the lesion site. We termed them AO cells, based on their concomitant activity of astro- and oligodendroglial genes. By fate mapping using PLP- and GFAP-split Cre complementation and NG2-CreERT2 mice we observed that major portions of AO cells surprisingly differentiated into astrocytes. Using repeated long-term in vivo two-photon laser-scanning microscopy (2P-LSM) we followed oligodendrocytes after injury. We observed their conversion into astrocytes via the AO cell stage with silencing of the PLP promoter and simultaneous activation of the GFAP promoter. In addition, we provide evidence that this oligodendrocyte-to-astrocyte conversion depends on local cues. At the lesion site higher expression levels of various glial differentiation factors were detected. And indeed, local injection of IL-6 promoted the formation of AO cells. In summary, our findings highlight the plastic potential of oligodendrocytes in acute brain trauma. An altered environmental milieu affects gene expression programs of mature oligodendrocytes and induces a plastic differentiation stage with astrogliogenic potential via transitional AO cells.

Increased brain growth in escaped rainbow trout

Recent examples of rapid brain size plasticity in response to novel laboratory environments suggest that fish brain size is a flexible trait, allowing growth or shrinkage of brain tissue based on short term needs. Nevertheless, it remains to be seen if plasticity of fish brain size is relevant to natural environmental conditions. Here, using rainbow trout escaped from a farming operation as a natural experiment, we demonstrate that adult fish brain size can change rapidly in response to life in a natural lake environment. Specifically, escaped trout had on average 15% heavier brains relative to body size than captive trout after living for about 7 months in the lake. Because relative brain size of most escaped trout fell above the range of variation seen within the captive trout population, we conclude that increased brain size was achieved by plasticity after escape. Brain morphology analysis showed that the most anterior regions (olfactory bulbs and rest of telencephalon) contributed most to the increase in overall brain size in escaped trout. Relative size of the heart ventricle, another organ which can be subject to plastic changes under variable environmental conditions in fish, did not differ between escaped and captive trout. Massive and selective brain growth under the changed environmental conditions associated with escape from holding pens highlighted the plastic potential of fish brain size and suggests that a shift to increased complexity of life in the wild setting of a lake imposed greatly increased cognitive requirements on escaped trout.

Plasticidade fenotípica de Psidium cattleianum (Myrtaceae) em ambiente insular e continental na baía Babitonga em São Francisco do Sul, Santa Catarina

A plasticidade fenotípica permite aos vegetais a sobrevivência e sucesso reprodutivo em meios com distintas condições ambientais. Ambientes insulares são altamente restritivos devido à características como alta salinidade e incidência luminosa e deficiência nutricional do solo, as quais atuam como filtro ambiental para o estabelecimento de espécies. O presente estudo objetivou avaliar a plasticidade fenotípica de Psidium cattleianum (Myrtaceae), comparando populações co-ocorrentes em ilha e continente na Baía Babitonga/SC. Para tanto, foram selecionados 10 indivíduos em cada ambiente, dos quais foram coletadas 35 folhas maduras e de sol para análises morfoanatômicas e fisiológicas, posterior tratamento estatístico em ambiente R e cálculo do Índice de Plasticidade fenotípica (IPF). Análise química do solo foi procedida por meio de amostras compostas de 10 coletas por ambiente. O ambiente insular apresenta solo menos ácido, com maior conteúdo de matéria orgânica, salinidade e disponibilidade de água quando comparado ao continente, porém com menor capacidade de troca catiônica (CTC). A intensidade de luz apresentou maior incidência sobre as plantas da ilha. Em razão da heterogeneidade ambiental, diferenças estatisticamente significativas foram registradas para os atributos arquiteturais e morfoanatômicos das populações, representando ajustes funcionais desencadeados por um filtro ambiental. Os três primeiros eixos da PCA explicaram 64,35% da variação de dados, como maior expressão dos atributos de massas fresca e seca, teores de clorofila e espessura do parênquima lacunoso. Para o IPF, todos os atributos avaliados mostraram valores abaixo de 0,3, indicando o baixo potencial plástico entre as populações de P. cattleianum, porém com diferenças nas estratégias ecológicas que otimizam a alocação de recursos nos ambientes estudados. Phenotypic plasticity of co-current Psidium cattleianum (Myrtaceae) in an island and continental environment at Babitonga Bay in São Francisco do Sul, Santa CatarinaA B S T R A C TPhenotypic plasticity allows plants survival and to reproduce successfully in face of environmental changes. This study aimed to investigate, on an individual scale, the response of Psidium cattleianum (Myrtaceae) in two distinct environmental conditions: island and mainland in Babitonga Bay, São Francisco do Sul, Santa Catarina. For this purpose, two populations comprising 10 individuals were selected in each study area, from which 35 mature sun leaves were collected for morphoanatomical and physiological analysis; soil chemical analysis was performed on composed samples formed by 10 collections per area. The statistical treatment was performed in R environment and also the Phenotypic Plasticity Index (IPF) was calculated. The island environment has less acid soils, with higher organic matter content, salinity and water availability when compared to mainland, but with lower cation exchange capacity (CTC), besides higher light intensity. Due to areas heterogeneity, statistically significant differences were recorded for the morphoanatomical and physiological attributes of the populations, representing functional adjustments triggered by environmental filters. The first three axes of the PCA explained 64.35% of the data variation, with greater expression of fresh and dry mass attributes, chlorophyll contents and thickness of spongy parenchyma. For the IPF, all the attributes evaluated showed values below 0.3, indicating the low plastic potential among P. cattleianum populations, but with differences in ecological strategies that optimize resource allocation in the studied environments.Keywords: araçá, environmental heterogeneity, functional adjustments, ombrophilous forest, plastic potential.