Contrast Adaptation Contributes to Contrast-Invariance of Orientation Tuning of Primate V1 Cells

BACKGROUND: Studies in rodents and carnivores have shown that orientation tuning width of single neurons does not change when stimulus contrast is modified. However, in these studies, stimuli were presented for a relatively long duration (e. g., 4 seconds), making it possible that contrast adaptation contributed to contrast-invariance of orientation tuning. Our first purpose was to determine, in marmoset area V1, whether orientation tuning is still contrast-invariant with the stimulation duration is comparable to that of a visual fixation. METHODOLOGY/PRINCIPAL FINDINGS: We performed extracellular recordings and examined orientation tuning of single-units using static sine-wave gratings that were flashed for 200 msec. Sixteen orientations and three contrast levels, representing low, medium and high values in the range of effective contrasts for each neuron, were randomly intermixed. Contrast adaptation being a slow phenomenon, cells did not have enough time to adapt to each contrast individually. With this stimulation protocol, we found that the tuning width obtained at intermediate contrast was reduced to 89% (median), and that at low contrast to 76%, of that obtained at high contrast. Therefore, when probed with briefly flashed stimuli, orientation tuning is not contrast-invariant in marmoset V1. Our second purpose was to determine whether contrast adaptation contributes to contrast-invariance of orientation tuning. Stationary gratings were presented, as previously, for 200 msec with randomly varying orientations, but the contrast was kept constant within stimulation blocks lasting >20 sec, allowing for adaptation to the single contrast in use. In these conditions, tuning widths obtained at low contrast were still significantly less than at high contrast (median 85%). However, tuning widths obtained with medium and high contrast stimuli no longer differed significantly. CONCLUSIONS/SIGNIFICANCE: Orientation tuning does not appear to be contrast-invariant when briefly flashed stimuli vary in both contrast and orientation, but contrast adaptation partially restores contrast-invariance of orientation tuning

Hystricognathy vs Sciurognathy in the Rodent Jaw: A New Morphometric Assessment of Hystricognathy Applied to the Living Fossil Laonastes (Diatomyidae)

While exceptional for an intense diversification of lineages, the evolutionary history of the order Rodentia comprises only a limited number of morphological morphotypes for the mandible. This situation could partly explain the intense debates about the taxonomic position of the latest described member of this clade, the Laotian rock rat Laonastes aenigmamus (Diatomyidae). This discovery has re-launched the debate on the definition of the Hystricognathi suborder identified using the angle of the jaw relative to the plane of the incisors. Our study aims to end this ambiguity. For clarity, it became necessary to revisit the entire morphological diversity of the mandible in extant and extinct rodents. However, current and past rodent diversity brings out the limitations of the qualitative descriptive approach and highlights the need for a quantitative approach. Here, we present the first descriptive comparison of the masticatory apparatus within the Ctenohystrica clade, in combining classic comparative anatomy with morphometrical methods. First, we quantified the shape of the mandible in rodents using 3D landmarks. Then, the analysis of osteological features was compared to myological features in order to understand the biomechanical origin of this morphological diversity. Among the morphological variation observed, the mandible of Laonastes aenigmamus displays an intermediate association of features that could be considered neither as sciurognathous nor as hystricognathous

Genetic integrity of European wildcats: Variation across biomes mandates geographically tailored conservation strategies

Hybridisation between domestic and wild taxa can pose severe threats to wildlife conservation, and human-induced hybridisation, often linked to species' introductions and habitat degradation, may promote reproductive opportunities between species for which natural interbreeding would be highly unlikely. Using a biome-specific approach, we examine the effects of a suite of ecological drivers on the European wildcat's genetic integrity, while assessing the role played by protected areas in this process. We used genotype data from 1217 putative European wildcat samples from 13 European countries to assess the effects of landcover, disturbance and legal landscape protection on the European wildcat's genetic integrity across European biomes, through generalised linear models within a Bayesian framework. Overall, we found European wildcats to have genetic integrity levels above the wildcat-hybrid threshold (ca. 83%; threshold = 80%). However, Mediterranean and Temperate Insular biomes (i.e., Scotland) revealed lower levels, with 74% and 46% expected genetic integrity, respectively. We found that different drivers shape the level of genetic introgression across biomes, although forest integrity seems to be a common factor promoting European wildcat genetic integrity. Wildcat genetic integrity remains high, regardless of landscape legal protection, in biomes where populations appear to be healthy and show recent local range expansions. However, in biomes more susceptible to hybridisation, even protected areas show limited effectiveness in mitigating this threat. In the face of the detected patterns, we recommend that species conservation and management plans should be biome- and landscape-context-specific to ensure effective wildcat conservation, especially in the Mediterranean and Temperate Insular biomes.Thanks are due to FCT/MCTES for the financial support to cE3c (UIDB/00329/2020), through national funds, and the co-funding by the FEDER, within the PT2020 Partnership Agreement and Compete 2020. PM was supported by UID/BIA/50027/2021 with funding from FCT/MCTES through national funds. FDR was supported by a postdoctoral contract from the University of Málaga (I Plan Propio de Investigación y Transferencia, call 2020). This study was partly funded by research projects CGL2009-10741, funded by the Spanish Ministry of Science and Innovation and EU-FEDER, and OAPN 352/2011, funded by the Organismo Autónomo Parques Nacionales (Spain). Luxembourg sample collection has been co-funded by the Ministry of Environment, Climate and Sustainable Development of Luxembourg. We would like to thank the Bavarian Forest National Park Administration for the approval and support in collecting samples.Peer reviewe

Inhibitors of ectonucleotidases have paradoxical effects on synaptic transmission in the mouse cortex

International audienceExtracellular adenosine plays prominent roles in the brain in both physiological and pathological conditions. Adenosine can be generated following the degradation of extracellular nucleotides by various types of ectonucleotidases. Several ectonucleotidases are present in the brain parenchyma: ecto-nucleotide triphosphate diphosphohydrolases 1 and 3 (NTPDase 1 and 3), ecto-nucleotide pyrophosphatase/ phosphodiesterase 1 (NPP 1), ecto-5’-nucleotidase (eN), and tissue non-specific alkaline phosphatase (TNAP, whose function in the brain has received little attention). Here we examined, in a living brain preparation, the role of these ectonucleotidases in generating extracellular adenosine. We recorded local field potentials evoked by electrical stimulation of the lateral olfactory tract in the mouse piriform cortex in vitro. Variations in adenosine level were evaluated by measuring changes in presynaptic inhibition generated by adenosine A1 receptors (A1Rs) activation. A1R-mediated presynaptic inhibition was present endogenously and was enhanced by bath-applied AMP and ATP. We hypothesized that inhibiting ectonucleotidases would reduce extracellular adenosine concentration, which would result in a weakening of presynaptic inhibition. However, inhibiting TNAP had no effect in controlling endogenous adenosine action and no effect on presynaptic inhibition induced by bath-applied AMP. Furthermore, contrary to our expectation, inhibiting TNAP reinforced, rather than reduced, presynaptic inhibition induced by bath-applied ATP. Similarly, inhibition of NTPDase 1 and 3, NPP1, and eN induced stronger, rather than weaker presynaptic inhibition, both in endogenous condition and with bath-applied ATP and AMP. Consequently, attempts to suppress the functions of extracellular adenosine by blocking its extracellular synthesis in living brain tissue could have functional impacts opposite to those anticipated

DETC2003/DAC-48746 A DESIGN ALTERNATIVES ASSESSMENT AND MANAGEMENT APPROACH

ABSTRACT One of the objectives of concurrent engineering has been to integrate more and more knowledge as soon as possible during the product development process. In such a method and owing to designer creativity, new design solutions are carried out. Design alternatives then appear; the differences can be relative to the functions, the technology, the materials or the manufacturing process as well. This paper presents some first specifications in modelling those design alternatives. Much more design solutions can then be kept in designers' mind instead of focusing on the a priori best solution. The final solution is therefore chosen depending on every point of view involved in the design process. First of all this work aimed at defining the new knowledge that have to be taken into account in the product modelling in order to support the design alternatives management. Those new model elements must currently be integrated or linked with already-known product and design process models. The alternatives modelling has secondly been tested on very simple design examples. Afterwards, the design of a surgical simulator has been carried out that pointed out the real benefits and the feasibility of the alternatives modelling

Product meta-modelling: an approach for linking product models

International audienceOne of the objectives of concurrent engineering is to ensure the management of product data during all its life cycle. So we need some tools able to organize and support the representation of a lot of data. As a single model could not fulfil the specificity of each design phase, we use two product models and define the link between their formalisms (including data types, structure, and evolution laws). For having a formal and intelligible mapping of the type of data and of the evolution laws of both models, two static meta-models have been defined. These meta-models use the UML class diagram

Percent change in orientation tuning width vs. percent change in tuned response amplitude.

<p>In these scatter plots, the <i>x</i>-axis represents percent change in tuned response amplitude and the <i>y</i>-axis represents percent change in HWHH. A. Medium vs. high contrast, mixed contrasts condition. B. Low vs. high contrast, mixed contrasts condition. C. Low vs. medium contrast, mixed contrasts condition. In these three scatter plots, most data points are located in the quadrant delimited by 0 and 100% on both x and y axis, indicating that most cells showed both reduced response amplitude and reduced HWHH when contrast was decreased. However, the two variables were not significantly correlated. D. Medium vs. high contrast, constant contrast condition. E. Low vs. high contrast, constant contrast condition. F. Low vs. medium contrast, constant contrast condition. In the scatter plots in E and F, most data points can be found in the quadrant delimited by 0 and 100% on both x and y axes, indicating that most cells showed both reduced response amplitude and reduced HWHH when contrast was decreased. This is not the case for the scatter plot in D, reflecting the fact that orientation tuning width was not different, on average, between medium and high contrast after adaptation. There is, however, a significant inverse relationship between the two variables in this case. The line corresponds to the linear relationship between the two variables.</p

Changes in relative untuned response amplitude with different contrasts.

<p>A. Cumulative distribution for the three contrasts in the mixed contrasts condition. The RURA expresses the proportion of response amplitude that lacks orientation selectivity, relative to the total response amplitude. Values close to zero indicate null response to the orientation orthogonal to the preferred one. Values less than zero indicate firing rates lower than spontaneous activity, suggesting cross-orientation suppression. Values larger than zero indicate responses to orthogonal stimuli. B. Distribution of differences in RURA with different contrasts, in the mixed contrasts condition. Upper histogram: RURA obtained with high contrast minus RURA obtained with medium contrast. Middle histogram: RURA obtained with high contrast minus RURA obtained with low contrast. Lower histogram: RURA obtained with medium contrast minus RURA obtained with low contrast. At the population level, a significant difference was observed between high and medium contrast only, with larger RURA, on average, at high contrast. C. Cumulative distributions for each of the three contrasts, for the constant contrast blocks. D. Distribution of differences in RURA with different contrasts, for the constant contrast blocks. RURA values obtained with high contrast were significantly larger than those obtained with either medium (upper histogram) or low contrast (middle histogram). RURA did not differ between medium and low contrasts (lower histogram). We did not test differences in RURA at the single cell level as RURA calculation combines two parameters, each with its own associated standard error.</p

The effects of contrast and contrast adaptation on HWHH.

<p>A. Cumulative distribution of HWHH. Data in red were obtained with the mixed contrasts block and data in green obtained with constant contrast blocks. The effect of matched contrast adaptation is a narrowing of the distributions, with the largest shift observed for the low contrast. B. Distributions of percent change in HWHH for one contrast in two stimulation regimes. HWHH obtained in the constant contrast block for a given contrast (matched adaptation) is expressed as a percentage of the one obtained for the same contrast in the mixed contrasts block (mismatched adaptation). Cells showing significant (t-test, p<0.05) decrease in HWHH with adaptation to constant contrast are indicated in black, and cells showing significant increase in HWHH by hachure. Upper histogram: adaptation to high contrast resulted in a small but significant reduction of HWHH compared to adaptation to mixed contrasts (median: 96.3%). Middle histogram: adaptation to medium contrast resulted in a small but significant increase in HWHH compared to adapting to mixed contrasts (median: 105.0%). Lower histogram: adaptation to low contrast resulted in a significant and larger increase in HWHH compared to adapting to mixed contrasts (median: 120.7%).</p