Biology subjects

Richard, B.

Publications and source records attributed to Richard, B..

6 recordsLinked to original sources

bioRxiv2025

Neural responses to binocular in-phase and anti-phase stimuli

Binocular vision fuses compatible inputs from the two eyes into a single percept, whereas incompatible inputs can produce rivalry, lustre, or diplopia. We measured neural responses to binocular stimuli with different phase relationships to test predictions from contemporary binocular combination models. Steady-State Visually Evoked Potentials (SSVEPs) were recorded from 15 observers in response to monocular and binocular stimulation at 3 Hz, using either On/Off or counterphase flicker with varied spatial and temporal phase relationships. On/Off flicker elicited responses at the fundamental frequency (3 Hz), and its integer harmonics, while counterphase flicker generated responses at the even integer harmonics (6Hz, 12Hz, 18Hz). Manipulating phase relationships modulated these response patterns, including a reduction in the fundamental amplitude for On/Off flicker. The data were modelled with a series of binocular combination algorithms, ranging in complexity from a simple linear sum to a two-stage binocular gain-control model with parallel monocular and binocular phase-selective channels. The model required parallel monocular channels to account for our data, whereas phase selectivity was not essential. Overall, the two-stage contrast gain-control model remains a powerful and flexible framework for describing binocular combinations across various experimental conditions and modalities.

neuroscience↗

bioRxiv2025

Etiology and epidemiology of branch dieback and fruit blight and necrosis of English walnut in France

English walnut (Juglans regia L.) is an economically-important fruit crop worldwide, particularly in France, where it is the second most important fruit crop after apples in terms of cultivated area. Walnut orchards are targeted by numerous diseases, but new symptoms have been widely observed since 2015 in France, consisting in typical branch dieback and fruit blight and necrosis. Herein, both symptomatic and asymptomatic twigs and husks were collected from 12 commercial French walnut orchards from the two main production areas located in the South of France from 2020 to 2022. Overall, Botryosphaeriaceae, Colletotrichum, Diaporthe, and Fusarium species were consistently isolated from symptomatic husks and twigs. Among these taxa, B. dothidea and C. godetiae were significantly more associated with symptomatic husks, contrary to D. eres and F. juglandicola, more frequently isolated from symptomatic twigs, as also confirmed by ITS2 metabarcoding sequencing. Tissue type was the primary factor significantly impacting the composition of the fungal communities (R{superscript 2} = 16.6%), followed by sampling campaign and production area (R{superscript 2} = 11.6% and 4.6%, respectively). We also found that Neofusicoccum and Diaporthe were significantly more associated with warm and dry years, unlike Colletotrichum. Pathogenicity tests revealed that only Botryosphaeriaceae and Diaporthe species were pathogenic on walnut fruits and twigs, with B. dothidea and N. parvum being the most aggressive species. Several significant positive and negative correlations were identified based on SparCC co-occurrence networks and correlograms based on prevalence data. In particular, the positive correlation between Colletotrichum and Fusarium species on symptomatic twigs was highlighted by both methods. This work is the first comprehensive etiological and epidemiological study of branch dieback and fruit blight and necrosis of English walnut in France. Author SummaryEnglish walnut is an economically important crop, mainly produced in China, in the United States and in Turkey while in Europe, France is one of the biggest producers. Although widespread in nut orchards abroad, new symptoms, including fruit necroses and branch dieback, were observed for the first time in 2015 in France. We then conducted sampling campaigns between 2020 and 2022 to collect walnut husks and twigs in the two main French production areas. Exploration of the associated microbiota revealed the presence of six predominant fungal species, even in samples without symptoms. We then investigated the capacity of these species to cause lesions on twigs and fruits. Among all species, Neofusicoccum parvum was the most aggressive on both organs while other species were mainly aggressive on only twigs or husks. In addition, we evidenced that the presence of some species was favored by warm and dry weather or inversely cold and wet weather. We also found negative correlations between certain species (in particular between N. parvum and Diaporthe eres), suggesting that some species probably prevented the other from further colonization. Overall, we identified the species specifically associated with the disease in France and the factors influencing the disease risk. This work will enable us to better identify the best strategies to combat this disease.

microbiology↗

bioRxiv2021

Syndecan-1 is overexpressed in human thoracic aneurysm but is dispensable for the disease progression in vivo

Glycosaminoglycans (GAGs) pooling has been considered since long as one of the histopathological characteristics defining thoracic aortic aneurysm (TAA) together with smooth muscle cells (SMCs) apoptosis and elastin fibers degradation. However, few information is provided about GAGs composition or potential implication in TAA pathology. Syndecan-1 (Sdc-1) is a heparan sulfate proteoglycan that is implicated in extracellular matrix (ECM) interaction and assembly, regulation of SMCs phenotype and various aspects of inflammation in the vascular wall. In the current work, the regulation of Sdc-1 protein was examined in human TAA by ELISA and immunohistochemistry. In addition, the role of Sdc-1 was evaluated in descending TAA in vivo using a mouse model combining both aortic wall weakening and hypertension. Our results showed that Sdc-1 protein is over expressed in human TAA aortas compared to healthy counterparts and that SMCs are the major cell type expressing Sdc-1. Similarly, in the mouse model used, Sdc-1 expression was increased in TAA aortas compared to healthy samples. Although its protective role against abdominal aneurysm has been reported, we observed that Sdc-1 was dispensable for TAA prevalence or rupture. In addition, Sdc-1 deficiency did not alter the extent of aortic wall dilatation, elastin degradation, collagen deposition, or leukocyte recruitment in our TAA model. These findings suggest that Sdc-1 could be a biomarker revealing TAA pathology. Future investigations could uncover the underlying mechanisms leading to Sdc-1 expression alteration in TAA.

pathology↗

bioRxiv2021

Immersion in Modified Reality: Sensitivity to the Slope (α) of the Amplitude Spectrum is Dependent on the α of Recently Viewed Environments

Scenes contain many statistical regularities that could benefit visual processing if accounted for by the visual system. One such statistic is the orientation-averaged slope () of the amplitude spectrum of natural scenes. Human observers show different discrimination sensitivity to : sensitivity is highest for values between 1.0 and 1.2 and decreases as is steepened or shallowed. The range of for peak discrimination sensitivity is concordant with the average of natural scenes, which may indicate that visual mechanisms are optimized to process information at values commonly encountered in the environment. Here we explore the association between peak discrimination sensitivity and the most viewed s in natural environments. Specifically, we verified whether discrimination sensitivity depends on the recently viewed environments. Observers were immersed, using a Head-Mounted Display, in an environment that was either unaltered or had its average steepened or shallowed by 0.4. Discrimination thresholds were affected by the average shift in , but this effect was most prominent following adaptation to a shallowed environment. We modeled these data with a Bayesian observer and explored whether a change in the prior or a change in the likelihood best explained the psychophysical effects. Change in discrimination thresholds following adaptation could be explained by a shift in the central tendency of the prior concordant with the shift of the environment, in addition to a change in the likelihood. Our findings suggest that expectations on the occurrence of that result from a lifetime of exposure remain plastic and able to accommodate for the statistical structure of recently viewed environments.

neuroscience↗

bioRxiv2021

Climate-change risk analysis for global urban forests

Urban forests (i.e. all vegetation present in urban areas), provide environmental and socioeconomic benefits1 to more than half of the global population2. Projected climate change threatens these benefits to society3-5. Here, we assess vulnerability to climate change of 16,006 plant species present in the urban forests of 1,010 cities within 93 countries, using three vulnerability metrics: exposure, safety margin and risk. Exposure expresses the magnitude of projected changes in climate in a given area, safety margin measures species sensitivity to climate change, and risk is the difference between exposure and safety margin6. We identified 9,676 (60.5%) and 8,344 (52.1%) species exceeding their current climatic tolerance (i.e. safety margin) for mean annual temperature (MAT) and annual precipitation (AP), respectively. By 2050, 13,479 (84.2%) and 9,960 (62.2%) species are predicted to be at risk from projected changes in MAT and AP, respectively, with risk increasing in cities at lower latitudes. Our results can aid evaluation of the impacts of climate change on urban forests and identify the species most at risk. Considering future climates when selecting species for urban plantings will enhance the long-term societal benefits provided by urban forests, including their contribution to mitigating the magnitude and impacts of climate change.

ecology↗

bioRxiv2018

Dynamic properties of internal noise probed by modulating binocular rivalry

Neural systems are inherently noisy, and this noise can affect our perception from moment to moment. This is particularly apparent in binocular rivalry, where our perception of competing stimuli shown to the left and right eyes alternates over time in a seemingly random fashion. We investigated internal noise using binocular rivalry by modulating rivalling stimuli using dynamic sequences of external noise of various rates and amplitudes. As well as measuring the effect on dominance durations, we repeated each external noise sequence twice, and assessed the consistency of percepts across repetitions. External noise modulations with standard deviations above 4% contrast increased consistency scores above baseline, and were most effective at 1/8Hz. A computational model of rivalry in which internal noise has a 1/f (pink) temporal amplitude spectrum, and a standard deviation of 16%, provided the best account of our data, and was able to correctly predict perception in additional conditions. Our novel technique provides detailed estimates of the dynamic properties of internal noise during binocular rivalry, and by extension the stochastic processes that drive our perception and other types of spontaneous brain activity.\n\nSignificance statementAlthough our perception of the world appears constant, sensory representations are variable because of the noisy nature of biological neurons. Here we used a binocular rivalry paradigm, in which conflicting images are shown to the two eyes, to probe the properties of this internal variability. Using a novel paradigm in which the contrasts of rivalling stimuli are modulated by two independent external noise streams, we infer the amplitude and character of this internal noise. The temporal amplitude spectrum of the noise has a 1/f spectrum, similar to that of natural visual input, and consistent with the idea that the visual system evolved to match its environment.

neuroscience↗