Biology subjects

Gaillard, C.

Publications and source records attributed to Gaillard, C..

10 recordsLinked to original sources

bioRxiv2025

Overexpression of the sugar transporter VvHT5 turns grapevine into a better host for Botrytis cinerea

Sugars are key modulators of plant-pathogen interactions, serving both as metabolic resources and as signaling molecules that influence defense outcomes. In grapevine (Vitis vinifera), the hexose transporter VvHT5, an ortholog of Arabidopsis thaliana STP13, is strongly induced during fungal infections, suggesting a role in defense-related sugar partitioning. Here, we examined the function of VvHT5 in grapevine susceptibility to the necrotrophic fungus Botrytis cinerea. Transgenic lines overexpressing VvHT5 were generated in two cultivars, Thompson Seedless and Chardonnay, and displayed increased sugar uptake in leaves. Upon B. cinerea inoculation, these lines exhibited enhanced lesion development and fungal proliferation, contrasting with the tolerance phenotype previously observed in A. thaliana expressing VvHT5. Dual RNA-seq analysis revealed that VvHT5 overexpression triggers a transcriptional landscape favoring carbohydrate metabolism, cell wall remodeling, and attenuation of defense responses, paralleled by upregulation of fungal genes involved in sugar acquisition and virulence. These results demonstrate that while VvHT5 contributes to restricting sugar availability to pathogens in Arabidopsis, its constitutive activation in grapevine enhances host suitability for B. cinerea. Our findings highlight the complexity of sugar-mediated interactions and underscore the importance of host context in determining the outcome of plant-pathogen competition for carbon resources. HIGHLIGHTSO_LIVvHT5 overexpression increases Botrytis cinerea susceptibility in grapevine C_LIO_LIDual RNA-seq uncovers coordinated transcriptional shifts in host and pathogen C_LIO_LIVvHT5 reprograms sugar partitioning and defense-associated metabolism C_LIO_LIContrasting STP13-like responses between grapevine and Arabidopsis C_LIO_LISugar uptake activity of VvHT5 promotes fungal access to host carbon C_LI

plant biology↗

bioRxiv2024

Frequency coding of multisensory integration in the local field potentials of the medial pulvinar

The pulvinar is a posterior thalamic nucleus, with a heterogeneous anatomo-functional organization. It is divided into four parts, including the medial pulvinar, which is densely connected with primary unisensory and multisensory cortical regions, and subcortical structures, including the superior colliculus. Based on this connectivity, the medial pulvinar may play an important role in sensory processing and multisensory integration. However, its contribution to multisensory integration has rarely been directly investigated. To fill this knowledge gap, two macaque monkeys were trained on a fixation task, during which auditory, visual and audiovisual stimuli were presented. We characterize local field potentials of the medial pulvinar associated with these stimuli. In the temporal domain, we describe an early and a late period showing multisensory integration, both dominated by sub-additive processes (the audiovisual response is inferior to the sum of the unisensory responses). In the frequency domain, multisensory integration, mostly sub-additive, is predominant in the lower frequencies (90% of recorded signals in 4.5-8.5Hz and 96% in 8.5-20Hz). Prevalence largely decreases in high frequencies (54% in 35-60Hz, 37% in 60-120Hz). This suggests that the medial pulvinar is a multisensory hub, integrating visual and auditory information in different frequency bands and contributing to cortico-pulvino-cortical multisensory computational loops.

neuroscience↗

bioRxiv2024

Functional traits and phylogeny predict vertical foraging in terrestrial mammals and birds

Earths ecosystems are characterized by numerous gradients related to the distribution of environmental conditions and resources. Niche theory predicts that animals will evolve traits to exploit changing resource availability and environmental conditions across these gradients. Much work has been done examining how animal traits like body mass and diet change across gradients from regional to global scales. Environmental and resource gradients in the vertical dimension tend to exhibit strong changes over relatively short distances due to the influence of elevation and vegetation. Vegetation structure may be an especially important vertical axis as it contributes to strong gradients in micro- climate, food resources, and predation risk. To investigate interrelationships between the vertical niche and its presumed drivers, we use functional traits, phylogenies, and predation risk to predict the vertical foraging niche for 4,828 mammals and 9,437 birds globally. To provide biogeographic context to the predictive analysis, we use species ranges to map geographic distributions of the vertical foraging niche and relationships between the niche and its presumed drivers. Linking trait databases with species range maps revealed distinct global distributions of vertical foraging niches for mammals and birds. The most important predictors of these niches varied by taxon but there were several systematic relationships. Diet, body mass, and phylogeny were strong predictors of vertical foraging niche across mammal and bird species. Percent fruit in diet exhibited progressively more positive relationships with higher canopy foraging positions. Predation pressure was relatively unimportant in predicting most vertical foraging niches for birds and mammals but displayed a positive trend with arboreal foraging. Geographic hotspots for the importance of fruit in both mammal and bird diets included the Andes-Amazon transition zone, the Amazon Basin, and New Guinea. Our results provide support for the theory of resource driven vertical niche partitioning but also reveal that vertical niches are strongly associated with phylogeny, suggesting niche conservatism in numerous mammal and bird families. Geographic patterns in variable importance values suggest multiple mechanisms behind spatial structure in eco- evolutionary relationships, including latitudinal gradients in vegetation structure and composition, historical patterns of island isolation (in Southeast Asia), and the influence of habitat heterogeneity driven by tectonic processes (in South America).

ecology↗

bioRxiv2023

Distinct neural states encode task identity in frontal eye field and interact with its core spatial properties

The prefrontal cortex (PFC) plays a key role in selecting, maintaining and representing sensory information, and in its integration with our current internal goals and expectations, implementing such cognitive processes as executive functions, attention, decision making and working memory. Performing computation over all of these functional cognitive processes and dynamically shifting from one to the other based on task demands requires a complex functional organization and a high degree of coding flexibility. The PFC cells show a non-linear mixed selectivity characterized by specific tuning for multiple task- and behaviour related parameters. This non-linear mixed selectivity thought to allow for a high-dimensional representation of information. Here, we asked if the PFC is mainly involved in specific task-parameters representation, or if it additionally holds a higher order representation for task-identity. We thus trained two macaques to perform three different tasks: a memory guided saccade task and two detection tasks involving different attention mechanisms. Multi-unit activity was recorded in the frontal eye field, bilaterally, while monkeys performed these three tasks in a same session. Using demixed Principal Component Analysis, we found a two-dimensional neural state that characterized each of these tasks. The lower dimensional representation of the activity recorded during the performance of the two attentional tasks were more similar to each other than to the memory-guided saccade task. Furthermore, we report that task and spatial information are non-linearly mixed, a signature of a high-dimensional neural representation. Overall, this indicates that PFC encodes task identity information and flexibly adjusts its sensory processes as a function of the specific ongoing task. Significance StatementOne long lasting question in cognitive neuroscience is whether PFC mainly represents the different parameters that are needed to perform any given task, or if it additionally holds a higher order representation for task-identity. We recorded from the macaque frontal eye fields while monkeys performed a memory guided saccade task and two detection tasks involving different attention mechanisms. We found a task-identity neural state in which the two attentional tasks were represented similarly to each other but differently from the memory-guided saccade task. We also report that task and spatial information are non-linearly mixed, a signature of a high-dimensional neuronal representation. Overall, this indicates that PFC encodes task identity information and flexibly adjusts its sensory processes as a function of the specific ongoing task.

neuroscience↗

bioRxiv2022

Neural resources shift under Methylphenidate: a computational approach to examine anxiety-cognition interplay

The reciprocal interplay between anxiety and cognition is well documented. Anxiety negatively impacts cognition, while cognitive engagement can down-regulate anxiety. The brain mechanisms and dynamics underlying such interplay are not fully understood. To study this question, we experimentally and orthogonally manipulated anxiety (using a threat of shock paradigm) and cognition (using methylphenidate; MPH). The effects of these manipulations on the brain and behavior were evaluated in 50 healthy participants (25 MPH, 25 placebo), using an n-back working memory fMRI task (with low and high load conditions). Behaviorally, improved response accuracy was observed as a main effect of the drug across all conditions. We employed two approaches to understand the neural mechanisms underlying MPH-based cognitive enhancement in safe and threat conditions. First, we performed a hypothesis-driven computational analysis using a mathematical framework to examine how MPH putatively affects cognitive enhancement in the face of induced anxiety across two levels of cognitive load. Second, we performed an exploratory data analysis using Topological Data Analysis (TDA)-based Mapper to examine changes in spatiotemporal brain activity across the entire cortex. Both approaches provided converging evidence that MPH facilitated greater differential engagement of neural resources (brain activity) across low and high working memory load conditions. Furthermore, load-based differential management of neural resources reflects enhanced efficiency that is most powerful during higher load and induced anxiety conditions. Overall, our results provide novel insights regarding brain mechanisms that facilitate cognitive enhancement under MPH and, in future research, may be used to help mitigate anxiety-related cognitive underperformance.

neuroscience↗

bioRxiv2021

Attentional brain rhythms during prolonged cognitive activity

As routine and lower demand cognitive tasks are taken over by automated assistive systems, human operators are increasingly required to sustain cognitive demand over long periods of time. This has been reported to have long term adverse effects on cardiovascular and mental health. However, it remains unclear whether prolonged cognitive activity results in a monotonic decrease in the efficiency of the recruited brain processes, or whether the brain is able to sustain functions over time spans of one hour and more. Here, we show that during working sessions of one hour or more, contrary to the prediction of a monotonic decline, behavioral performance in both humans and non-human primates consistently fluctuates between periods of optimal and suboptimal performance at a very slow rhythm of circa 5 cycles per hour. These fluctuations are observed in both high attentional (in non-human primates) and low attentional (in humans) demand conditions. They coincide with fluctuations in pupil diameter, indicating underlying changes in arousal and information-processing load. Accordingly, we show that these rhythmic behavioral fluctuations correlate, at the neurophysiological level, with fluctuations in the informational attention orientation and perception processing capacity of prefrontal neuronal populations. We further identify specific markers of these fluctuations in LFP power, LFP coherence and spike-field coherence, pointing towards long-range rhythmic modulatory inputs to the prefrontal cortex rather than a local prefrontal origin. These results shed light on the resilience of brain mechanisms to sustained effort and have direct implications on how to optimize high cognitive demand working and learning environments.

neuroscience↗

bioRxiv2020

Information-based signal selection improves decoding of attention spotlight from multi-units & local field potentials and enhances correlation with behavior.

The ability to access brain information in real-time is crucial both for a better understanding of cognitive functions and for the development of therapeutic applications based on brain-machine interfaces. Great success has been achieved in the field of neural motor prosthesis. Progress is still needed in the real-time decoding of higher-order cognitive processes such as covert attention. Recently, we showed that we can track the location of the attentional spotlight using classification methods applied to prefrontal multi-unit activity (MUA) in the non-human primate (Astrand et al., 2016). Importantly, we demonstrated that the decoded (x,y) attentional spotlight parametrically correlates with the behavior of the monkeys thus validating our decoding of attention. We also demonstrate that this spotlight is extremely dynamic (Gaillard et al., 2020). Here, in order to get closer to non-invasive decoding applications, we extend our previous work to local field potential signals (LFP). Specifically, we achieve, for the first time, high decoding accuracy of the (x,y) location of the attentional spotlight from prefrontal LFP signals, to a degree comparable to that achieved from MUA signals, and we show that this LFP content is predictive of behavior. This LFP attention-related information is maximal in the gamma band. In addition, we introduce a novel two-step decoding procedure based on the labelling of maximally attention-informative trials during the decoding procedure. This procedure strongly improves the correlation between our real-time MUA and LFP based decoding and behavioral performance, thus further refining the functional relevance of this real-time decoding of the (x,y) locus of attention. This improvement is more marked for LFP signals than for MUA signals, suggesting that LFP signals may contain other sources of task-related variability than spatial attention information. Overall, this study demonstrates that the attentional spotlight can be accessed from LFP frequency content, in real-time, and can be used to drive high-information content cognitive brain machine interfaces for the development of new therapeutic strategies. HighlightsWe use machine learning to decode attention spotlight from prefrontal MUA & LFP. We achieve high decoding accuracy of (x,y) spatial attention spotlight. (x,y) attention spotlight position accuracy is maximal from LFP gamma frequency range. MUA and LFP decoded attention position predicts behavioral performances. Selecting high information signals improves decoding and behavioral correlates.

neuroscience↗

bioRxiv2019

Rhythmic variations in prefrontal inter-neuronal correlations, their underlying mechanisms and their behavioral correlates

Functional neuronal correlations between pairs of neurons are thought to play an important role in neuronal information processing and optimal neuronal computations during attention, perception, decision-making and learning. These noise correlations are often assumed to be stable in time. However, recent studies suggest that cognitive processes are rhythmic, this rhythmicity accounting for variations in overt behavioral performance. Whether this rhythmicity coincides with variations in shared noise variability is unknown. Here, we perform simultaneous recordings from the macaque frontal eye fields, while animals are engaged in a spatial memory task. We report that noise correlations in prefrontal cortex fluctuate rhythmically in the high alpha (10-16Hz) and beta (20-30Hz) frequency ranges. Importantly, these rhythmic modulations in shared neuronal variability account for dynamic changes in overt behavioral performance. They also coincide with increased spike-LFP phase coupling in these specific frequency ranges, the spatial profile of which vary between superficial and deep cortical layers. Finally, we demonstrate, using an artificial neuronal model, that rhythmic variations in noise correlation oscillations parsimoniously arise from long range (LFP) and local spike-LFP phase coupling mechanisms. Thus a significant portion of noise correlation fluctuations can be attributed to long-range global network rhythmicity.

neuroscience↗

bioRxiv2019

Prefrontal attentional saccades explore space at an alpha rhythm

Recent studies suggest that attention samples space rhythmically through oscillatory interactions in the frontoparietal network. However, the precise mechanism through which the prefrontal cortex, at the source of attention control signals, organizes this rhythmic exploration of space remains unknown. We show that, when decoded at a high spatial (0.1{degrees}) and temporal resolution (50ms), the prefrontal covert attentional spotlight, aka the minds eye, continuously explores space at an alpha 7-12 Hz rhythm. When sensory events are presented at a specific optimal phase (resp. anti-phase) with respect to this rhythm, sensory encoding and behavioral report are accurate (resp. poor). We propose that this rhythmic prefrontal attentional spotlight dynamics corresponds to a continuous overt exploration of space via alpha-clocked attentional saccades. These attentional saccades are highly flexible, their pattern of space exploration depending both on within-trial and across-task contingencies. These results are discussed in the context of exploration and exploitation strategies and prefrontal top-down attentional control.\n\nHighlightsO_LIThe decoded prefrontal attentional spotlight samples visual space in rhythmic cycles\nC_LIO_LIThis rhythmic attentional exploration predicts neuronal sensory processing accuracy\nC_LIO_LIThis rhythmic attentional exploration predicts overt behavioral accuracy\nC_LIO_LIThese rhythmic cycles define alpha-clocked attentional saccades\nC_LIO_LISpace exploration by attentional saccades is highly flexible and under top-down control\nC_LI

neuroscience↗

bioRxiv2019

Interneuronal correlations dynamically adjust to task demands at multiple time-scales

Functional neuronal correlations between pairs of neurons are thought to play an important role in neuronal information processing and optimal neuronal computations during attention, perception, decision-making and learning. Here, we report dynamic changes in prefrontal neuronal noise correlations at multiple time-scales, as a function of task contingencies. Specifically, we record neuronal activity from the macaque frontal eye fields, a cortical region at the source of spatial attention top-down control, while the animals are engaged in tasks of varying cognitive demands. First, we show that noise correlations decrease as cognitive engagement and task demands increase, both across tasks and within-trials. Second, we demonstrate, for the first time, rhythmic modulations of noise correlations in the alpha and beta frequency ranges that account both for overt behavioral performance and for layer specific modulations in spike-field coherence. All this taken together demonstrates a strong functional role of noise correlations in cognitive flexibility.

neuroscience↗