Biology subjects

Leblanc, H.

Publications and source records attributed to Leblanc, H..

4 recordsLinked to original sources

bioRxiv2025

Monitoring tropical forests with light drones: ensuring spatial and temporal consistency in stereophotogrammetric products

O_LILight drones provide a cheap and effective tool to monitor forest canopy, especially in tropical and equatorial contexts, where infrastructure and resources are limiting. In these regions, good quality optical satellite images are rare, yet the stakes are maximal to characterize forest function, dynamics, diversity, and phenology, and more generally the vegetation-climate interplay. C_LIO_LIWe describe a complete processing chain based on photogrammetric tools that seeks to optimize the spatial and spectral coherence between repeat image mosaics at centimetric resolution. Our target is to allow individual tree-level monitoring over tens to hundreds of hectare scales with consumer grade equipment (i.e., quadcopter with stabilized RGB camera, standard GNSS positioning). C_LIO_LIWe demonstrate the increase in spatial precision achieved using Time-SIFT and Arosics algorithms, which allow (individually and synergistically) to reduce global and local spatial misalignment between mosaics from several meters to a few centimeters. Time-SIFT provides the advantage of increased robustness in initial image alignment and 3D reconstruction, and hence reduces occasional distortions or data gaps. Using Agisofts color and white balance corrections combined with the use of vegetation indices provides meaningful quantitative signal despite considerable changes in acquisition conditions. C_LIO_LIIn particular, indices that are less sensitive to illumination changes, like the green chromatic coordinate (GCC), allowed evidencing a seasonal signal over four years of monitoring in the evergreen moist forest at Paracou in French Guiana. The signal was decorrelated from obvious geometrical effect (sun height), and provided information on the vegetative stage at tree, species, and stand levels. C_LI Data/Code for peer reviewThe complete processing chain, as well as the data and scripts used for producing the analyses presented here, are available for review on Zenodo: https://zenodo.org/records/15449377?token=eyJhbGciOiJIUzUxMiJ9.eyJpZCI6IjdjNWExMzIzLThkNDMtNDllNy1iYWY4LTY2MGZlZjkyZmQ3OCIsImRhdGEiOnt9LCJyYW5kb20iOiI5MGQ4NTE2YTE4OGViNDQ3YTFiZmMyYTFkZDlhZTZmMiJ9.CsJ0VRuQ90A1qzO1VJC1Q9eXFSp1N5UpeJlyr6otgXRPlf-I-jcwBJ6ytiBbbu8enCNJ2Ke6-oxNV8aeJ_AWIw

ecology↗

bioRxiv2021

Social Reactivation of Fear Engrams Enhances Recall and Reinstatement

For group-living species such as humans and rodents, conspecific interactions pervasively shape emotion (1-3), attention (4), and cognitive ability (5-8). Higher-order cognitive processes such as memory within a social brain are thus interlaced with social influences. Traditional laboratory rodent cages offer a limited but nonetheless rich multi-modal landscape of communication, including auditory calls (9-12), chemical signaling (13, 14), and tactile stimulation (15, 16). The absence of such social encounters in singly housed animals results in cognitive impairments and depression-like phenotypes (17), likely obscuring how the social brain has evolved to function. It is thus important to understand the relationship between social context and how individuals process memories. As social interaction recruits hippocampal (18) and amygdalar (19) circuitry that also serves as hubs for non-social memory traces(20-24), we hypothesized that pre-existing ensembles in these regions can be modulated by social experiences and lead to changes in memory expression. Here we show that stressful social experiences enhance the recall of previously acquired fear memories in male but not female mice. Activity-dependent tagging of cells in the dentate gyrus (DG) during fear learning revealed that these ensembles were endogenously reactivated during the social experiences in males. These reactivated cells were shown to be functional components of engrams, as optogenetic stimulation of the cells active during the social experience in previously fear conditioned animals was sufficient to drive fear-related behaviors. Our findings suggest that social encounters can reactivate pre-existing DG engrams and thereby strengthen discrete memories. Significance StatementSocial environments can bolster and protect cognitive abilities. However, the relationship between social stimuli and individually learned memories remains enigmatic. Our work reveals that exposure to a stressed, naive non-familiar conspecific or to the ambient olfactory-auditory cues of a recently stressed familiar conspecific induces reactivation of the cellular ensembles associated with a fear memory in the hippocampus. Artificially activating the hippocampal ensemble active during the social experience induces fearful behaviors only in animals that have previously acquired a negative memory, suggesting a fear-driving function of the reactivated ensembles and demonstrating the interaction between individual history and social experience. The neural resurgence of fear-driving ensembles during social experiences leads to a context-specific enhancement of fear recall. Our findings provide evidence that unlike directly physical stressors, ambient social stimuli can reactivate and amplify an individuals memories.

neuroscience↗

bioRxiv2020

Chronic optogenetic stimulation of hippocampal engrams variably modulates social behaviors in mice

The hippocampus processes both spatial-temporal information and emotionally salient experiences. To test the functional properties of discrete sets of cells in the dorsal dentate gyrus (dDG), we examined whether chronic optogenetic reactivation of these ensembles was sufficient to modulate social behaviors in mice. We found that chronic reactivation of dDG cells in male mice was sufficient to enhance social behaviors in a female exposure task when compared to pre-stimulation levels. However, chronic reactivation of these cells was not sufficient to modulate group differences in a separate subset of social behaviors, and multi-region analysis of neural activity did not yield detectable differences in immediate-early gene expression or neurogenesis, suggesting a dissociation between our chronic stimulation-induced behavioral effects and underlying neural responses. Together, our results demonstrate that chronic optogenetic stimulation of cells processing valent experiences enduringly and unidirectionally modulates social interactions between male and female mice.

neuroscience↗

bioRxiv2019

Odor Modulates the Temporal Dynamics of Fear Memory Consolidation

Systems consolidation (SC) theory proposes that recent, contextually rich memories are stored in the hippocampus (HPC). As these memories become remote, they are believed to rely more heavily on cortical structures within the prefrontal cortex (PFC), where they lose much of their contextual detail and become schematized. Odor is a particularly evocative cue for intense remote memory recall and despite these memories being remote, they are highly contextual. In instances such as post-traumatic stress disorder (PTSD), intense remote memory recall can occur years after trauma, which seemingly contradicts SC. We hypothesized that odor may shift the organization of salient or fearful memories such that when paired with an odor at the time of encoding, they are delayed in the de-contextualization process that occurs across time, and retrieval may still rely on the HPC, where memories are imbued with contextually rich information, even at remote time points. We investigated this by tagging odor- and non-odor-associated fear memories in male c57BL/6 mice and assessed recall and c-Fos expression in the dorsal CA1 (dCA1) and prelimbic cortex (PL) 1 d or 21 d later. In support of SC, our data showed that recent memories were more dCA1-dependent whereas remote memories were more PL-dependent. However, we also found that odor influenced this temporal dynamic biasing the memory system from the PL to the dCA1 when odor cues were present. Behaviorally, inhibiting the dCA1 with activity-dependent DREADDs had no effect on recall at 1 d and unexpectedly caused an increase in freezing at 21 d. Together, these findings demonstrate that odor can shift the organization of fear memories at the systems level.

neuroscience↗