Biology subjects

Tremblay, S.

Publications and source records attributed to Tremblay, S..

10 recordsLinked to original sources

bioRxiv2026

Optimizing Intermittent Theta-Burst Stimulation: The Effects of Pulse Parameters on Corticospinal Excitability

Objective. Intermittent theta burst stimulation (iTBS) is a repetitive transcranial magnetic stimulation (rTMS) protocol used in clinical settings to alleviate symptoms of psychiatric disorders. Although the pulse parameters currently used in iTBS have remained unchanged since the first treatments, recent controllable TMS devices allow for the personalization of pulse shape and duration, opening the possibility of testing the efficacy of other pulse parameters in modulating corticospinal excitability (CSE). Methods. In a repeated-measures design, changes in CSE were induced by the administration of iTBS over the left primary motor cortex under three different conditions: long bidirectional pulse (L-Bi), long quasi-unidirectional pulse (L-QU), and a control short quasi-unidirectional pulse (S-QU). We assessed TMS-induced motor evoked potentials before and up to 70 minutes after iTBS. We hypothesized that L-QU pulses would induce greater facilitation than other conditions. Results. A mixed linear model showed that all conditions induced increased MEPs compared to baseline. However, the L-Bi pulse led to a larger and more sustained MEP increase than both unidirectional pulses, while the S-QU pulse appeared less effective in modulating CSE. We observed large within- and between-subject variability in responsiveness to the iTBS protocols. Conclusion. These results suggest that L-Bi pulses in iTBS protocols are more potent than unidirectional pulses in inducing CSE changes in the cortex of healthy adults. The individual variability in response to iTBS and the potential clinical relevance of these findings are discussed.

neuroscience↗

bioRxiv2026

The Metabolome of Drosophila Reveals Exercise-Induced Stress and Anti-Inflammatory Response

Exercise is a known remedy for metabolic disorders, including obesity and type II diabetes. In humans and some model organisms, exercise is classified into different types and intensities based on the mode of exercise and the devices used. Since Drosophila has emerged as a model for exercise research, several devices have been developed for exercise training. These devices vary in mechanisms of operation; for example, the Power Tower (PT) uses a repeated drop-and-hit mechanism, and the TreadWheel (TW) uses end-over-end rotation. This variation in mechanisms that trigger the negative geotaxis of flies could impact exercise outcomes, and it remains unclear how this variation drives the response of flies to exercise training. Stress is a known response to exercise in humans and mice. Stress in Drosophila can be induced by various conditions, including heat, cold, chemical exposure, and other environmental stressors, but there is little information on exercise-induced stress. It is also unclear whether different devices elicit distinct stress responses or whether the exercise-induced stress response is similar to other stress responses (e.g., thermal, chemical). To explore the effects of device, sex, and genotype on multiple metabolic pathways, we used an untargeted metabolomics approach to further elucidate the molecular mechanisms of exercise. As no studies have directly examined the exercise metabolome of Drosophila, this study is the first to explore the metabolome of flies post-exercise. Our results revealed that exercising on different devices elicits varying responses and reshapes the metabolome of flies. We also identified specific small compounds that may be linked to stress and inflammatory response more in the PT-exercised flies than in the TW-exercised flies. Overall, the exercise device effect interacted with sex effect and genotype, such that male and female flies have different metabolite compositions post-exercise on TW and PT.

Molecular Biology↗

bioRxiv2026

Mid-superior temporal sulcus encodes spatial context and behavioral state in freely moving macaques

Primate neuroscience has traditionally studied the brain under highly constrained conditions, limiting our understanding of neural function during real-world behavior. The mid-superior temporal sulcus (mSTS) is implicated in social perception, but its role during unconstrained behavior has not been tested. Here we performed wireless depth-electrode recordings from both banks of mSTS in macaques freely exploring a large three-dimensional arena, combined with 3D pose tracking and behavioral segmentation. Neural encoding models revealed mSTS firing rates were jointly modulated by spatial position, body kinematics, and geometric visual proxies, preferentially encoded in allocentric coordinates but with a shift toward body-centric encoding during vertical exploration. Neural populations carried decodable information about discrete behavioral syllables, with broad temporal generalization and neural similarity that tracked the sequential structure of behavior. Population manifold analysis revealed that the same behavior occupied different regions of population space at different spatial locations, and population dynamics showed structured organization around behavioral transitions. Together, these results suggest that mSTS populations carry joint information about spatial context and behavioral state during natural behavior.

neuroscience↗

bioRxiv2025

Lateral inhibition governs ancestral cellular patterning in fossil and extant liverworts

The incompleteness of the fossil record and the absence of genetic information limit our ability to understand ancient developmental processes and reconstruct their evolution. Here, we use comparative and mathematical analyses to uncover an evolutionarily conserved patterning mechanism underlying liverwort oil body cell specification. We demonstrate that patterns of oil body cell homologs in fossils of the oldest known liverwort (Metzgeriothallus sharonae) exhibit the spatial organization characteristic of lateral inhibition. A mechanism with local activation and lateral inhibition not only reproduces the patterns observed in fossils, but also oil body cell patterns in the extant liverworts Treubia lacunosa, Apotreubia nana, and Marchantia polymorpha. Our results point to an ancestral patterning mechanism that has been modulated by lineage-specific selective pressures over evolutionary time.

developmental biology↗

bioRxiv2025

Homology of the dark cells of Paleozoic liverworts with the specialized oil body cells of modern liverworts (Marchantiophyta)

O_LIOil bodies are a synapomorphy of liverworts (Marchantiophyta), a major group of land plants with a sparse fossil record. Paleozoic liverworts sometimes possess dark cells that appear similar in distribution to liverwort oil body cells. The Middle Devonian Metzgeriothallus sharonae provides an opportunity for comparison with modern liverworts. C_LIO_LIShale samples were collected and the carbonaceous fossils isolated by acid maceration. Museum shale specimens of Pallaviciniites devonicus were also obtained and processed. The relative location, composition, frequency and spatial distribution of the fossil dark cells was compared to that of oil cells in extant taxa. C_LIO_LIChemical characterization of the fossil dark cells is consistent with cells that contained lipids, the main component of oil bodies. Quantitative analyses revealed that the frequency and spatial distribution of dark cells are comparable to oil body cells. The dark cells of M. sharonae show clumping near the thallus edge, suggesting an anti-herbivore function. C_LIO_LIThese results support the hypothesis that the dark cells of Paleozoic liverworts and the oil body cells of extant lineages are homologous structures with a shared developmental origin, providing a new character that can be used to assign fossils and that sheds light on the evolution and function of liverwort oil bodies. C_LI

paleontology↗

bioRxiv2024

Microstructural Correlates of Cognitive and Motor Functioning Revealed via Multimodal Multivariate Analysis

Recent advances in cognitive neuroscience emphasise the importance of healthy white matter (WM) for optimal behavioural functioning. It is now widely accepted that brain connectivity via WM contributes to the emergence of behaviour. However, the association between the microstructure of WM fibres and behaviour is poorly understood due to the indirect and overlapping nature of methods used to assess microstructure. Here, we used the Mahalanobis Distance (D2) to integrate 10 metrics of WM derived from multimodal neuroimaging that have strong ties to microstructure. The D2 metric was chosen because it accounts for metrics' covariance as it measures the voxelwise distance between every subject and the average; thus providing a robust multiparametric assessment of microstructure. We used multivariate correlation to examine voxelwise WM-behaviour associations with two cognitive and two motor tasks, which allowed us to compare within and across behavioural domains. We observed that behaviour is organised in cognitive, motor, and integrative components that have widespread associations with WM, from frontal to parietal regions. Notably, the decomposition of these factors shows that tasks traditionally labelled as cognitive also contain motor components that map onto motor-related WM patterns, and that motor tasks likewise contain non-motor components linked to distinct WM microstructural features. Our results highlight the complex nature of the links between microstructure and behaviour, and support the relevance of multivariate modelling when examining brain-behaviour associations.

neuroscience↗

bioRxiv2023

Neural signatures of natural behavior in socializing macaques

Our understanding of the neurobiology of primate behavior largely derives from artificial tasks in highly-controlled laboratory settings, overlooking most natural behaviors primate brains evolved to produce1-3. In particular, how primates navigate the multidimensional social relationships that structure daily life4 and shape survival and reproductive success5 remains largely unexplored at the single neuron level. Here, we combine ethological analysis with new wireless recording technologies to uncover neural signatures of natural behavior in unrestrained, socially interacting pairs of rhesus macaques. Single neuron and population activity in prefrontal and temporal cortex unveiled robust encoding of 24 species-typical behaviors, which was strongly modulated by the presence and identity of surrounding monkeys. Male-female partners demonstrated near-perfect reciprocity in grooming, a key behavioral mechanism supporting friendships and alliances6, and neural activity maintained a running account of these social investments. When confronted with an aggressive intruder, behavioral and neural population responses reflected empathy and were buffered by the presence of a partner. By employing an ethological approach to the study of primate neurobiology, we reveal a highly-distributed neurophysiological ledger of social dynamics, a potential computational foundation supporting communal life in primate societies, including our own.

neuroscience↗

bioRxiv2022

A single-cell multi-omic atlas spanning the adult rhesus macaque brain

Cataloging the diverse cellular architecture of the primate brain is crucial for understanding cognition, behavior and disease in humans. Here, we generated a brain-wide single-cell multimodal molecular atlas of the rhesus macaque brain. Altogether, we profiled 2.58M transcriptomes and 1.59M epigenomes from single nuclei sampled from 30 regions across the adult brain. Cell composition differed extensively across the brain, revealing cellular signatures of region-specific functions. We also identified 1.19M candidate regulatory elements, many novel, allowing us to explore the landscape of cis-regulatory grammar and neurological disease risk in a cell-type-specific manner. Together, this multi-omic atlas provides an open resource for investigating the evolution of the human brain and identifying novel targets for disease interventions.

neuroscience↗

bioRxiv2022

Non-necessary neural activity in the primate cortex

When neuroscientists record neural activity from the brain, they often conclude that neural responses observed during task performance are indicative of the functional role of the brain area(s) studied. In humans and nonhuman primates, it is often hard to combine recordings and causal techniques within the same experiment, leaving the possibility that the activity recorded may be epiphenomenal rather than reflecting a specific functional role. Currently, the prevalence of epiphenomenal neural activity in the cortex is unknown. To estimate the extent of such activity in primates, we chronically recorded neural activity in the prefrontal cortex of the same monkeys using the same neural implants during the performance of four different cognitive tasks. The four tasks were carefully selected such that only one of them causally depends on the brain area recorded, as demonstrated by previous double dissociation studies. Using the four most common single neuron analyses methods in the field, we found that the prevalence and strength of neural correlates were just as high across all four tasks, including for the three tasks that do not depend on this brain area. These results suggest that the probability of observing epiphenomenal activity in primate cortex is high, which can mislead investigators relying on neural recording or imaging to map brain function. One-Sentence SummaryTremblay, Testard and colleagues show that inferring a brain areas function from neural recordings alone could be misleading.

neuroscience↗

bioRxiv2022

Neural cognitive signals during spontaneous movements in the macaque

The single neuron basis of cognitive processing in primates has mostly been studied in laboratory settings where movements are severely restricted. It is unclear, therefore, how natural movements might affect neural signatures of cognition in the brain. Moreover, studies in mice indicate that body movements, when measured, account for most of the neural dynamics in the cortex. To examine this issue, we recorded from single neuron ensembles in the prefrontal cortex in moving monkeys performing a cognitive task and characterized eyes, head, and body movements using video tracking. Despite significant trial-to-trial movement variability, single neuron tuning could be precisely measured and decision signals accurately decoded on a single-trial basis. Creating or abolishing spontaneous movements through head restraint and task manipulations had no measurable impact on neural responses. However, encoding models showed that uninstructed movements explained as much neural variance as task variables, with most of them aligned to task events. These results demonstrate that cognitive signals in the cortex are robust to natural movements, but also that unmeasured movements are potential confounds in cognitive neurophysiology experiments.

neuroscience↗