Biology subjects

Bauer, J.

Publications and source records attributed to Bauer, J..

28 records · Page 2Linked to original sources

bioRxiv2023

Sensory experience steers representational drift in mouse visual cortex

Representational drift - the gradual continuous change of neuronal representations - has been observed across many brain areas. It is unclear whether drift is caused by synaptic plasticity elicited by sensory experience, or by the intrinsic volatility of synapses. Here, using chronic two-photon calcium imaging in mouse primary visual cortex, we find that the preferred stimulus orientation of individual neurons slowly drifts over the course of weeks. By using cylinder lens goggles to limit visual experience to a narrow range of orientations, we show that the direction of drift, but not its magnitude, is biased by the statistics of visual input. A network model suggests that drift of preferred orientation largely results from synaptic volatility, which under normal visual conditions is counteracted by experience-driven Hebbian mechanisms, stabilizing preferred orientation. Under deprivation conditions these Hebbian mechanisms enable adaptation. Thus, Hebbian synaptic plasticity steers drift to match the statistics of the environment.

neuroscience↗

bioRxiv2022

Eyeball translations affect saccadic eye movements beyond brainstem control

Vision requires that we rotate our eyes frequently to look at informative structures in the scene. Eye movements are planned by the brain but their execution depends on the mechanical properties of the oculomotor plant, i.e, the arrangement of eyeball position, muscle insertions and pulley locations. Therefore, the biomechanics of rotations is sensitive to eyeball translation because it changes muscle levers. Eyeball translations are little researched as they are difficult to measure with conventional techniques. Here we study the effects of eyeball translation on the coordination of gaze rotation by high-speed MRI recordings of saccadic eye movements during blinks, which are known to produce strong translations. We found that saccades during blinks massively overshoot their targets, and that these overshoots occur in a transient fashion such that the eye is back on target at the time the blink ends. These dynamic overshoots were tightly coupled to the eyeball translation, both in time and in size. Saccades made without blinks were also accompanied by small amounts of transient eyeball retraction, the size of which scaled with saccade amplitude. These findings demonstrate the complex interaction between rotation and translation movements of the eye. The mechanical consequences of eyeball translation on oculomotor control should be considered along with the neural implementation in the brain to understand the generation of eye movements and their disorders.

neuroscience↗

bioRxiv2022

Interrelated effects of age and parenthood on whole-brain controllability: protective effects of parenthood in mothers

BackgroundControllability is a measure of the brains ability to orchestrate neural activity which can be quantified in terms of properties of the brains network connectivity. Evidence from the literature suggests that aging can exert a general effect on whole-brain controllability. Mounting evidence, on the other hand, suggests that parenthood and motherhood in particular lead to long-lasting changes in brain architecture that effectively slow down brain aging. We hypothesize that parenthood might preserve brain controllability properties from aging. MethodsIn a sample of 814 healthy individuals (aged 33.9{+/-}12.7 years, 522 females), we estimate whole-brain controllability and compare the aging effects in subjects with vs. those without children. We use diffusion tensor imaging (DTI) to estimate the brain structural connectome. The level of brain control is then calculated from the connectomic properties of the brain structure. Specifically, we measure the network control over many low-energy state transitions (average controllability) and the network control over difficult-to-reach states (modal controllability). Results and conclusionIn nulliparous females, whole-brain average controllability increases, and modal controllability decreases with age, a trend that we do not observe in parous females. Statistical comparison of the controllability metrics shows that modal controllability is higher and average controllability is lower in parous females compared to nulliparous females. In men, we observed the same trend, but the difference between nulliparous and parous males do not reach statistical significance. Our results provide strong evidence that parenthood contradicts aging effects on brain controllability and the effect is stronger in mothers.

neuroscience↗

bioRxiv2022

All the ways your eyes can move if you don't look: Eyeball lifting, retraction and compression during blinks

Blinks occur frequently in normal life and have increasingly been linked to perceptual and cognitive effects. However, the oculomechanics of blink-related eye movements are much less researched than other types of eye movements. While it has been observed that the eye is being pulled back into its socket during a blink, possibly due to co-contraction of extraocular muscles, this elusive eye motion has not been studied in detail due to the technical difficulties that go along with a closed eyelid. Here we use dynamic magnetic resonance imaging (MRI) to obtain videos of this motion and analyse the kinematics with the recently developed MREyeTrack algorithm. We show that the eye is not only retracted but also lifted up during a blink. For some participants we observed eyeball lifting by up to 3 mm, far exceeding the amount of translation believed to occur during natural eye movements. Slow blinks can be accompanied by large tonic rotations of up to 15{degrees}. Furthermore, we collected evidence that the co-contraction of extraocular muscles leads to a slight compression of the eyeball. These findings demonstrate the surprising complexity of ocular motility and offer new opportunities to study orbital mechanics in health and disease.

neuroscience↗

bioRxiv2020

Selective connectivity limits functional binocularity in the retinogeniculate pathway of the mouse

Eye-specific segregation of retinal ganglion cell (RGC) axons in the dorsal lateral geniculate nucleus (dLGN) is considered a hallmark of visual system development. However, a recent anatomical study showed that nearly half of the neurons in dLGN of adult mice still receive input from both retinae, but functional data about binocularity in mature dLGN is conflicting. Here, we found that a variable but small fraction of thalamocortical neurons is binocular in vivo. Using dual-channel optogenetics in vitro we correspondingly found that dLGN neurons are dominated by retinogeniculate input from one eye only, although most neurons also received small but detectable input from the non-dominant eye. Anatomical overlap between RGC axons and dLGN neuron dendrites did not explain this strong bias towards monocularity. Our data rather suggest that functional input selection and refinement, leaving the remaining non-dominant eye inputs in a juvenile-like state, underlies the prevalent monocularity of neurons in dLGN.

neuroscience↗

bioRxiv2020

Tracking Single Particles for Hours via Continuous DNA-mediated Fluorophore Exchange

Fluorophores are commonly used to covalently label biomolecules for monitoring their motion in single particle tracking experiments. However, photobleaching is still a major bottleneck in these experiments, as the fluorophores finite photon budget typically limits observation times to merely a few seconds. Here, we overcome this inherent constraint via continuous fluorophore exchange based on DNA-PAINT, whereby fluorescently-labeled oligonucleotides bind to a 54 bp single-stranded DNA handle attached to the molecule of interest. When we assayed our approach in vitro by tracking single DNA origami, first surface-immobilized and subsequently diffusing on supported lipid bilayers, we were able to observe these origami for up to hours without losing their fluorescence signals. Our versatile and easily implemented labeling approach allows monitoring single-molecule motion and interactions over unprecedented observation periods, opening the doors to advanced quantitative studies.

biophysics↗

bioRxiv2020

High-resolution influenza mapping of a city reveals socioeconomic determinants of transmission within and between urban quarters

With two-thirds of the global population projected to be living in urban areas by 2050, understanding the transmission patterns of viral pathogens within cities is crucial for effective prevention strategies. Here, in unprecedented spatial resolution, we analysed the socioeconomic determinants of influenza transmission in a European city. We combined geographical and epidemiological data with whole genome sequencing of influenza viruses at the scale of urban quarters and statistical blocks, the smallest geographic subdivisions within a city. We observed annually re-occurring geographic clusters of influenza incidences, mainly associated with net income, and independent of population density and living space. Vaccination against influenza was also mainly associated with household income and was linked to the likelihood of influenza-like illness within an urban quarter. Transmissions patterns within and between quarters were complex. High-resolution city-level epidemiological studies combined with social science surveys such as this will be essential for understanding seasonal and pandemic transmission chains and delivering tailored public health information and vaccination programs at the municipal level.

microbiology↗

bioRxiv2020

Dynamic inhibition of sensory responses mediated by an olfactory corticofugal system

Processing of sensory information is substantially modulated by centrifugal projections from higher cortical areas, yet their behavioral relevance and underlying neural mechanisms remain unclear in most cases. The anterior olfactory nucleus (AON) is part of the olfactory cortex and its extensive connections to lower and higher brain centers put it in a prime position to modulate early sensory information in the olfactory system. Here, we show that optogenetic activation of AON neurons in awake animals was not perceived as an odorant equivalent cue. However, AON activation during odorant presentation reliably suppressed odor responses. This AON mediated effect was fast and constant across odors and concentrations. Likewise, activation of glutamatergic AON projections to the olfactory bulb (OB) transiently inhibited the excitability of mitral/tufted cells (MTCs) that relay olfactory input to cortex. Single-unit MTC recordings revealed that optogenetic activation of glutamatergic AON terminals in the OB transiently decreased sensory-evoked MTC spiking, regardless of the strength or polarity of the sensory response. These findings suggest that glutamatergic AON projections to the OB suppress early olfactory processing by inhibiting OB output neurons and that the AON can dynamically gate sensory throughput to the cortex. Significance StatementThe anterior olfactory nucleus (AON) as an olfactory information processing area sends extensive projections to lower and higher brain centers but the behavioral consequences of its activation have been scarcely investigated. Using behavioral tests in combination with optogenetic manipulation we show that in contrast to what has been suggested previously, the AON does not seem to form odor percepts but instead suppresses odor responses across odorants and concentrations. Furthermore, this study shows that glutamatergic cortical projections to the olfactory bulb suppress olfactory processing by inhibiting output neurons, pointing to a potential mechanisms by which the olfactory cortex can actively and dynamically gate sensory throughput to higher brain centers. HighlightsAON stimulation suppresses odor responses across odorants and concentrations AON activation is not perceived as an odorant equivalent cue The AON dynamically shapes olfactory bulb output on a fast timescale AON input to the olfactory bulb strongly suppresses mitral/tufted cells firing

neuroscience↗

bioRxiv2018

Studying the fate of tumor extracellular vesicles at high spatio-temporal resolution using the zebrafish embryo

Tumor extracellular vesicles (tumor EVs) mediate the communication between tumor and stromal cells mostly to the benefit of tumor progression. Notably, tumor EVs have been reported to travel in the blood circulation, reach specific distant organs and locally modify the microenvironment. However, visualizing these events in vivo still faces major hurdles. Here, we show a new method for tracking individual circulating tumor EVs in a living organism: we combine novel, bright and specific fluorescent membrane probes, MemBright, with the transparent zebrafish embryo as an animal model. We provide the first description of tumor EVs hemodynamic behavior and document their arrest before internalization. Using transgenic lines, we show that circulating tumor EVs are uptaken by endothelial cells and blood patrolling macrophages, but not by leukocytes, and subsequently stored in acidic degradative compartments. Finally, we prove that the MemBright can be used to follow naturally released tumor EVs in vivo. Overall, our study demonstrates the usefulness and prospects of zebrafish embryo to track tumor EVs in vivo.\n\nHighlightsO_LIMemBright, a new family of membrane probes, allows for bright and specific staining of EVs\nC_LIO_LIZebrafish melanoma EVs are very similar to human and mouse melanoma EVs in morphology and protein content\nC_LIO_LIThe zebrafish embryo is an adapted model to precisely track tumor EVs dynamics and fate in a living organism from light to electron microscopy\nC_LIO_LICirculating tumor EVs are rapidly uptaken by endothelial cells and patrolling macrophages\nC_LIO_LICorrelated light and electron microscopy can be used in zebrafish to identify cells and compartments uptaking tumor EVs\nC_LI\n\nBlurbDispersion of tumor extracellular vesicles (EVs) throughout the body promotes tumor progression. However the behavior of tumor EVs in body fluids remains mysterious due to their small size and the absence of adapted animal model. Here we show that the zebrafish embryo can be used to track circulating tumor EVs in vivo and provide the first high-resolution description of their dissemination and uptake.

cell biology↗

bioRxiv2017

Mapping Cortical Brain Asymmetry in 17,141 Healthy Individuals Worldwide via the ENIGMA Consortium

Hemispheric asymmetry is a cardinal feature of human brain organization. Altered brain asymmetry has also been linked to some cognitive and neuropsychiatric disorders. Here the ENIGMA consortium presents the largest ever analysis of cerebral cortical asymmetry and its variability across individuals. Cortical thickness and surface area were assessed in MRI scans of 17,141 healthy individuals from 99 datasets worldwide. Results revealed widespread asymmetries at both hemispheric and regional levels, with a generally thicker cortex but smaller surface area in the left hemisphere relative to the right. Regionally, asymmetries of cortical thickness and/or surface area were found in the inferior frontal gyrus, transverse temporal gyrus, parahippocampal gyrus, and entorhinal cortex. These regions are involved in lateralized functions, including language and visuospatial processing. In addition to population-level asymmetries, variability in brain asymmetry was related to sex, age, and brain size (indexed by intracranial volume). Interestingly, we did not find significant associations between asymmetries and handedness. Finally, with two independent pedigree datasets (N = 1,443 and 1,113, respectively), we found several asymmetries showing modest but highly reliable heritability. The structural asymmetries identified, and their variabilities and heritability provide a reference resource for future studies on the genetic basis of brain asymmetry and altered laterality in cognitive, neurological, and psychiatric disorders.\n\nSignificance StatementLeft-right asymmetry is a key feature of the human brain's structure and function. It remains unclear which cortical regions are asymmetrical on average in the population, and how biological factors such as age, sex and genetic variation affect these asymmetries. Here we describe by far the largest ever study of cerebral cortical brain asymmetry, based on data from 17,141 participants. We found a global anterior-posterior 'torque' pattern in cortical thickness, together with various regional asymmetries at the population level, which have not been previously described, as well as effects of age, sex, and heritability estimates. From these data, we have created an on-line resource that will serve future studies of human brain anatomy in health and disease.

neuroscience↗