Biology subjects

Lowet, E.

Publications and source records attributed to Lowet, E..

12 recordsLinked to original sources

bioRxiv2026

Tracking multi-site somatic voltage dynamics via high-speed fiber photometry

Investigating neural circuit dynamics across distributed brain regions in awake, behaving animals is crucial for understanding complex behavior. Genetically encoded voltage indicators (GEVIs) offer a powerful approach to tracking transmembrane voltage with high temporal and cellular specificity. However, scaling high-sensitivity GEVI recordings across multiple brain regions and multiple animals simultaneously remains a major technical challenge. Furthermore, it is unclear whether soma-targeted GEVIs - typically used for single-cell resolution imaging - can be effectively adapted for fiber photometry. Here, we show that a sCMOS-based widefield imaging system achieves sensitive dual-color multi-site fiber photometry using soma-targeted GEVI indicators with high temporal resolution. We validated this approach in the mouse hippocampal CA1, capturing theta (3-10Hz) and gamma (30-80Hz) rhythms and theta-gamma cross-frequency coupling. Additionally, we recorded high-frequency neural entrainment (>100 Hz) and somatic depolarization induced by electrical stimulation in CA1. Lastly, we tracked synchronized neural activity between the bilateral CA1s as well as multi-site dual-color imaging across CA1 and cortex simultaneously in three freely running mice. This work provides a scalable, accessible platform for high-speed optical electrophysiology in distributed neural circuits. Key points- Implementation of a sCMOS-based widefield imaging setup for sensitive and scalable fiber photometry and cellular imaging. - Demonstration of population multi-site and inter-animal voltage imaging with soma-targeted genetically encoded voltage indicators. - Tracking of high-frequency gamma and high-gamma (>100Hz) neural entrainment

neuroscience↗

bioRxiv2025

High frequency electrical stimulation entrains fast spiking interneurons and bidirectionally modulates information processing

BackgroundClinical intracranial electrical stimulation often deploys trains of high frequency pulses. While brief bursts of stimulation are known to heterogeneously modulate neuronal spiking, it is unclear how trains of high frequency pulses influence neural dynamics. ObjectiveAs fast spiking interneurons (FSIs) can support rapid firing, we seek to determine how high frequency stimulation modulates FSIs. MethodsWe characterized the real-time effect of one-second-long local stimulation at 40 versus 140 Hz on parvalbumin positive interneurons, known as FSIs, in motor and visual cortices in awake mice using near kilohertz voltage imaging, free of electrical stimulation artifact. ResultsStimulation at 140 Hz, like 40 Hz, heterogeneously modulates individual FSIs membrane voltage in both cortices, leading to complex temporal dynamics. FSIs in both cortices are robustly entrained by 40 Hz stimulation, even though 40 Hz led to prominent membrane hyperpolarization in visual cortex but not motor cortex. Intriguingly, visual cortical FSIs, but not motor cortical ones, were reliably entrained by 140 Hz stimulation. Finally, while stimulation consistently reduced the response amplitude of visual cortical FSIs to visual flickers, response temporal precision is bidirectionally modulated. ConclusionHigh frequency electrical stimulation mediates brain-region specific entrainment of FSIs, and bidirectionally modulates FSI temporal processing of synaptic inputs. Thus, high frequency stimulation can differentially engage inhibitory neurons in different brain regions to modulate network information processing. HighlightsO_LIEvoked membrane potential (Vm) responses are frequency and brain region specific C_LIO_LI140 Hz stimulation entrains the Vm of visual, but not motor, cortical FSIs C_LIO_LI140 Hz, but not 40 Hz, is effective at reducing Vm amplitude to visual flickers C_LIO_LIStimulation bidirectionally modulates Vm response timing to visual inputs C_LIO_LIVisual cortical FSIs are suppressed by 40 Hz stimulation, unlike other conditions C_LI

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bioRxiv2024

Beta-frequency sensory stimulation enhances gait rhythmicity through strengthened coupling between striatal networks and stepping movement

Stepping movement is delta (1-4 Hz) rhythmic and depends on sensory inputs. In addition to delta rhythms, beta (10-30 Hz) frequency dynamics are also prominent in the motor circuits and are coupled to neuronal delta rhythms both at the network and the cellular levels. Since beta rhythms are broadly supported by cortical and subcortical sensorimotor circuits, we explore how beta-frequency sensory stimulation influences delta-rhythmic stepping movement, and dorsal striatal circuit regulation of stepping. We delivered audiovisual stimulation at 10 Hz or 145 Hz to mice voluntarily locomoting, while simultaneously recording stepping movement, striatal cellular calcium dynamics and local field potentials (LFPs). We found that 10 Hz, but not 145 Hz stimulation prominently entrained striatal LFPs. Even though sensory stimulation at both frequencies promoted locomotion and desynchronized striatal network, only 10 Hz stimulation enhanced the delta rhythmicity of stepping movement and strengthened the coupling between stepping and striatal LFP delta and beta oscillations. These results demonstrate that higher frequency sensory stimulation can modulate lower frequency dorsal striatal neural dynamics and improve stepping rhythmicity, highlighting the translational potential of non-invasive beta-frequency sensory stimulation for improving gait.

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bioRxiv2024

Interleaved single and bursting spiking resonance in neurons

Under in vivo conditions, CA1 pyramidal cells from the hippocampus display transitions from single spikes to bursts. It is believed that subthreshold hyperpolarization and depolarization, also known as down and up-states, play a pivotal role in these transitions. Nevertheless, a central impediment to correlating suprathreshold (spiking) and subthreshold activity has been the technical difficulties of this type of recordings, even with widely used calcium imaging or multielectrode recordings. Recent work using voltage imaging with genetically encoded voltage indicators has been able to correlate spiking patterns with subthreshold activity in a variety of CA1 neurons, and recent computational models have been able to capture these transitions. In this work, we used a computational model of a CA1 pyramidal cell to investigate the role of intrinsic conductances and oscillatory patterns in generating down and up-states and their modulation in the transition from single spiking to bursting. Specifically, the emergence of distinct spiking resonances between these two spiking modes that share the same voltage traces in the presence of theta or gamma oscillatory inputs, a phenomenon we call interleaved single and bursting spiking resonance. We noticed that these resonances do not necessarily overlap in frequency or amplitude, underscoring their relevance for providing flexibility to neural processing. We studied the conductance values of three current types that are thought to be critical for the bursting behavior: persistent sodium current (INaP) and its conductance GNaP, delayed rectifier potassium (IKDR) and its conductance GKDR, and hyperpolarization-activated current (Ih) and its conductance Gh. We conclude that the intricate interplay of ionic currents significantly influences the neuronal firing patterns, transitioning from single to burst firing during sustained depolarization. Specifically, the intermediate levels of GNaP and GKDR facilitate spiking resonance at gamma frequency inputs. The resonance characteristics vary between single and burst firing modes, each displaying distinct amplitudes and resonant frequencies. Furthermore, low GNaP and high GKDR values lock bursting to theta frequencies, while high GNaP and low GKDR values lock single spiking to gamma frequencies. Lastly, the duration of quiet intervals plays a crucial role in determining the likelihood of transitioning to either bursting or single spiking modes. We confirmed that the same features were present in previously recorded in vivo voltage-imaging data. Understanding these dynamics provides valuable insights into the fundamental mechanisms underlying neuronal excitability under in vivo conditions. Author summarySince discovering that neurons in the hippocampus can encode spatial position through phase precession, many experiments have explored how specific theta and gamma oscillations influence location specificity in the brain. However, the individual neuronal properties and dynamics behind these behaviors are still being uncovered. Previously, we found that stereotypical bursting and single-spike firing in pyramidal neurons are linked to these oscillations and further associated with an animal entering or leaving a place field. Advances in voltage-imaging techniques have enabled us to assess these properties more precisely. Our study shows that different frequencies can independently trigger these stereotypical spikes, demonstrating a complex pattern where the same cell can be double-coded: a phenomenon we called interleaved resonance. Additionally, we found that this coding can be modulated by persistent sodium and delayed-rectifier potassium currents. Moreover, these neurons are more likely to burst following long periods of silence. These findings provide new insights into the mechanisms underlying neural coding in the hippocampus and how it relates to behavior.

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bioRxiv2023

Large-scale deep tissue voltage imaging with targeted illumination confocal microscopy

Voltage imaging with cellular specificity has been made possible by the tremendous advances in genetically encoded voltage indicators (GEVIs). However, the kilohertz rates required for voltage imaging lead to weak signals. Moreover, out-of-focus fluorescence and tissue scattering produce background that both undermines signal-to-noise ratio (SNR) and induces crosstalk between cells, making reliable in vivo imaging in densely labeled tissue highly challenging. We describe a microscope that combines the distinct advantages of targeted illumination and confocal gating, while also maximizing signal detection efficiency. The resulting benefits in SNR and crosstalk reduction are quantified experimentally and theoretically. Our microscope provides a versatile solution for enabling high-fidelity in vivo voltage imaging at large scales and penetration depths, which we demonstrate across a wide range of imaging conditions and different GEVI classes.

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bioRxiv2023

Stimulus representations in visual cortex shaped by spatial attention and microsaccades

SUMMARY/ABSTRACTMicrosaccades (MSs) are commonly associated with spatially directed attention, but how they affect visual processing is still not clear. We studied MSs in a task in which the animal was randomly cued to attend to a target stimulus and ignore distractors, and it was rewarded for detecting a color change in the target. We found that the enhancement of firing rates normally found with attention to a cued stimulus was delayed until the first MS directed towards that stimulus. Once that MS occurred, attention to the target was engaged and there were persistent effects of attention on firing rates for the remainder of the trial. These effects were found in the superficial and deep layers of V4 as well as the lateral pulvinar and IT cortex. Although the tuning curves of V4 cells do not change depending on the locus of spatial attention, we found pronounced effects of MS direction on stimulus representations that persisted for the length of the trial in V4. In intervals following a MS towards the target in the RF, stimulus decoding from population activity was substantially better than in intervals following a MS away from the target. Likewise, turning curves of cells were substantially sharper following a MS towards the target in the RF. This sharpening appeared to result from both a "refreshing" of the initial transient sensory response to stimulus onset, and a magnification of the effects of attention in this condition. MSs to the target also enhanced the neuronal response to the behaviorally relevant target color change and led to faster reaction times. These results thus reveal a major link between spatial attention, object processing and its coordination with eye movements.

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bioRxiv2022

Membrane Voltage Dynamics of Parvalbumin Interneurons Orchestrate Hippocampal Theta Rhythmicity

Hippocampal network activity at theta frequencies (5-10Hz) is important for behavior. However, it remains unclear how behaviorally-relevant network theta rhythms arise and interact with cellular dynamics to dictate spike timing. We performed membrane voltage (Vm) imaging of individual CA1 pyramidal cells and parvalbumin interneurons with simultaneous local field potential (LFP) recordings in mice during locomotion. We found that Vm theta rhythms organize spike timing in both cell types regardless of behavioral conditions, but the Vm of parvalbumin interneurons is better synchronized with LFP. The temporal relationships between spikes and LFP theta reliably reflect the Vm-LFP relationships in parvalbumin cells, but not in pyramidal cells. Thus, cellular theta rhythms broadly organize spike timing in CA1 neurons, and parvalbumin interneurons are critical in coordinating network theta rhythms. One-Sentence SummaryCellular membrane voltage of parvalbumin interneurons organizes spiking and network dynamics in the hippocampus.

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bioRxiv2022

Single and complex spikes relay distinct frequency-dependent circuit information in the hippocampus

Hippocampal neurons generate either single spikes or stereotyped bursts of spikes known as complex spikes. Although single and complex spikes co-occur in the same neuron, their contribution to information processing remains unclear. We analyzed hippocampal CA1 neurons in awake mice and in behaving rats, combining cellular membrane voltage imaging with optogenetics and extracellular recordings. We found that network-driven subthreshold membrane rhythms in the theta versus gamma frequencies preferably entrained complex versus single spikes in individual neurons. Optogenetic membrane perturbation revealed a causal link between subthreshold theta and gamma power and the initiation of complex versus single spikes. Further, single and complex spikes exhibited different place field properties and frequency-dependent coding during spatial navigation. Thus, individual hippocampal neurons do not integrate theta and gamma rhythms into a combined spike timing code, but instead, transmit frequency-specific information as distinct output modes of single versus complex spikes during spatial cognition.

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bioRxiv2022

Deep brain stimulation creates information lesion through membrane depolarization

Deep brain stimulation (DBS) is a promising neuromodulation therapy that alters neural activity via intracranial electrical stimulation. However, the neurophysiological mechanisms of DBS remain largely unknown, because of the difficulty of obtaining cellular resolution recordings without electrical interference. Here, we performed high-speed membrane voltage fluorescence imaging of individual hippocampal CA1 neurons during DBS in awake mice. We discovered that DBS, delivered at either 40Hz or 140Hz, reliably depolarizes somatic membrane potentials. Further, DBS enhanced spike rates and paced membrane voltage and spike timing at the stimulation frequency, though more prominent at 40Hz than 140Hz. To determine how DBS induced membrane voltage change impacts neurons ability to process inputs, we optogenetically evoked membrane depolarization. We found that neurons become unreliable in responding to optogenetic inputs during DBS, particularly during 140Hz DBS. These results demonstrate that DBS produces powerful membrane depolarization that interferes with neurons ability to process inputs, creating information lesion.

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bioRxiv2021

Large-scale voltage imaging in the brain using targeted illumination

Recent improvements in genetically encoded voltage indicators enabled optical imaging of action potentials and subthreshold membrane voltage dynamics from single neurons in the mammalian brain. To perform high speed voltage imaging, widefield microscopy remains an essential tool for recording activity from many neurons simultaneously over a large anatomical area. However, the lack of optical sectioning makes widefield microscopy more prone to background signal contamination, and thus far voltage imaging using fully genetically encoded voltage indicators remains limited to simultaneous sampling of a few cells over a restricted field-of-view. We here demonstrate a strategy for large scale voltage imaging using the fully genetically encoded voltage indicator SomArchon and targeted illumination. We implemented a simple, low-cost digital micromirror device based targeted illumination strategy to restrict illumination to the cells of interest, and systematically quantified the improvement of this microscopy design theoretically and experimentally with SomArchon expressing neurons in single layer cell cultures and in the brains of awake mice. We found that targeted illumination, in comparison to widefield illumination, increased SomArchon signal contrast and reduced background cross-contamination in the brain. Such improvement permitted the reduction of illumination intensity, and thus reduced fluorescence photobleaching and prolonged imaging duration. When coupled with a high-speed, large area sCMOS camera, we routinely imaged tens of spiking neurons simultaneously over minutes in the brain. Thus, the widefield microscopy design with an integrated targeted illumination system described here offers a simple solution for voltage imaging analysis of large neuron populations in behaving animals.

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bioRxiv2020

Oscillatory activity in alpha/beta frequencies coordinates auditory and prefrontal cortices during extinction learning

Cortical synchrony is theorized to contribute to communication between connected networks during executive functioning. To understand the functional role of neural synchrony in cognitive flexibility, we recorded from auditory cortex (AC) and medial prefrontal cortex (mPFC), while mice performed an auditory extinction learning task. We found that while animals gradually showed reduced responding to the unrewarded tone over hundreds of trials, the power of local field potential (LFP) oscillations (8-18 Hz, centered at alpha/beta frequencies) in AC and mPFC exhibited immediate and robust increases, prior to behavioral changes. The strength of LFP alpha/beta power in the mPFC, but not AC, was strongly correlated with the behavioral performance that mice would achieve later in the training session. Further, we found that coherence between AC and mPFC at 8-18Hz was selectively enhanced only after mice learned to suppress licking, and this LFP coherence increase coincided with a reduction in spiking rate for the unrewarded tone in AC. These results reveal that enhanced interactions between PFC and AC is an inherent property of auditory discrimination learning, and that coordinated alpha/beta oscillations contribute to cognitive flexibility.

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bioRxiv2019

Empirically Constrained Network Models for Contrast-dependent Modulation of Gamma Rhythm in V1

Here we present experimentally constrained computational models of gamma rhythm and use these to investigate gamma oscillation instability. To this end, we extracted empirical constraints for PING (Pyramidal Interneuron Network Gamma) models from monkey single-unit and LFP responses recorded during contrast variation. These constraints implied weak rather than strong PING, connectivity between excitatory (E) and inhibitory (I) cells within specific bounds, and input strength variations that modulated E but not I cells. Constrained models showed valid behaviours, including gamma frequency increases with contrast and power saturation or decay at high contrasts. The route to gamma instability involved increased heterogeneity of E cells with increasing input triggering a breakdown of I cell pacemaker function. We illustrate the models capacity to resolve disputes in the literature. Our work is relevant for the range of cognitive operations to which gamma oscillations contribute and could serve as a basis for future, more complex models.

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