Biology subjects

Znamenskiy, P.

Publications and source records attributed to Znamenskiy, P..

7 recordsLinked to original sources

bioRxiv2025

Topographic alignment of auditory inputs to the visual cortex

Sensory cortical areas send long-range projections to cortical areas from other sensory modalities, supporting multisensory integration to generate a unified representation of the external world. However, the organizational principles underlying these extensive cross-modal connections remain poorly understood. In this study, we investigated the anatomical and functional organisation of auditory cortex inputs in the visual cortex. We found that populations of anatomically segregated auditory cortex neurons project to different visual cortical areas, broadcasting distinct auditory information to the dorsal and ventral visual processing streams. While sound frequency information was homogenously distributed across visual cortical areas, sound location information was differentially broadcast across the visual cortex. Specifically, sound azimuth and elevation were differentially encoded across visual cortical areas and streams matching the retinotopic bias of the target area. These findings suggest that cross-modal cortico-cortical connections follow a simple rule whereby specialised projection pathways are topographically aligned with the organisational principles of the target sensory area, ensuring spatially coherent integration of multisensory signals.

neuroscience↗

bioRxiv2025

Barcoded Rabies In Situ Connectomics for high-throughput reconstruction of neural circuits

Sequencing of oligonucleotide barcodes holds promise as a high-throughput approach for reconstructing synaptic connectivity at scale (1). Rabies viruses can act as a vehicle for barcode transmission, thanks to their ability to spread between synaptically connected cells (2, 3). However, applying barcoded rabies viruses to map synaptic connections in vivo has proved challenging (4-7). Here, we develop Barcoded Rabies In Situ Connectomics (BRISC) for high-throughput connectivity mapping in the mouse brain. To ensure that the majority of post-synaptic "starter" neurons are uniquely labeled with distinct barcode sequences, we first generated libraries of rabies viruses with sufficient diversity to label >1000 neurons uniquely. To minimize the probability of barcode transmission between starter neurons, we developed a strategy to tightly control their density. We then applied BRISC to map inputs of single neurons in the primary visual cortex (V1). Using in situ sequencing, we read out the expression of viral barcodes in rabies-infected neurons, while preserving spatial information. We then matched barcode sequences between starter and presynaptic neurons, mapping the inputs of 385 neurons and identifying 7,814 putative synaptic connections. The resulting connectivity matrix revealed layer- and cell-type-specific local connectivity rules and topographic organization of long-range inputs to V1. These results show that BRISC can simultaneously resolve the synaptic connectivity of hundreds of neurons while preserving spatial information, enabling reconstruction of neural circuits at an unprecedented scale.

neuroscience↗

bioRxiv2025

PhotoNeuro: A compact photodetector for synchronization of visual stimulus presentation during behavioral experiments in neuroscience.

Presenting visual stimuli in neuroscience experiments often requires the combination of analogue signals that carry information about the visual cue presented on the LCD display. Such signals are often sensed by photodetectors and recorded in analogue to digital converter (ADC) acquisition boards. The use of open-source visual programming languages such as Bonsai is becoming more and more popular. They are often used in combination with other open-source hardware such as Arduino development boards. These microcontroller-based boards can be used to automate behavioural experiments: e.g., actuate valves and motors and acquire analogue signals on their ADC channels. LCDs and other modern display allow fast presentation of arbitrary visual stimuli and are widely used for psychophysics and neuroscience experiments. However, most displays do not provide hardware timestamping options and are intrinsically nonlinear. Solving this limitation often requires a direct recording of the light emitted by the display with a photodiode. Such photodetectors are are often amplified at higher voltages and hard to integrate in most common recording systems that use microcontrollers. The other drawback commonly found by neuroscience researchers in commercial devices is the relatively big footprint that the sensor occupies on the screen which, ideally should be minimised so not to interfere with the stimuli presentation. In this paper we present a small footprint photodetector that can be easily replicated and operates at 5V making it suitable to use with common development boards and the visual programming language Bonsai that is commonly used for experiment creation and control. Additionally, we share a version that includes four photodiodes in small area (400 mm2). Specifications table O_TBL View this table: org.highwire.dtl.DTLVardef@7bafcforg.highwire.dtl.DTLVardef@5353ccorg.highwire.dtl.DTLVardef@a29f47org.highwire.dtl.DTLVardef@86f5d2org.highwire.dtl.DTLVardef@74da5f_HPS_FORMAT_FIGEXP M_TBL C_TBL

neuroscience↗

bioRxiv2024

A depth map of visual space in the primary visual cortex

Depth perception is essential for visually-guided behavior. Computer vision algorithms use depth maps to encode distances in three-dimensional scenes but it is unknown whether such depth maps are generated by animal visual systems. To answer this question, we focused on motion parallax, a depth cue relying on visual motion resulting from movement of the observer. As neurons in the mouse primary visual cortex (V1) are broadly modulated by locomotion, we hypothesized that they may integrate vision- and locomotion-related signals to estimate depth from motion parallax. Using recordings in a three-dimensional virtual reality environment, we found that conjunctive coding of visual and self-motion speeds gave rise to depth-selective neuronal responses. Depth-selective neurons could be characterized by three-dimensional receptive fields, responding to specific virtual depths and retinotopic locations. Neurons tuned to a broad range of virtual depths were found across all sampled retinotopic locations, showing that motion parallax generates a depth map of visual space in V1.

neuroscience↗

bioRxiv2019

Mesoscale cortical dynamics reflect the interaction of sensory evidence and temporal expectation during perceptual decision-making

How sensory evidence is transformed across multiple brain regions to influence behavior remains poorly understood. We trained mice in a visual change detection task designed to separate the covert antecedents of choices from activity associated with their execution. Widefield calcium imaging across dorsal cortex revealed fundamentally different dynamics of activity underlying these processes. While signals related to execution of choice were widespread, fluctuations in sensory evidence in the absence of overt motor responses triggered a confined activity cascade, beginning with transient modulation of visual cortex, followed by sustained recruitment of secondary and primary motor cortex. The activation of motor cortex by sensory evidence was selectively gated by animals expectation of when the stimulus was likely to change. These results identify distinct activation profiles of specific cortical areas during decision-making, and show that the recruitment of motor cortex depends on the interaction of sensory evidence and expectation.

neuroscience↗

bioRxiv2018

Functional selectivity and specific connectivity of inhibitory neurons in primary visual cortex

In the cerebral cortex, the interaction of excitatory and inhibitory synaptic inputs shapes the responses of neurons to sensory stimuli, stabilizes network dynamics1 and improves the efficiency and robustness of the neural code2-4. Excitatory neurons receive inhibitory inputs that track excitation5-8. However, how this co-tuning of excitation and inhibition is achieved by cortical circuits is unclear, since inhibitory interneurons are thought to pool the inputs of nearby excitatory cells and provide them with non-specific inhibition proportional to the activity of the local network9-13. Here we show that although parvalbumin-expressing (PV) inhibitory cells in mouse primary visual cortex make connections with the majority of nearby pyramidal cells, the strength of their synaptic connections is structured according to the similarity of the cells responses. Individual PV cells strongly inhibit those pyramidal cells that provide them with strong excitation and share their visual selectivity. This fine-tuning of synaptic weights supports co-tuning of inhibitory and excitatory inputs onto individual pyramidal cells despite dense connectivity between inhibitory and excitatory neurons. Our results indicate that individual PV cells are preferentially integrated into subnetworks of inter-connected, co-tuned pyramidal cells, stabilising their recurrent dynamics. Conversely, weak but dense inhibitory connectivity between subnetworks is sufficient to support competition between them, de-correlating their output. We suggest that the history and structure of correlated firing adjusts the weights of both inhibitory and excitatory connections, supporting stable amplification and selective recruitment of cortical subnetworks.

neuroscience↗

bioRxiv2017

Exclusive functional subnetworks of intracortical projection neurons in primary visual cortex

The rules by which neurons in neocortex choose their synaptic partners are not fully understood. In sensory cortex, intermingled neurons encode different attributes of sensory inputs and relay them to different long-range targets. While neurons with similar responses to sensory stimuli make connections preferentially, the relationship between synaptic connectivity within an area and long-range projection target remains unclear. We examined the local connectivity and visual responses of primary visual cortex neurons projecting to anterolateral (AL) and posteromedial (PM) higher visual areas in mice. Although the response properties of layer 2/3 neurons projecting to different targets were often similar, they avoided making connections with each other. Thus, projection target acts independently of response similarity to constrain local synaptic connectivity of cortical neurons. We propose that this segregated connectivity rule reduces the crosstalk between different populations of projection neurons, allowing top-down signal to modulate the activity of these output channels independently.

neuroscience↗