1,721,025 research outputs found
Recommended from our members
Improving and Assessing Monosynaptic Rabies Tracing as a Tool for Cortical Circuit Tracing
Full text linkThe mammalian cerebral cortex is composed of a diversity of neuronal cell types with distinct morphology, molecular composition, and electrophysiological properties. These neurons connect to one another to form complex microcircuits that underlie brain cortical processing. Thus, deciphering the precise input and output connectivity patterns of different neuronal cell types is conducive to understanding their functional roles in cortical processing. To this end monosynaptic rabies tracing has been widely used for cortical circuit tracing studies and has had great impact on the understanding of neural circuit organization. Still, the advent of single-cell genomic technologies has unveiled that the extent of neuronal diversity may be much greater than originally imagined, raising new questions about the connectivity patterns of these more precisely defined cell subtypes. Our understanding of cortical circuit organization could benefit from higher throughput methods of assigning inputs to neuronal cell types and the ability to assign cells to finer subtypes. Chapter 1 explores the feasibility of combining monosynaptic rabies tracing with single-nuclei RNA-sequencing (snRNAseq) to identify the transcriptomic cell types that provide presynaptic inputs to defined populations of neurons. We found that, despite global and cell-type-specific rabies-induced transcription changes, rabies-infected cortical cells can still be classified according to established transcriptomic cell types when utilizing transcriptome-wide RNA profiles. In Chapter 2, we characterize the interlaminar synaptic connectivity of mouse primary visual cortex (V1) at the transcriptomic level using the newly developed method Single Transcriptome Assisted Rabies Tracing (START). We found that START generates results consistent with established circuit models validating the utility of START as a circuit tracing tool. More importantly, with the improved cell type granularity achieved with transcriptomic characterization of inputs, we were able to uncover subtypes of somatostatin and parvalbumin interneurons that provide input to L2/3 and L6 CT excitatory neurons. Finally, Chapter 3 describes the efficiency of rabies transsynaptic spread from starter cells to input neurons. We found that about 40% of inputs are labeled transsynaptically. Altogether, this dissertation reveals how transcriptomically defined cell-types are organized in V1 and introduces a novel circuit tracing technique that will expand the repertoire of tools available to neuroscientists
Recommended from our members
Functional Diversity of Corticothalamic Pathways Underlying Visual Processing
Full text linkThe cerebral cortex and the thalamus are in constant communication with one another, and their interactions are thought to underlie fundamental brain functions such as perception, attention, sleep, cognitive flexibility, and even consciousness. Still, a multitude of questions remains as to how corticothalamic interactions subserve these functions. This dissertation explores one major aspect of these interactions - how the cortex communicates with the thalamus, using the mouse visual system as model. This is an area in which considerable groundwork has been laid by decades of research into the underlying anatomy and physiology of these connections, which have led to influential hypotheses about how those attributes may relate to function. Yet, many of these hypotheses have been left untested, due to challenges and technical limitations in selectively perturbing different corticothalamic pathways and assessing their in vivo functions in an awake animal. In this dissertation, modern advances in mouse transgenics, extracellular electrophysiology, and circuit manipulation are harnessed to directly assess how distinct populations of corticothalamic neurons contribute to visual thalamic processing in vivo. Chapter 1 explores the role that a unique population of corticothalamic neurons in layer 6 of the mouse primary visual cortex play in the dorsolateral geniculate nucleus and the pulvinar, which represent two distinct classes of visual thalamic nuclei. By using optogenetics to selectively stimulate these neurons, we find that they act similarly upon both classes of thalamic nuclei, yet their influence in both is highly dynamic and dependent upon the context of their activation. In Chapter 2, the endogenous function of these layer 6 corticothalamic neurons is further examined with optogenetic inactivation and contrasted with that of an additional corticothalamic population in cortical layer 5 that exclusively projects to the pulvinar. We find novel evidence in support of longstanding hypotheses that layer 5 corticothalamic projections “drive” visual responses in the pulvinar, whereas the layer 6 projections play a fundamentally “modulatory” role. Altogether, this dissertation reveals how functionally distinct corticothalamic pathways influence the visual thalamus and suggests fundamental principles in how corticothalamic communication is organized for sensory processing in the awake, behaving animal
Recommended from our members
Improving Viral Tools for Neural Circuit Dissection: Monosynaptic Anterograde Tracing and Recombinase-Dependent AAV Expression of Sensitive Transgenes
Full text linkThe complex tangle of synaptic connections made by the myriad of neural cell types in mammalian nervous system, each with their own genetic, chemical, and electrophysiological properties, are the basis of neural computation and thus perception, motivation, and behavior. As such, it is a fundamental task of neuroscience to map neural connectivity in a cell-type specific manner and develop robust technologies to this end. This dissertation describes two such technologies. First, targeted deletion and in vivo transcomplementation of the Herpes Simplex Virus 1 (HSV) gene UL6 in the anterograde strain H129 allows for the selective labeling of postsynaptic populations from specific neuronal cell types in a cre-dependent manner. Second, the cause of transgene expressing in off-target cells from recombinase-dependent recombinant adeno-associated virus (AAV) will be described, along with efforts toward improved methods in AAV production for “leakless” expression of sensitive transgenes. Both techniques will expand the available toolkit of the modern systems neuroscientist and provide a means by which to tackle previously intractable questions
Recommended from our members
State-Dependence is State-Dependent: Local and Global Influences of Spatial Selection and Locomotion in Mouse Primary Visual Cortex
Full text linkOver the past decade, mice have emerged as a useful model for studying vision, owing in large part to their genetic tractability. Such studies have also yielded the unexpected and fascinating finding that movement, particularly locomotion, has a striking effect on cortical visual activity in mice. The discovery of so-called state-dependent visual processing suggested that the role of even primary sensory areas is not as simple as previously thought. Many studies showed that locomotion enhances visual neural activity, but few directly examined whether it actually improved sensory perception in a behavioral task. For my dissertation project I addressed this by examining the interactions between locomotion-dependent modulation of brain state and different goal-directed sensory selection brain states. Two groups of mice were trained to visually monitor either one of two locations (selective) or both (non-selective) for a contrast change, and this simple difference produced a spatially selective and non-selective brain state in primary visual cortex (V1), respectively. Locomotion affected the two groups of mice differently, impairing performance and neural representations of visual information of selective mice, while having no effect on non-selective mice. These and other results suggest that these two groups of mice use local versus global mechanisms to perform their respective tasks, and in the case of selective mice, the global influence of locomotion disrupts their locally modulated brain state and impairs performance. Locomotion influences brain state differently, depending on the whether the animal employs a spatially selective state to perform its task. Thus, state-dependence is state-dependent. These findings demonstrate the importance of studying complex interactions, and argue for reducing reductionism in neuroscience as we gain the necessary technology to carry out such studies. Moving forward, this mouse model will do just that, and enable investigation into the cell type and circuit mechanisms underlying these phenomena. Wading into the enormous complexity of the brain may ultimately be the only way to understand how it works as a whole
Recommended from our members
Multiscale circuit analysis of visual information processing
Full text linkThe brain organizes information across multiple scales, from molecules to circuits to systems. Information is processed in stages, becoming increasingly refined and specialized at each level. We developed technologies to analyze information processing across multiple scales simultaneously. We answer several previously inaccessible questions about the structure and function of the mouse visual system (summarized in Chapter 1). Direction of motion is first encoded by retinal ganglion cells (RGCs). We developed a method to image the responses of anatomically-identified neurons in the LGN. We found that LGN organizes direction information in a laminar pattern partially predicted by RGC inputs; only posterior and anterior directions are encoded in the superficial layer. This information is refined; direction-selective LGN neurons are more sharply tuned than RGCs. The superficial LGN integrates direction information, forming axis-of-motion selectivity for anterior-posterior motion (Chapter 2).Understanding information integration by microcircuits requires novel technologies to study the structure and function of microcircuits in the intact brain. In Chapter 3, we developed a technology to target monosynaptic inputs to a single visual cortical neuron for gene manipulation and fine-scale cell labeling in vivo. We labeled inputs across the intact brain.Single circuits in V1 and higher visual areas process signals from the LGN and other areas to compute increasingly specialized visual information. We developed methods to define visual cortical areas across the entire visual cortex down to single cell resolution in the same animal, within the same day (Chapter 4). We compared the response properties of populations of neurons from 7 visual areas. Extrastriate cortex processes motion information up to 3 times the temporal frequency than V1. A subset of areas maintains high spatial frequency tuning of V1, while another group prefers approximately half the spatial frequency. Extrastriate visual areas are more orientation selective and some are more direction selective. We apply a novel rabies virus to measure the fine-scale structure and function of neurons in V1 providing monosynaptic input to an extrastriate visual area (Appendix). This technology may help integrate across the scales investigated in each chapter to understand how information is transformed at each processing stage by specialized microcircuits
Recommended from our members
Organization of Spatiotemporal Frequency Tuning in the Mouse Visual System
Full text linkThe mouse visual cortex is a hierarchical and distributed system that consists of primary visual cortex and several higher visual cortical areas. Historically, the low acuity of the mouse visual system garnered little interest in the neuroscience community, so many key principles about visual and cortical circuits were first discovered in primate and cat vision. As transgenic mice and genetically targeted viral tools and novel recording methods developed, a renewed interest and appreciation in the mouse visual system has emerged. A detailed understanding of the mouse visual system on its own, as well as in comparison with other species, is critical for understanding how different visual areas and their cell types work to process visual input. In chapter one, two methods for recording single cell activity are used to measure the spatiotemporal frequency and direction tuning properties of deep layer cortical neurons in primary visual cortex and two higher visual areas. While previous studies have characterized the functional tuning properties of superficial (layer 2 and layer 3) neurons in mice, the tuning properties of deep layer (layer 5 and 6) and different projection classes of layer 5 neurons have been less well characterized. We use extracellular electrophysiology and two-photon calcium imaging and find that while deeper layer neurons are specialized for different spatial and temporal frequencies, there is also a greater overlap in tuning preferences than previously reported in superficial layers. We also find much stronger direction tuning in extratelencephalically projecting layer 5 neurons compared to intratelencephalically projecting layer 5 neurons in multiple visual areas. In chapter two, we examine if two different transgenic mouse lines label layer 4 neurons that may represent different spatial and temporal frequency channels in mice to determine if the organization of spatial and temporal frequency channels is conserved from primates. We find that the neurons labelled in layer 4 by these two mouse lines are both morphologically and functionally different. Together, this dissertation seeks to use modern neuroscience tools to elucidate a more detailed understanding of the functional organization of visual tuning in the mouse visual system
Recommended from our members
Interlaminar Connectivity in Mouse Primary Visual Cortex
Full text linkA distinguishing feature of the mammalian cerebral cortex is its laminar architecture, each layer containing a unique composition of neuronal types with distinct morphologies, molecular markers, and electrophysiological properties. These neurons form precise, specific synaptic connections with one another to form complex microcircuits that underlie sensory information processing. By compartmentalizing computation into layers, the cortex can efficiently channel and transform information to represent and interact with the external world. Therefore, deciphering the precise input and output connectivity structure of different neuronal types in the context of their respective layers is necessary to fully appreciate their unique functional roles in the representation and manipulation of sensory information. This dissertation builds on the traditional idea of a canonical interlaminar circuit by characterizing fundamental intracortical connections between excitatory and inhibitory cell types. Chapter 1 explores the relative functional input distributions from 5 layer-specific excitatory subpopulations to 4 cell types in mouse primary visual cortex (V1). By optogenetically activating these excitatory subpopulations and recording from targeted excitatory and inhibitory subtypes across cortical layers 2/3-6, I elucidate a complex interlaminar network that provides a novel framework for visual information processing. In Chapter 2, I approach the interlaminar connectivity of mouse V1 from a transcriptomic perspective using our newly developed method Single Transcriptome Assisted Rabies Tracing (START). By combining rabies tracing using glycoprotein (G)-deleted rabies virus (RVdG) with snRNAseq, we identify, and transcriptomic ally characterize cells projecting to the same layer-specific subpopulations as in Chapter 1. We find that START generates results consistent with established circuit models validating the utility of START as a circuit tracing tool. More importantly, with the increased cell type granularity achieved with transcriptomic characterization of inputs, we were able to uncover specific subtypes of somatostatin and parvalbumin interneurons that provide input to excitatory cells across layers. Taken together, findings from Chapters 1 and 2 demonstrate layer and cell type specificity in cortical circuit structure, indicating that a cell’s laminar position and synaptic connectivity are deeply intertwined with its functional role. Understanding cell type diversity in the context of circuit architecture forms the foundation of a novel framework for cortical information processing
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Recommended from our members
Optogenetic Dissection of Cell Types and Circuits in Mouse Visual Cortex
Full text linkWhile many observations make it clear that cell types and specificity of connections matter, we still lack a mechanistic understanding of how cell types and their specific pattern of connectivity might contribute uniquely to cortical computations. To understand the contributions of cell types and circuits in mouse visual cortex we have taken advantage of multi-feature Boolean logical expression of light sensitive cationic channel (channelrhodopsin-ChR2) and whole cell dual patch recordings in living brain slices. Using these tools, we have identified unique electrophysiology and connectivity patterns of vasoactive intestinal peptide (VIP) expressing interneuron subtypes (Chapter 2). We have also introduced methods that will enable single cell resolution mapping of inhibitory inputs in the future (Chapter 3). Finally in Appendix A, we identified three layer 5 pyramidal cell types in mouse visual cortex based on intrinsic electrophysiology, visual responses, and long range connectivity. Better understanding of highly specific cell types and circuits in mouse models will help us better classify and treat psychiatric disorders in humans where inhibitory circuit dysfunctions have been implicated
- …
