Stephen Baccus - US grants

DESCRIPTION (Verbatim from applicant's abstract): The proposed research will examine how the cellular mechanisms of the retina operate together as a neural circuit to process visual information. Emphasis is placed on how population activity of retinal ganglion cells can be accounted for by a description of the cellular and synaptic mechanisms of other retinal circuit elements. The light responses of retinal interneurons will be monitored by intracellular recording while simultaneously recording activity in about 50 ganglion cells using a multi-electrode array. Intracellular stimulation will reveal how the synaptic output of interneurons affects the responses of ganglion cells. The morphology of retinal interneurons will be measured and correlated with their functional output to ganglion cell activity. The specific retinal processes that will be examined are the synaptic connections that produce correlated firing of ganglion cells, the cellular mechanisms of adaptation to contrast and spatial scale, and the influence of amacrine cells on ganglion cell activity. Because a description of how cellular elements combine together to produce population activity is not clear in the retina or any other neural system, this research will reveal basic principles of functional neural circuitry and may provide a framework to detect and characterize defects in visual processing.

[unreadable] DESCRIPTION (provided by applicant): This proposal will study how the circuitry of the vertebrate retina translates the visual scene into a complex language of electrical impulses in the optic nerve. One of the largest gaps in neuroscience is in the explaining of systems-level processes like vision in terms of cellular-level mechanisms. The retina is one of the best places in which to bridge this gap because of the basic properties that are already known of its cell types, and because of growing knowledge about the complex, adaptive visual processing the retina performs. The specific goals of this project are to 1) Directly measure functional connections of amacrine cells, a diverse type of inhibitory interneuron, to the output of the retina, and determine the overall organization of these circuits. 2) Understand how amacrine cells change the visual responses of retinal ganglion cells. 3) Understand how these functional properties change during adaptation to the visual scene. A number of techniques are combined to create a general program for determining how the retinal circuit functions. An array of extracellular electrodes is used to record the light responses of many ganglion cells at once. Simultaneously, intracellular recordings monitor the visual responses of interneurons in the circuit. Injection of current into these interneurons allows direct measurement of functional connections, revealing how the interneuron's output affects the overall output of the operating circuit. The resulting large sets of data are summarized with mathematical models that confirm our understanding of the neural circuitry. This combined approach promises general insight into the function of neural circuits. The loss of retinal function is a prevalent aspect of many widespread diseases that produce blindness, including retinitis pigmentosa and macular degeneration. It is expected that learning how the retinal circuitry processes visual scenes will aid in the development of a retinal electronic prosthetic device and early diagnostic tests for the progression of retinal disorders. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Neural circuits are the processing units of the brain, formed by networks of thousands or millions of nerve cells that transform information. The retina is the only neural circuit in the central nervous system (CNS) that can be removed intact and its entire natural input delivered to hundreds of thousands of cells with millisecond precision. It is also the only neural circuit of the CNS that can potentially be replaced by an electronic prosthesis in cases of disease. A substantial barrier to this therapeutic goal is a detailed understanding of the internal processing of information in the retina - the neural code. To understand the two sequential layers of processing in the retinal circuit, we will take a divide-and- conquer approach to understanding the neural code by simultaneously recording at two different levels in the circuit using a novel combination of techniques. Visual scenes are projected from a video monitor onto the photoreceptor layer of an isolated, intact salamander or mouse retina. An infrared two-photon laser-scanning microscope is used in conjunction with a voltage-sensitive dye to record the activity of ~ 100 interneurons. To do this, we will use second harmonic generation imaging, a technique that selectively images the membrane potential of neurons using dyes with minimal pharmacological effects. Simultaneously, an array of sixty electrodes is used to record action potentials in the output cells of the retina that comprise the optic nerve. We will use measured visual responses at two layers of the retina to separately model outer and inner retinal processing. We will also use simultaneous recordings from interneuron and ganglion cell populations to test whether the inner retina compresses the visual scene by reducing redundancy contained in its synaptic input. These results will have immediate applicability to the emerging field of retinal prostheses. The objective of a retinal prosthesis system is to treat prevalent diseases such as age-related macular degeneration and retinitis pigmentosa by replacing the function of the damaged retina with a high resolution electronic circuit. Measurements of the retinal neural code will be directly useful for incorporation into subretinal and epiretinal prostheses systems. PUBLIC HEALTH RELEVANCE: The proposed research uses optical imaging and multielectrode recording to study how cells of the vertebrate retina process and transmit information through the optic nerve. The retina is a complex network of many cell types, each of which carries a different aspect of information about the visual scene. By understanding how this transformation occurs, we will gain a better understanding of how these cells and their connections degenerate during retinal disease. This information is also essential in the design of treatments for retinal degenerative diseases. In particular, because these studies will produce measurements of the neural code of the retina at two different levels, the results will immediately be suitable for incorporation into electronic retinal prosthesis systems.

Studies of the visual system face a number of challenges, two of which are the intricacy of the cell types and synaptic connections that comprise the nervous system, and the complexity of the computational processes that underlie vision. Although the retina is one of the most characterized and well understood neural circuits of the visual system, it nonetheless has a great diversity of cell types, connections and computations. The normal function of the retina is to convey information about natural visual scenes, which have complex spatial and temporal structure. The processing of natural scenes has the greatest relevance towards a fundamental understanding retinal function, and the greatest clinical relevance. Yet most studies of retinal visual processing and circuitry focus on responses to simple artificial stimuli rarely encountered normally, such as flashing spots, drifting stripes and flickering checkerboards. With respect to retinal cell types greatest diversity lies in a class of inhibitory interneurons known as amacrine cells. These cells make extensive lateral and feedback connections, and although they form stereotyped connections between each other, excitatory bipolar cells, and ganglion cells that transit signals in the optic nerve, the functional effects of nearly all of these cell types are poorly understood. This proposal aims towards a direct characterization of the functional effects of amacrine cells under ethologically relevant stimuli, including natural scenes. We combine approaches of perturbation and recording using electrical and optical methods as well as computational modeling to characterize the specific contributions of amacrine cells to stimuli that include the representation of moving objects. We take advantage of recently developed computational approaches that can simultaneously capture the retinal response to a broad range of stimuli including natural scenes, capture a wide range of phenomena previously characterized only with artificial stimuli, and that have internal units highly correlated with retinal interneurons. Our goals are to 1) Create a quantitative understanding of the functional contributions of a class of sustained amacrine cells in the salamander retina for specific stimuli including those that represent moving objects and natural scenes, and test hypotheses related to dynamic effects on visual sensitivity and sensory features generated by those amacrine cells 2) Use molecularly defined amacrine cells in the mouse to quantitatively characterize the functional contribution of specific amacrine cell types to specific stimuli including artificial moving objects and natural scenes. These studies create a new way to generate and test hypotheses related to the quantitative effect of any interneuron on retinal output under any visual stimulus. Understanding how retinal circuitry creates visual processing under natural scenes is critical to our understanding of retinal mechanisms and diseases involving the degeneration of the retinal circuitry. In addition, the computational descriptions of retinal responses will be directly useful in the design of electronic retinal prosthesis systems.

DESCRIPTION (provided by applicant): The goal of this project is to understand the effects of ultrasound (US) on neural activity. US can modify action potential activity in neurons in vitro and in vivo without damaging neural tissue. This phenomenon can be applied in powerful new tools for basic and clinical neuroscience, with broad impact on public health issues related to mental and neurological disorders. To guide and hasten the development of these new tools, our research will provide insight into the physical, biophysical and neural mechanisms underlying US neurostimulation. Our approach is unique in combining technology development with mechanistic studies of US neurostimulation at levels of complexity ranging from the single cell to the whole animal. Our prior and preliminary results suggest that US radiation force causes tissue displacement, resulting in cell membrane strain and thereby affecting neural activity through changes in ion channel activity or neurotransmitter exocytosis. We will investigate this hypothesis by combining US neurostimulation with EEG recording and radiation force imaging in rats, optical displacement measurements and multielectrode recording in the salamander and rat retina in vitro and in vivo, and electrophysiological measurements of ion channel activity and exocytosis in single HEK and PC12 cells. We will also test alternative hypotheses related to two other physical effects of US, cavitation and heating. To distinguish these mechanisms from radiation force we will examine the dependence of US neurostimulation on frequency and intensity. To facilitate these experiments, we will develop and implement new US devices, allowing US to be applied with multifocal and micron-scale resolution. US neurostimulation is likely to have significant impact on public health. Brain stimulation therapies are used to treat Parkinson's disease, dystonia, and epilepsy and hold promise for many others. Compared to current brain stimulation techniques that rely on invasive implanted electrodes or have limited spatial resolution and depth penetration (e.g., transcranial magnetic stimulation), US offers an ideal combination of spatial resolution, depth penetration, and non-invasiveness. US neurostimlation can also be implemented in prosthetic devices; for example, to stimulate retinal circuitry to restore vision. In addition, US neurostimulation promises to become an enormously useful research tool in basic neuroscience, and is therefore relevant to all mental and neurological disorders of public health concern. However, all of these outcomes depend on the ability to apply US neurostimulation safely and with well-controlled, predictable results. Achieving this goal requires a detailed mechanistic understanding of US neurostimulation that our multidisciplinary research project will provide.

DESCRIPTION (provided by applicant): Like many neural circuits of the brain, the retina is composed of a network of cells with greatly varying anatomical and physiological properties. The most diverse types of cells, both in the retina and cortex, are inhibitory interneurons. Retina amacrine cells comprise over thirty types and influence the responses of ganglion cells, the output cells of the retina. Although the anatomy and physiology of amacrine cells have long been studied, there is little understanding as to whether they have specific and distinct roles, rather than each serving a similar, general function. A substantial barrier to the understanding of inhibitory interneurons has been technical limitations on studying single cells among a diverse population. This proposal seeks to characterize the population of inhibitory amacrine cells using a novel approach to optically record the visual responses of the amacrine cell population while simultaneously recording populations of ganglion cells using an electrode array. This project focuses on responses to moving visual stimuli, which are ecologically important and critical to behavior and perception. The first aim of this proposal will measure the responses of a nearly complete amacrine population to moving stimuli and compare these with simultaneously recorded responses in the ganglion cell population. By measuring the similarity in responses between amacrine and ganglion cell populations, these experiments will test the hypothesis that amacrine cells are divided into two broad classes: one that resembles the more simple bipolar cell representation and one that is more tightly correlated with specific retinal ganglion cells. Te second aim of this proposal uses optical imaging and simultaneous intracellular and multielectrode recording to test the hypothesis that amacrine cells inhibit ganglion cells that the are correlated with under visual motion, despite the wide variation of preferred visual stimuli across amacrine cells. Finally, the third aim of this proposal will take advantage of our novel approach of directly perturbing individual interneurons intracellularly to test whether many types of amacrine cells act to reduce correlations in the ganglion cell population for different types of natural stimuli, thus creating an efficient representation of the visual scene. These studies will not only add to the knowledge of how an inhibitory population represents and transforms visual information, but will also test general principles applicable to all neural circuits. The results wll have immediate applicability to the emerging field of retinal prostheses. The objective of a retinal prosthesis system is to treat prevalent diseases such as age-related macular degeneration and retinitis pigmentosa by replacing the function of the damaged retina with a high-resolution electronic circuit. Measurements of the retinal neural code and the computations that are performed will be directly useful for incorporation into these prostheses systems.

Advanced Computational Core PROJECT SUMMARY The Stanford Vision Advanced Computational Core will provide support in computer storage, high performance computing and programming for vision research. The Core will support hardware and system administration services for an existing central computing resource, known as the Stanford Virtual Computing Service (VCS), which consists of storage and high performance computing accessible through a high-speed network. A second aspect of the Core is to support programming services to facilitate the exchange of adaptation of special purpose software and algorithms between laboratories that have a need for computational modeling and analysis, but whose personnel lack sufficient computational expertise. The Core will be supervised by Stephen Baccus, Associate Professor in the Department of Neurobiology, an NEI-funded investigator who has extensive expertise in using computational and experimental approaches to understand the retina and visual system.

DESCRIPTION (provided by applicant): The goal of this project is to understand the effects of ultrasound (US) on neural activity. US can modify action potential activity in neurons in vitro and in vivo without damaging neural tissue. This phenomenon can be applied in powerful new tools for basic and clinical neuroscience, with broad impact on public health issues related to mental and neurological disorders. To guide and hasten the development of these new tools, our research will provide insight into the physical, biophysical and neural mechanisms underlying US neurostimulation. Our approach is unique in combining technology development with mechanistic studies of US neurostimulation at levels of complexity ranging from the single cell to the whole animal. Our prior and preliminary results suggest that US radiation force causes tissue displacement, resulting in cell membrane strain and thereby affecting neural activity through changes in ion channel activity or neurotransmitter exocytosis. We will investigate this hypothesis by combining US neurostimulation with EEG recording and radiation force imaging in rats, optical displacement measurements and multielectrode recording in the salamander and rat retina in vitro and in vivo, and electrophysiological measurements of ion channel activity and exocytosis in single HEK and PC12 cells. We will also test alternative hypotheses related to two other physical effects of US, cavitation and heating. To distinguish these mechanisms from radiation force we will examine the dependence of US neurostimulation on frequency and intensity. To facilitate these experiments, we will develop and implement new US devices, allowing US to be applied with multifocal and micron-scale resolution. US neurostimulation is likely to have significant impact on public health. Brain stimulation therapies are used to treat Parkinson's disease, dystonia, and epilepsy and hold promise for many others. Compared to current brain stimulation techniques that rely on invasive implanted electrodes or have limited spatial resolution and depth penetration (e.g., transcranial magnetic stimulation), US offers an ideal combination of spatial resolution, depth penetration, and non-invasiveness. US neurostimlation can also be implemented in prosthetic devices; for example, to stimulate retinal circuitry to restore vision. In addition, US neurostimulation promises to become an enormously useful research tool in basic neuroscience, and is therefore relevant to all mental and neurological disorders of public health concern. However, all of these outcomes depend on the ability to apply US neurostimulation safely and with well-controlled, predictable results. Achieving this goal requires a detailed mechanistic understanding of US neurostimulation that our multidisciplinary research project will provide.

PROJECT SUMMARY The goal of this project is to understand the neurobiological underpinnings of the effects of ultrasound (US) on neural activity. US can modify action potential activity in neurons in vitro and in vivo without damaging neural tissue. This phenomenon can be applied in powerful new tools for basic and clinical neuroscience, with broad impact on public health issues related to mental and neurological disorders. To guide use of this new tool, our research will provide insight into the physical, biophysical and neural mechanisms underlying US neuromodulation. Our approach is unique in applying and integrating mechanistic studies of US neuromodulation at levels of complexity ranging from the single cell to the whole animal. We aim to understand the relationship between US 1) the physical processes that transform acoustic energy to effects on biological systems and the resulting measurable physical variables (Aim 1), 2) the biophysical transduction processes together with the resulting measurable biophysical effects (Aim 2) 3) the subsequent neural integration processes that lead to the final output of the neural system or behavior (Aim 3). We will address these questions in experiments across three model systems (the in vivo mouse model, in vitro salamander and mouse retina, and single hippocampal pyramidal cells in acute and cultured brain slices), focusing on hypotheses guided by our results thus far. US neuromodulation is likely to have significant impact on public health. Brain stimulation therapies are used to treat Parkinson's disease, dystonia, and epilepsy and hold promise for many others. Compared to current brain stimulation techniques that rely on invasive implanted electrodes or have limited spatial resolution and depth penetration (e.g., transcranial magnetic stimulation), US offers an ideal combination of spatial resolution, depth penetration, and non-invasiveness. US neuromodulation can also be implemented in prosthetic devices; for example, to stimulate retinal circuitry to restore vision. In addition, US neuromodulation promises to become an enormously useful research tool in basic neuroscience, and it is therefore relevant to all mental and neurological disorders of public health concern. However, all these outcomes depend on the ability to apply US neuromodulation with well-controlled, predictable results. Achieving this goal requires a detailed mechanistic understanding of US neuromodulation that our multidisciplinary research project will provide.