Stephen D. Van Hooser - US grants

DESCRIPTION (provided by applicant): In the mammalian visual system, signals are relayed from the retina to the primary visual cortex (V1) via the lateral geniculate nucleus (LGN). Over the past 30 years, three main cell types with very different properties have been identified in the LGN: parvocellular, magnocellular, and koniocellular. How do V1 cells interpret spike trains from different types of LGN cells? We propose experiments to explore the synaptic physiology of connections from LGN to V1. In one set of experiments, we will record action potentials from many individual cells in the squirrel LGN using tetrodes, and record from single units in V1 using conventional electrodes. We will fully characterize the physiological properties of the LGN and V1 cells in response to natural input, and look for evidence of monosynaptic connections using cross-correlation techniques. We will see if LGN cells only contact V1 cells with similar properties or if the connections are diffuse. In a second line of experiments, we will record many LGN cells using tetrodes and will make whole cell (intracellular) recordings in V1. We will fully characterize the LGN and V1 cells, and, using spike-triggered averaging, we will look for monosynaptic connections between the LGN and V1 cells. Finally, we will characterize the synaptic dynamics of these connections. Understanding the transfer of information from LGN to V1 will aid in understanding developmental diseases such as amblyopia, and understanding how cortical cells function will aid in understanding many diseases or injuries of the cortex such as Alzheimer's and stroke, and this knowledge will inspire treatments for these ailments.

DESCRIPTION (provided by applicant): In cerebral cortex, horizontal connections link cells with their near neighbors and with neurons millimeters apart. While previous anatomical and physiological studies have suggested that long-range horizontal connections do not contribute to basic response tuning properties but instead serve to modulate these responses, it is possible that the more numerous short-range horizontal connections actually participate in sensory response tuning. Here, we propose experiments to investigate the role of short-range horizontal connections in cortical computations. In the first set of experiments, we will record the activity of dozens of closely-spaced layer 2/3 neurons using two-photon imaging of calcium dye to characterize fine scale organization of retinotopic and orientation maps. In addition to serving as a baseline for manipulations of short-range horizontal connections, we will study the interactions between the mapping of retinotopic location and orientation selectivity to see if functional parameters are mapped independently or if abrupt changes in one mapped parameter correlate with abrupt changes in another parameter. In our second and third sets of experiments, we will study the influence of short-range horizontal connections by manipulating activity of small groups of neurons and re-measuring retinotopic location and orientation selectivity in neighboring cells. In Aim 2, we will reduce activity in some layer 2/3 cells by stimulus adaptation with high contrast, oriented drifting gratings. In Aim 3, we will inactivate or stimulate small groups of neurons with microintophoresis of either GABA or glutamate. If short-range horizontal connections play a role in basic response tuning properties, we would expect to see shifts in receptive field location or orientation preferences. These tuning preferences should shift away from the preferences of inactivated cells and should shift towards preferences of stimulated cells. Two-photon calcium imaging will allow us to 1) record activity of immediate neighbors to manipulated cells, 2) directly monitor the extent of our manipulations, and 3) examine the dependence of response shifts on distance. Our long-term goals are to understand principles of cortical organization and cellular mechanisms underlying visual responses in the mammalian visual system. The experiments we propose here will build the foundation for attaining this goal. This knowledge will provide key insights into the normal function of the human visual system that will be useful for understanding the impact of disease or injury on cortical function, such as the developmental disease amblyopia, stroke, or cortical reorganization following retinal lesions.

The goal of the present research project is to uncover how the astonishingly complex structure of human and animal brains emerges during development and how it becomes well-suited to perform highly sophisticated behaviors. The PIs will use the latest multi-electrode, imaging and opto-genetic methods of electrophysiology to measure the functional development of neural circuits in the visual cortex from eye opening until the full maturity of the visual system. If successful, this project will reveal how incoming visual stimuli are combined with previous visual memories stored in the brain to interpret the visual environment. This work will illuminate how experience influences the development of the circuitry in the visual cortex. The potential scientific impact of this research is extremely high because it can, through using the visual system as a model example, clarify of how the brain adapts to the environment to perform its function. This work will have a broader impact on the advancement of science, as students and postdoctoral fellows will be trained to integrate the study of behaving animals with advanced neural recording and stimulation technologies. Further, the computer code for performing recordings and analysis will be published on the authors? websites, and the authors will provide instructional tutorials so that others can build upon the methods developed here. The resulting data will be published on the authors? websites so other scientists can examine and extend the results. Finally, insights gained about how the environment influences the development of neural circuitry are likely to have implications that could reach as far as designing more effective educational tools and creating more supportive work environments.

PROJECT SUMMARY: Abnormal gene expression or abnormal sensory experience during development has a profound and permanent impact on the construction of brain circuits. Many developmental diseases likely do not arise from a single defect that is present in all sufferers, but rather from the systems-level impact of the interaction of any number of malfunctioning circuit elements. In order to understand how the elements of brain circuits interact during development and to shed light on how these processes go awry in diseases or injuries, it is important to investigate whole systems in the intact, living brain. To this end, we have developed a system via which we can study how individual mammalian cortical neurons change their properties when the circuit is modified by behaviorally relevant stimuli. This application proposes studies of the circuit mechanisms underlying the experience-dependent development of motion selectivity in the ferret visual cortex. At the time of eye opening, ferret visual cortex exhibits orientation selectivity and orientation columns, but neurons are not yet selective for direction-of- motion, a property of most mature neurons in this species. Motion selectivity (that is, direction selectivity) arises in the days and weeks following eye opening, and requires visual experience. However, recent experiments show that this experience has a primarily permissive influence on development, in that many parameters such as direction preference angle and speed tuning are primarily determined before the onset of visual experience. The first aim addresses the degree to which the activity in the cortex before eye opening determines the tuning parameters that can be uncovered through visual experience. We will provide animals with artificial experience with carefully designed ?arbitrary? patterns to examine how tuning parameters can be modified. Alternatively, the activity in cortex before eye opening may itself be permissive and activity-independent factors may determine tuning parameters. The second aim tests a novel hypothesis about the development of functional connections in early development. The classic idea is that connections are substantially overproduced and that experience and plasticity serve to prune inappropriate connections. Instead, we will test the idea that receptive fields start out small and grow in a manner that is largely determined at the onset of visual experience. The third aim directly examines the functional connections between LGN and cortex that might underlie direction selectivity and its development. Concurrently with the aims, a computational model of the ferret visual cortex will be constructed to illuminate the possible combinations of synaptic plasticity rules and initial circuit structure that could underlie the development of direction selectivity and speed tuning.

A fundamental goal for understanding the brain and mammalian and human intelligence, and to understand how processing goes awry in genetic and developmental diseases, is to understand the principles of operation of cerebral cortex. A key step is to understand canonical operations carried out by cortex. Here we will explore the operations of cortical circuitry in experiments guided by a new theory of a candidate canonical circuit operation. Sensory cortex must globally integrate localized sensory input to parse objects and support perception. In individual neurons, this manifests as modulation of responses to local stimuli by context or top-down influences such as attention and as interactions between local stimuli in driving responses (normalization). These interactions tend to be suppressive for stronger stimuli but more weakly suppressive or facilitative for weaker stimuli. Recent theoretical work in Dr. Miller's lab has proposed a novel cortical circuit motif, the stabilized supralinear network (SSN), that provides a simple unified explanation for a wide variety of neural responses related to global integration. The model serves as a guide for new experimental explorations of cortical circuitry in Dr. Van Hooser's laboratory, using both traditional experimental recording techniques and his recently developed novel optical methods for manipulating cortical activity with high spatial and temporal resolution. The SSN model, if successful, will be elaborated to best explain experimental results. In Aim 1, the light-activated channel channelrhodopsin2 (ChR2) and an optical stimulation system are used to drive activity of cortical circuits in precise spatial and temporal patterns to test the contribution of cortical circuits to normalization and contextual modulation including various SSN predictions about them. In Aim 2, the balance of drive to excitatory (E) vs. inhibitory (I) cells within the cortex will be altered using viruses that largely restrict expression of ChR2 to E or I cells. This will test SSN model predictions involving modulation of network gain by modulatory input biased toward E or I cells, mechanisms of attentional modulation, and the dependence of a paradoxical result -­ adding drive to I cells reduces steady-state I responses -- on the spatial pattern of drive to I cells and level of cortical activation. RELEVANCE (See instructions): We will test the predictions of a powerful framework for understanding how sensory cortex globally integrates multiple sources of input, bottom-up and top-down, to produce neuronal responses and ultimately perception. Understanding circuit changes that cause breakdown of this cortical operation may provide insight into disorders such as autism and schizophrenia, which show deficits in contextual or global processing. Understanding global integration will be necessary for the creation of prosthetic devices to treat blindness and other disorders.

PROJECT SUMMARY Technology for recording from the brain is developing at a breakneck pace. But the digital integration of data acquired from different recording technologies is an impediment to the rapid adoption of these technologies across labs, and also makes analysis by interested 3rd parties, such as theorists, difficult. This lack of integration is a major barrier to scientific inquiry, as labs cannot easily analyze each other's data. Funding agencies are increasingly concerned with reproducibility, rigor, and distribution of data, even though there is no generally accepted ?library? process for sharing these data. Common data interfaces would facilitate the development of common analysis code, leading to an increase in code testing and robustness, and an increase in reproducibility and rigor. In this proposal, a data interface standard for neurophysiological and imaging data is developed. The standard is not a file format but rather is a systematic means of specifying and accessing data used in the neurosciences, including voltage waveforms, imaging data, spike times of neurons, and intensity values in regions-of-interest within imaging data. Versions are developed in Matlab and Python, but the data interface standard can be written in any programming language. The proposal includes the development of file readers for several Multifunction Data Acquisition Devices, 2-photon microscopes, stimulus devices, and ?apps? for imaging, spike, and stimulus analysis. The ease and power of the interface is tested in multiple data access events involving graduate students and postdoctoral researchers in neuroscience. Two of these sessions are reviewed by an outside group with expertise in interface design and human factors. The standard is revised after each session to improve ease and power. The proposal also includes the conversion of several data sets from a variety of systems neuroscientists and modelers, including BRAIN researchers. These data sets include neural recordings, laboratory stimuli, and behavioral data, and range from long-duration recordings of central pattern generators, to long-duration recordings of cortical neurons, to studies of navigation and taste perception. Conversion of these data sets will force the development team to ensure that these data can be specified easily, and also provide a first group of data sets for other scientists or amateurs to analyze. The long range goal is to enable experimentalists, theorists, and even amateurs to exchange data easily and to begin meaningful analysis within the hour of download. This has the capability to transform neuroscience into a discipline more like astronomy, where data is widely shared and many theorists and amateurs contribute to new discoveries.

Project Summary A new generation of optical and optogenetic tools is allowing rapid progress in our understanding of fundamental processes in the living brain and how these processes go awry in disease. One of the key technologies underlying in vivo imaging is 2-photon microscopy, which allows fluorescent material deep within the brain to be examined. In recent years, there have been major technological improvements in 2-photon imaging systems that allow for faster and deeper imaging. These new 2-photon imaging technologies allow qualitatively new types of studies. Resonant- scanning technology that permits imaging at 30Hz allows neuroscientists to study neural responses to single stimuli, on single trials, without averaging across time or trials. This 30Hz rate of acquisition is also faster than many of the movement artifacts that occur within the living brain, such as respiration and heart beats, allowing for artifact correction rather than blurring, and permits the study of sub- neuron features such as dendrites and dendritic spines. New laser technology and new optical tools allow the use of longer-wavelength indicators (such as red indicators), which can be stimulated and examined at much greater depths than the traditional shorter-wavelength indicators. In short, recent technological improvements have had a transformative impact on 2-photon imaging. This project will provide NIH-funded systems neuroscientists at Brandeis University with a sustainable, state-of-the-art in vivo 2-photon imaging station with accompanying instrumentation for animal anesthesia, physiological monitoring, visual stimulation, and behavioral monitoring of eye movements and movements on a treadmill. The clusters of instrumentation that will be assembled have been carefully selected for performing advanced brain imaging in the living brain while animals are anesthetized or are engaged in behaviors of interest. Currently, Brandeis has no in vivo resonant- scanning 2-photon microscope, and this shared instrumentation will be a game-changing improvement in our capabilities. The shared instrumentation will be placed in the middle of our systems neuroscience labs to allow for synergistic interactions among the users. Importantly, this equipment will immediately permit advances in our understanding of neural plasticity, neural development, visual perception, taste perception, navigation, and decision making.