Ilana B. Witten - US grants

DESCRIPTION (Provided by the applicant) Abstract: Despite the debilitating nature of addiction, and its associated societal and economic cost, there is currently no effective treatment. Here we propose to develop a bold new approach to the rampant neural plasticity induced by drugs of abuse. Although drug-induced plasticity is thought to be at the heart of the disease, it has not been possible to design circuit- level therapies to counteract these plastic changes because of technological limitations. My lab is now uniquely positioned to finally innovate such an approach, because of our expertise in both counteract the new field of optogenetics (the optical control of neural activity) and the emerging analysis of circuit-level mechanisms underlying addiction. To create this new approach to counteract addiction-related behavior, we will develop a novel panel of next-generation technologies togenetically and functionally target selected cell-types in rats. In order to counteract drug-induced plasticity, we will apply the new targeting technologies to activate the aversion and extinction in synchrony with the circuits that encode the drug experience, thereby circuits involved in weakening the drug-related associations and alleviating addiction-related behavior. Thus, we present here both a powerful new concept for the treatment of addiction, as well as the development of enabling technologies to achieve this vision. Public Health Relevance: Addiction is a devastating illness which destroys the lives of millions of people in the United States, is associated with enormous economic and societal cost, and is virtually without treatment. By developing a panel of new technologies designed to control neural activity in the appropriate cell-types in a rodent model of addiction, we open the door to the development of an exciting new approach to counteract drug-induced plasticity and addiction-related behavior.

? DESCRIPTION (provided by applicant): Working memory, the ability to temporarily hold multiple pieces of information for mental manipulation, is central to virtually all cognitive abiliies. Working memory has been closely associated with multiple kinds of neural activity dynamics, such as persistent neural activity, activity ramps, and activity sequences. The neural circuit mechanisms of these dynamics remain unclear. This proposal will apply advanced technologies such as virtual reality, automated monitoring of behavior, in vivo microscopy, ontogenetic, and neural circuit reconstruction to solve fundamental problems in the understanding of working memory. The accumulation of evidence over time scales of seconds, a type of working memory critical for decision-making, will be used as a test bed for studying working memory. The proposal will build upon a rodent evidence-accumulation paradigm that allows quantitative, temporally precise parameterization of working memory and decision-making. The paradigm will be implemented with head-fixed rodents behaving in a virtual reality system (Aim 1), providing mechanical stability that enables the use of two-photon calcium imaging to observe neural activity related to working memory in the neocortex, basal ganglia, and cerebellum (Aim 3). Brain activity will also be perturbed using ontogenetic to probe the roles of brain regions and specific cell types in the formation and stabilization of memory (Aim 2). Finally, we will develop methods for probing the roles of cell types and connectivity in working memory through correlative serial electron microscopy and light microscopy as well as imaging of population responses to ontogenetic stimulation of single cells or groups of cells (Aim 4). This three-year project will produce a catalog of the types of neural circuit dynamics that are related to working memory across many brain regions. In subsequent years, this catalog will be mechanistically investigated by the anatomical and physiological methods developed in Aim 4. The long-term goal of this project is to arrive at a complete, brain-wide understanding of the cellular and circut mechanisms of activity dynamics related to working memory. The understanding is expected to take the form of a new generation of models containing cognitive variables distributed across brain regions, as well as models that explicitly represent neural circuit dynamics. This achievement will be a crucial step towards a mechanistic understanding of the neural basis of cognition.

? DESCRIPTION (provided by applicant): Working memory is an essential cognitive function central to virtually all behaviors. Despite the fact that we know which brain areas and which neuromodulators are involved in working memory, we know very little about which neurons need to be activated when to enable working memory. This gap in our knowledge arose because of the technical difficulty in manipulating and monitoring neural activity in genetically- and anatomically- defined cell-types with sufficiently high temporal resolution. In order to overcome this challenge and elucidate some of the causal neural dynamics for working memory, we propose to combine multiple synergistic approaches, including a rat optogenetic model that we have previously developed to target dopaminergic neurons, in vivo electrophysiological recordings, and fluorescence-based monitoring of neural activity in freely behaving animals (with gCaMP6). In Aim 1, we will optogenetically inhibit several cortical and striatal circuits eiter during the updating, maintenance, or readout of working memory to determine which aspect of working memory each circuit supports. In Aims 2, we will monitor neural activity in dopaminergic neurons using gCaMP6 to determine how dopaminergic dynamics correlate with working memory performance. In Aim 3, we will generate different patterns of dopaminergic stimulation (e.g. tonic vs phasic) to determine the causal relationship between working memory performance and dopaminergic activity dynamics. In Aim 4, we will integrate dopaminergic stimulation with electrophysiological recordings in dorsal striatum and prelimbic cortex to isolate the downstream changes in neural activity mediated by dopaminergic activity. Together, this work will provide new insights into the neural circuit mechanisms underlying working memory, with implications for both basic science and an understanding of the working memory dysfunction in various psychiatric disorders.

Project Summary Working memory, the ability to temporarily hold multiple pieces of information in mind for manipulation, is central to virtually all cognitive abilities. Recent technical advances have opened an unprecedented opportunity to comprehensively dissect the neural circuit mechanisms of this ability across multiple brain areas. The task to be studied is a common form of decision-making that is based on the gradual accumulation of sensory evidence and thus relies on working memory. A team of leading experts propose to investigate the neural basis of this behavior using the latest techniques, including virtual reality, high-throughput automated behavioral training, large-scale cellular-resolution imaging in behaving rodents, manipulation of neural activity in specific brain areas and cell types, and automated anatomical reconstruction. In particular, the researchers will identify key brain regions that are required for this decision task through systematic, temporally specific inactivations via optogenetics technology, across all of dorsal cortex and in key subcortical areas, and use quantitative model-fitting to evaluate the effects. They will use state-of-the-art two-photon calcium imaging methods and electrophysiology to characterize the information flow in many individual neurons within these brain areas during the task. In addition, they will use cutting-edge anatomical reconstructions and new functional connectivity methods, within and across brain regions, to evaluate the interactions of these physiologically characterized neurons. The long-term goal of this project is to arrive at a complete, brain-wide understanding of the cellular and circuit mechanisms of activity dynamics related to working memory. Finally, they will use sophisticated computational methods to incorporate this new understanding into a realistic circuit model that will support a tightly integrated process of model-guided experimental design, in which the model suggests the most informative experiments and their results are then fed back to improve the model?s fidelity. This process is expected to produce the most accurate and detailed multi-brain-region biophysical circuit model of a cognitive process in existence. In addition, the proposed research will enable researchers to generate and test a variety of hypotheses about the neural basis of evidence accumulation, working memory, and decision-making. Taken together, these achievements will represent a crucial step toward a mechanistic understanding of how the brain works with information.

Project Summary: Project 3, Neural Coding and Dynamics?Subcortical Regions Working memory, the ability to temporarily hold multiple pieces of information in mind for manipulation, is central to virtually all cognitive abilities. This multi-component research project aims to comprehensively dissect the neural circuit mechanisms of this ability across multiple brain areas. The individual parts of the project cohere conceptually, in part, because they all involve rodents trained to perform a type of decision-making task that is based on the gradual accumulation of sensory evidence and thus relies on working memory. Although most previous characterization of neural correlates of working memory and decision making has focused on cortical regions, there is growing appreciation that subcortical regions contribute to these processes as well. Thus, this project focuses on characterization of the neural dynamics underlying working memory and decision-making in a network of subcortical regions. Specifically, cellular-resolution two- and three-photon calcium imaging will be used to characterize neural coding and dynamics in dopamine neurons in the ventral tegmental area and substantial nigra, granule cells and Purkinje cells of the cerebellum, medium spiny neurons in the striatum, and pyramidal cells in the hippocampus. This data will be supplemented with multi-electrode recordings, which capture fast neural activity that calcium imaging cannot. The experiments will combine these two data types for the first time in the setting of a working memory and decision-making task. The results from this project, together with those from another component that investigates similar measures in neocortex, are expected to provide an unprecedented amount of data that will give new insight into the processing of task-relevant information during a cognitive task across a wide variety of cortical and subcortical areas. Another component will combine these results with temporally and spatially specific inactivation data from the other two components to build and constrain a biophysically realistic, multi-region computational model of the behavior.