Understanding Circuits

 DESCRIPTION (provided by applicant): To address the core question underlying the Obama Brain Initiative to better understand the function of complex brain circuits, we propose a multi-scale recording and data analysis project to study the dynamical interactions between sensory cortex, motor cortex, and the basal ganglia in the process of motor planning and execution. The multi-scale approach will involve simultaneous recordings at the cellular, network, and systems level in head-fixed behaving mice trained to perform a rewarded locomotor task.

 DESCRIPTION (provided by applicant): The anatomical substrates and cellular mechanisms underlying reward-dependent learning have been studied for decades, but the specific circuit and network interactions between the cortex, striatum, and midbrain that mediate action selection have not been systematically investigated. Here, we bring together three different investigators with specialized expertise in each of these three brain regions.

Abstract The goal of this proposal is to develop robust in vitro human cell-derived microphysical systems which faithfully represent key features of the developing human neocortex in vivo. Our work addresses three key challenges that have limited the development of these systems to date: (1) Building robust and reproducible organoids at high throughput. To obtain meaningful, statistically significant results from genetic and non-genetic perturbations, it is necessary to develop organoid systems which are robust and can be reproducibly assayed in large numbers.

PROJECT SUMMARY Understanding of many aspects of the human brain is currently limited due to the lack of appropriate model systems that recapitulate the heterogenous nature of the human brain and the ethical and practical limitations of working with human brain tissue from patients. To overcome these challenges, we employ three-dimensional brain organoids, derived from human pluripotent stem cells, that recapitulate key features of human cortical development.

Experimental models of the human developing brain are needed to investigate human-specific aspects of brain development, evolution, and neurological disease. Progress in the field has been hampered by the lack of models, considering that the endogenous developing human brain cannot be directly investigated; animal models often fail to recapitulate human disorders and cannot feasibly be used to study complex polygenic states spanning many genes.

The human induced pluripotent stem cell (hiPSC) technology promises major advances in disease modeling and personalized medicine. Using hiPSCs, organoid systems have been generated in recent years that resemble the identity of several brain regions, including cortex, basal ganglia, cerebellum and spinal cord. Major shortfalls of these models are the lack of a reproducible topography of the cell types and tissue architecture that are generated, and the failure to recapitulate the full range of cellular and molecular diversity that characterizes in vivo systems.

SUMMARY The modular organization of the cerebral cortex is defined by anatomically and functionally segregated cortical columns, as well as layer-specific anatomical and functional connections that span multiple columns. Dysregulation of the developmental processes governing cortical formation can result in dysmorphic features that have been implicated in numerous neurological and psychiatric disorders.

Project Summary We propose to leverage new and existing transcriptomic and epigenetic datasets from mouse, marmoset, macaque and human brain to develop refined approaches for brain cell type enhancer selection for creating cell- type specific enhancer adeno-associated viruses (AAVs), and to make inroads toward prediction of brain-wide expression specificity.

Systematic experimental access to diverse neuronal cell types is a prerequisite to deciphering brain circuit organization, function, and dysfunction. Thus fundamental progress in neuroscience urgently needs cell type access technologies that are specific, comprehensive, easy to use, affordable, scalable, and general across animal species. Most if not all current genetic approaches to cell type targeting are based on genome and DNA engineering, which has inherent limitations in achieving the desired tool features.

PROJECT SUMMARY: This team initiative will provide the broad neuroscience community with a cell type-specific adeno- associated virus (AAV) armamentarium for easy and non-invasive implementation of novel and emerging molecular tools for anatomical and functional analysis of the nervous system in rodents, non-human primates, and human organoids. We will characterize engineered AAV capsids for cell type- and brain region-specific gene delivery (Aim 1).