Reissue of RFA-MH-22-115 to comply with DMSP policy. The purpose of this Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative is to encourage applications that will develop and validate novel tools to facilitate the detailed analysis and manipulation of complex circuits and provide insights into cellular interactions that underlie brain function. Critical advances in the treatment of brain disorders in human populations are hindered by our lack of ability to monitor and manipulate circuitry in safe, minimally-invasive ways. Clinical intervention with novel cell and circuit specific tools will require extensive focused research designed to remove barriers to delivery of gene therapies. In addition to identification and removal of barriers, the need to specifically target dysfunctional circuitry poses additional challenges. Neuroscience has experienced an impressive influx of exciting new research tools in the past decade, especially since the launch of the BRAIN Initiative. However, the majority of these cutting edge tools have been developed for use in model organisms, primarily rodents, fish and flies. These cutting edge tools, such as viral delivery of genetic constructs, are increasingly adaptable to large brains and more importantly are emerging as potential human therapeutic strategies for brain disorders. A pressing need to develop tools for use in large brains, more directly relevant to the human brain is the focus of this initiative. The new tools and technologies should inform and/or exploit cell-type and/or circuit-level specificity. Plans for validating the utility of the tool/technology will be an essential feature of a successful application.