This Funding Opportunity Announcement (FOA) is issued as an initiative of the NIH Blueprint for Neuroscience Research. The Neuroscience Blueprint is a collaborative framework through which 16 NIH Institutes, Centers and Offices jointly support neuroscience-related research, with the aim of accelerating discoveries and reducing the burden of nervous system disorders (for further information, see http://neuroscienceblueprint.nih.gov/). Applications are solicited for support of projects that will develop probes, instrumentation, and other tools for understanding, monitoring, and manipulating nervous system plasticity. This FOA will focus on the development of tools or techniques that will significantly advance the current state of the art in neuroplasticity research. Although applications will not be restricted to a particular type of technology, we are especially interested in applications that seek to harness the ability to assess and manipulate activity with exquisite subcellular resolution, and in cells specified by their circuit connectivity and/or transmitter phenotype.