PROJECT SUMMARY / ABSTRACT To survive, animals must learn appropriate associations between sensory cues and motor actions through a process of trial and error. We expect that this learning will strengthen the synaptic connections between neurons representing the sensory cue and neurons initiating the motor action. The strengthened synapses may be direct synaptic connections between these neuronal populations or via systems intermediate between these neurons, i.e., a “plastic brain circuit” or “pathway.” Synaptic plasticity has been observed in many different brain areas, and the mechanisms are moderately well understood. However, we have struggled to identify which plastic brain circuit underlies, specifically, the sensory cue-to-motor action association that is learned through the process of trial and error. This is due, in part, to the fact that many brain areas undergo plastic changes during learning, as the experience of learning recruits a variety of different cognitive processes, including sensory detection, motor control, feedback, working memory and reinforcement learning -- cognitive processes that all engage different brain areas and distributed networks. During my postdoc, I developed an approach to assign these cognitive functions to different brain circuits for a case of trial and error learning in mice. The approach involved an innovative behavior paradigm and optogenetic tools that are spatially and temporally precise. Mice learned to associate the optogenetic activation of visual cortex (cue) with a forelimb reach to grab a food pellet (motor action). As a result of my postdoc work, I now know which neurons in the brain encode this cue and which are required to initiate this motor action. Therefore I am now equipped to identify the plastic brain circuit underlying the learned association between this cue and this action. Here I propose to study the brain circuit between the cue-encoding neurons and the neurons necessary to initiate the motor action, in vivo while mice learn the cue-action association. I will study the flow of neural activity from the cue- encoding neurons in the visual cortex to the neurons in the superior colliculus that are necessary to initiate the motor action. In Aim 1, I will identify changes in the cued activity in visual cortex over learning. In Aim 2, I will determine how activity in the superior colliculus changes over learning. In Aim 3, I will determine whether the output of this pathway is sufficient to trigger the motor action after learning. Hence this work speaks directly to a key goal of the Brain Initiative, to “demonstrate causal links between brain activity and behavior.” I will learn in vivo two-photon imaging for Aim 1 under the guidance of Dr. Sabatini, an expert at this technique. Aims 2 and 3 will be conducted in the independent phase using in vivo electrophysiology, a technique with which I have extensive experience. These experiments will help to identify a pathway from visual cortex to ...