45Locomotion has a global impact on circuit function throughout the cortex, including regulation of 46 spatiotemporal dynamics in primary visual cortex (V1). The mechanisms driving state-changes 47 in V1 result in a 2-3 fold gain of responsiveness to visual stimuli. To determine whether 48 locomotion-mediated increases in response gain improve the perception of spatial acuity we 49 developed a head-fixed task in which mice were free to run or sit still during acuity testing. 50 Spatial acuity, ranging from 0.1 to 0.7 cycles/°, was assessed before and after 3-4 weeks of 51 reward-based training in adult mice. Training on vertical orientations once a day improved the 52 average performance across mice by 22.5 ± 0.05%. Improvement transferred to non-trained 53 orientations presented at 45°, indicating that the improvement in acuity generalized. 54Furthermore we designed a second closed-loop task in which acuity threshold could be directly 55 assessed in a single session. Using this design, we established that acuity threshold matched 56 the upper limit of the trained spatial frequency; in two mice spatial acuity threshold reached as 57 high as 1.5 cycles/°. During the 3-4 weeks of training we collected a sufficient number of 58 stimulus trials in which mice performed above chance but below 100% accuracy. Using this 59 subset of stimulus trials, we found that perceptual acuity was not enhanced on trials in which 60 mice were running compared to trials in which mice were still. Our results demonstrate that 61 perception of spatial acuity is not improved by locomotion. 62 63In the acuity task, performance accuracy averaged across the first two baseline sessions 129 was greater than 0.7 at 0.46 cycles/° for all mice, and greater than 0.7 for half of the mice at 130 0.58 cycles/°, and less than 0.7 for all mice except one at 0.7 cycles/°. These performance 131 values are consistent with values obtained using the visual water task (Hosang et al., 2018; 132

Anatomical methods for determining cell-type specific connectivity are essential to inspire and constrain our understanding of neural circuit function. We developed new genetically-encoded reagents for fluorescence-synapse labeling and connectivity analysis in brain tissue, using a fluorogen-activating protein (FAP)-or YFP-coupled, postsynaptically-localized neuroligin-1 targeting sequence (FAP/YFPpost). Sparse viral expression of FAP/YFPpost with the cell-filling, red fluorophore dTomato (dTom) enabled high-throughput, compartment-specific localization of synapses across diverse neuron types in mouse somatosensory cortex. High-resolution confocal image stacks of virally-transduced neurons were used for 3D reconstructions of postsynaptic cells and automated detection of synaptic puncta. We took advantage of the bright, far-red emission of FAPpost puncta for multichannel fluorescence alignment of dendrites, synapses, and presynaptic neurites to assess subtype-specific inhibitory connectivity onto L2 neocortical pyramidal (Pyr) neurons. Quantitative and compartment-specific comparisons show that PV inputs are the dominant source of inhibition at both the soma and across all dendritic branches examined and were particularly concentrated at the primary apical dendrite, a previously unrecognized compartment of L2 Pyr neurons. Our fluorescence-based synapse labeling reagents will facilitate large-scale and cell-type specific quantitation of changes in synaptic connectivity across development, learning, and disease states.