The posterior parietal cortex (PPC) mediates cognitive motor functions including motor planning and action understanding. The latter process is thought to occur via ‘mirror’ neurons, which fire both when an animal performs an action and when it observes a cohort performing the same action. The extraordinary tuning properties of PPC cells require the convergence of sensory and motor inputs from several areas, but the function of these inputs is ill-defined since it is not yet feasible in humans or primates to reversibly inhibit targeted anatomical projections. I propose to overcome this by studying PPC in rodents, and will apply optogenetic tools and multi-tetrode recordings to characterize the function of selected cortical inputs to PPC. Similar to motor planning functions for hand or eye movements in primates, the rodent PPC encodes upcoming locomotor movements, and a growing literature suggests that rodents have a mirror system. I thus propose two related research programmes focusing on action planning and the mirror mechanism. The first project will determine if behavioral coding in PPC changes between a foraging task, in which behavior is spontaneous, and during navigational planning in a working memory-based T-maze. I will then determine if silencing fronto-parietal anatomical connections at different phases of the T-maze tasks disrupts motor planning and decision making functions in PPC. Next, I will record from PPC while rats observe cohorts performing the T-maze task to determine if the rat PPC contains mirror neurons. If I find mirror cells in rats, I will optically silence visual and frontal inputs to PPC to determine if they confer mirror selectivity to PPC. These experiments will reveal the anatomical circuitry underlying action planning and the mirror system in a way which cannot be achieved in primate models, and will open the door for studying mirror cells in rodent models of human mental disorders, including autism and Fragile-X syndrome.