There are two loop circuits connecting the prefrontal cortex and subcortical brain regions: the 'large loop' circuit, in which information loops through several brain regions, and the 'small loop' circuit, which connects the prefrontal cortex directly to the mediodorsal (MD) thalamus. They are thought to be an important neural basis for the generation of higher brain functions. In this project, we aim to elucidate the functions of these two cortico-subcortical loop circuits in monkeys (non-human primates), which have a highly developed prefrontal cortex, using state-of-the-art brain circuit manipulation techniques and large-scale neural activity recordings.