Schematic representation of circuits within the midbrain network in birds. Purple: projection from layer 10 in the OTm to the Ipc, SLu and Imc. Red: the projections of cholinergic neurons in the Ipc and SLu to both the OTv (blue) and OTm (purple). Green: the projections of GABAergic neurons in the Imc to the OTm (purple) and to the Ipc and SLu (red). Abbreviations: Imc, nucleus isthmi pars magnocellularis; Ipc, nucleus isthmi pars parvocellularis; OTm, multimodal and motor optic tectum; OTv, visual optic tectum; SLu, nucleus semilunaris. Based on data from Wang et al., 2004 and 2006.