Ephrin ligands are a family of proteins that bind on to the ephrin receptors. They are involved in axon guidance, visual mapping from the retina to the superior colliculus. This is analogous to a computer keyboard and mapping in terms of the American Standard Code for Information Interchange, or ASCII, on screen characters. In mammals, seeing is mediated by projections to the thalamus and on to the cortex. The retina senses and transmits light to retinal ganglion cells (RGCs). There are more than twenty types of RGCs projecting from the retina to parts of the brain. The chapter describes the relationship between the three parts of the cerebellum and its connections to the brainstem and frontal cortex. This gives rise to the unique technique of bilateral cerebellar stimulation, which is the foundation for Bilateral Affective Reprocessing of Thoughts (BART) psychotherapy.