Oculomotor Thalamus and Efference Copy

Abstract The oculomotor system is a network of neural circuitry that controls where one looks. Because the purpose of looking around a scene is to see details, the oculomotor system is closely tied to the visual system. A central hub for visuo-oculomotor coordination is the thalamus. Specific regions of the thalamus collect information from the rest of the central nervous system. A few salient examples are the pulvinar and mediodorsal thalamus (MD) that receive midbrain input, the ventrolateral thalamic nuclei that receive cerebellar input, and the lateral geniculate nucleus (LGN) that receives retinal input. In turn, these thalamic regions project to visual and oculomotor regions of cerebral cortex. A major signal conveyed by all these connections is neural activity related to eye movements. Broadly speaking, the oculomotor thalamus is the collection of nuclei that convey eye movement signals. The signals are used for both generating eye movements and monitoring them. The monitoring function, known as efference copy, allows the visual system to compensate for blur and image shifts caused by fast eye movements. This chapter outlines the current state of conceptual understanding about the role of the oculomotor thalamus in perception and behavior. The narrative approach is to consolidate the conclusions from many laboratories about the nuclei, connections, signals, and functions of the neural systems involved.