What is the thalamus?
The thalamus is a structure positioned right above the brainstem. Its main function is to act as a "sensory relay station," meaning it takes incoming sensory information and appropriately sends it to the cerebral cortex for complex processing.
Let's think about the cerebral cortex as executive board members for the company, Brain Co. This company's goal is to take things that people see, hear, smell, and touch to create personalized experiences. These experiences include things like emotions, thoughts, and physical movements. The board members want to decide how these personalized experiences turn out, but they need a way of managing the overwhelming amount of sensory information presented to their company.
Brain Co. has several stores that are each specialized in collecting different types of sensory information. To run efficiently, they need a regional manager that will assess the stores' work to decide which cerebral cortex board member would be most interested in this type of information for experience personalization. The thalamus acts as Brain Co.'s regional manager.
In this role, the thalamus has a handy organizational scheme to compartmentalize overwhelming amounts of information. The thalamus organizes all of these different sensory inputs using "nuclei," or bundles of specialized neurons that differ slightly among each nucleus.
There might be ~50 specialized thalamic nuclei, but the most popular ones are served up in this nigiri. Further, each nucleus deals with potentially more than one type of sensory information, so the most well-established are listed above.
Brain Co.'s organizational structure for different types of information is laid out in "cortico-basal loops." These loops are responsible for different functions, like emotion, cognition, and movement.
 DeLong, M. R., & Wichmann, T. (2007). Circuits and circuit disorders of the basal ganglia. Archives of neurology, 64(1), 20-24.
 Lambert, C., Simon, H., Colman, J., & Barrick, T. R. (2017). Defining thalamic nuclei and topographic connectivity gradients in vivo. Neuroimage, 158, 466-479.