Illustration showing the anatomy of the inner brain. The diencephalon is a region at the core of the brain. It is the connection between the brain stem (centre bottom) and the cerebrum cerebrum (folded area) and consists of three grey matter structures, the thalamus, the hypothalamus and the epithalamus. The corpus callosum is a long brain structure in the middle of the brain shaped like a sideways C. Distinct parts of the inner brain perform numerous vital functions, from regulating sleep to the formation of memories.