The diencephalon appears at the upper end of the brain stem between the brain stem and cerebrum. All the diencephalic subdivisions include the term thalamus, and they include dorsal thalamus/thalamus epithalamus, hypothalamus, metathalamus, and subthalamus. Each of these regions has many subnuclei. All our senses with the exception of olfaction are processed through the dorsal thalamus. The thalamus also plays an important role in sleep, wakefulness, consciousness, learning, and memory. All the ascending fiber pathways from the spinal cord and brain stem terminate upon nuclei in the diencephalon, and this is the basis for crude awareness of many of these senses at this level. The thalamus/dorsal thalamus is the largest zone, and it is the primary provider of information from the spinal cord and brain stem onto the cerebral cortex permitting the cerebral cortex to do its many functions. The thalamus is the final processing station for systems that project to the cerebral cortex; thus, it serves an important integrative function. Many sensations are first crudely appreciated at thalamic levels, including pain, touch, taste, and vibration except for olfaction. The discriminative processes associated with these sensations, as well as tactile discrimination, vision, audition, and taste, are elevated to consciousness in the cerebral hemisphere. Glutamate is the principal transmitter in the thalamus.