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The diencephalon can be divided into four areas, which are interposed between the brain stem and cerebral hemispheres. The four subdivisions include the  hypothalamus to be discussed in a separate lecture, the ventral thalamus containing the subthalamic nucleus already discussed, the epithalamus which is made up mostly of the pineal body, and the dorsal thalamus (henceforth referred to as the thalamus). Anatomically, the dorsal thalamus subdivided in 50-60 nuclear groups. The focus of this review is its functional anatomy. In the spinal cord and brain stem portions of the course certain relay nuclei of the thalamus that transfer information from sub-cortical structures to the cerebral cortex. By virtue of these relay functions that encompass the major senses and motor systems, the thalamus is often referred to as the gateway to the cortex. The thalamus has numerous connections to other areas of the brain as well, and these are thought to be important in the integration of cerebral, cerebellar, and brainstem activity. Branches of the posterior cerebral artery supply much of the thalamus. Occlusion of these small branches results in a number of symptoms characteristic of the thalamic syndrome.