The thalamus consists of a large collection of relatively distinct subdivisions or cellular clusters, or nuclei, all aggregated deep within the telencephon. The thalamus contains nuclei that receive sensory input from spinal and brainstem circuits. It processes information from visual, auditory, somatic sensory, taste, pain and thermal modalities. The thalamus makes numerous interconnections with different areas of the neocortex as well as with other nuclei of the telencephalon. It receives most of its downstream inputs from a variety of neuronal clusters lying in the medulla and brainstem. The thalamus relays and translates streams of impulses arriving from all its inputs and regulates and transmits processed information to different layers of the cerebral cortex.

The thalamus lies above the hypothalamus with which it makes some connections. Both the thalamus and hypothalamus are symmetrically mirrored on the two sides of the brain and the two nuclear groupings of both regions abut along the midline. Some thalamic nuclei may interconnect between homologous nuclei on the two sides

Below we display coronal sections stained for cell bodies. These cross sections are arranged from front (rostral) to back (caudal). The sequentially arranged sections are to be viewed as one does in reading lines of text in a book.