The thalamus (from Greek , "chamber") is a symmetrical structure of two halves, within the vertebratebrain, situated between the cerebral cortex and the midbrain. Some of its functions are the relaying of sensory and motor signals to the cerebral cortex, and the regulation of consciousness, sleep, and alertness. The two parts of the thalamus surround the third ventricle. It is the main product of the embryonicdiencephalon.