What Is It, Location, Function, and More
Author:Maria Emfietzoglou, MD
Editors:Alyssa Haag,Ian Mannarino, MD, MBA,Kelsey LaFayette, DNP, RN, FNP-C
Illustrator:Jessica Reynolds, MS
Copyeditor:David G. Walker
What is the thalamus?
The thalamus, an egg-shaped structure made up of thalamic nuclei, is part of the brain that relays sensory and motor signals from various locations (e.g., the basal ganglia, medial lemniscus, the retina) to the cerebral cortex. Additionally, the thalamus plays a role in alertness, sleep, and consciousness as well as learning and memory.
Where is the thalamus located?
The thalamus is located deep in the human midbrain, hidden between the cerebral hemispheres. On a mid-sagittal section through the brain, the central part of the brain is occupied by the diencephalon (i.e., the thalamus and hypothalamus) that surrounds the third ventricle cavity. The hypothalamus (a small brain structure that plays an important role in homeostasis and hormone regulation) creates the floor and inferolateral walls of the third ventricle. Superior to (or on top of) the hypothalamus is the thalamus, which is separated from the hypothalamus by the hypothalamic sulcus. Finally, anterior to (or in front of) the hypothalamus resides the optic chiasm (i.e., the point where the two optic nerves cross over each other).
What is the function of the thalamus?
Because the thalamus is connected with almost all parts of the central nervous system, including the brainstem and the cerebral cortex, the thalamus influences many different processes in the brain. The thalamus is a part of almost every sensory pathway where it serves as a major sensory relay station. It receives input from various locations in the body, combines and processes this information, and then typically forwards it to the cerebral cortex. The thalamus plays a role in modulating movement through its connections with the basal ganglia, cerebellum, and frontal lobe. It can also influence motivated behaviors (i.e., behaviors in pursuit of a goal, such as seeking food when hungry) via connections with the hypothalamus and the frontal lobe. The thalamus can also alter levels of consciousness by communicating with the reticular formation of the brainstem.The thalamus is composed of densely packed neuronal cell bodies known as thalamic nuclei. The different thalamic nuclei are involved in the various functions of the thalamus. One of the most important nuclei is the ventral posterolateral (VPL) nucleus, which transmits sensory signals (e.g., vibration, pain, pressure, proprioception, light touch, and temperature) from the medial lemniscus and the spinothalamic tract to the somatosensory cortex, which is a structure located in the parietal lobe of the brain that is involved in the of processing of various sensory signals. Additionally, there is the ventral posteromedial (VPM) nucleus, which is involved in processing sensations from the face and is also involved in taste sensation (i.e., receives information from the trigeminal and the gustatory pathways and projects to the somatosensory cortex). Another thalamic nucleus is the ventral lateral (VL) nucleus, which relays motor information and can influence movements. The medial geniculate nucleus of the thalamus projects to the primary auditory cortex of the temporal lobe and is involved in hearing. Finally, the lateral geniculate nucleus receives input from the retina via the optic nerve fibers, optic chiasm, and optic tract and then projects to the visual cortex of the occipital lobe via the optic radiation.
What are examples of thalamic disorders?
Thalamic disorders are typically secondary to stroke, either ischemic or hemorrhagic, but can also be due to migraines, metabolic disease (e.g., thiamine deficiency), inflammatory disease (e.g., Behcet disease), infection (e.g., bacterial abscess), brain injury, or tumors. Thalamic disorders that occur after stroke often present with paresthesias but may also manifest as a painful itching; burning sensation; or allodynia, which is a feeling of excessive pain after a painless stimulation on the contralateral side of the infarct. Individuals may also develop weakness on one side of the body, difficulty swallowing or speaking, and vision loss. Thalamic disorders might also present with memory loss, confusion, agitation, and sleeping disturbances.
Diagnosis of thalamic disorders typically begins with a thorough patient history in order to understand the clinical presentation followed by imaging studies, such as brain CT and MRI, to confirm the diagnosis. Treatment depends on the cause and can include medications such as thrombolytics (e.g., tenecteplase) for stroke, antibiotics for brain infections, thiamine supplementation, and/or surgical procedures in case of brain injury or tumor.
What are the most important facts to know about the thalamus?
The thalamus is a small yet complex brain structure that plays an important role in sensation, movement, motivated behaviors, and consciousness. It has a role in relaying motor and sensory information from various locations to the cerebral cortex. Anatomically, it is located between the two cerebral hemispheres and is part of the diencephalon, a brain structure that also includes the hypothalamus. Dysfunction of the thalamus is typically caused by stroke, migraine, metabolic disease, brain infection, injury, or tumor. Signs and symptoms of thalamic disorders vary and can include paresthesias, burning sensation, allodynia, weakness on one side of the body, vision loss, memory loss and confusion.
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Related linksNervous system anatomy and physiology
Anatomy of the diencephalon
Resources for research and reference
Gould, D. J. (2014). Neuroanatomy (5th ed.). Philadelphia. Wolters Kluwer Health/Lippincott Williams & Wilkins.
Le, T., Bhushan, V., Sochat, M., Sylvester, P., Mehlman, M., & Kallianos, K. (2020). First aid for the® USMLE. New York. McGraw-Hill Medical.
Neuro-Ophthalmic Manifestations of Thalamic Disease. In American Academy of Ophthalmology. Retrieved May 4, 2022, from https://eyewiki.aao.org/Neuro-Ophthalmic_Manifestations_of_Thalamic_Disease
Renard, D., Castelnovo, G., Campello, C., Bouly, S., Le Floch, A., Thouvenot, E., Wacogne, A., & Taieb G. (2014). Thalamic lesions: A radiological review. Behavioural Neurology, 2014. DOI: 10.1155/2014/154631Splittgerber, R., & Snell, R. S. (2019). Snell’s clinical neuroanatomy (8th ed.). Philadelphia. Wolters Kluwer.