Thalamus Anatomy, Function, & Disorders

By Olivia Guy-Evans, published June 09, 2021

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The thalamus is situated at the core of the diencephalon, which is a part of the forebrain also containing the hypothalamus, epithalamus, and subthalamus. 

The thalamus is often described as the relay station of the brain as a great deal of information that reaches the cerebral cortex, first stops in the thalamus before being sent to its destination. 

All of our senses, with the exception of smell, are outed through the thalamus before being directed to other areas of the brain for processing

There are two thalami, one in each hemisphere of the brain. They lie above the brain stem and the midbrain (or mesencephalon), which allows for connections of nerve fibers to reach the cerebral cortex in all directions. 

This structure of the brain is able to relay and integrate a variety of motor and sensory signals between the higher centers of the brain and the peripheries. 

The thalamus is mostly comprised of grey matter but is also surrounded by two layers of white matter. They are oval shaped in appearance, almost looking like eggs, with two protuberances on the surface. 

One of these is known as the medial geniculate bodies, which are important for the processing of auditory information. The other is the lateral geniculate bodies, which are responsible for the processing of visual sensory inputs. 

 The thalamus is made up of different types of nuclei, each of which serve a unique purpose, from relaying sensory and motor signals to the regulation of consciousness and alertness.

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Function

As the thalamus is heavily involved in relaying information between the cortex and the brain stem, as well as within different cortical structures, it contributes to many brain processes. 

Historically believed to only be related to sensory relay in visual, auditory, somatosensory, and gustatory systems, it has since been found to be involved in many other functions beyond these. 

Below are a list of some of the associated functions:

• Contributions to perception
• Relaying motor information
• Relaying sensory information
• Role in memory
• Alertness and attention
• Consciousness and awareness
• Role in cognition

Connections to structures such as the hippocampus and other parts of the limbic system suggest the thalamus plays a role in memory, especially episodic memory, as well as with learning and emotions.

 The thalamus is also believed to be involved in the regulation of sleep, wakefulness, and arousal. The thalamus filters through information between the brain and the body. 

Every sensory function, except for olfaction (sense of smell) has a thalamic nucleus that receives, processes, and transmits information to associated areas within the cerebral cortex. 

Generally, the connections between the sensory organs of the body and the thalamus are contralateral, meaning they communicate with the opposite side of the body. 

Whereas the connections between the thalamus and the cerebral cortex are ipsilateral, meaning they communicate on the same side of the brain.

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Nuclei within the thalamus

The thalamus is made up of a series of nuclei, all of which are responsible for the relay of different sensory signals. 

The nuclei are both excitatory and inhibitory in nature and receive sensory or motor information from the body, presenting selected information via the nerve fibers to the cerebral cortex. 

 Described below are a list of some of the main groups of nuclei within the thalamus and what they are responsible for:

Disorders

Since the thalamus acts as a relay station from which it sends input and receives output from many brain structures, damage to this area can impact many brain functions. 

Below is a list of symptoms which may be associated with damage to the thalamus:

• Amnesia
• Aphasia
• Difficulties with attention
• Impaired movement
• Impaired posture
• Chronic pain
• Sleepiness
• Loss of alertness and activation
• Impaired processing of sensory information
• Apathy

As the thalamus plays a key role in the sleep-wake regulation, damage to this area has been implicated in consciousness related disorders, as well as resulting in individuals being in a coma. 

Due to the thalamus being important for generating normal sleep thalamocortical rhythms, sleep disorders may result from damage such as insomnia. 

 Language deficits because of thalamic damage, known as thalamic aphasia, can result in difficulties with lexical semantics. Similarly, this can cause verbal paraphasia, which is a speech disturbance, presenting as jumbled up words or meaningless speech. 

 Disorders of the thalamus can also manifest itself in the form of sensory loss, movement disorders, pain syndromes, and visual disorders. A stroke is a common cause for many disorders of the thalamus. 

Thalamic pain syndrome can occur when there are disturbances in one of the pathways of the thalamus which affects the sensation of temperature following a stroke. This can result in tingling or burning pain, as well as discomfort with temperature changes. 

Months after having a thalamic stroke, this can eventually lead to severe chronic pain. Stokes of the thalamus have also found to produce symptoms of uncoordinated involuntary movements of the body due to affecting the pathways associated with motor movements.

It has been found that patients with schizophrenia had significantly less thalamic volume in comparison to those without schizophrenia (Coscia et al., 2009). 

Reduced thalamic size was suggested to be correlated with worse neuropsychological functioning and specific deficits in language, motor, and executive skills. 

This implies that the differences in thalamic structure are significantly related to some of the symptoms of schizophrenia. Another study was conducted to investigate the thalamic differences in those with Autism. 

It was discovered that autistic males had lower and weaker increases in functional connectivity with their thalamus (Tomasi & Volkow, 2019). 

It has also been found that there was non-typical thalamic connectivity in the temporal and motor areas of those with autism (Woodward et al., 2017).

APA Style References

Coscia, D. M., Narr, K. L., Robinson, D. G., Hamilton, L. S., Sevy, S., Burdick, K. E., Gunduz-Bruce, H., McCormack, J., Bilder, R. M. & Szeszko, P. R. (2009). Volumetric and shape analysis of the thalamus in first‐episode schizophrenia. Human brain mapping, 30(4), 1236-1245. Crumbie, L. (2020, November 13). Thalamus. Kenhub.

Gummadavelli, A. and Blumenfeld, . Hal (2018, September 7). Thalamus. Encyclopedia Britannica. https://www.britannica.com/science/thalamus https://www.kenhub.com/en/library/anatomy/thalamus

Mandal, A. (2021, February 15). What is the Thalamus? News Medical Life Sciences. https://www.news-medical.net/health/What-is-the-Thalamus.aspx#:~:text=The%20thalamus%20is%20a%20small,signals%20to%20the%20cerebral%20cortex

Tomasi, D., & Volkow, N. D. (2019). Reduced local and increased long-range functional connectivity of the thalamus in autism spectrum disorder. Cerebral Cortex, 29(2), 573-585.

Torrico, T. J., & Munakomi, S. (2019). Neuroanatomy, Thalamus.

Woodward, N. D., Giraldo-Chica, M., Rogers, B., & Cascio, C. J. (2017). Thalamocortical dysconnectivity in autism spectrum disorder: an analysis of the autism brain imaging data exchange. Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, 2(1), 76-84.