If the word "thalamus" sounds like Greek to you, you have hit the nail on the head! It is a Greek word that means "inner chamber." The thalamus is an egg-shaped structure residing in the center of the brain, above the brainstem. We have two thalami, one on each side of the brain. People sometimes describe it as an information relay station, but what does the thalamus do?
The thalamus resides between the midbrain and the cerebral cortex, with a multitude of nerve connections to both. Its principal function is to relay motor and sensory information to the cerebral cortex. The thalamus also plays a vital role in consciousness, alertness, sleep, learning, and memory.
The thalamus is called a relay station because all sensory (except olfaction) and motor information that goes to the cortex first makes a pit-stop at the thalamus before going off to its various destinations.
What Does The Thalamus Do?
The thalamus is more than just a gatekeeper of information before it heads to the cortex. It also plays a vital role in different types of higher-order brain processing.
Description Of the Thalamus
The brain is made up of fluid-filled spaces called ventricles. Each oval-shaped thalamus is about two inches long and sits symmetrically on either side of the third ventricle.
The thalamus mainly consists of gray matter, but two layers of white matter surround the structure. The egg-shaped thalami have two protrusions on the surface. (2)
One of these is essential in processing auditory information and is called the medial geniculate body. The other is called the lateral geniculate body, which processes visual input.
Nuclei Within The Thalamus
The thalamus consists of several types of nuclei, each designed to deal with different kinds of sensory information. The nuclei receive motor and sensory signals from the body and send selected data to the cerebral cortex via the nerve fibers.
The Anterior Nucleus
Scientists believe that the anterior nucleus is involved in memory because of its extensive connections to the hippocampus. This nucleus is also linked to the mammillothalamic tract and the cingulate gyrus, which processes emotions and regulates behavior. (4)
These areas are connected to the limbic system, which sends information to the anterior nucleus, which then projects it to the cingulate gyrus.
The Dorsomedial Nucleus
The dorsomedial nucleus is involved in memory and emotional behavior. It relays information from the olfactory cortex and the amygdala to the limbic system and the prefrontal cortex. From there, it goes to the prefrontal association cortex. This nucleus plays an essential role in attention, planning, organization, and higher cognitive thinking.
The Ventral Posterolateral And Ventral Posteromedial Nucleus
These nuclei send information to the somatosensory cortex, which processes and receives sensory information about the body. The trigeminal nerve sends information about the face to the ventral posteromedial nucleus.
The Ventral Anterior And Ventrolateral Nucleus.
The basal ganglia and cerebellum send motor input to the ventral anterior and the ventrolateral nuclei. They play a part in motor functions.
The Lateral Posterior Nucleus
The lateral posterior nucleus is involved in integrating sensory input and applying it to cognitive functions. It can also determine which visual stimuli stand out the most, and is active in visually guided behaviors.
The Pulvinar Nucleus Nucleus
This nucleus has extensive connections to the visual cortex and plays a role in processing visual stimuli. It projects to the striatum and the amygdala, relaying visual data to guide precise movements.
The Reticular Nucleus
The reticular nucleus forms the exterior covering of the thalamus. It does not project outwards to the cortex but organizes the information from other nuclei in the thalamus.
Functions Of The Thalamus
The thalamus performs many functions, which include the following: (3)
- Relaying sensory information
- Relaying motor information
- Prioritzing attention
- Plays a role in consciousness
- It plays a role in memory and cognition.
The Thalamus Relays Sensory Information
The sensory relay nuclei include the lateral geniculate body, medial geniculate body, and the ventral posterior nucleus.
Sensory data travels to the thalamus, which sends it to a nucleus tailored for processing that type of sensory information. From there, it goes to the corresponding area in the cortex for further processing. (1)
For example, visual information from the retina travels to the lateral geniculate body in the thalamus, which specializes in handling visual data. It then goes to the primary visual cortex. All the senses except smell have similar pathways through the thalamus.
Receptors in different parts of the body transmit sensory impulses to the thalamus. These impulses arrive in the thalamus as a sensation. It transfers this sensation to the cerebral cortex, which interprets it as temperature, pain, or touch. (4)
The Thalamus Relays Motor Information
Similar to the way the thalamus relays the sensory information, it uses motor nuclei to relay motor information to the cortex. (5)
The ventral anterior (VA) nucleus is responsible for the induction, performance, and control of some voluntary movement.
The VA nucleus relays its information to the primary motor cortex, the premotor cortex, and the supplementary motor area.
The ventral lateral (VL) nucleus plays a significant role in fine motor control and balance.
The Thalamus Prioritizes Attention
The thalamus receives a vast amount of information at once, and one has to wonder how we manage to focus on the appropriate stimulus. Our brains throw much of the irrelevant information through selective filtering. For example, when we watch a movie, we focus on the film and tend not to hear other noises in the theater. (6)
We know that connections project from the thalamus to the cortex, and some projecting back to the thalamus. We can explain the reciprocal connectivity with selective filtering.
When the cortex receives the information it deems important, it sends a message back to the part of the thalamus known as the reticular nucleus. The thalamus uses the GABA neurotransmitter to inhibit the transmission of irrelevant signals back to the cortex.
The Thalamus Plays A Role In Sleep And Consciousness
The thalamus relays information from our senses to the cerebral cortex. The thalamus is quiet during most stages of our sleep, enabling us to tune out whatever is happening in the world around us. But the thalamus is active during REM sleep, sending the cortex sounds, images, and other sensations that work their way into our dreams. (7)
The thalamus works together with the hypothalamus and the basal telencephalon to regulate sleep patterns.
The thalamus' intralaminar nuclei contain thalamocortical neurons that send signals throughout the cortex. When the brain activates these neurons, they release excitatory amino acids, including glutamate and aspartate, which contribute to cortex excitation and alertness.
These neurons emit single action potentials at regular intervals while awake. When we fall asleep, they start firing in bursts, enabling the cortex to display the synchronized EEG sleep pattern. (8)
The Thalamus Plays A Role In Memory And Cognition
The thalamus relays information to the relevant areas of the cerebral cortex, but scientists now realize that its functions go beyond this. The thalamus forms part of the limbic system, a section of the brain associated with emotions, learning, and memory. (9)
Conditions And Disorders Related To The Thalamus
The thalamus is the hub from which sensory and motor information travels to the appropriate region of the cerebral cortex. If damaged, it can seriously affect many of your body's functions. (3)
Symptoms of a damaged thalamus may include:
- Amnesia or memory loss.
- Apathy - lack of enthusiasm or interest in life.
- Aphasia – the loss of the ability to speak or understand language
- Struggling with attention, loss of alertness.
- Struggling to process sensory information.
- Impaired movement
- Chronic pain
A damaged thalamus can cause the following conditions:
- Unconsciousness or possibly a coma.
- Sleep disorders, including insomnia or fatal familial insomnia, an inability to sleep, eventually leading to death.
- Thalamic aphasia – muddled words, incomprehensible speech
- Vision issues, such as vision loss or sensitivity to light.
- Movement disorders, such as tremors.
- Pain syndromes, such as thalamic pain syndrome (burning or tingling)
Damage to the thalamus usually originates from thalamic strokes or tumors in the thalamus.
The Thalamus And Fatal Familial Insomnia
Fatal familial insomnia results from a hereditary prion (protein type) that attacks a specific chromosome. Insomnia escalates to a complete inability to sleep. The patient experiences panic attacks, phobias, and paranoia. They lose weight rapidly, develop dementia, and lose their ability to speak before passing away.
Thalamic Pain Syndrome
A stroke in the thalamus can cause thalamic pain syndrome. Symptoms include burning or aching on one side of the body, and mood swings often accompany the pain. (10)
The Thalamus And Akinetic Mutism
Bilateral ischemia (restriction of blood flow) can cause akinetic mutism. This condition leaves the person with a tendency not to move or speak. Although they are not paralyzed, they have almost no motor functions like speech, gestures, and facial expressions but still display alertness. They become inactive and answer in monosyllabic whispers. (11)
Damage to the thalamus can cause a disorder known as aphasia, where a patient struggles with speech or understanding what other people are saying. There are different types of aphasia. (12)
Receptive aphasia occurs when patients don't understand what others are saying and can not express themselves. Usually, they are unaware of their disorder. It may seem they're able to speak fluidly, but often their conversation is muddled or out of context.
Expressive aphasia patients recognize their own deficiencies. They understand speech and writing but struggle to speak and write smoothly.
Global aphasia is the most severe version of the disorder, with patients struggling with both expressive and receptive language abilities. They experience extreme difficulty in speaking fluidly, understanding speech, reading, and writing.
Creutzfeldt-Jakob Disease Damages The Thalamus
Creutzfeldt-Jakob Disease is a rare disease that very quickly causes brain degeneration. It causes symptoms similar to those of dementia. Prions develop and multiply in the brain cells, and the condition escalates quickly. It is fatal, and there is no treatment. (13)
Korsakoff Syndrome And The Thalamus
Korsakoff Syndrom is a central nervous system disorder resulting from a thiamine deficiency, which is also linked to and exacerbated by the excessive intake of alcohol. It is an amnestic-confabulatory disorder that has the following seven symptoms: (14)
- Anterograde amnesia (a loss of memory of things after the onset of symptoms).
- Retrograde amnesia (the memory loss going back a while before the onset of symptoms).
- Fixation amnesia (where a person cannot remember what has happened minutes before).
- Confabulation occurs when a person invents memories and believes they are true.
- Minimal conversation content.
- Lack of insight.
- Apathy (a person loses interest in things quickly and appears indifferent to changes).
This syndrome can damage a part of the brain known as the mammillothalamic fasciculus, which extends into the thalamus.
Symptoms can vary depending on which area of the thalamus was damaged, but there are also some general symptoms.
- Loss of feeling
- Difficulty moving or keeping your balance
- Speech difficulties
- Vision problems
- Sleep issues
- Attention span decrease
- Thalamic pain
- Memory loss
Thalamic strokes can be ischemic (resulting from a blocked artery) or hemorrhagic (resulting from a ruptured blood vessel). Treatment for the former will involve clot removal medication and possibly surgery to remove the clot. Treating the latter will include stopping blood-thinning medicines, high blood pressure medication, and surgery to repair the ruptured blood vessel and fix other faulty arteries.
Once you've had a thalamic stroke, you stand a higher chance of having subsequent ones. Wise lifestyle choices can help to prevent this. You should follow a healthy diet, stop smoking, exercise regularly, and maintain a healthy weight. (15)
Treatment For Thalamus Damage
People with Parkinson's disease are candidates for deep brain stimulation if their symptoms have not improved with medication. Surgeons will implant electrodes in the brain that send electrical impulses that change or block activities causing Parkinson's symptoms. (16)
Depending on the damage to the thalamus, various therapies could treat the symptoms a patient experiences.
- Physical therapy may be necessary for any physical disabilities or for rebuilding strength in a muscle or limb.
- Occupational therapy could help with performing everyday tasks.
- Speech therapy could assist with aphasia and other speech problems.
- Cognitive therapy may help with memory loss.
- Counseling or joining support groups may help you cope with your symptoms and adjust to the new normal.
The thalamus is an all-important relay station, sending critical information back and forth to the cerebral cortex. Without it, you will struggle to make sense of this world, as it interprets sensory and motor signals before sending them off to the relevant parts of the brain. So, be thankful for your thalamus.