Thalamus

 

The thalamus, the yellow section on the drawing above, is an important brain nucleus and is considered one of the intermediate brain, together with the pituitary gland and the hypothalamus. It is the most 'wired' portion of the brain.

 

Introduction

Foreword: The brain works together as a single unit. Brain functions are distributed throughout the brain regions and arise from the exchange between the regions. Nevertheless, symptoms can be identified per brain region.


Do you only want the short summary? Then follow this link.


Do you only want to read the possible symptoms per core group and per adjacent brain regions? Follow this link.

 

Do you want to know more about the anatomy, functions, and potential damage per core group? Then follow this link.

Thalamus: most wired part of the brain

The thalamus is an important relay station deep within the brain. Virtually all sensory information – such as what you see, feel, and hear – is transmitted via the thalamus to the cerebral cortex.

It helps to focus attention on important information and filter out less important stimuli.

It also assists with movement, memory, emotions, and with being conscious, awake, and alert.

It plays a role in akinetic mutism. This is a syndrome, a consequence of brain injury, in which the person speaks little or not at all (mutism) and moves little or not at all (akinesia). The person may follow you with their eyes but otherwise appears apathetic and does almost nothing of their own accord.

Thalamus is derived from the Greek word for hidden central inner chamber or bedroom; θάλαμος, because it lies deep within the brain and forms the 'central' chamber.

It is a deep-seated central nucleus in the brain

  • virtually all sensory information (except smell) enters it first
  • it distributes and organizes information before it goes to the cerebral cortex
  • it is in contact with almost all parts of the cortex via thousands of connections

You can therefore view the thalamus as the central inner chamber where information first enters and is forwarded

Senses

 l

Thalamus

(central inner chamber)

  l

Cerebral Cortex

 

Gateway to the Cerebral Cortex

The connections from the thalamus to the cerebral cortex return from the cortex to the thalamus.


This is called the thalamo-cortico-thalamic circuit. As a result, minor thalamic lesions can mimic cerebral cortex syndromes, and in some syndromes, the specialization of the cerebral hemisphere can be recognized.


As a gateway to the cerebral cortex, the thalamus has to transmit many sensory stimuli (except smell), but it must also filter stimuli, allowing healthy individuals to "shut off" certain stimuli. It is therefore one of the so-called "filters" (stimulus filters), a control center to help the brain focus on important and unimportant stimuli.

The main core groups of the thalamus and adjacent structures (in the diencephalon)

Important to know:

The thalamus works closely with other brain regions. The symptoms a person experiences may correspond to damage to a specific core group, but are often also determined by the cooperation between different brain networks.
The following anatomical terms explain the names of the core groups:

The image below is a schematic anatomical representation. The exact shape, size, and mutual boundaries of the core groups may vary slightly depending on the anatomical cross-section and the anatomical reference work.

 

Discussion of the image of the thalamus viewed from the side (lateral view) with the adjacent metathalamus

 

The image shows the main nuclear groups of the thalamus in a lateral view. The thalamus consists of various nuclear groups that receive, process, and transmit information to the cerebral cortex. Not all nuclear groups are fully visible from this view. Therefore, hidden or partially hidden structures are indicated with a curved gray arrow, while straight black arrows point to structures that are directly visible.

The lamina medullaris interna (Y-shaped white matter tract) divides the thalamus into different anatomical nuclear groups.

The intralaminar nuclei are located within this white matter tract. The midline nuclei lie directly along the third ventricle and are barely visible from a lateral view. The reticular nucleus forms a thin layer on the outside of the thalamus and plays an important role in regulating the information processed by the thalamus.

 

Located at the posterior side are the lateral knee-form body (LGN (Medial Geniculate Nucleus)) and the medial knee-form body (MGN (Medial Geniculate Nucleus)). Together, they form the metathalamus. The LGN processes visual information, while the MGN is involved in processing auditory information.

The illustration is based on the anatomical classification as described in Gray's Anatomy, supplemented and verified with Mai & Paxinos and Blumenfeld.

For each section, we elaborate on the following:

  • Where are the nuclei located?
  • From where do they receive information?
  • Where do they send information?
  • What do these nuclei do?
  • Possible consequences of damage
  • What do you notice about this in daily life?
  • Important to know
  • In-depth information for healthcare professionals
  • Anatomical references

 

The list is written in plain language (B1 level), but is based on authoritative anatomical and neurological literature, including Gray's Anatomy, Mai & Paxinos, and Blumenfeld. Where scientific insights are still developing, this is indicated in the text. In this way, we combine understandable explanations with current medical knowledge.

 

1. Anterior core group

Where is this core group located?

Located at the front (rostral) of the dorsal (back) thalamus. Forms an important node in the limbic network.

(The limbic network is responsible for understanding, regulating, and processing emotions)

 

Receives information from
Primarily the mammillary bodies (limbic network)

 

Sends information to
The cingulate gyrus

 

What does this core group do?

  • Helps form new memories
  • Helps remember events
  • Supports learning new information
  • Links memories to emotions.

 

Possible consequences of damage

  • Difficulty remembering new information
  • Forgetfulness - Problems remembering recent events
  • Sometimes difficulty remembering events chronologically
  • Sometimes difficulty learning
  • Sometimes difficulty remembering events in the correct order
  • Sometimes changes in motivation or emotions.

 

What do you notice about this in daily life?

New appointments or conversations are forgotten more quickly. Inability to encode information (anterograde amnesia) and memory disorders.

Important to know
Isolated damage is rare.
This core group is part of Papez's circle, a network in the brain that is important for pre-memory and emotions. They play a role in episodic memory (life events, the life story).

2. Mediodorsal core group (MD)

Where is this core group located?

The mediodorsal core group (MD) is located on the inside (medial) of the dorsal thalamus, directly next to the third ventricle.

 

Receives information from
Limbic structures and other parts of the brain

 

Sends information to
Brain areas involved in planning and decision-making

 

What does this core group do?

This core group works closely with the prefrontal cortex and plays an important role in so-called executive functions, such as organizing, maintaining an overview, weighing the consequences of choices.

  • Planning
  • Making decisions
  • Maintaining attention
  • Working memory (briefly remembering and using information)
  • Processing emotions (assessing emotions, adapting behavior to social situations, regulating emotional responses)
  • Social behavior
  • Weighing choices and their consequences.

 

Possible consequences of damage

Common consequences

  • difficulty planning and organizing
  • problems with concentration
  • easily distracted
  • difficulty making decisions
  • forgetfulness, especially regarding new information
  • reduced initiative

Occasional consequences

  • changes in social behavior
  • difficulty assessing appropriate behavior
  • reacting more flatly to emotions or, conversely, reacting more emotionally
  • difficulty maintaining an overview of complex tasks
  • sometimes changes in social behavior
  • a memory gap is sometimes filled with fabrications (anterograde amnesia). Forgetting the sequence (sequence amnesia). There is damage to executive functions: executive function disorders (executive function disorders)

 

What do you notice about this in daily life?

  • that it becomes harder to plan a day
  • that it takes longer to make choices
  • doing multiple tasks at once quickly becomes too much
  • that conversations are harder to follow when a lot of information is given at once
  • that appointments are forgotten more quickly
  • that others notice that you take less initiative or react differently in social situations

 

Important to know
Intelligence is usually retained, but it may become more difficult to apply knowledge effectively in daily life.

 

In-depth study for the professional

Akinetic mutism may occur when certain parts of the thalamus, particularly the paramedian thalamus (specifically the mediodorsal nucleus (MD) and parts of the intralaminar nuclei), are damaged on both sides.

This usually occurs due to a stroke in the supply area of ​​the paramedian thalamic arteries.

The thalamus plays three important roles in this process:

  1. Consciousness and alertness – The intralaminar nuclei are part of the ascending activating system (ARAS). Damage reduces mental activation.
  2. Motivation to act – The mediodorsal nucleus is connected to the prefrontal cortex and the limbic system. With damage, the inner urge to start speaking or moving often disappears.
  3. Initiating behavior – The thalamus forms a link in the fronto-thalamo-basal ganglia networks necessary to initiate voluntary actions.

The result is that a person appears awake and has the eyes open, but hardly speaks or moves spontaneously. The muscles are usually not paralyzed and language need not be severely impaired. The biggest problem is the failure of goal-directed behavior to get started.

 

3. Lateral dorsal core group (LD)

Where is this core group located?

The lateral dorsal core group (LD) is located on the upper side of the dorsal thalamus, directly behind the anterior core group. The LD is part of the limbic network and is connected via connections to, among others, the cingulate cortex and the hippocampus.

Assists with memory, spatial orientation, and attention.

  • Forming and retrieving memories
  • Orienting in space
  • Recognizing the environment
  • Focusing attention on important information
  • Combining spatial information with memories

Possible consequences of damage

Common consequences

  • Difficulty orienting oneself in a familiar environment
  • Problems with spatial memory
  • Difficulty maintaining an overview in an unfamiliar environment

Occasional consequences

  • Difficulty finding familiar routes
  • Reduced attention to spatial information
  • Mild problems remembering places or locations

 

What do you notice in daily life?

  • That it is more difficult to find your way in a familiar environment
  • That it takes longer to remember a new route
  • That you lose your bearings more quickly in a busy building, such as a hospital or shopping center
  • That you sometimes have to think about a route that used to come naturally.

Important to know
Damage to only the lateral dorsal core group is rare. Symptoms usually arise because other parts of the memory and orientation network are also damaged. As a result, the symptoms are often mild and can easily be overlooked.

4. Lateral posterior core group (LP)

Where is this core group located? It is located behind the LD - Lateral dorsal core group (see tab above at 4) and in front of the pulvinar (see tab below at 5).

 

What does this core group do? The LP (Lateral posterior core group) primarily helps the brain to give meaning to what you see, in cooperation with other brain regions.

 

  • Combining visual information with information from other senses
  • Focusing attention on important events in the environment
  • Recognizing the spatial position of objects
    Processing complex visual information
  • The cooperation of different brain regions during perception

 

Consequences of injury Damage can lead to difficulty maintaining an overview and visual attention.

Common consequences

  • Difficulty focusing attention on what you see
  • Problems processing complex visual information
  • Difficulty maintaining an overview in a busy environment
  • Difficulty with spatial orientation


Occasional consequences

  • Reduced eye-hand coordination during visual tasks
  • Difficulty estimating the location of objects

Sometimes reduced attention to stimuli on the opposite side of the room, especially with more extensive injury.

 

What do you notice in daily life?

  • It becomes harder to find something on a crowded table
  • Busy environments, such as a supermarket or station, become cluttered more quickly
  • It takes more effort to pick up an object you see lying there
  • You sometimes overlook something even though you are looking at it.

 

Important to know!

It is not a primary visual center. Damage to only the lateral-posterior core group is rare. Symptoms usually occur in conjunction with damage to other parts of the thalamus or the parietal cortex. As a result, the symptoms can vary from person to person.

Pulvinar

Where is this core group located?

It is the largest posterior part of the dorsal thalamus.

What does this core group do?

It assists with attention, complex visual processing, and information integration.

 

  • The pulvinar helps combine information from different senses, such as sight, hearing, and touch. This ensures that the brain gets a clearer picture of the environment.
  • The pulvinar helps the brain to quickly determine
    where your attention should go and to connect information from different brain regions.
  • Focusing and maintaining attention
  • Processing complex visual information
    The pulvinar works together with the visual parts of the brain. It receives information from the superior colliculi (a part of the midbrain).
  • It helps in processing visual reflexes
    It helps focus attention on important visual details such as color, shape, or location in a complex environment
    Recognizing objects and faces
    Combining information from different senses
    Orienting in space
    Filtering important and less important information
    Learning and remembering, especially regarding things we see and visual memories
    Processing emotional stimuli, particularly how we deal with emotions and how we connect with others.

Possible consequences of damage

Damage may lead to problems with attention and spatial orientation.

Common consequences

  • Difficulty focusing attention
  • Problems processing complex visual information
  • Difficulty maintaining an overview in a busy environment
  • Problems with spatial orientation
  • Slower processing of visual stimuli

 

Occasional consequences

  • Difficulty recognizing objects or faces in a busy environment
  • Reduced attention to stimuli on the opposite side of the room
  • Difficulty combining information from different senses
  • Problems with eye movements while searching for an object.

 

Damage to the pulvinar may disrupt visual reflexes, which may lead to problems focusing attention on important visual details.

Another part of the thalamus, the reticular nucleus of the thalamus, also likely helps the brain focus on the most important details of what you see.

 

What do you notice about this in daily life?

Difficulty finding an object in a busy environment

 

Important to know! The pulvinar works closely with multiple brain regions. Neglect and visual attention disorders may occur, but are usually more severe when the parietal cortex or other thalamic nuclei are also damaged.

  • Damage to the right pulvinar can cause left-sided spatial neglect / failure to notice (neglect).
  • Damage to the left pulvinar can cause word-finding difficulties.

Two specific nuclei: the pulvinar at the back of the thalamus and a nucleus in the middle at the bottom, the nucleus reticularis thalami, have partially overlapping functions:

 

Two  nuclei: the pulvinar at the back of the thalamus and a nucleus in the middle at the bottom, the nucleus reticularis thalami, have partially overlapping functions:

FUNCTION PULVINAR NUCLEUS RETICULARIS THALAMI
Attention regulation mostly visual general and modeling
Visual processing strongly involved supports visual attention
Integration of sensory information multisensory filters unwanted information
Role in consciousness less direct, more in perception crucial for alertness and focus

6. Ventral anterior core group (VA)

Where is this core group located? The Anterior side of the ventral thalamus.

The ventral anterior core group (VA) is located at the anterior side of the ventral thalamus, in front of the ventral lateral core group (VL). The VA primarily receives information from the basal ganglia and transmits it to the premotor cortex and the supplementary motor cortex.

Receives information from
The basal ganglia; especially the globus pallidus internus (GPi) and the substantia nigra pars reticulata (SNr)

 

Sends information to
Brain regions that prepare movements

 

What does this core group do?
It helps preparing and initiating voluntary movements.
It ensures that movements are properly prepared before they are executed.

  • Preparing movements
  • Planning goal-directed movements
  • Choosing the right movement

  • Initiating voluntary movements

  • Ensuring the smooth execution of sequential movements

     

The ventral anterior nucleus helps control movements via connections with the basal ganglia, which are the basal nuclei important for movement, balance, posture, and eye movements.

Possible consequences of damage Damage may lead to difficulty initiating movements.

Common consequences

  • Difficulty starting a movement
  • Slower movements
  • Less fluid movements
  • Difficulty planning sequential movements

Occasional consequences

  • Less spontaneous movements
  • Problems performing learned movements
  • Mild coordination problems with complex movements.

 

What do you notice about this in daily life?

Everyday activities start less smoothly.

  • It takes longer to start a movement
  • You start walking hesitantly
  • You have difficulty performing multiple movements in succession
  • Actions such as getting dressed or cooking take more time
  • Your movements feel less natural

 

Important to know! Muscle strength is usually preserved.

The VA does not directly control the muscles. This core group primarily assists in preparing and planning movements. Muscle strength is usually preserved, but initiating and organizing movements may be more difficult.

For healthcare professionals:

The VA receives afferent projections from the globus pallidus internus (GPi) and the substantia nigra parsreticulata (SNr). The efferent projections run mainly to the premotor cortex (BA6) and the supplementary motor area (SMA).

7. Ventral lateral core group (VL)

Where is this core group located?

Briefly: Behind the VA ventral anterior core group (see drop-down menu 6.) in the ventral thalamus.


In detail: The ventral lateral core group (VL) is located in the ventral part of the dorsal thalamus, directly behind the ventral anterior core group (VA) and in front of the sensory nuclei (VPL see 8. and VPM see 9.).

The VL forms an important link between the cerebellum, the basal ganglia, and the motor cortex.

Receives information from

  • The cerebellum (the main input comes from the
    nucleus dentatus of the cerebellum)
  • The basal ganglia

Sends information to

  • The primary motor cortex
  • Brain areas involved in performing voluntary movements

As a result, the VL helps to execute movements accurately and smoothly.

 

What does this core group do?

  • Performing voluntary movements
  • Ensuring movements proceed smoothly
  • Coordinating movements
  • Precisely controlling arm and leg movements
  • Adjusting movements during execution

 

The VL helps ensure that movements proceed smoothly, accurately, and are well-coordinated.

Possible consequences of damage

  • Less smooth movements
  • Coordination problems
  • Difficulty with precise movements

Common consequences:

  • Less smooth movements
  • Problems with coordination
  • Difficulty with precise movements
  • Slower execution of movements
  • Difficulty adjusting a movement during execution

Sometimes occurring consequences:

  • Mild balance problems
  • Difficulty with fine motor skills
  • Less fluent speech if other motor areas are also affected.

What do you notice about this in daily life?

  • Writing is less neat
  • A cup or glass is held less firmly
  • Fastening buttons or turning a key takes more effort
  • Movements are less fluid
  • Walking feels less smooth

Important to know

Here you can download a document by Emmanuel Carrera M.D. and Julien Bogousslavsky, M.D., containing more information about thalamus injury and behavior.

Thalamus and behavior

PDF – 709,5 KB 10300 downloads

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