Thalamus

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

The thalamus consists of six functional separate core groups where information from other parts of the nervous system is transferred to specific areas of the cerebral cortex.

The thalamo cortical connections are bidirectional; they lead from the thalamus to the cortex and from the cortex back to the thalamus. This is called Thalamo-cortico-thalame circuit. The result of this is that small thalamus injury may "mimic" cortex syndromes. In some syndromes the specialization of the brain hemisphere can be recognized.

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 must 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).

The thalamus is also associated with wakefulness, sleep, consciousness, vigilance (alertness), motor skills, emotions related to an event, and akinetic mutism. This is a syndrome, resulting from brain injury, in which the person no longer speaks or speaks less (mutism) and has little or no movement (akinesia). The person can follow you with their eyes but otherwise appears apathetic.

Six core groups

The thalamus has six distinct core groups that produce specific symptoms when injured. These groups transmit information from other parts of the nervous system to specific areas in the cerebral cortex.

The core groups of the thalamus:

Location of the lesion in the thalamus and associated syndrome:
1. Anterior thalamic nucleus: Inability to memorize information (anterograde amnesia)
2. Anterior medial nucleus: Filling a gap in memory with fabrications (anterograde amnesia). Forgetting sequences (sequence amnesia). Executive function disorders (executive function disorders).
Executive functions include: goal-oriented and flexible planning, monitoring and adjusting actions, logic, strategy, and problem solving. 3. Intralaminar nuclei: Apathy and attention deficit disorder
4. Left pulvinar: word-finding disorders
5. Right pulvinar: Left-sided spatial neglect/failure to notice (neglect)
6. Large bilateral medial thalamic lesions including the
intralaminar nuclei: Coma and somnolence

7. Contralateral Motor Nuclei: Hemilateral motor neglect, temporary lack of movement without loss of strength
8. Visual Somatosensory and Nociceptive Nuclei (Contralateral):

• Visual field loss (sector anopia) on the opposite side of the body
  
• Reduced body sensation (hemihypesthesia)
  
• Reduced pain sensitivity on one side of the body (hemihypalgesia)
  
• Reduced sense of taste
  
• Thalamic pain on the opposite side of the body
  
• Pain on one side of the body
  
• Pain may be felt in the legs, arms, and face. Pain, burning, stabbing, and pricking sensations are present
  Changes in the weather or certain movements or activities may further aggravate the condition.
  The pain caused by a stroke in the thalamus is called "Déjerine-Roussy syndrome."

The thalamo-cortico-thalamic circuit is associated with awakening, vigilance and consciousness. Damage to a portion of the thalamus is associated with risk of coma.

Damage in a portion of the thalamus may lead to sensory changes in a body part.

Damage here can also cause movement disorders, lack of movement (motor disturbances). Difficulties referred to are: visual field loss, decreased taste, reduced pain sensation, decreased sensation in one side of the body, word finding difficulties. Which problem occurs is dependent on the location of the lesion in the thalamus.

Behavioral changes depending on the location of the thalamus injury may include:

• Apathy
• persevere: not being able to stop a thought or an action, not being able to let go of what keeps the mind
• consider important any not-related information
  

Also memory loss and personality changes may occur.

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