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.
Location of the injury
1. Inability to inculcate information (anterograde amnesia)
1. Anterior thalamic nucleus
2. Possible syndromes
- Filling a gap in memory with figments (anterograde amnesia)
- Losing the order (order amnesia)
- Impairment in executive functions
Executive functions are:
- purposeful and flexible planning
- checking and adjusting actions, logic, strategy
- Problem solving
2. Anterior medial nucleus
3. Apathy and attention disorder
3. Intralaminar nuclei
4. Disorders in word finding
4. Left pulvinar
5. Left-sided spatial neglect
5. Right pulvinar
6. Drowsiness and coma (somnolence and coma)
6. Large bilateral medial thalamic lesions including the intralaminar nuclei
7. Hemiplegic motor neglect, temporary lack of movement without power loss
7. "motor" cores contralateral
8. Possible syndromes
- Loss of visual Field (sectoranopsia)
- Reduction of the sensitivity of the body (hemihypesthesia)
- Decreased sensitivity to pain on one side of the body (hemihypalgesia)
- Decreased taste
- Thalamic pain
8. Visual somatosensory and nociceptive cores (contralateral)
The core groups of the thalamus:
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 can 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:
- 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.