Thalamus, its functions and thalamic syndrome

The thalamus is the large mass of gray matter in the dorsal part of the diencephalon of the brain with several functions such as relaying of sensory signals, including motor signals, to the cerebral cortex and the regulation of consciousness, sleep, and alertness.

1. THALAMUS BY Dr. Muhammad Saifullah Punjab Medical College, Faisalabad.

2. Thalamus - Introduction The thalamus (from Greek = inner chamber) is a midline symmetrical structure within the brains of vertebrates including humans, situated between the cerebral cortex and midbrain. Its function includes relaying sensory and motor signals to the cerebral cortex,  along with the regulation of consciousness, sleep, and alertness.

3. Thalamus The thalamus comprises right and left halves, each egg-shaped which form the walls of the third ventricle. The two halves are joined in the midline by an intrathalamic adhesion or massa intermedia . Each hemi thalamus is divided into 3 main groups of nuclei (medial, anterior, and ventral-posterior).

4. Thalamic Nuclei From a functional viewpoint, there are 2 major classes of thalamic nuclei: Specific Nonspecific. “Specific” Nuclei are so called because they are interconnected with localized regions of the cerebral cortex. “Non-specific” Nuclei are interconnected in a diffuse manner to many cortical regions.

5. SPECIFIC NUCLEI

6. Sensory nuclei Somatosensory relay nuclei: T he ventroposterior nuclear complex receives somatosensory information about the contralateral half of the body and face, and that it projects to the ipsilateral somatosensory cortex. Visual relay nucleus: The lateral geniculate nucleus receives input from the retina via the optic tract and projects to primary visual cortex (area 17). Auditory relay nucleus: The medial geniculate nucleus receives auditory input from inferior colliculus and projects to primary auditory cortex (superior temporal gyrus ).

7. Motor nuclei The ventral lateral and ventral anterior nuclei provide information which influence posture and movement. Limbic nuclei The anterior and dorsomedial nuclei provide input to the cerebral cortex from areas of the brain involved in learning, memory, and the control of emotions.

8. Association nuclei The pulvinar , lateral dorsal, and lateral posterior nuclei are particularly developed to carry out higher order functions such as speech.

9. NON-SPECIFIC NUCLEI

10. Non-specific Nuclei The midline, intralaminar and centromedian nuclei are non-specific nuclei. The are thought of as an extension of the brainstem reticular formation and thus regulate alertness and deep sleep.

11. Functions of Thalamus It acts as a relay between a variety of subcortical areas and the cerebral cortex. Role in regulating states of sleep and wakefulness . Thus damage to the thalamus can lead to permanent coma. Thalamus is functionally connected to the hippocampus. So, it is crucial for human episodic memory . The thalamic regions also provide differentiation of the functioning of recollective and familiarity memory. The thalamus provides the specific channels from the basal ganglia and cerebellum to the cortical motor areas.

12. Thalamus – Relay system

13. Thalamic Pain Syndrome It is a condition developed after a stroke causing damage to the thalamus . Ischemic strokes and Hemorrhagic strokes can cause lesions in the thalamus. 8% of all stroke patients experience thalamic pain syndrome. Symptoms are preceded by numbness in the affected side leading to burning, tingling sensations and hypersensitivity ( allodynia ).

14. Treatment (Thalamic syndrome) Medical Opiod Analgesics (Codeine & Morphine) Anti- depressents ( Amitriptyline ) Anti- convulsants ( Pregabalin ) Electical stimulation Brain stimulation Spinal cord stimulation (cheap & less invasive) Radiation therapy (Long term treatment)

15. References Wikipedia, the free encyclopedia. Guyton’s text book of Physiology Lecture 33. The Thalamus by C.Chalk