The thalamus is a midline brain structure that relays sensory and motor signals to the cerebral cortex. It regulates consciousness, sleep, and alertness. The thalamus contains several nuclei that have different functions. Lesions in the thalamus can cause sensory loss or a thalamic syndrome on the opposite side of the body, characterized by spontaneous pain.

1. Thalamus - Dr. Chintan

2. Thalamus
• The thalamus is a midline symmetrical structure of two
halves, situated between the cerebral cortex and the midbrain.
• Some of its functions are the relaying of sensory and motor
signals to the cerebral cortex and the regulation of
consciousness, sleep and alertness.
• All sensory pathways, except olfactory, relay in the thalamus
before reaching the cortex
• Medially borders the third ventricle and laterally borders
the internal capsule
• It is the main product of the embryonic diencephalon.

3. Thalamic nuclei
• anterior nuclear of thalamus
• medial nuclear group (or dorsomedial nucleus)
• Intralaminar nuclear group (Intralaminar nuclei)
• anterior (rostral) group
• paracentral nucleus
• central lateral nucleus
• central medial nucleus
• posterior (caudal) intralaminar group
• centromedian nucleus

4. Thalamic nuclei
• posterior region
• pulvinar
• lateral posterior nucleus
• lateral dorsal nucleus
• ventral nuclear group
• ventral anterior nucleus
• ventral lateral nucleus
• ventral posterior nucleus
• ----------------ventral posterolateral
• ----------------ventral posteromedial
• medial geniculate body
• lateral geniculate body

7. Connections

8. Connections

9. Connections

11. Functions
• [I] SENSORY FUNCTIONS
• 1. Relay Station for Sensory Impulses
• Somatic Sensation –
• In Ventral-Posterior part of Lateral Nuclei via
• - Medial Lemniscus: Kinesthetic, Fine Touch and
Vibration.
• - Spinal Lemniscus: Crude Touch, Pain and Temperature.
• - Trigeminal Lemniscus: From Face.
• Auditory Sensation –
• In Medial Geniculate Body via Lat. Lemniscus.
• Visual Sensation –
• In Lateral Geniculate Body via Optic Tract

12. Functions
• 2. Crude Sensory Center
• - Partial Perception of Pain
• 3. Relay Station for Non-specific
Impulses
• As a part of Reticular Activating System
(R.A.S.) it contributes in control of different
states of consciousness, e.g. Waking, Sleep,
Meditative.

13. Functions
• [II] MOTOR FUNCTIONS
• Contributes in Planning and Smooth Performance of
Voluntary Movements through Its connections with
• - Neocortex - Neocerebellum and - Basal ganglia.
• [III] MOTIVATIONAL / EMOTIONAL FUNCTIONS
• Forms a part of Limbic System contributing in
• - Subjective Feeling of Emotions and
• - Personality.

14. LESIONS OF THE
THALAMUS• Sensory Loss
• These lesions usually result from thrombosis or hemorrhage
of one of the arteries that supply the thalamus.
• Since the thalamus receives sensory impulses from the
opposite side of the body, the disability resulting from a
lesion within it will be confined to the contralateral side of the
body.
• There may be a major impairment of all forms of sensation,
which include light touch, tactile localization and
discrimination, and loss of appreciation of joint movements.

15. LESIONS OF THE
THALAMUS• Thalamic Syndrome
• Dejerine – Roussy syndrome or thalamic pain
syndrome
• This syndrome may occur as the patient is recovering
from a thalamic infarct – blockage of thalamogeniculate
branch of PCA – Posteroventral & posterolateral
• Spontaneous pain, which is often excessive (thalamic
overreaction), occurs on the opposite side of the body.
• The painful sensation may be aroused by light touch or by
cold, and may fail to respond to powerful analgesic drugs.

16. LESIONS OF THE
THALAMUS• Thalamic Syndrome
• Initial lack of sensation and tingling in the opposite side of
the body.
• Weeks to months later, numbness can develop into severe
and chronic pain that is not proportional to an
environmental stimulus, called dysaesthesia or allodynia
• Astereognosis, thalamic phantom limb
• Ataxia, hypotonia, muscle weakness, involuntary movements,
thalamic hand (athetoid hand – flexion of wrist,
hyperextended fingers)

17. THANQ…