The thalamus is a large mass of gray matter located in the cerebrum that serves as a relay station for sensory and motor signals to and from the cerebral cortex. It has several nuclei that are involved in functions like sensory processing, motor control, arousal, memory, and cognition. The thalamus receives inputs from various subcortical structures and sends outputs to different regions of the cerebral cortex via fiber tracts called thalamic radiations. Damage to the thalamus can result in thalamic syndromes characterized by abnormal pain or sensory processing.

2. The term thalamus derives from a Greek word that means “inner chamber” or
“meeting place”.
The thalamus is the largest component of the diencephalon
• Rostrocaudal dimension of about 30 mm, height of about 20 mm, width of about
20 mm, and an estimated 10 million neurons in each hemisphere.
• The term diencephalon includes the following structures: epithalamus, thalamus
(including the met thalamus), hypothalamus, and sub thalamus.
• Thalamus lies medially in the cerebrum. Dorsal aspect form the floor of the IV
ventricle, bounded medially by III ventricle, laterally by internal capsule and
basal ganglia; ventrally it is continuous with sub thalamus.
THALAMUS

3. The thalamus serves primarily as a relay station that modulates and coordinates
the function of various systems.
• Locus for integration, modulation, and intercommunication between various
systems.
• Has important motor, sensory, arousal, memory, behavioral, limbic, and
cognitive functions.
• The largest source of afferent fibers to thalamus is cerebral cortex and cortex is
the primary destination for thalamic projections.
• Many systems and fibers converge on the thalamus.

4. Thalamus is a part of diencephalon.
Diencephalon divided into 4 regions;
•Thalamus
•Hypothalamus
•Epithalamus
•Ventral thalamus(or subthalamus)

7. Thalamus
•Large mass of grey matter,lies immediately lateral to third ventricle
•The thalamus is an ovoid nuclear mass, c.4cm long, which borders the
dorsal part of third ventricle.
Two poles;
Anterior pole(or end)
-Lies behind the interventricular foramen
Posterior pole(or end)
-Also called PULVINAR
-Lies just above and lateral to superior colliculus.

8. Thalamus
Posterior
pole or
pulvinar
Superior
colliculus
Interventricular
foramina
Anterior pole

9. Superior(dorsal) surface;
-The superior (dorsal) surface of the thalamus is covered by a thin layer of
white matter, the stratum zonale.
-It extends laterally from the line of reflection of the ependyma (taenia
thalami), and forms the roof of the third ventricle.
-This curved surface is separated from the
overlying body of the fornix by the choroid
fissure with the tela choroidea within it.
-More laterally it forms part of the floor of the lateral ventricle.
-Related laterally to caudate nucleus.
-Seperated from caudate nucleus stria
terminalis and thalamostriate vein.

10. Superior surface

11. SURFACES OF THE THALAMUS
Superior surface
Medial surface
Inferior surface

12. THE MEDIAL SURFACE
•The medial surface of the thalamus is the superior (dorsal) part of the lateral
wall of the third ventricle.
•It is usually connected to the contralateral thalamus by an interthalamic
adhesion behind the interventricular foramina.
•The boundary with the hypothalamus is marked by an indistinct hypothalamic
sulcus, which curves from the upper end of the cerebral aqueduct to the
interventricular foramen.
•The thalamus is continuous with the midbrain tegmentum, the subthalamus and
the hypothalamus

13. Medial surface

14. Medial surface of thalamus
Midbrain tegmentum
Hypothalamus

15. •Inferior surface of the tegmentum is related to hypothalamus anteriorly and
to ventral thalamus posteriorly.
•The ventral thalamus separates the thalamus from tegmentum of midbrain.
INFERIOR SURFACE OF THALAMUS

16. INTERNAL STRUCTURE OF THE THALAMUS
Thalamus consists of mainly of grey matter.
Superior surface is covered by a thin layer of white matter called stratum
zonale.
Lateral surface is covered by a similar layer called external medullary layer.
Internally, the thalamus is divided into anterior, medial and lateral nuclear
groups by a vertical Y-shaped sheet of white matter, the internal medullary
lamina.
Nuclei of the anterior part.
Anterior nucleus.
Nuclei in the medial part
Largest nuclei among them medial dorsal nucleus.

17. NUCLEI IN THE LATERAL PART
Ventral group Lateral group
Ventral anterior nucleus
Ventral lateral nucleus
Or
Ventral intermediate nucleus
Ventral posterior nucleus
Lateral dorsal
nucleus
Lateral posterior
nucleus
Pulvinar

18. OTHER THALAMIC NUCLEI
•Intralaminar nuclei
Embedded within the internal medullary Lamina
•Midline nuclei
Scattered cells between medial part of the thalamus and ependyma of third
ventricle.
•Medial and lateral geniculate bodies
Now included under the thalamus.

19. Nuclei Of Thalamus

20. Schematic diagram showing the major nuclear groups of the
thalamus

21. • The thalamus is traversed by a band of myelinated fibers, the internal
medullary lamina, which runs along the rostrocaudal extent of the thalamus.
• The internal medullary lamina separates the medial from the lateral group of
nuclei.
• Rostrally and caudally, the internal medullary lamina splits to enclose the
anterior and intralaminar nuclear groups, respectively.
• The internal medullary lamina contains intrathalamic fibers connecting the
different nuclei of the thalamus with each other.

22. • Another medullated band, the external medullary lamina, forms the lateral
boundary of the thalamus medial to the internal capsule.
• Between the external medullary lamina and the internal capsule is the reticular
nucleus of the thalamus.
• The external medullary lamina contains nerve fibers leaving or entering the
thalamus on their way to or from the adjacent capsule

23. • The anterior tubercle of the thalamus (dorsal surface of the most rostral
part of the thalamus) is formed by the anterior nuclear group.
• Consists of two nuclei: principal anterior and anterodorsal.
• The anterior group of thalamic nuclei has reciprocal connections with the
hypothalamus (mamillary bodies) and the cerebral cortex (cingulate gyrus).
• The anterior group also receives significant input from the hippocampal
formation of the cerebral cortex (subiculum and presubiculum) via the
fornix
ANTERIOR NUCLEAR GROUP

24. • The anterior nuclear group of the thalamus is part of the limbic system,
which is concerned with emotional behavior and memory mechanisms.
• Discrete damage to the mamillothalamic tract has been associated with
deficits in a specific type of memory, episodic long-term memory, with relative
sparing of short term memory and intellectual capacities.

25. Schematic diagram showing the reciprocal connections among the
anterior nucleus of the thalamus, mamillary body and cingulate gyrus.

26. • Of the medial nuclear group, the dorsomedial nucleus is the most highly
developed in humans.
• In histologic sections stained for cells, three divisions of the dorsomedial
nucleus are recognized: a dorsomedial magnocellular division located
rostrally, a dorsolateral parvicellular division located caudally, and a
paralaminar division adjacent to the internal medullary lamina.
• It also receives inputs from the temporal neocortex (via the inferior thalamic
peduncle), amygdaloid nucleus and substantia nigra pars reticulata, and
adjacent thalamic nuclei, particularly the lateral and intralaminar groups.
• The dorsomedial nucleus belongs to a neural system concerned with
affective behavior, decision making and judgment, memory, and the
integration of somatic and visceral activity.
MEDIAL NUCLEAR GROUP

27. LATERAL NUCLEAR GROUP
• The lateral nuclear group of the thalamus is subdivided into two groups, dorsal
and ventral.
1. DORSAL SUBGROUP:
• This subgroup includes, from rostral to caudal, the lateral dorsal, lateral
posterior, and pulvinar nuclei.
• The lateral dorsal nucleus, although anatomically part of the dorsal tier of the
lateral group of thalamic nuclei, is functionally part of the anterior group of
thalamic nuclei, with which it collectively forms the limbic thalamus.

28. • Similar to the anterior group of thalamic nuclei, the lateral dorsal nucleus
receives inputs from the hippocampus (via the fornix) and an uncertain input
from the mamillary bodies and projects to the cingulate gyrus.
• The borderline between the lateral posterior nucleus and the pulvinar nucleus is
vague, and the term pulvinar– lateral posterior complex has been used to refer to
this nuclear complex.
• The pulvinar–lateral posterior complex has reciprocal connections caudally
with the lateral geniculate body and rostrally with the association areas of the
parietal, temporal, and occipital cortices . It also receives inputs from the
pretectal area and superior colliculus.

29. Schematic diagram showing the major afferent and efferent
connections of the pulvinar.

30. 2. VENTRAL SUBGROUP:
• This subgroup includes the ventral anterior, ventral lateral, and ventral
posterior nuclei.
• The neural connectivity and functions of this subgroup are much better
understood than those of the dorsal subgroup. In contrast to the dorsal
subgroup, which belongs to the multimodal association thalamic nuclei, the
ventral subgroup belongs to the modality-specific thalamic nuclei.
• These nuclei share the following characteristics:
-They receive a direct input from the long ascending tracts.
-They have reciprocal relationships with specific cortical areas.
-They degenerate on ablation of the specific cortical area to which they project

32. CONNECTIONS OF THE THALAMUS
•Afferent impulses from large number of subcortical centers converge to the
thalamus.
•Visual and aduditory impulses reach the lateral and medial geniculate bodies.
•Sensation of taste are conveyed to the thalamus through solitariothalamic
fibers.
•Thalamus does not receive direct olfactory impulses they probably reach
through amygdaloid complex.
•Thalamus receive profuse connections from all part of cerebral cortex,
cerebellum and corpus striatum.

33. Thalamus is there fore regarded as integrating centre where information of
all sources is brought together.
The information from thalamus is projected to whole of the cerebral cortex
through thalamo-cortical projection.
Thalamocortical fibers form large bundles known as thalamic radiations
or thalamic radiation.
Thalamic radiations
Superior thalamic
radiation
(dorsal )
Posterior thalamic radiations
( caudal )
Ventral thalamic
radiation

34. Thalamus
Superior thalamic radiations
Posterior thalamic radiation
Anterior thalamic radiations
Thalamic Radiations

35. CONNECTION OF VENTRAL GROUP OF NUCLEI
Most important connection of thalamus are from ventral posterior nucleus
Cerebral Cortex
(somatosensory area,3 1 2)
Ventral Posterior Nucleus
Medial part Lateral part
Trigeminothalamic tract Medial leminiscus
Solitariothalamic tract Spinothalamic tract

36. • Blood supply of the thalamus is derived from four parent vessels: basilar root of
the posterior cerebral, posterior cerebral, posterior communicating, and internal
carotid.
• The basilar root of the posterior cerebral artery, via paramedian branches,
supplies the medial thalamic territory.
• The posterior cerebral artery, via its geniculothalamic branch, supplies the
posterolateral thalamic territory.
• The posterior communicating artery, via the tuberothalamic branch, supplies
the anterolateral thalamic territory.
• The internal carotid artery, via its anterior choroidal branch, supplies the
lateral thalamic territory.
BLOOD SUPPLY OF THE THALAMUS

37. •Thalamic syndrome (or thalamic pain syndrome) is a condition that can be
associated with inadequate blood supply from the posterior cerebral artery.
•Rare neurological disorder in which the body becomes hypersensitive to pain as
a result of damage to the thalamus, a part of the brain that affects sensation
•Primary symptoms are pain and loss of sensation, usually in the face, arms,
and/or legs.
•Pain or discomfort may be felt[1] after being mildly touched or even in the
absence of a stimulus.
•The pain associated with thalamic syndrome may be made worse by exposure to
heat or cold and by emotional distress. Sometimes, this may include even such
emotions as those brought on by listening to music.
•It is also known as "Dejerine-Roussy disease", after Joseph Jules Dejerine and
Gustave Roussy
THALAMIC SYNDROME

38. • A multiplicity of neurologic signs and symptoms has been reported in disorders
of the thalamus.
These reflect
• (1) the anatomic and functional heterogeneity of the thalamus.
• (2) simultaneous involvement of several nuclei even by discrete vascular
lesions due to the fact that arterial vascular territories in the thalamus cross
nuclear boundaries.
• (3) simultaneous involvement of neighboring areas such as the midbrain in
paramedian thalamic vascular lesions, the internal capsule in lateral thalamic
vascular lesions, and the sub thalamus in posterior thalamic vascular lesions.
CLINICAL CORRELATES OF THALAMIC
ANATOMY

40. THANK YOU