The thalamus is a paired structure located in the diencephalon that relays sensory and motor information to and from the cerebral cortex. It contains several nuclei that can be categorized as specific relay nuclei, association nuclei, and nonspecific nuclei. The thalamus plays a key role in sensory relay, feedback loops between cortex and subcortical structures, and regulating arousal and attention. Lesions of the thalamus can cause motor, sensory, cognitive and arousal disturbances depending on the location within the thalamus.

1. Thalamus
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2. The Diencephalon(“between brain,”)
1. The dorsal thalamus or thalamus proper
2. The hypothalamus,
3. The subthalamus,
4. The Epithalamus - habenular nuclei and pineal
body
 habenular nuclei
major link between limbic structures, the
basal ganglia, and the midbrain.
 pineal body functional contributions are not
clear (thought to help regulate circadian
rhythms –in some species, not in man)

3. .
• The thalamus both structurally and
functionally occupies a central position in the
brain.
• It makes up the bulk of the diencephalon.
• There are two thalami, one for each
hemisphere of the brain, and these are often
connected across the midline by nervous
tissue, the massa intermedia

4. .
Coronal

5. -
axial brain sections

6. -

8. .
• It is a paired oval mass that surrounds the third
ventricle and lies medial to the posterior limb of
the internal capsule
• Its anteroventral surface continuous with the
hypothalamus, while more posteriorly it lies
above the zona incerta and the subthalamic nuclei
and eventually over the red nucleus of the
midbrain

9. .
• Each half of the thalamus is separated into three
major divisions by a more or less vertical sheet of
myelinated fibers called the internal medullary
lamina.
• This lamina creates a medial and a lateral division
and then, as a result of its bifurcation near the
anterior pole of the thalamus, this lamina
produces an anterior division
• The thalamus is composed of a number of
discrete nuclear groups that can be differentiated
on the basis of structural and functional
considerations

11. Thalamic nuclei

12. .
Three different types of nuclei:
1. Specific relay nuclei
 relay sensory and motor information to
specific sensory and motor areas of the
cerebral cortex. e.g. the medial and lateral
geniculate bodies, relay nuclei for the auditory
and visual systems.
 motor regulatory information from the basal
ganglia and cerebellum is also relayed in the
thalamus as part of this set of nuclei
 are located in the lateral nuclear mass.

13. . .
1a. Sensory:
• VPL, ventral posterolateral nucleus: somatosensory -
relay to the appropriate areas of the post-central gyrus,
areas 1, 2, and 3, the sensory homunculus.
• VPM, ventral posteromedial nucleus: from the trigeminal
system (TG), i.e., the face- relayed to the facial area of
the postcentral gyrus).
• MGB, medial geniculate body (nucleus): nucleus for the
auditory fibers from the inferior colliculus, - relay to the
transverse gyri of Heschl on the superior temporal gyri in
the lateral fissure
• LGB, lateral geniculate body (nucleus): the relay nucleus
for the visual fibers from the ganglion cells of the retina
to the calcarine cortex.

14. .
1b. Motor
VA and VL, ventral anterior and ventral lateral: Fibers to
these nuclei originate in the globus pallidus and
substantia nigra (pars reticulata) as well as the
cerebellum, and are relayed to the motor and premotor
areas of the cerebral cortex, as well as the
supplementary motor cortex

15. .
2. Association nuclei.
 These are connected to broad areas of the cerebral
cortex known as the association areas.
DM-Dorsomedial, from many of the thalamic nuclei as
well as from parts of the limbic system (hypothalamus
and amygdala) to the prefrontal cortex
AN- anterior nuclei
LD- lateral dorsal nucleus
Pul, pulvinar- part of the visual relay

16. .
3. Nonspecific nuclei
 These scattered nuclei have other or multiple
connections.
 Some of these nuclei are located within the
internal medullary lamina and are often
referred to as the intralaminar nuclei - does not
have the strong reciprocal connections with the
cortex like the other nuclei.
 Some form part of the ascending reticular
activating system, which is involved in the
regulation of our state of consciousness and
arousal

17. Connection of the thalamus

18. -

19. Functions of Thalamus
.

20. -
1. A relay station for just about all sensory
information traveling from peripheral receptors to
the cortex.
–All sensory input (with the exception of
olfaction) is relayed through the thalamus prior
to entering the cortex.
–The thalamus might either dampen or facilitate
certain sensory inputs prior to their transmission
to the cortex.
• Play a role in the preliminary processing (e.g.,
integration or decoding) of incoming sensory
information.

21. -
2. The final common pathway in most, if not all,
cortical–subcortical feedback loops
–The thalamus is a critical component of the
extensive feedback loops for motor, cognitive,
and emotional systems that project from the
cortex to the basal ganglia (and cerebellum)
and back to the cortex via discrete thalamic
pathways
–Some thalamic nuclei receive input directly
from the cortex and project directly back to
those discrete cortical regions- reciprocal
connection

22. .
3. Plays key roles in cortical arousal and selective
attention, both necessary to efficient execution
of those behavioral goals or programs.
–Parts of the thalamus play an important role
in the maintenance and regulation of the
state of consciousness, and also possibly
attention, as part of the ascending reticular
activating system
–The thalamus plays a major role in activating
or arousing the cortex.

23. Lesions of Thalamus
.

24. .
Vascular disturbances
• Symptoms associated with hemorrhages or
infarctions of thalamus
• Thalamic lesions often extend beyond its
boundaries
• Lesions that are restricted to the thalamic
“motor” nuclei (primarily VA and VL) cause
transient motor symptoms, such as
hemiparesis, but permanent deficits are more
likely the result of invasion of the genu or
posterior limb of the internal capsule.

25. .
1. Motor – muscle weakness, gaze palsy,
ataxia, aphasia
2. Somatosensory disturbances – sensory
loss, thalamic pain, Visual field defects
3. Cognitive/arousal disturbances –
• Memory disturbance-dementia
• Mental confusion; disturbance of
consciousness