The thalamus is a paired symmetrical structure located in the center of the brain that relays sensory and motor signals between the brainstem and cerebral cortex. It is divided into several nuclei that have distinct connections and functions. The document provides detailed information on the anatomy, physiology, functional organization and clinical syndromes associated with lesions of different thalamic nuclei. Key points include a description of the gross anatomy and location of the thalamus, its blood supply, the nuclei and their connections, and syndromes associated with infarcts in the posterolateral and medial thalamic territories.

1. Thalamus
-Dr. Sachin A. Adukia

2. Headings
 Introduction
 Anatomy: Gross and Location (with normal MRI
sections)
 Physiology
 Functional Anatomy
 Neurobiochemistry
 Thalamus infarction and Syndromes
 Theraputic importance

3. Introduction
 Thalamus (Greek) means “inner chamber” or
“meeting place”
 Historical interest
 Earlier – “Optic Thalamus” and chamber of vision- 2nd century AD;
Galen.
 Later - Prefix “optic” was dropped - when discovered that sensory
modalities other than vision are also processed in the thalamus

4. Primary Divisions of the Brain

6. The Diencephalon
 Relay between the brainstem & cerebral
cortex
 Dorsal-posterior structures
 Epithalamus
 Thalamus
 Metathalamus
 Medial geniculate body – auditory relay
 Lateral geniculate body – visual relay
 Ventral-anterior structure
 Hypothalamus

7. Thalamus
 Largest component of the diencephalon.
 Paired symmetrical structure in the brain, perched on top of the brainstem
 Near the center of the brain,
 located obliquely (about 30°) and symmetrically on each side of the third v
entricle
 Both parts of this structure are each about the size and shape of a walnut.
 Dimensions:
 Rostrocaudal (AP) - 30 mm, height - 20 mm, width - 20 mm,
 estimated 10 million neurons in each half
 Location and Relation:
 Thalamus lies medially in the cerebrum.
 bounded medially by III venticle
 laterally by internal capsule and basal ganglia
 ventrally continuous with subthalamus.

9. Thalamus- Axial View

10. Thalamus- Sagittal View

11. Thalamus- Coronal View

12. Thalamus- Coronal View
3rd ventricle

13. Thalamus- Coronal View
Internal capsule

14. Thalamus- Coronal View
Mediodorsal nucleus Internal capsule

15. Thalamus- Blood Supply
Posterior communicating artery
paramedian thalamic-
subthalamic arteries
inferolateral (thalamogeniculate)
arteries
posterior (medial and lateral)
choroidal arteries.
All are branches of PCA.
ADDITIONALLY…
The ICA, via its anterior choroidal
branch, supplies the lateral thalamic
territory.

16. Thalamus Physiology (Overview)
 Primarily - 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 projection fibres from the Thalamus
 Characteristically, thalamic connections are reciprocal, that is, the target of the
axonal projection of any given thalamic nucleus sends back fibers to that
nucleus. Nevertheless, thalamocortical projections are often larger than their
corticothalamic counterparts

17. Functional Anatomy of the Thalamus
It is subdivided into the following major nuclear groups on the basis of their
rostrocaudal and mediolateral location within the thalamus:
Anterior
Medial
Lateral
Intralaminar and reticular
Midline
Posterior

18. Thalamic Nuclei
 Internal medullary lamina divides the thalamus
into medial and lateral groups of nuclei
 It houses the intralaminar nuclei, which include
the centromedian(CM) and parafascicular (PF)
nuclei, among others
 lamina splits into two leaves anteriorly and
encloses the anterior nucleus
 The medial group has only one nucleus: the
dorsomedial nucleus (DM)
 lateral group - several nuclei divided into
 small superior or dorsal tier
 much larger inferior or ventral tier of nuclei.

20.  Thalamus is traversed by a band of myelinated fibers, the internal
medullary lamina, which runs along its rostrocaudal extent
 The internal medullary lamina contains intrathalamic fibers
connecting the different nuclei of the thalamus with each other
 External medullary lamina, forms the lateral boundary of the
thalamus medial to the internal capsule. It contains nerve fibers
leaving or entering the thalamus on their way to or from the adjacent
capsule
 Between the external medullary lamina and the internal capsule is the
Thalamic reticular nucleus.

21. 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

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

24. MEDIAL NUCLEAR GROUP
 The dorsomedial nucleus is reciprocally connected with the
prefrontal cortex (areas 9, 10, 11, and 12), via the anterior
thalamic peduncle, and with the frontal eye fields (area 8)
 Receives inputs from
 the temporal neocortex (via the inferior thalamic peduncle)
 amygdaloid nucleus and substantia nigra pars reticulata
 adjacent thalamic nuclei (lateral and intralaminar groups)
 Concerned with affective behavior, decision making and
judgment, memory, and the integration of somatic and visceral
activity.

25. Schematic diagram showing the
major afferent and efferent
connections of the Dorsomedial
Nucleus of the thalamus

26. Clinical Importance of DM nucleus
 Bilateral lesions of the dorsomedial nucleus result in a
syndrome of lost physical self-activation, manifested by
apathy, indifference, and poor motivation.
 The reciprocal connections between the prefrontal cortex
and the dorsomedial nucleus can be interrupted
surgically to relieve severe anxiety states and other
psychiatric disorders.
 This operation, known as prefrontal lobotomy is rarely
practiced nowadays, having been replaced largely by
medical treatment

27. Lateral group of Nuclei
(Overview)

29. Lateral nuclear group
is subdivided into two groups: dorsal and ventral
 Dorsal Subgroup
from rostral to caudal: lateral dorsal - LD, lateral posterior,
and pulvinar nuclei
 Similar to the anterior group nuclei, the LD nucleus
receives inputs from the hippocampus (via the fornix) and
mamillary bodies and projects to the cingulate gyrus
 The Pulvinar - Lateral posterior complex has reciprocal
connections
 caudally with the lateral geniculate body
 rostrally with association areas of parietal, temporal and occipital
cortices
 It also receives inputs from the pretectal area and superior colliculus

30.  The pulvinar is a relay station
between subcortical visual
centers and their respective
association cortices in the
temporal, parietal, and occipital
lobes.
 Has a role in selective visual
attention.
 Plays a role in speech
mechanisms.
Stimulation of pulvinar of
dominant hemisphere has
produced nominal aphasia
 Has role in pain mechanisms.
Lesions in the pulvinar : effective
in the treatment of intractable
pain

32. Ventral Subgroup
(ventral anterior, ventral lateral, and ventral posterior 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

33. Connections of Ventral Anterior Nuclei
INPUTS
 GABAergic inhibitory input
 Globus pallidus:- Pallidal fibers terminate in the lateral portion of the
ventral anterior nucleus
 Substantia nigra pars reticulata:- Nigral afferents terminate in the
medial portion
 Excitatory
 Premotor and prefrontal cortices (areas 6 and 8)
RECIPROCAL CONNECTIONS
 Intralaminar thalamic nuclei
OUTPUTS
 Major output to:- premotor cortices and to wide areas of the prefrontal
cortex, including the frontal eye fields.
 A major relay station in the motor pathways from the basal ganglia to the
cerebral cortex (is involved in regulation of movement)

35. Ventral lateral nucleus
located caudal to the Ventral Anterior nucleus, plays a role in motor integration
ventral anterior and ventral lateral nuclei together comprise MOTOR THALAMUS.
AFFERENT FIBERS TO THE VENTRAL LATERAL NUCLEUS:
 Deep cerebellar nuclei
 Globus pallidus (internal segment)
 Primary motor cortex (area 4)
EFFERENT FIBERS
 mainly go to primary motor cortex
 nonprimary somatosensory areas in the parietal cortex (areas 5 and 7)
 premotor and supplementary motor cortices

36. Ventral posterior nucleus
located in the caudal part of the thalamus
 Receives the long ascending tracts conveying sensory modalities
(including taste) from the contralateral half of the body and face.
 The ventral posterior nucleus is made up of two parts:
 ventral posterior medial (VPM) nucleus- receives the trigeminal
lemniscus and taste fibers
 ventral posterior lateral (VPL) nucleus- receives the medial lemniscus
and spinothalamic tracts.
 Both nuclei also receive input from the primary somatosensory cortex
 The output from both is to primary somatosensory cortex (area 1, 2,
and 3).
 The VPL and VPM nuclei collectively comprise - ventrobasal complex

38. Intralaminar Nuclei
 The Intralaminar nuclei- divided into caudal and rostral groups.
 The Caudal group includes the centromedian and parafascicular nuclei
 The Rostral group includes the paracentral, centrolateral, and centromedial
nuclei
 Afferent connections
 Reticular formation of the brain stem (major input)
 Cerebellum : The dentatorubrothalamic system
 Spinothalamic and trigeminal lemniscus
 Globus pallidus
 Cerebral cortex
 Efferent Connections
 Other thalamic nuclei (influences cortical activity via other thalamic nuclei)
 The striatum (caudate and putamen)

39. Reticular nucleus
 Is a continuation of the reticular formation of the brainstem
into the diencephalon.
 Afferents from the cerebral cortex and other thalamic nuclei.
 The former are collaterals of corticothalamic projections, and
the latter are collaterals of thalamocortical projections.
 Efferent projections to other thalamic nuclei. The inhibitory
neurotransmitter in this projection is GABA.
 It plays a role in integrating and gating activities of thalamic
nuclei

40. METATHALAMUS
(refers to two thalamic nuclei, the Medial Geniculate and Lateral Geniculate)
Lateral Geniculate Nucleus
 This is a relay thalamic nucleus in the visual system.
 It receives fibers from the optic tract conveying impulses from both retinae
 The efferent outflow from the lateral geniculate nucleus forms the optic
radiation of the internal capsule (retrolenticular part) to the primary visual
cortex in the occipital lobe
Medial Geniculate Nucleus
This is a relay nucleus in the auditory system.
It receives fibers from the lateral lemniscus directly or, more frequently, after
a synapse in the inferior colliculus.
efferent outflow from the MG nucleus forms the auditory radiation of the
internal capsule (sublenticular part) to the primary auditory cortex in temporal
lobe (areas 41 and 42)

41. Other nomenclature system
 This system groups thalamic nuclei into the following categories:
 (1) motor
 (2) sensory
 (3) limbic
 (4) associative
 (5) nonspecific and reticular.
 The motor group receives motor inputs from the basal ganglia
(ventral anterior, ventral lateral) or the cerebellum (ventral lateral)
and projects to the premotor and primary motor cortices.

 The sensory group receives inputs from ascending somatosensory
(ventral posterior lateral and medial), auditory (medial geniculate),
and visual (lateral geniculate) systems.
 The limbic group is related to limbic structures (mamillary
bodies, hippocampus, cingulate gyrus).

42. Neurobiochemistry of Thalamus
 Neurotransmitters identified in the thalamus:
 GABA is the inhibitory neurotransmitter in
Afferent terminals from the GP and in local circuit neurons,
and in efferent projections of the reticular nucleus and lateral
geniculate nucleus; and
 Glutamate and aspartate are the excitatory neurotransmitters in
 corticothalamic and cerebellar terminals
and in thalamocortical projection neurons.
 Others:
 substance P, somatostatin, neuropeptide Y, enkephalin, and
cholecystokinin

43. Thalamic Infarcts and Syndromes
 The conglomerate of signs and symptoms associated
with thalamic lesions includes the following:
sensory disturbances, thalamic pain, hemiparesis,
dyskinesias, disturbances of consciousness, memory
disturbances, affective disturbances, and disorders of
language
 Most thalamic infarcts are reported in the
posterolateral and the medial thalamic territories
supplied by the geniculothalamic and paramedian
arteries, respectively

44. Posterolateral Thalamic Territory
(geniculothalamic artery, a branch of the posterior cerebral artery)
 signs and symptoms associated with posterolateral thalamic territory infarcts
comprise the thalamic syndrome of Dejerine and Roussy.
 In this syndrome, severe, persistent, paroxysmal, and often intolerable pain
(thalamic pain) resistant to analgesic medications occurs at the time of injury or
following a period of transient hemiparesis, hemiataxia, choreiform
movements, and hemisensory loss
 Cutaneous stimuli trigger paroxysmal exacerbations of the pain that outlast the
stimulus. Because the perception of “epicritic” pain (from a pinprick) is reduced
on the painful areas, this symptom is known as anesthesia dolorosa, or painful
anesthesia
 An athetoid posture of the contralateral hand (thalamic hand) may appear 2 or
more weeks following lesions in this territory.
 The hand is flexed and pronated at the wrist and MCP joints and extended at the
interphalangeal joints.
 The fingers may be abducted.
 The thumb is either abducted or pushed against the palm.

45. Thalamic hand with the corresponding MRI

46. T2-weighted axial magnetic resonance image (MRI) showing an
infarct (arrow) in the posterolateral thalamic territory

47. Medial territory of the thalamus
 Infarcts in the medial territory of the thalamus are associated with
occlusion of the paramedian branches of the basilar root of the
posterior cerebral artery.
 hallmark - drowsiness.
 In addition, there are abnormalities in recent memory, attention,
intellect, vertical gaze, and occasionally, mild hemiparesis or
hemiataxia.
 No sensory deficits as a rule.
 Utilization behavior, although characteristic of frontal lobe damage,
has been reported

48. Two syndromes asso. with medial thalamus territory :
Akinetic mutism and Kleine-Levin syndrome
 In akinetic mutism (persistent vegetative state), patients
appear awake and maintain a sleep-wake cycle but are
unable to communicate in any way.
 The Kleine-Levin syndrome (hypersomnia-bulimia
syndrome) is characterized by recurrent periods (lasting 1 to
2 weeks every 3 to 6 months) in adolescent males of
excessive somnolence, hyperphagia (compulsive eating),
hypersexual behavior (sexual disinhibition), and impaired
recent memory, and eventually ending with recovery.
 A confusional state, hallucinosis, irritability, or a
schizophreniform state may occur around the time of the
attacks

49. T2-weighted axial MRI showing an infarct (arrow) in the
medial thalamic territory

50. Thalamic pain syndromes
The four types are differentiated from each other on the basis of
 the presence or absence in each of central (thalamic) pain
proprioceptive sensations (vibration, touch, joint)
 exteroceptive sensations (pain and temperature)
and abnormalities in somatosensory evoked potentials

51. Memory deficits
(may be transient or permanent)
 Discrete lesions of the thalamus can cause severe and
lasting memory deficits
 three distinct behavioral and anatomic types of memory
impairment
 Severe encoding defects
 A milder form characterized by severe distractibility
 Disturbances in verbal memory (retrieval, registration,
and retention)
 Memory disturbances are most common with bilateral
thalamic lesions but do occur with unilateral lesions of
either side

52. Alien hand syndrome
 Defined as unwilled, uncontrollable movements of an upper
limb together with failure to recognize ownership of a limb in
the absence of visual cues
 Most cases are associated with lesions in the corpus callosum
and mesial frontal area
 also been reported in infarcts involving the posterolateral and
anterolateral thalamic territories:
 ventral posterior
 ventral lateral
 dorsomedial nuclei

53. Thalamic Acalculia
 Infarctions in the left anterolateral thalamic territory
supplied by the tuberothalamic artery have been
reported to produce acalculia.
 The lesion usually involves the ventral lateral and
dorsomedial thalamic nuclei

54. Language Deficits
 Dominant hemisphere thalamic lesions may cause a transient deficit in
language.
 Three types have been described:
 medial
 anterolateral
 lateral.
 medial type, involving the dorsomedial and centromedian nuclei:-
 is characterized by anomia and attentionally induced language impairment.
 anterolateral type, involves ventral anterior (anterolateral thalamic
territory):-
 aphasic syndrome resembling transcortical aphasia.
 lateral thalamic territory:
 mild anomia

55. CLINICAL IMPORTANCE
 Discrete lesions in various regions of the thalamus, and, more recently,
deep brain stimulation (DBS) through implanted electrodes, are
increasingly used for the treatment of:
 Parkinsonian and essential tremor,
 dystonia,
 pain,
 epilepsy,
 manifestations of Gilles de la Tourette's syndrome.
 Essential tremor can be treated by DBS with electrodes in the ventrolateral
nucleus. The ventrolateral nucleus includes the nuclei Ventralis
Intermedius (VIM) and ventralis oralis posterior (VOP).
 Treatment of the tremor is the most extensively used and best understood
DBS thalamic procedure