Anatomical classification of thalamic nuclei

General

The thalamus is divided into 3 parts by the Y shaped internal medullary laminar.


graph LR
    A[Thalamus] --> B[Anterior]
    A --> C[Medial]
    A --> D[Lateral]

    B --> B1[Anterior nucleus]
    C --> C1[Medial dorsal nucleus]

    D --> D1[Dorsal group]
    D --> D2[Ventral group]

    D1 --> D1a[Lateral dorsal]
    D1 --> D1b[Lateral posterior]
    D1 --> D1c[Pulvinar]

    D2 --> D2a[Ventral anterior nucleus]
    D2 --> D2b[Ventral lateral nucleus]
    D2 --> D2c[Ventral posterior nucleus]

    D2c --> D2c1[Ventral posteromedial nucleus]
    D2c --> D2c2[Ventral posterolateral nucleus]

Anterior Group of Thalamic Nuclei (Limbic/memory)

Subiculum → fornix → ant thalamic nuclei

Diagram shows how the frontal thalamic radiation goes through ant limb of internal capsule

Function: Memory

Part of circuit of Papez for recent memory.

Receives fibres from the mamillary body through the mamillothalamic tract.

Efferent fibres project to the cingulate gyrus through the anterior or frontal thalamic radiation (through the ant limb of internal capsule)


graph TD
    A[Mammillary body] -->|Mammillothalamic tract| B[Anterior nuclei]
    B -->|Anterior thalamic radiation| C[Cingulate gyrus]

Visceral function regulation

Medial Group of Thalamic Nuclei (Sensory integration /emotion/personality)

The large nucleus in the medial group

Afferent connections

Olfactory areas
Piriform lobe
Amygdala
Hypothalamus
Corpus striatum

Efferent connections

Prefrontal cortex through anterior or frontal thalamic radiation.

Function

Integration of olfactory, visceral and somatic functions and in the mediation of visceral and somatic reflexes
Involved in controlling emotional states
A role in determining the personality of the individual

Deficit

Decrease in anxiety, tension and aggression.


graph TD
    A[Amygdaloid nucleus] --> B{Medial dorsal nucleus}
    C[Olfactory cortex] --> B
    D[Globus pallidus] --> B
    B <--> E[Prefrontal cortex]

Lateral Part of Thalamus

Ventral (lateral) Group of Thalamic Nuclei (mainly relay nuclei) (motor/sensory)

Ventral anterior nucleus (motor)

Afferent

Globus pallidus and
Substantia nigra pars reticularis

Efferent

Premotor area
Supplemental motor areas of the cerebral cortex

Through

Superior thalamic radiation.


graph TD
    subgraph "Cerebral Cortex"
        CC1[Premotor area 6]
        CC2[Motor area 4]
    end

    subgraph "Thalamic Nuclei"
        TN1[Ventral anterior nucleus]
        TN2[Ventral lateral nucleus]
    end

    
        I1[From globus pallidus and substantia nigra]
        I2[From dentate nucleus of cerebellum]
    

    I1 --> TN1
    I1 --- TN2
    I2 --> TN2

    TN1 --> CC1
    TN2 --> CC2

Ventral lateral nucleus (motor)

Two parts

Ventrolateral pars oralis (VLo)

Located anteriorly
Afferent

GP
Ipsilateral internal globus pallidus → thalamic fasciculus → pars oralis
Vestibular nuclei
Precentral motor cortex

Efferent

SMA
Lateral premotor cortex

Ventrolateral pars caudalis (VLc)

Located Posteriorly
Afferent

Contralateral deep cerebellar (dentate) nuclei
Vestibular nuclei
Precentral motor cortex.

Efferent

Area 4 of primary motor cortex

Through

Superior thalamic radiation.

Function:

Coordinate and plan movement
The ventral lateral nucleus is active during both passive and active movements of the contralateral part of the body. It also has a role in relaying motor feedback from the cerebellum to the cerebral cortex

Ventral posterior nucleus (most clinically important) (Sensory)

Two parts

Ventral posterolateral

Afferent:

Medial lemniscus
Spinothalamic tract

Efferent:

Sensory cortex


graph TD
subgraph "Cerebral Cortex"
CC["Somatosensory areas (Areas 3, 2, 1)"]
end

subgraph "Ventral Posterior Nucleus"
VPN[Ventral posterior nucleus]
VPN_Medial["Medial part (VPM)"]
VPN_Lateral["Lateral part (VPL)"]
end

Input_Medial[Trigeminothalamic tract<br>Solitariothalamic tract]
Input_Lateral[Medial lemniscus<br>Spinothalamic tract]

Input_Medial --> VPN_Medial
Input_Lateral --> VPN_Lateral

VPN_Medial --> VPN
VPN_Lateral --> VPN

VPN --> CC

Ventral posteromedial

Afferent

CN7/9/10 → Nucleus solitarius → solitary tract (Solitariothalamic fibres) (See taste) → thalamus
Contralateral spinal nucleus of CN5 → ipsilateral ventral trigeminothalamic tract (pain & temp sensation) (See)
Contralateral principal sensory nuclei of CN5 → crosses midline → joins Ipsilateral dorsal trigeminothalamic tract (proprioception & touch)

Efferent

Primary sensory cortex
Parietal operculum (area 43) aka gustatory cortex

Afferent

Terminations of the major sensory pathways ascending from the spinal cord and brainstem

Medial lemniscus
Spinothalamic tract
Trigeminal lemniscus
Solitariothalamic fibres

There is topographic distribution of the fibres within the nucleus

Fibres from the lowest parts of the body end in the most lateral part of the nucleus.

Medial lemniscus and spinothalamic tract carrying sensations from the limbs and trunk end in the ventral posterolateral part,
Trigeminal fibres (from the head) and solitariothalamic tract (from taste) end in the ventral posteromedial part

Different layers of cells within the nucleus respond to different modalities of sensation.

Efferent

Sensory area of the cerebral cortex (SI, areas 3,2,1)

by fibres passing through the posterior limb of the internal capsule (superior thalamic radiation).

Second somatosensory area (SII) located in the parietal operculum (of the insula).

Somatosensory relays

Dorsal group of thalamic nuclei

Lateral dorsal nucleus

Afferent

other thalamic nuclei (mainly from the medial and anterior group).

Efferent: Enters the Limbic lobe

Cingulate gyrus
Parahippocampal gyrus
Hippocampal formation

Function

Emotional behaviour


graph TD
   
        A[Anterior and medial group of thalamic nuclei] --> B(Lateral dorsal)
        B --> C
        subgraph Cerebral cortex
	        C[Cingulate and parahippocampal gyrus and hippocampus] 
        end

Lateral posterior nucleus

Afferent

receives fibres from other thalamic nuclei (mainly from the ventral posterior group).

Efferent

To superior parietal lobule (Somatosensory association cortex).

Function

sensory processing


graph TD
    
        A[Ventral posterior groups of thalamic nuclei] --> B(Lateral posterior)
        B --> C
        subgraph Cerebral cortex
            C[Superior parietal lobule area 5, 7]
        end

Pulvinar

means "pillow" of the thalamus

Located at posterior part of the thalamus

Has 2 free surfaces:

Inferior surface:

Forms the roof of the wing of the ambient cistern

Posterior surface:

Divided into two halves;

Lateral half: is the anterior wall of the atrium of the lateral ventricle,
Medial half: is the roof of the quadrigeminal cistern.

Afferent

Metathalamus

Lateral geniculate body
Medial geniculate body

Superior colliculus.

Extrageniculate visual pathway: SC → pulvinar → secondary visual cortex (area 18/19)

Vs geniculate visual pathway from LGB directly to primary visual cortex (area 17)

Efferent

Occipital lobes
Parietal lobes
Temporal lobes

Primary auditory and auditory association areas in the temporal lobe through inferior thalamic radiation

Function

A lower visual centre.


graph TD
    
        A[Lateral and medial geniculate bodies, superior colliculus] --> B(Pulvinar)
        B --> C
        subgraph Cerebral cortex
        C[Association areas of parietal, occipital and temporal lobes]
        end

Other Connections Intralaminar nuclei:

Arnts et al 2023

Intralaminar nuclei


graph TD
        A[Superior colliculus] --> B
        C[Reticular formation] --> B
        D[Collaterals] --> B
        E[Spinothalamic tracts] --> B
        E --> F
        G[Cerebellar nuclei] --> F
        H[Substantia nigra] --> F
        I[Globus pallidus] --> F
    subgraph Intralaminar-Nuclei
				B(Anterior group)
		    F(Posterior group)
    end
		    Intralaminar-Nuclei --> Cerebral-Cortex
		    Intralaminar-Nuclei --"Diffuse projection" --> Cerebral-Cortex

    subgraph Cerebral-Cortex
        K[Other areas]
        L[Motor and premotor]
        
    end
				IntralaminarNuclei --> M(Striatum)

Divided into two subgroups:

Anterior (Rostral) Group: (aka: Rostral intralaminar nuclei)

Central Medial Nucleus

Afferent

Cerebral cortex
Vestibular nuclei
Globus pallidus
Superior colliculus
Reticular formation
Spinothalamic tract
Its physiological role involves attention and arousal, including control of the level of cortical activity

Efferent

Subthalamic nucleus and putamen.

Function:

Attention and arousal
Control of the level of cortical activity

Paracentral Nucleus

Function:

Arousal, awareness, executive cognitive functioning, and response to visceral pain stimuli

Central Lateral Nucleus (CL)

Function:

Pain perception

For all

Reticular activating system (reticular formation) → Rostral intralaminar nuclei → diffuse cortical areas
Function: Thalamic pacemaker

Posterior (Caudal) Group - Aka Centromedian-Parafascicular complex (CM-Pf)

Centromedian nucleus (part of the posterior sub group)

Most important
Afferent

Cerebral cortex (Area 4 (primary motor))
Globus pallidus

Efferent

Caudate nucleus
Putamen

Function:

Extrapyramidal motor system
Attention and arousal
Mental and cognitive function

Centromedian nucleus is located within a unique fibre pathway called the internal medullary lamina

Parafascicular nuclei

Parafascicular nuclei → area 6 (SMA) → caudate
Function:

Arousal and attention

Esp unexpected stimuli

Motor behaviour

Precisely represent vector components of velocity, with a strong preference for ipsiversive movements

Stimulation: ipsiversive (movement that turn part of the body towards the same side of the body) head turning
Inhibition: stopped turning and produced downward movements

Midline nuclei

Consist of several small groups of neurons (but there is controversy regarding the groups to be included under this heading).

Located on the medial surface of the thalamus in the interthalamic connection.

The connections of the nuclei are mainly with the limbic system.

Afferents

Noradrenergic, Serotoninergic, and cholinergic bundles ascending from the brainstem.
Brainstem reticular formation

Efferent

Limbic structure

Function:

Memory and arousal


graph LR
    
        A[Collaterals from spinothalamic tracts] --> B(MIDLINE NUCLEI)
        C[Reticular formation] --> B
        D[Noradrenergic fibres from locus coeruleus] --> B
        E[Serotoninergic fibres from raphe nuclei] --> B
        F[Periaqueductal grey matter] --> B
        G[Hypothalamus] --> B
        H[Amygdaloid complex] --> B
        I[Nucleus accumbens] --> B
        
        B --> Cerebral-Cortex
        
		subgraph Cerebral-Cortex
        J[Orbitofrontal cingulate]
        K[Hippocampal formation]
		end
		   
			   J --> B

Reticular nucleus

Located on the lateral surface of the thalamus

Between

The external medullary lamina
The internal capsule

Afferent

Collateral branches of thalamocortical and corticothalamic fibres

Efferent

Other thalamic nuclei

Function:

Modulates influence that thalamus on cortex