Thalamus

The thalamus is a large, ovoid structure in the dorsal part of the diencephalon that is located between the cerebral cortex Cerebral cortex The cerebral cortex is the largest and most developed part of the human brain and CNS. Occupying the upper part of the cranial cavity, the cerebral cortex has 4 lobes and is divided into 2 hemispheres that are joined centrally by the corpus callosum. Cerebral Cortex and midbrain, consisting of several interconnected nuclei of gray matter separated by the laminae of white matter. The thalamus is the main conductor of information that passes between the cerebral cortex Cerebral cortex The cerebral cortex is the largest and most developed part of the human brain and CNS. Occupying the upper part of the cranial cavity, the cerebral cortex has 4 lobes and is divided into 2 hemispheres that are joined centrally by the corpus callosum. Cerebral Cortex and the periphery, spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord, or brain stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain Stem and is divided into the anterior, medial, and lateral parts. Each part contains groups of nuclei that function as relay centers for sensory impulses and for the modulation of motor responses via interconnections with the basal ganglia Basal Ganglia Basal ganglia are a group of subcortical nuclear agglomerations involved in movement, and are located deep to the cerebral hemispheres. Basal ganglia include the striatum (caudate nucleus and putamen), globus pallidus, substantia nigra, and subthalamic nucleus. Basal Ganglia.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Table of Contents

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Gross Anatomy

Gross features

  • Bilateral structure with identical halves called thalami:
    • The halves are connected by the interthalamic adhesion.
    • The interthalamic adhesion is not a commissure and contains no neurons.
    • Rather, the interthalamic adhesion is composed of glial cells that do not participate in interthalamic “crosstalk.”
  • Ovoid in shape
  • Approximately 4 cm in length
  • Location:
    • Superior (cephalad) to the midbrain (mesencephalon)
    • Inferior (deep) to the cerebral cortex Cerebral cortex The cerebral cortex is the largest and most developed part of the human brain and CNS. Occupying the upper part of the cranial cavity, the cerebral cortex has 4 lobes and is divided into 2 hemispheres that are joined centrally by the corpus callosum. Cerebral Cortex
  • Borders:
    • Anterior: forms the posterior wall of the interventricular foramen (of Monro)
    • Posterior: extends beyond the 3rd ventricle
    • Medial: forms the lateral wall of the 3rd ventricle
    • Lateral: contacts the descending posterior limb of the internal capsule
    • Superior: separated from the body of the fornix by the tela choroidea
    • Inferior: joins the hypothalamus Hypothalamus The hypothalamus is a collection of various nuclei within the diencephalon in the center of the brain. The hypothalamus plays a vital role in endocrine regulation as the primary regulator of the pituitary gland, and it is the major point of integration between the central nervous and endocrine systems. Hypothalamus and is continuous with the lemnisci of the tegmentum
  • Divided into several gray matter (neuronal cell bodies) nuclei by the white matter (axons) laminae:
    • External medullary laminae cover the lateral surface of the thalamus.
    • Internal laminae divide the thalamic nuclei into separate groups.
  • Thalamic nuclei:
    • Anterior nuclei
    • Ventral posteromedial nuclei
    • Ventral posterolateral nuclei
    • Ventral anterior and lateral nuclei
    • Dorsomedial nuclei
    • Pulvinar
    • Medial geniculate body
    • Lateral geniculate body
    • Intralaminar/midline nuclei
Table: Thalamic nuclei
Nucleus Major input Major output Function
Anterior Mammillary body and hippocampal formation Cingulate gyrus Limbic pathway
Ventral posteromedial Trigeminothalamic tract and rostral solitary nucleus Primary somatosensory cortex and gustatory cortex Touch, position, pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, and temperature from face; taste
Ventral posterolateral Dorsal column-medial lemniscus and anterolateral tract Primary somatosensory cortex Sense of pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain and temperature, touch, and position
Ventral anterior Basal ganglia Motor, premotor, and diffuse Motor planning
Ventral lateral Cerebellum Cerebellum The cerebellum, Latin for "little brain," is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum Motor and premotor cortex Motor planning and control
Dorsomedial Amygdala, olfactory cortex, limbic basal ganglia Basal Ganglia Basal ganglia are a group of subcortical nuclear agglomerations involved in movement, and are located deep to the cerebral hemispheres. Basal ganglia include the striatum (caudate nucleus and putamen), globus pallidus, substantia nigra, and subthalamic nucleus. Basal Ganglia Frontal cortex Limbic pathway, major relay to frontal cortex
Pulvinar Visual, auditory, and other sensory pathways Parietal, occipital, and areas of temporal association Sensory integration and visual attention
Medial geniculate Inferior colliculus Primary auditory cortex Hearing
Lateral geniculate Retina (optic tract) Primary visual cortex Vision
Intralaminar Reticular formation, spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord, hypothalamus Hypothalamus The hypothalamus is a collection of various nuclei within the diencephalon in the center of the brain. The hypothalamus plays a vital role in endocrine regulation as the primary regulator of the pituitary gland, and it is the major point of integration between the central nervous and endocrine systems. Hypothalamus Limbic cortex and basal ganglia Basal Ganglia Basal ganglia are a group of subcortical nuclear agglomerations involved in movement, and are located deep to the cerebral hemispheres. Basal ganglia include the striatum (caudate nucleus and putamen), globus pallidus, substantia nigra, and subthalamic nucleus. Basal Ganglia Arousal, motivation, affect, pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain
Location of the thalamus in a midsagittal section of the human brain

Location of the thalamus in a midsagittal section of the human brain

Image by BioDigital, edited by Lecturio

Microscopic structure

  • Thalamic nuclei consist of cell bodies of excitatory and inhibitory neurons.
  • Dendrites receive sensory information from all over the body.
  • Sensory information is “filtered” and presented to the cortex via axons known as the thalamocortical radiations.
  • Thalamic neuronal connections also include:
    • Hippocampus
    • Mammillary bodies
    • Fornix
    • Limbic system Limbic system The limbic system is a neuronal network that mediates emotion and motivation, while also playing a role in learning and memory. The extended neural network is vital to numerous basic psychological functions and plays an invaluable role in processing and responding to environmental stimuli. Limbic System

Functions

  • Regulation and maintenance of consciousness (alertness/wakefulness) and sleep Sleep Sleep is a reversible phase of diminished responsiveness, motor activity, and metabolism. This process is a complex and dynamic phenomenon, occurring in 4-5 cycles a night, and generally divided into non-rapid eye movement (NREM) sleep and REM sleep stages. Physiology of Sleep
  • Filtering of sensory information for selective presentation to the cerebral cortex Cerebral cortex The cerebral cortex is the largest and most developed part of the human brain and CNS. Occupying the upper part of the cranial cavity, the cerebral cortex has 4 lobes and is divided into 2 hemispheres that are joined centrally by the corpus callosum. Cerebral Cortex:
    • Olfactory inputs exist but are not filtered or modified.
    • All other sensory stimuli undergo processing in the thalamus prior to transmission to the cortical centers.
  • Modulation of motor responses via interconnections with the basal ganglia Basal Ganglia Basal ganglia are a group of subcortical nuclear agglomerations involved in movement, and are located deep to the cerebral hemispheres. Basal ganglia include the striatum (caudate nucleus and putamen), globus pallidus, substantia nigra, and subthalamic nucleus. Basal Ganglia

Vasculature

  • Supplied by branches of the posterior cerebral artery
  • Blood supply to the thalamus is divided into 4 regions: 
    • Anterior
    • Inferolateral
    • Paramedian
    • Posterior

Embryologic development

  • Develops from alar plate (dorsal surface ectoderm of the neural tube)
  • Grows from the prosencephalon
Development-of-the-thalamus

Development of the thalamus from the prosencephalon, where it forms the diencephalon, comprising the thalamus, hypothalamus Hypothalamus The hypothalamus is a collection of various nuclei within the diencephalon in the center of the brain. The hypothalamus plays a vital role in endocrine regulation as the primary regulator of the pituitary gland, and it is the major point of integration between the central nervous and endocrine systems. Hypothalamus, and epithalamus

Image: “Primary and Secondary Vesicle Stages of Development ” by Phil Schatz. License: CC BY 4.0, edited by Lecturio.

Anterior Nuclei

The anterior nuclei are subdivided into 3 sections with inputs from the mammillary bodies and hippocampus and output to the cingulate gyrus. The anterior nuclei are associated with learning, memory, and emotion.

  • Consists of 3 subdivisions:
    • Anteroventral
    • Anteromedial
    • Anterodorsal
  • Inputs:
    • Mammillary body
    • Hippocampal formation
    • Limbic system Limbic system The limbic system is a neuronal network that mediates emotion and motivation, while also playing a role in learning and memory. The extended neural network is vital to numerous basic psychological functions and plays an invaluable role in processing and responding to environmental stimuli. Limbic System
  • Output: cingulate gyrus in the cerebral cortex Cerebral cortex The cerebral cortex is the largest and most developed part of the human brain and CNS. Occupying the upper part of the cranial cavity, the cerebral cortex has 4 lobes and is divided into 2 hemispheres that are joined centrally by the corpus callosum. Cerebral Cortex
  • Functions:
    • Learning
    • Memory
    • Emotions
Anterior nucleus of thalamus

Location of the anterior nucleus within the thalamus: Note its central and anterior location within this hemisection of the brain.

Image by Lecturio.

Ventral Posteromedial/Posterolateral Nuclei

The ventral posteromedial and ventral posterolateral nuclei are associated with inputs from the rostral solitary nucleus and trigeminothalamic tract and outputs to the primary somatosensory cortex and frontal operculum/insula.

  • Ventral posteromedial nucleus:
    • Receives and distributes information regarding touch, position, pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, and temperature from the face as well as gustatory information
    • Inputs:
      • Trigeminothalamic tract: sensory information from the face and oral cavity
      •  Rostral solitary nucleus: gustatory information
    • Outputs:
      • Primary somatosensory cortex
      • Gustatory cortex (frontal operculum and insula)
    • Functions:
      • Relays somatosensory cranial nerve inputs (touch, position, pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, and temperature from the face)
      • Relays gustation to the cortex
  • Ventral posterolateral nucleus:
    • Receives and distributes information regarding touch, position, pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, and temperature from the body and relays it to the somatosensory cortex
    • Includes sensory inputs from the body and limbs:
      • Dorsal column medial lemniscus (pressure, vibration, fine touch, and proprioception)
      • Spinothalamic tract:
        • Lateral: pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain and temperature
        • Anterior: crude touch and pressure
    • Outputs: somatosensory cortex (perception of sensations, touch, vibration, pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, and temperature)
    • Functions: relays somatosensory spinal inputs to the somatosensory cortex

Ventral Anterior and Ventral Lateral Nuclei

The ventral anterior and ventral lateral nuclei are associated with inputs from the basal ganglia Basal Ganglia Basal ganglia are a group of subcortical nuclear agglomerations involved in movement, and are located deep to the cerebral hemispheres. Basal ganglia include the striatum (caudate nucleus and putamen), globus pallidus, substantia nigra, and subthalamic nucleus. Basal Ganglia and cerebellum and output to the frontal lobe. Both nuclei are also associated with various motor pathways.

  • Ventral anterior nucleus:
    • Input: basal ganglia Basal Ganglia Basal ganglia are a group of subcortical nuclear agglomerations involved in movement, and are located deep to the cerebral hemispheres. Basal ganglia include the striatum (caudate nucleus and putamen), globus pallidus, substantia nigra, and subthalamic nucleus. Basal Ganglia
    • Outputs: frontal lobe to the motor, premotor, and supplementary motor cortices
    • Function: relays basal ganglia Basal Ganglia Basal ganglia are a group of subcortical nuclear agglomerations involved in movement, and are located deep to the cerebral hemispheres. Basal ganglia include the striatum (caudate nucleus and putamen), globus pallidus, substantia nigra, and subthalamic nucleus. Basal Ganglia inputs to motor cortices for motor planning
  • Ventral lateral nucleus:
    • Input: cerebellum
    • Outputs: frontal lobe to the motor, premotor, and supplementary motor cortices
    • Function: relays cerebellar inputs to motor cortices for motor planning and control
Val nuclei of thalamus

Location of the ventral anterior and ventral lateral nuclei

Image by Lecturio.

Dorsomedial Nuclei

The dorsomedial nuclei are associated with inputs from the amygdala, olfactory centers, and basal ganglia Basal Ganglia Basal ganglia are a group of subcortical nuclear agglomerations involved in movement, and are located deep to the cerebral hemispheres. Basal ganglia include the striatum (caudate nucleus and putamen), globus pallidus, substantia nigra, and subthalamic nucleus. Basal Ganglia and output to the frontal cortex. The dorsomedial nuclei are associated with various limbic pathways.

  • Inputs:
    • Amygdala
    • Olfactory
    • Limbic basal ganglia Basal Ganglia Basal ganglia are a group of subcortical nuclear agglomerations involved in movement, and are located deep to the cerebral hemispheres. Basal ganglia include the striatum (caudate nucleus and putamen), globus pallidus, substantia nigra, and subthalamic nucleus. Basal Ganglia
  • Outputs:
    • Frontal cortex
    • Prefrontal association areas
  • Functions:
    • Emotions
    • Cognition
    • Learning
Nuclei that make up the thalamus and their respective projections

Nuclei that make up the thalamus and their respective projections: Note the dorsomedial (mediodorsal) nucleus located medially on the dorsal aspect of the thalamus with projections to the prefrontal cortex.
VA: ventral anterior
VL: ventral lateral
VPL: ventral posterolateral
VPM: ventral posteromedial
LD: lateral dorsal
LP: lateral posterior

Image by Lecturio.

Pulvinar

The pulvinar is associated with inputs from the superior colliculus, visual areas, auditory complex, and other sensory pathways, and outputs to the parietotemporal association areas. The pulvinar is associated with various visual and sensory pathways.

  • Consists of 3 primary subdivisions:
    • Medial
    • Lateral
    • Inferior
  • Inputs:
    • Visual inputs from the superior colliculus and extrastriate visual areas
    • Auditory
    • Other sensory pathways
  • Output: parietotemporal-occipital association area
  • Functions:
    • The precise functions are unknown.
    • Believed to be involved in orientation toward visual, auditory, and other sensory stimuli
Pulvinar nucleus of thalamus

Location of the pulvinar, which is the posterior expansion of the thalamus overhanging the superior colliculus

Image by Lecturio.

Medial and Lateral Geniculate Bodies

The medial and lateral geniculate bodies are associated with inputs from the inferior colliculus and retina and outputs to the temporal lobe and visual cortex, and are involved in various auditory and visual pathways.

  • Medial geniculate body:
    • Part of the auditory pathway
    • Input: inferior colliculus
    • Output: auditory cortex of the temporal lobe
    • Function: relays auditory input to the cortex
  • Lateral geniculate body:
    • Main relay station of the visual pathway Visual pathway The primary visual pathway consists of a relay system, beginning at the retina, whose ganglion cell axons form the optic nerve. The optic nerve fibers from each eye hemidecussate in the optic chiasm (OC), with nasal fibers joining the temporal fibers of the contralateral nerve. Signals are then transmitted to the primary visual cortex of the occipital lobe. The Visual Pathway and Related Disorders
    • Organized in 6 layers:
      • Layers 1 and 2 consist of large neurons.
      • Layers 3–6 consist of smaller neurons.
    • Inputs:
      • Retina/optic nerve
      • Contralateral nasal hemiretina projects to layers 1, 4, and 6.
      • Ipsilateral temporal hemiretina projects to layers 2, 3, and 5.
    • Outputs:
      • Primary visual cortex in the occipital lobe
      • Efferent fibers retain the visuotopic, layered organization as they project to the visual cortex.
    • Function: relays visual inputs to the primary visual cortex
Mgb and lgb of thalamus

Location of the LGB and MGB of the thalamus

Image by Lecturio.

Intralaminar/Midline Nuclei

Intralaminar and midline nuclei are associated with inputs from the spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord, hypothalamus Hypothalamus The hypothalamus is a collection of various nuclei within the diencephalon in the center of the brain. The hypothalamus plays a vital role in endocrine regulation as the primary regulator of the pituitary gland, and it is the major point of integration between the central nervous and endocrine systems. Hypothalamus, and descending reticular formation, and outputs to the basal ganglia Basal Ganglia Basal ganglia are a group of subcortical nuclear agglomerations involved in movement, and are located deep to the cerebral hemispheres. Basal ganglia include the striatum (caudate nucleus and putamen), globus pallidus, substantia nigra, and subthalamic nucleus. Basal Ganglia and limbic system. Both nuclei are associated with various emotional and sensory pathways.

  • Involved in arousal and part of the reticular activating system
  • Inputs:
    • Ascending reticular formation
    • Spinal cord
    • Hypothalamus
  • Outputs:
    • Limbic cortex
    • Basal ganglia
  • Functions:
    • Arousal
    • Motivation
    • Affect
    • Pain

Clinical Relevance

  • Auditory pathways: The auditory system consists of a series of interconnected parts from the external ear itself, to the middle and inner ear, and to the cortical regions that process auditory stimuli.
  • Brainstem: consists of the midbrain, pons, and medulla oblongata. The brainstem is a stalk-like structure that connects the cerebrum with the spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord and is a major relay station for sensory, motor, and autonomic information.
  • Cerebral cortex: a layer of gray matter covering the surface of each cerebral hemisphere, folded into gyri that are separated by sulci. The cerebral cortex Cerebral cortex The cerebral cortex is the largest and most developed part of the human brain and CNS. Occupying the upper part of the cranial cavity, the cerebral cortex has 4 lobes and is divided into 2 hemispheres that are joined centrally by the corpus callosum. Cerebral Cortex functions in higher-order mental functions.
  • Visual system: consists of a series of interdependent parts from the organization of the eye and retina to the cortical regions. The visual system is primarily located in the occipital lobe and processes visual stimuli.

References

  1. Sadler, T. (2014). Langman’s Medical Embryology, 13th edition. Lippincott Williams & Wilkins.
  2. Shkoukani, M.A., Chen, M., Vong, A. (2013). Cleft Lip – A Comprehensive Review. Front Pediatr. 1, 53. https://doi.org/10.3389/fped.2013.00053
  3. Berkowitz, A.L. (Ed.). (2016). Clinical Neurology and Neuroanatomy: A Localization-Based Approach. McGraw-Hill. 
  4. Kibble, J.D. (Ed.). (2020). Neurophysiology in The Big Picture Physiology: Medical Course & Step 1 Review, 2e. McGraw-Hill.
  5. Martin, J. (2021). The visual system in Neuroanatomy: Text and Atlas, 5e. McGraw-Hill.
  6. Purves, D. (2001). Visual Field Defects in Neuroscience (2nd ed.). Sunderland (MA): Sinauer Associates. https://www.ncbi.nlm.nih.gov/books/NBK10912/
  7. Shakkottai, V.G., Lomen-Hoerth, C. (2019). Nervous System Disorders. In Hammer G.D., McPhee S.J. (Eds.), Pathophysiology of Disease: An Introduction to Clinical Medicine, 8e. McGraw-Hill.
  8. Waxman, S. (2020). The Visual System. In Clinical Neuroanatomy, 29e. McGraw-Hill.

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