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The Thalamus

Notes

The Thalamus

Sections


thalamus - anatomy and physiology

Think of it as a "mini-brain" within the brain.

Brain Atlas: Thalamus

The internal medullary lamina

  • Lies along the anterior–posterior axis of the thalamus and bifurcates, anteriorly.

The anterior thalamic group

  • Lies within this bifurcation and communicates with the limbic system (in particular with the mammillary bodies and cingulate gyrus as part of the Papez circuit).

The medial group nuclei

  • The dorsomedial nucleus connects with the prefrontal cortex.

The lateral group nuclei

Divides into dorsal and ventral subgroups.

The ventral subgroup

  • The ventroanterior nucleus connects with the basal ganglia.
  • The ventrolateral nucleus connects with the cerebellum, red nucleus, and, to a lesser extent, the basal ganglia.
  • The ventroposterior nucleus further divides into medial and lateral nuclei, both of which receive sensory afferents (medial from the face, lateral from the body) and project them to the somatosensory cortex.
  • Sensory information in the thalamus has a very specific somatosensory map in which the fist is adjacent to the mouth.
    • Small ventroposterior strokes in the lateral portion of the ventroposteromedial nucleus and medial portion of the ventroposterolateral nucleus result in the characteristic cheiro-oral syndrome in which there is loss of sensation around the mouth and in the fist contralateral to the side of the thalamic infarct.
    • The ventroposterior inferior nucleus is a less commonly discussed nucleus.

The dorsal subgroup

  • The dorsolateral nucleus: communicates with the limbic system (along with the anterior group nuclei).
  • The lateral posterior nucleus, and posteriorly: visual attention.

Clinical Correlation: Dorsal Thalamic Stroke

  • The pulvinar (part of the extrageniculate visual pathway).
    • Important for visual attention.

The intralaminar group

  • Most notably helps form the ascending arousal system for wakefulness.

The midline group nuclei

  • Function in limbic-related processes and have important hippocampal connections.

Metathalamus

Posterior group nuclei

  • Span posteriorly from the caudal pole of the ventroposterior nucleus to the medial geniculate nucleus and they also extend medial to the medial geniculate nucleus.
  • Posterior nuclear group has broad cortical connections: secondary somatosensory cortical projections of the posterior nucleus, which are involved in nociceptive sensory processing.

Thalamic reticular nucleus

Advanced Thalamic Anatomy

  • The anterior nuclear group comprises the principal anterior and anterodorsal nuclei.
  • In nonhuman species, the principal anterior nucleus is subdivided into the anteromedial and anteroventral nuclei.
  • The posterior nuclear group comprises the posterior, limitans, and suprageniculate nuclei.
  • The intralaminar nuclei divide into caudal and rostral subgroups and has diffuse connections, including projections to other thalamic nuclei, notably the ventroanterior and ventrolateral nuclei, the basal ganglia, cortical and subcortical areas, and helps form the ascending arousal system.
    • The caudal subgroup is the most notable; it comprises the centromedian and parafascicular nuclei.
    • The rostral subgroup comprises a cluster of closely related nuclei: the central medial, paracentral, and central lateral nuclei.
  • The midline nuclear group, by at least one definition, comprises the rhomboid, parataenial, paraventricular, and reuniens nuclei — the reuniens nucleus lies immediately ventral to the interthalamic adhesion.

Divides into dorsal and ventral subgroups.

  • The ventroanterior nucleus connects with the basal ganglia but there is tremendous inconsistency in the literature about ventroanterior nuclear afferent and efferent projections – texts variably state that the ventroanterior nucleus projects to primary motor cortex as well as premotor cortex or simply the premotor cortex and variably state whether its afferent fibers are primarily from the basal ganglia or cerebellum.

USMLE HIGHLIGHTS

The anterior thalamic group

  • Lies within this bifurcation and communicates with the limbic system (in particular with the mammillary bodies and cingulate gyrus as part of the Papez circuit).

The lateral group nuclei

  • The ventroanterior nucleus connects with the basal ganglia.
  • The ventrolateral nucleus connects with the cerebellum, red nucleus, and, to a lesser extent, the basal ganglia.
  • The ventroposterior nucleus further divides into medial and lateral nuclei, both of which receive sensory afferents (medial from the face, lateral from the body) and project them to the somatosensory cortex.
  • Sensory information in the thalamus has a very specific somatosensory map in which the fist is adjacent to the mouth.
    • Small ventroposterior strokes in the lateral portion of the ventroposteromedial nucleus and medial portion of the ventroposterolateral nucleus result in the characteristic cheiro-oral syndrome in which there is loss of sensation around the mouth and in the fist contralateral to the side of the thalamic infarct.
    • The ventroposterior inferior nucleus is a less commonly discussed nucleus.

The dorsal subgroup

  • The pulvinar (part of the extrageniculate visual pathway).
    • Important for visual attention.

Metathalamus