Thalamus

Anatomy

• The largest part of the diencephalon; two egg-shaped masses forming the lateral walls of the third ventricle, joined by the interthalamic adhesion.
• Anterior, medial and lateral groups divided by the internal medullary lamina.
• Nuclei: VPL/VPM (somatosensory), LGN (vision), MGN (hearing), VA/VL (motor), mediodorsal (PFC), anterior (limbic), pulvinar (visual attention), reticular (GABAergic gate), intralaminar (arousal).
• Blood supply: PCA (thalamoperforating and thalamogeniculate arteries), posterior communicating and anterior choroidal arteries.

Substructures

7 substructures; each has its own page.

• Anterior Nuclear Group ANThe thalamic station of the Papez circuit: relays information from the mammillary body to the cingulate cortex, supporting episodic memory and…
• Mediodorsal Nucleus MDThe thalamic partner of the prefrontal cortex: carries out working memory, decision-making and reward learning together with prefrontal circuits.
• Ventral Anterior Nucleus VAA motor planning station that relays basal ganglia output to premotor and prefrontal cortex.
• Ventral Lateral Group (Dorsal Part) VLdThe dorsal part of the ventral lateral region: the area holding the relay nuclei that pass cerebellar and basal ganglia input to motor cortex.
• Ventral Lateral Group (Ventral Part) VLvThe ventral part of the ventral lateral region: an area next to the motor and sensory relay nuclei, reciprocally connected with the cortex.
• Central Lateral – Lateral Posterior – Medial Pulvinar CL-LP-MPuA group containing the arousal-related intralaminar central lateral nucleus and the lateral posterior and medial pulvinar nuclei linked to…
• Pulvinar PulThe largest thalamic nucleus: regulates visual attention, salience and communication between cortical areas.

Functions

• Relay and filtering of sensory information to the cortex (except smell).
• Sleep–wake and level of consciousness; thalamocortical rhythms and sleep spindles (reticular nucleus).
• Attention: the pulvinar and the reticular “gate” mechanism.
• Relaying basal ganglia and cerebellar output to motor cortex (VA/VL).
• Working memory and executive function (mediodorsal–PFC); memory (anterior nucleus — Papez).

Connections and chemistry

• The whole cortex (thalamocortical and corticothalamic projections)
• Basal ganglia (GPi → VA/VL)
• Cerebellum (dentate → VL)
• Hippocampus and mammillary body (anterior nucleus)
• Glutamate (projection), GABA (reticular), acetylcholine and noradrenaline inputs

Development

Developmental course through childhood and adolescence.

• Thalamocortical axons guide the mapping of cortical areas in the fetal period.
• Sleep spindles appear in infancy (~2–3 months); thalamocortical connections mature through childhood.
• Reduced thalamic volume and connectivity after preterm birth.

Clinical

• Childhood absence epilepsy: a disorder of thalamocortical rhythm; T-type calcium channels are the target of ethosuximide. Ethosuximide and valproate are more effective than lamotrigine; because valproate causes attention problems more often, ethosuximide is the first choice (Glauser et al., 2010). A
• Schizophrenia: reduced thalamic volume and PFC–thalamus connectivity (also in early-onset cases). In adult studies, sleep spindles (12–16 Hz NREM oscillations generated by the thalamic reticular nucleus) are markedly reduced; the finding is stable across the night, not due to antipsychotics and related to cognitive performance (Ferrarelli et al., 2007, 2010). A candidate biomarker. B
• Tourette syndrome and OCD: the thalamic link of the CSTC circuit. In ENIGMA-OCD, the thalamus is larger in unmedicated children (d = 0.38), whereas in adults the pallidum is larger and the hippocampus smaller. The biology of child and adult OCD may differ (Boedhoe et al., 2017). A
• Differences in sensory gating in ASD and schizophrenia.

Treatment

This region from the perspective of medication, psychotherapy and neuromodulation. Letter badges are evidence levels.

• Absence epilepsy: start with ethosuximide; freedom from treatment failure at 16 weeks was 53% with ethosuximide, 58% with valproate and 29% with lamotrigine; attention problems in 49% with valproate vs 33% with ethosuximide (Glauser et al., 2010; 453 children). Ethosuximide is not enough if generalized tonic-clonic seizures are also present. A
• Deep brain stimulation in Tourette syndrome: in an international registry (185 patients, 31 centers) the most frequent target was the centromedian thalamus; at 12 months motor tics fell by about 38% and vocal tics by 43%; stimulation-related speech disturbance and paresthesia are common but reversible (Martinez-Ramirez et al., 2018). Only in refractory, severe cases. C
• Deep brain stimulation and focused ultrasound of the thalamic VIM nucleus in essential tremor (adults). B

Assessment

Neuropsychological tasks and measures that probe this region's function.

• EEG: sleep spindles, 3 Hz spike-and-wave in absence seizures
• Sensory gating: P50 suppression, prepulse inhibition (PPI)
• Attention tests

Lesions and damage

Clinical findings expected with damage or dysfunction.

• Thalamic pain syndrome (Dejerine-Roussy), contralateral sensory loss.
• Thalamic amnesia (anterior/mediodorsal); Wernicke encephalopathy (thiamine deficiency — reported in adolescents with anorexia or after bariatric surgery).
• Bilateral paramedian infarction: hypersomnia, apathy, vertical gaze palsy.

In the model

How this structure is defined in the 3D model, and the data source.

CerebrA thalamus label. When selected, seven nuclear groups divided according to the Najdenovska et al. (2018) atlas appear inside.

References

Full citations for the card; links go to the paper (DOI) or a PubMed search.

1. Glauser TA et al. Ethosuximide, valproic acid, and lamotrigine in childhood absence epilepsy. N Engl J Med 2010;362:790–799. Search PubMed
2. Ferrarelli F et al. Reduced sleep spindle activity in schizophrenia patients. Am J Psychiatry 2007;164(3):483–492. Search PubMed
3. Boedhoe PSW et al. Distinct subcortical volume alterations in pediatric and adult OCD: a worldwide meta- and mega-analysis. Am J Psychiatry 2017. Search PubMed
4. Martinez-Ramirez D et al. Efficacy and safety of deep brain stimulation in Tourette syndrome: the International Tourette Syndrome Deep Brain Stimulation Public Database and Registry. JAMA Neurol 2018;75(3):353–359. Search PubMed