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ventral posteromedial nucleus

NeuroanatomyNervous systemCentral nervous systemThalamusSomatosensory systemSpecial senses (gustatory)

Summary

The ventral posteromedial (VPM) nucleus is a thalamic relay nucleus that transmits somatosensory information (touch, pain, temperature, proprioception) from the face and oral cavity, as well as taste, to the cerebral cortex. It receives input from the trigeminothalamic tracts (and gustatory fibers from the nucleus solitarius) and projects to the primary somatosensory cortex (postcentral gyrus, face area) and gustatory cortex. Think: VPM = face (“Make Faces”); VPL = body (“Lower body/Limbs”).

Detail

**Location and basics** - Part of the ventral posterior nucleus of the thalamus, along with the ventral posterolateral (VPL) nucleus. It is a specific (relay) nucleus. - Mnemonic: VPM = face (“M” for “Mouth/Make faces”); VPL = body and limbs (“L” for “Limbs/Lower”).

**Afferent pathways (inputs)** - Trigeminal lemniscus (ventral trigeminothalamic tract): 2nd-order neurons from the principal (chief) sensory nucleus (discriminative touch, vibration, proprioception of the face) and the spinal trigeminal nucleus (pain and temperature of the face). These fibers decussate, then ascend to the contralateral VPM. A smaller dorsal trigeminothalamic tract carries ipsilateral input from the principal sensory nucleus. - Gustatory input: taste from the rostral nucleus solitarius (gustatory nucleus; CN VII, IX, X) reaches the VPM (parvocellular part, VPMpc) ipsilaterally.

**Efferent pathways (outputs)** - Via the posterior limb of the internal capsule to: - The primary somatosensory cortex (S1; Brodmann areas 3, 1, 2), face region of the postcentral gyrus (lateral part of the homunculus). - The gustatory cortex (anterior insula and frontal operculum) for taste.

**Blood supply** - Thalamogeniculate branches of the posterior cerebral artery (PCA). The VPM/VPL region is also supplied by the thalamoperforators.

**Clinical significance** - Lacunar infarct or thalamic stroke (the classic cause is lacunar stroke from hypertension/lipohyalinosis) of the VPM/VPL causes a pure sensory stroke with contralateral loss of sensation in the face, arm, and leg. - Dejerine-Roussy syndrome (thalamic pain syndrome) follows a PCA thalamogeniculate infarct. It causes initial contralateral hemisensory loss, then, weeks to months later, severe, burning, intractable central post-stroke pain with allodynia and hyperpathia. Treat with amitriptyline, gabapentinoids, or lamotrigine. - Trigeminal neuralgia involves CN V and the trigeminal pathways; it is not a VPM lesion, but the VPM is part of the same pathway. - Face-related deficits seen with a lesion anywhere along the trigeminal pathway: - Lateral medullary (Wallenberg) syndrome (PICA): ipsilateral face pain/temperature loss and contralateral body pain/temperature loss, because the spinal trigeminal nucleus/tract is damaged before decussation. - VPM lesion: contralateral face sensory loss, with possible loss of taste.

**High-yield comparisons** - VPL: receives the medial lemniscus (dorsal column pathway) and spinothalamic tract, for body sensation → S1. - VPM: face sensation and taste → S1 (face) and gustatory cortex. - LGN: vision (CN II) → V1. MGN: hearing (inferior colliculus) → A1. - VL: motor input from the cerebellum and basal ganglia → motor cortex. VA: basal ganglia → motor/premotor cortex. - Pulvinar: associative visual functions.

**Quick pathway recap (face pain/temperature)** Free nerve endings of the face → CN V ganglion (trigeminal/Gasserian ganglion, 1st order) → spinal trigeminal nucleus (2nd order; decussates) → VPM of thalamus (3rd order) → posterior limb of the internal capsule → face area of S1.

Sources

  • First Aid for the USMLE Step 1 (Neuroscience: Thalamus)
  • Kaplan USMLE Step 1 Lecture Notes: Neuroscience
  • Pathoma/Sketchy Medical (Neuroanatomy: Thalamic nuclei)
  • Purves D, et al. Neuroscience. Sinauer Associates.
  • Kandel ER, et al. Principles of Neural Science. McGraw-Hill.
  • Costanzo LS. Physiology (Sensory Systems)

Reviewed by Medusa editorial — medical student review. Information here is for study reference only and is not medical advice. Spotted an error? Let us know.