Functional brainstem somatotopy of the trigeminal nerve during nociception

Results from a German functional imaging study in humans support the theory of a somatotopic arrangement next to the rostrocaudal axis within the brainstem with an onion-shaped pattern for stimulus sites on the face [1].

The trigeminal nerve plays a crucial role in the pathogenesis of primary headache disorders, such as migraine and cluster headache. The peripheral aspect of the trigeminal nerve distributes in 3 branches that innervate U-shaped dermatomes in the face. These branches enter the brainstem in somatotopic order: fibres from the ophthalmic branch (V1) enter the brainstem ventrally, fibres from the mandibular branch (V3) enter dorsally, and fibres from the maxillary branch (V2) enter between V1 and V2.

Besides these peripheral dermatomes, animal studies suggest an alternative dermatome in the central presentation of the spinal trigeminal nucleus [2]. Here, there is a so-called ‘onion-shaped pattern’ with fibres of the perioral regions represented more rostrally and those of the periauricular regions more caudally. Dr Lisa-Marie Sturm (University Clinic Hamburg Eppendorf, Germany) and colleagues investigated the somatotopic organisation of the trigeminal nerve within the brainstem in humans (NTC03999060) [1].

A 3-Tesla functional MRI study was conducted in 26 healthy volunteers. In total, 4 areas on the left hemiface were targeted using nociceptive electrical stimulation. Stimulated areas were chosen based on their representation within the brainstem, aimed to ensure adequate spatial resolution between the areas in the spinal trigeminal nucleus. A distinct blood-oxygen-level-dependent (BOLD) signal was found in the spinal trigeminal nucleus for each stimulus site on the face.

“There is a certain somatotopy of trigeminal afferent fibres in the spinal trigeminal nucleus,” Dr Sturm concluded. “The current assumption for an onion-ring model for nociceptive input of the trigeminal nerve is presumably also present in humans.”

1. Sturm ML. Trigeminal nerve: functional brainstem somatotopy during nociception. AL061, IHC 2021, 8–12 September.
2. Pfaller K, Arvidsson J. J Comp Neurol. 1988;268(1):91–108.

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Posted on 8 November 2021