Feasibility and reliability of intraorally evoked “nociceptive-specific” blink reflexes

Abstract

The "nociceptive-specific" blink reflex (nBR) evoked by extraoral stimulation has been used to assess trigeminal nociceptive processing in patients with trigeminal nerve damage regardless of the site of damage. This study aimed to: test the feasibility of nBR elicited by intraoral stimulation, compare intraoral and extraoral nBR, and assess the intrarater and interrater reliability of the intraoral nBR for the maxillary (V2) and mandibular (V3) branches of the trigeminal nerve. Materials and methods: In 17 healthy participants, nBR was elicited by stimulation of two extraoral and two intraoral sites by two operators and repeated intraorally by one operator. Main outcome variables were intraoral stimulus-evoked pain scores and nBR R2 responses at different stimulus intensities. Intraclass correlation coefficients (ICC) were used to assess reliability. Results: Dependent on the stimulus intensity, intraoral stimulation evoked R2 responses in up to 12/17 (70.6%) participants for V2 and up to 8/17 (47.1%) participants for V3. Pain scores (p<0.003) and R2 responses (p<0.004) increased with increasing intensities for V2, but not V3. The R2 responses were significantly smaller with intraoral stimulation compared to extraoral stimulation (p<0.014). Overall, ICCs were fair to excellent for V2 but poor for V3. Conclusion: Intraorally-evoked nBR was feasible in a subset of healthy participants and was less responsive than nBR with extraoral stimulation. The V2 nBR showed better reliability than V3.

Cerebellar somatotopy of the trigemino‐cervical complex during nociception

“…We also note, that we cannot rule out that our stimulations may have initiated a blink reflex, which could have had an effect on cerebellar activation (Upton & Cooper, 1976). However, since the blink reflex, as a defensive reflex, is generally triggered in pain also of the mental branch of the trigeminal nerve (Jääskeläinen & Peltola, 1994), intraoral (Pillai et al., 2020) and ear (tragus) stimulation (Weise et al., 2019), occipital stimulation (Busch et al., 2006) and even nociceptive input at the limbs (Coppola et al., 2007; Sambo et al., 2012), we do not suggest that eliciting this reflex would have influenced our results significantly. Furthermore, our results do not include the deep cerebellar nuclei, which are important for the output of the cerebellum, as due to their high iron content these structures are hardly visible using fMRI and would need higher field strength of the scanner as well as optimized fMRI protocols for reliable measurements (Küper et al., 2012).…”