Comparison of vagus sensory evoked potentials (VSEP) and auditory evoked potentials (AEP) in healthy subjects

Introduction: Measurement of vagus sensory evoked potentials (VSEP) after electric stimulation of the auricular branch of the vagus nerve in the external auditory channel was introduced by Fallgatter et al. (2003). VSEP may have clinical potential as a non-invasive tool for assessment of brainstem function. Here, we examined methodological characteristics of VSEP assessment in relation to auditory evoked potentials (AEP).

Methods: VSEP and AEP were studied in 10 healthy subjects (age 29.7±8.0 (mean±SD, 4 females). Far field potentials were recorded bipolarly from electrodes positioned at F3, F4, T3, T4, O1, O2, A1, A2, Fz and Cz after transcutaneous electric stimulation of the cutaneous representation of the vagus nerve at the inner side of the tragus using silver wires (VSEP) Electric stimulation of the antihelix served as a control condition. AEP were generated by a click stimulus (stimulation duration 0.1ms, frequency 15Hz, intensity 80 dB) via headphones. VSEP were elicited using 2×100 stimuli (stimulation duration 0.2ms, frequency 0.5Hz, intensity 7–8 mA). The following montages were used: F3-Fz, T3-O1, A1-Cz (left vagus nerve and left acoustic stimulation) and F4-Fz, T4-O2, A2-Cz (right vagus nerve and right acoustic stimulation). Peak latencies of early components (P1, N1, P2 (VSEP) and I – V (AEP)) and peak-to-peak amplitudes (P1-N1, N1-P2) were determined.

Results: VSEP were present and reproducible in all subjects. No potential could be elicited after stimulation of the antihelix. Detection of VSEP was easier in the T3-O1/T4-O2 and A1-Cz/A2-Cz condition compared to the F3-Fz/F4-Fz condition proposed previously. VSEP latencies (P1, N1, P2) were similar to the latencies of the AEP components I, II and IV. Interindividual variability of the peak latencies (and amplitudes) was higher in VSEP (A1-Cz/A2-Cz: P1 1.42±0.17ms, N1 2.59±0.30ms, P2 4.91±1.00ms) compared to AEP (A1-Cz/A2: I 1.71±0.14ms, II 2.91±0.14ms, 5.04±0.21ms).

Conclusions: VSEP can be reliably recorded in healthy subjects. However, interindividual variability is higher than AEP. Larger cohorts of healthy subjects have to be assessed in order to obtain stable reference values to assess sensitivity of this method in patients.

References: Fallgatter AJ et al., Far field potentials from the brain stem after transcutaneous vagus nerve stimulation. J Neural Transm. 2003 Dec;110(12):1437–43.