Acoustically Evoked Vestibular-Related Cortical Potentials

Introduction: The vestibular cortical areae have been under close anatomical and functional imaging scrutiny. fMRI and PET studies found vestibular-related activation on the posterior and fronto-insular margin, in particular PIVC, 3a and 2v. However, the timing of these activations following vestibular stimulation is not known. Loud acoustic stimuli around 500Hz excite the saccular sensory epithelium, resulting in ipsilateral neck muscle activation by the vestibular nuclei and its descending tracts (Vestibular-evoked myogenic potentials VEMP). This study explored centrally ascending information associated with these vestibular stimuli in comparison to acoustic stimuli known not to excite vestibular receptors (3000Hz).

Methods: 14 healthy right-handed subjects (Edinburgh handedness ≥80%) known to have bilateral VEMP N13/P24 Amplitudes >100mV at 500Hz/127dB(A)SPL and none at 3000Hz/118dB(A)SPL were exposed to each 2000 unilateral tone stimuli at 500 and 3000Hz on both ears separately in a random order with 400ms interstimulus intervals. A EEG DC recording was performed with a 10–20 EasyCap system (5000Hz sampling, 0,1mcV resolution) for post-processing with BrainVision Analyzer and BESA.

Results: Characteristic vestibular-related potentials were observed in all individual subjects, as well as in the grand average. Both 500 and 3000Hz unilateral stimulation resulted in a bilateral stapedius reflex around 18ms post stimulus and a frontal awareness potential around 100–150ms. BESA dipole analysis of 500Hz stimulation revealed a series of characteristic activations in the bilateral frontoinsular and parietoinsular margins between 20 to 140ms with preponderance towards the non-dominant right hemisphere in left-sided stimulation and equilateral activation in right-sided stimulation, in accordance with previous imaging studies. In differenzial analysis between 500Hz stimulation (evoking VEMPS) and 3000Hz (no VEMPS) these dipole activities persisted, whereas the stapedius reflex and frontal awareness potentials were largely cancelled out.

Discussion: Results indicate that specific vestibular-related cortical potentials can be evoked by acoustic VEMP stimulation as early as 20ms in vestibular-related regions, according to anatomical and functional imaging studies. Future studies using this paradigm will investigate amplitude and timing changes in specific vestibular pathologies.