Fig. 1. Time-series showing the raw action potentials recorded extracellularly from a single irregularly firing primary vestibular neuron (CV = 0.37) responsive to pitch-dynamic head rotation. Spikes discharged are shown before, during, and following 5 s pulses of cathodal (−60 μA) and anodal (+60 μA) constant-current galvanic stimulation delivered through an electrode implanted in the tensor tympani of the middle ear. Top panel exemplifies the irregularity of discharge over a reduced time scale covering 200 ms.

Fig. 2. Mean and 95% confidence intervals for changes in firing rate of irregularly (CV* > 0.1) and regularly (CV* < 0.1) discharging primary vestibular afferents induced during 60 μA anodal (darker bars) and cathodal (lighter bars) galvanic vestibular stimulation. Changes in neural firing rate to anodal stimulation are decreases in firing rate, whereas changes in neural firing rate to cathodal stimulation are increases in firing rate.

Fig. 3. Mean and 95% confidence intervals for normalised galvanic sensitivity () of irregularly discharging (CV* > 0.1; filled points) and regularly discharging (CV* < 0.1; hollow points) primary vestibular afferents to pulses of unilateral cathodal surface mastoidal GVS (620 μA SS) and tensor-tympanic GVS (TT) at 20, 40, and 60 μA intensities.

Fig. 4. Relationship between normalised gain for galvanic stimulation () and normalised coefficient of variation (CV*) for primary vestibular afferents tuned for dynamic head rotation ((A) canal) and static head tilts ((B) otolith). Among the dynamically activated neurons, white squares and solid line indicate tuning for yaw head rotation (YD); dark triangles and dashed line indicate tuning for pitch head rotation (PD); and white triangles and dotted line indicate tuning for roll head rotation (RD). Among the statically activated neurons, white circles and solid line indicate tuning for pitch head tilt (PS); dark circles and dashed line indicate tuning for roll head tilt (PD); stars and dotted line indicate tuning for pitch and roll head tilt (PRS). The R² values shown were obtained from correlations with CV* for each tuning category.

Fig. 5. Mean and 95% confidence intervals of normalised galvanic sensitivities of irregularly (solid points) and regularly (hollow points) primary vestibular afferents and their tuning for natural vestibular stimulation.

Mean firing rates of primary vestibular afferents with different discharge regularities and their natural tuning for static head tilt or dynamic head rotation