FIGURE 5.

(A) Irregular otolithic primary afferents are evoked by air conducted clicks at very short latencies (from Murofushi et al., 1995). Three examples of air conducted click-evoked action potentials (identified by inverted triangles) in three primary otolithic neurons. Superimposed recordings of responses to 5–10 clicks. Latencies from the onset of the click to the foot of the action potential were 0.5 ms (a,c) and 1.0 ms (b). b and c show responses at threshold-straddling intensities, so the action potential is not evoked on every presentation. Note that these action potentials (a, c) occur at such short latencies they precede the N1 wave of the acoustically evoked cochlear action potential (arrows). Time scales 1 ms. Reproduced from Murofushi et al. (1995) with Permission of Springer (B) Examples of sensitivity plots of neurons to BCV showing the high sensitivity of irregular neurons to increasing BCV stimulus strength as opposed to regular afferents. Each point shows the increase in firing rate as the percentage of baseline firing rate during a single stimulus presentation. Each line is the best fit calculation of the responses for one neuron (triangles - otolith neurons, circles-semicircular canal neurons; irregular afferents are blue and regular afferents are orange. The stimulus intensity is calculated in g, and is the root mean square of three axes as recorded by the skull-mounted triaxial accelerometer. Canal neurons and regular otolithic afferents are not activated by high stimulus levels. In contrast irregular otolithic afferents are activated at very low intensities and have a very steep increase in firing as intensity is increased. (C) Average sensitivities for neurons to BCV. The slopes of the best fitting lines in (B) are averaged for each class of neuron, and the average slope and 95% confidence intervals. The unit of sensitivity in this plot is per cent increase in firing rate per g above the resting discharge rate. The high sensitivity of otolith irregular neurons and the absence of response of otolith regular and semicircular canal neurons is clear. Reproduced from Curthoys and Vulovic (2011) with permission of Springer.