The head thrust test is primarily
based on the fact that inhibition of
primary and secondary vestibular
neurons cannot produce fewer
than 0 spikes per second.
Excitation can drive the discharge
rate from 90 to 300 or more spikes
per second. So when the healthy
side is excited for a high acceleration
head movement, the healthy
side will generate the larger part
of the VOR, since the disinhibition
of the ipsilateral type-1 neurons
by the contralateral SCC contributes
relatively little to the
VOR. Passive head impulses or
thrusts should be typically rapid
but with a small amplitude
(± 20 degrees).