INTRODUCTION:
We have previously shown that bone-conducted vibration to each mastoid in
humans results in small stimulus-locked horizontal and vertical eye
movements suggesting that the ipsilateral superior oblique and the
contralateral inferior rectus are activated. However, as torsional responses
were not measured we have repeated the study by measuring torsional as well
as horizontal and vertical responses in seven adult subjects during
different directions of gaze.
METHODS:
We measured stimulus-locked horizontal (H), vertical (V) and torsional (T)
eye movements during brief stimulation to the mastoid unilaterally and
bilaterally using a high-speed, high-resolution video technique.
Bone-conducted vibrations were delivered to each mastoid separately as well
as bilaterally using a Radioear B71 bone oscillator while the subjects
viewed targets 2 metres away situated straight ahead and 10° to the
right and left.
RESULTS:
For unilateral stimulation the eyes moved downwards when directed away from
the stimulated mastoid, along with bilateral counter-rolling away from the
side of stimulation. Horizontal movements were small, with little effect of
gaze position. Bilateral stimulation enhanced the downward responses.
CONCLUSIONS:
Bone conducted vibration to the mastoid in humans produces vertical and
torsional eye movements consistent with activation of the ipsilateral
superior oblique muscle, and the contralateral inferior oblique muscle to
produce counter rolling of the eyes away from the stimulated mastoid.
