C. Siebold et al., ROSTRAL FASTIGIAL NUCLEUS ACTIVITY IN THE ALERT MONKEY DURING 3-DIMENSIONAL PASSIVE HEAD MOVEMENTS, Journal of neurophysiology, 77(3), 1997, pp. 1432-1446
The fastigial nucleus (FN) receives vestibular information predominant
ly from Purkinje cells of the vermis. FN in the monkey can be divided
in a rostral part, related to spinal mechanisms, and a caudal part wit
h oculomotor functions. To understand the role of EN during movements
in space, single-unit activity in alert monkeys was recorded during pa
ssive three-dimensional head movements from rostral FN. Seated monkeys
were rotated sinusoidally around a horizontal earth-fixed axis (verti
cal stimulation) at different orientations 15 degrees apart (including
roll, pitch, vertical canal plane and intermediate planes). In additi
on, sinusoidal rotations around an earth-vertical axis (yaw stimulus)
included different roll and pitch positions (+/-10 degrees, +/-20 degr
ees). The latter positions were also used for static stimulation. One
hundred fifty-eight neurons in two monkeys were modulated during the s
inusoidal vertical search stimulation. The vast majority showed a unif
orm response pattern: a maximum at a specific head orientation (respon
se vector orientation) and a null response 90 degrees apart. Detailed
analysis was obtained from 111 neurons. On the basis of their phase re
lation during dynamic stimulation and their response to static tilt, t
hese neurons were classified as vertical semicircular canal related (n
= 79, 71.2%) or otolith related (n = 25; 22.5%). Only seven neurons d
id not follow the usual response pattern and were classified as comple
x neurons. For the vertical canal-related neurons (n = 79) all eight m
ajor response vector orientations (ipsilateral or contralateral anteri
or canal, posterior canal, roll, and nose-down and nose-up pitch) were
found in FN on one side. Neurons with ipsilateral orientations were m
ore numerous and on average more sensitive than those with contralater
al orientations. Twenty-eight percent of the vertical canal-related ne
urons also responded to horizontal canal stimulation. None of the vert
ical canal-related neurons responded to static tilt. Otolith-related n
eurons (n = 25) had a phase relation close to head position and were c
onsiderably less numerous than canal-related neurons. Except for pitch
, all other response vector orientations were found. Seventy percent o
f these neurons responding during dynamic stimulation also responded d
uring static tilt. The sensitivity during dynamic stimulation was alwa
ys higher than during static stimulation. Sixty-one percent of the oto
lith-related neurons responded also to horizontal canal stimulation. T
hese results show that in FN, robust vestibular signals are abundant.
Canal-related responses art much more common than otolith-related resp
onses. Although for many canal neurons the responses can be related to
single canal planes, convergence between vertical canals but also wit
h horizontal canals is common.