Operational unit responsible for plane-specific control of eye movement by cerebellar flocculus in cat

Abstract

1. Main findings in our previous studies are as follows: 1) there are three Purkinje cell zones running perpendicular to the long axis of the folia in the cat flocculus, 2) the caudal zone controls activity of the superior rectus (SR) and inferior oblique (IO) extraocular muscles via the y-group and oculomotor nucleus (OMN) neurons, and 3) the middle zone controls activity of the lateral (LR) and medial rectus (MR) muscles via the medial vestibular (MV) and abducens nucleus (ABN) neurons. In the present study, the neuronal pathways from the remaining rostral zone were investigated in the anesthetized cat. 2. Target neurons of rostral zone inhibition in the superior vestibular nucleus (SV) were identified by observing cessation of spontaneous discharges after rostral zone stimulation. Efferent projections were studied by the use of systematic microstimulation techniques. Unitary responses to stimulation of the eighth nerves were also investigated. 3. There are two types of the target neurons: 1) those, being located in the central and dorsal parts of the SV, project to the trochlear and oculomotor nuclei innervating superior oblique and inferior rectus muscles via the ipsilateral medial longitudinal fasciculus (MLF); and 2) those, being located along the dorsal border of the SV, project to the contralateral oculomotor nucleus innervating superior rectus and inferior oblique muscles via the extra-MLF route. 4. Both types receive monosynaptic anterior canal nerve input but not posterior canal nerve input. Some neurons receive polysynaptic excitatory input from the contralateral eighth nerve, although commissural inhibition was never observed. 5. From neuronal connections of the rostral and caudal zones and action of the extraocular muscles, it was expected that 1) activity changes of Purkinje cells in the rostral and/or caudal zones on one side resulted in conjugate eye movement in the plane of the anterior canal on the side of the activity changes, 2) cooperative increased activity on both sides resulted in conjugate downward eye movement, and 3) increased activity on one side and decreased activity on the other side resulted in conjugate rotatory eye movement. The rostral and caudal zones may be responsible for eye-movement control in the sagittal plane by cooperative activity changes on both sides and in the transverse plane by reciprocal activity changes on both sides. For eye-movement control in the anterior canal plane, Purkinje cell activity on one side would be sufficient to produce the required movement. In a functional sense, we call the rostral and caudal zones, the vertical-plane zones.(ABSTRACT TRUNCATED AT 400 WORDS)

Further evidence for selective difficulty of upward eye pursuit in juvenile monkeys: effects of optokinetic stimulation, static roll tilt, and active head movements

“…Similar mechanisms may also be involved in the directional asymmetry during head-free upward pursuit in this study (Table 2A). Asymmetry in floccular inhibition of VOR relay neurons is well known in rabbits and cats (Ito et al 1977;Hirai and Uchino 1984;Sato and Kawasaki 1990). Asymmetry in low frequency responses of anterior and posterior canal vestibulo-ocular neurons in the vestibular nuclei was also reported in alert cats when the animals were rotated on their side (Brettler and Baker 2003).…”

Head-Shaking Aids in the Diagnosis of Acute Audiovestibular Loss due to Anterior Inferior Cerebellar Artery Infarction

“…3 c), supplied by the AICA in most patients [Amarenco and Hauw, 1990;Amarenco et al, 1993]. The flocculus is known to send its inhibitory fibers to the central vestibulo-ocular reflex pathway from the anterior semicircular canal but not from the posterior canal [Ito et al, 1977;Sato and Kawasaki, 1990;Zhang et al, 1995]. Thus, damage to the flocculus or its output tract might disinhibit the anterior canal projections, causing upward drift of the eyes and downbeat nystagmus.…”

“…Instead, the flocculus, typically irrigated by AICA, may be a neural substrate for HSN in patients with AICA infarction. The flocculus is known to inhibit the central vestibulo-ocular reflex pathways from the horizontal canal, and the inhibition is more for those from the ipsilateral canal [Ito et al, 1977;Sato and Kawasaki, 1990;Zhang et al, 1995]. The inhibitory fibers project primarily to the rostral part of the vestibular complex [Langer et al, 1985;Nagao et al, 1997].…”

Gaze-Evoked and Perverted Head-Shaking Nystagmus in a Patient with Polycythemia Vera

“…The flocculus and paraflocculus are also possible neural substrates for perverted head-shaking nystagmus. The flocculus and paraflocculus are known to send their inhibitory fibres to the floccular target neurons in the anterior canal vestibulo-ocular reflex pathway, with less involvement of the posterior canal vestibulo-ocular reflex pathway (Ito et al, 1977;Sato and Kawasaki, 1990;Zhang et al, 1995). Thus, lesions involving the flocculus/paraflocculus could disinhibit anterior canal projections and cause upward drift of the eyes.…”