Eye movement related neurons in the cat pontine reticular formation: projection to the flocculus

This study examines projection to the cerebellar flocculus of eye movement-related neurons in the median and paramedian part of the cat pontine tegmentum between the trochlear and the abducens nucleus. They were identified by rhythmic activity related to horizontal vestibular nystagmus induced by sinusoidal rotation. These neurons were classified into several groups by their discharge patterns during nystagmus, using criteria of earlier studies on saccadic eye movements and vestibular nystagmus in the monkey. Electrical stimulation of the ipsilateral flocculus elicited antidromic spike responses in a number of burst-tonic neurons and long-lead and medium-lead burst neurons. These neurons were located in and around the medial longitudinal fasciculus, the nucleus raphe pontis and the nucleus reticularis tegmenti pontis. A few neurons tested were also activated antidromically by stimulation of the contralateral flocculus. In contrast, no pauser neurons were activated from the ipsilateral flocculus. It is concluded that eye movement-related neurons in the medial pontine tegmentum, except for pauser neurons, directly project to the flocculus and may convey information about eye movements of visual and vestibular origins to the flocculus.