ABSTRACT
The author recounts the process of discovery in Philip Teitelbaum's laboratory, which began with the observation of vestibular head stabilization in a rat with brainstem lesions, of the essential roles of the pontine reticular formation (PRF) in the rat in ipsiversive head as well as eye movements. The PRF in the rat appears to be in the pathways for most direction-changing movements of the eyes and head, leaving vestibular and optokinetic stabilizing movements intact and uninterrupted. The author postulates that a response to the sliding of feet or paws, or a "substrate-kinetic reflex," works together with vestibular and optokinetic reactions to stabilize an animal's directions of gaze and locomotion on the ground. Previously unpublished data are presented from later observations and recordings of rats with kainic acid lesions in the PRF, which support the conclusion that neurons in the PRF are essential for head as well as eye movements in the rat. In contrast, Volker Henn observed no obvious loss of head movements in monkeys that had a loss of fast eye movements from kainic acid lesions of the PRF. The author and others observed that quick phases of head nystagmus develop some time after quick phases of ocular nystagmus in normal human infants; in other words, after the PRF is functioning for eye movements. The author concludes that in primates, the pathway for head movements through the PRF has been replaced by a newer pathway, leaving certain PRF regions to be devoted to mediating only eye movements.
