Positional nystagmus of central type and its neural mechanism. 
Observations of Hallpike (1967) suggested that the neural mechanism responsible for positional nystagmus of central type, the direction-changing type of Nylén, was dependent upon derangement of compensatory eye reflexes subserved by neck proprioceptors and/or otolith organs in the presence of damage to the medial vestibular nuclei.  Clinical studies together with autopsy evidence have demonstrated that this phenomenon may present in the absence of otolith function thus confirming Hallpike's thesis that positional nystagmus of central type may well depend on an abnormal neck reflex.