Olivo-cochlear inhibition during physostigmine-induced activity in the pontine reticular formation in the decerebrate cat

The physiological role of the olivo-cochlear pathway has been questioned recently because this pathway has never been shown to be operative under natural conditions. In this study, cochlear potentials were recorded differentially between a wire electrode placed on the round window and an indifferent electrode attached to the nuchal muscles in decerebrate, decerebellate cats. Physostigmine was used to induce bout of rapid eye movement (REM) sleep. REM bouts were verified by recording burst activity in the brain stem pontine reticular formation and the inhibition of lumbar monosynaptic reflexes. Intravenous physostigmine increased the inhibition of N 1 caused by direct electrical stimulation of the crossed olivo-cochlear bundle in the absence of REM. Olivo-cochlear system inhibition was also recruited during physostigmine-induced REM sleep. It is concluded that the brain stem reticular formation can activate the olivo-cochlear bundle and can thereby produce inhibition in the cochlea.