CLICK-EVOKED RESPONSES FROM THE EXPOSED INTRACRANIAL PORTION OF THE 8TH NERVE DURING VESTIBULAR NERVE-SECTION - BIPOLAR AND MONOPOLAR RECORDINGS

We compare the click-evoked compound action potentials from the expose d intracranial portion of the eighth nerve using bipolar and monopolar recording electrodes in patients undergoing vestibular nerve section. It is assumed that a bipolar recording electrode will only record pro pagated neural activity in the auditory nerve, whereas a monopolar rec ording electrode may in addition record electrical activity that is co nducted passively to the recording site. The results of the present st udy confirm that the earliest detectable propagated neural activity in the intracranial portion of the auditory nerve occurs with a latency that is close to that of peak II of the brain-stem auditory evoked pot entials, and the results also confirm that the late components in the click-evoked compound action potentials that have been demonstrated pr eviously using the monopolar recording technique represent propagated neural activity in the auditory nerve. The results also indicate that the responses that are recorded by a bipolar recording electrode, when the small tips of which are placed on the eighth nerve when it is rel atively dry, represent only small populations of nerve fibers. Even wh en an attempt is made to align the two tips of a bipolar electrode wit h the course of the auditory nerve, this type of electrode may record from different populations of nerve fibers.