THRESHOLDS OF INTRACRANIALLY RECORDED AUDITORY FIELD POTENTIALS IN THE PIGEON COMPARED WITH COMPOUND ACTION-POTENTIAL THRESHOLDS

The compound action potential (CAP) thresholds provide a reliable indi cator for cochlear functional integrity during experimentation in bird s as well as in mammals, However, if experimental manipulations are ne cessary in the middle ear/inner ear spaces, the round window electrode s are often inconvenient, In search for an alternative for CAP recordi ngs, intracranial recordings of acoustically evoked field potentials f rom the nucleus angularis/magnocellularis were made in pigeons using s tereotactically placed electrodes, The responses were compared with th ose recorded from intracranial surface electrodes placed on the dura m ater and compared with CAP responses recorded from the round window, T he field potentials recorded from the nucleus angularis/magnocellulari s contain a significant contribution from the auditory nerve, as large in amplitude as the CAP recorded at the round window, The recordings from the intracranial surface electrodes were noisier and the contribu tion from the auditory nerve was too small to be used as a fast monito r of the condition of the inner ear, Threshold curves as a function of frequency could be determined with an automated method from the nucle us angularis/magnocellularis with the same sensitivity and accuracy as from the round window CAP within a few minutes, These results demonst rate that stereotactic recordings of field potentials from the nucleus magnocellularis/angularis region are a suitable alternative to reliab ly monitor the condition of the inner ear when round window electrodes cannot be used.