A fiber tract model of auditory brain-stem responses

The hypothesis that auditory brain-stem responses (ABRs) are generated by action potentials in fiber tracts was tested by recording from frog sciatic nerves in a volume conductor. Far-field recording of the sciatic nerve action potentials confirmed the rule that the initial response of the electrode toward which the action potentials are traveling is positive with respect to the electrode from which they are retreating. This rule explained the initial polarity of response for transverse and longitudinal recordings in humans, and why right and left ear clicks evoke responses of opposite polarity for transverse recording, but the same polarity for longitudinal recording. This result was true for all of the waves evoked, up to 8 msec latency. A later myogenic potential known as the postauricular response did not invert with the ear stimulated. The possibility of a dendritic contribution to the ABR was discussed. It was concluded that the components of the ABR are more satisfactorily explained by action potentials than by somatic or dendritic synaptic activity.