A Cortical Test of Auditory Function in Experimentally Deafened Cats

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Abstract
The correlation between behavioral audiograms and recordings of cortical potentials in experimentally deafened cats was studied. Curves expressing threshold elevation with respect to normal animals were prepared for both the behavioral and cortical responses. These were proportioned in accordance with an anatomical frequency scale and displayed above charts of cochlear histopathology. A mean value of 3 db greater loss for the behav-ioral test was obtained when the differences between correspond-ing pairs of behavioral and cortical threshold elevations at all frequencies in all animals were averaged algebraically. Hypotheses advanced to explain the discrepancies include the effects of: (1) uncontrolled physiological variance in the cortical recording procedure; (2) the fact that the absolute cortical threshold exceeds the absolute behavioral threshold by 30-40 db; (3) the use of an abrupt onset for the cortical tone pulse. The cortical test is the most practical and descriptive electrophysio-logical indicator of threshold cochlear function presently available, although it cannot be considered a precise substitute for behavioral threshold detns.