Development of early auditory-evoked responses in the cat

The post-natal development of the auditory-evoked responses to 1- and 4-kHz tone bursts has been studied in the cat with subcutaneous electrodes and signal-averaging techniques. A cochlear microphonic response antedates the earliest appearance of brain stem potentials by 1 or 2 days, and can be recorded in some animals on the first post-natal day with the 4-kHz stimulus. The earliest brain stem response consists of three or four low-voltage waves,which increase to six in the 2nd week. Latency shortening and amplitude growth occur for all waves, but are most pronounced in the later part of the response. The characteristics of the summating potential, and the variable influence of rate effects on wave amplitude are described for the different age-groups.