Bilateral recording of early auditory evoked responses in the cat.

The brain-stem electric responses of the cat evoked by a short 4 kHz tone burst have been differentially recorded between vertex and both ipsilateral and contralateral ear electrodes. Six vertex-positive waves can be recognised in both recordings. Animals with hereditary unilateral anacusis were studied in order to avoid cross-stimulation of the opposite ear. The cochlear microphonic and summating potential can be readily recorded in young animals, occur simultaneously in both tracings, and show polarity inversion at the contralateral electrode. The later neural potentials have the same polarity and practically identical latencies in the ipsilateral and contralateral recordings, whilst the first three brain-stem waves show approximate polarity inversion and variable latency relationships in the two recording situations. It is concluded that none of the brain-stem waves represents electric activity from a discrete generator.