Auditory brain stem responses to monoaural stimulation registered in symmetrical areas of cat's brain cortex.

In five anaesthetized cats (Nembutal 35 mg/kg) with 14 chronically implanted recording epidural electrodes the auditory brain stem responses (ABR) to monoaural stimulation (click) in symmetrical areas of the brain cortex were recorded. Each ABR to acoustic stimulus of sufficient intensity is formed by a complex of alternating five positive (P1-P5) and four negative (N1-N4) peaks; two further small peaks often follow on this complex. The amplitude of ABR peaks N3, P4, N4 and P5 to monoaural stimulation in symmetrical areas of cat's cortex was always higher in records from the hemisphere contralateral to the stimulated ear than in records from the ipsilateral one. The amplitude of P3 ABR peak behaved to the contrary--it was higher on ipsilateral hemisphere. On the other hand the amplitude of ABR peaks P1, N1, P2 and N2 to monoaural stimulation in symmetrical areas of the brain cortex showed no degree of lateralization in our experimental animals. The present findings support indirectly the presumption that each peak of the ABR is generated by a particular acoustic brain stem structure.