Genetic influences on binaural summation and recovery rate of the brainstem auditory evoked response

C57BL/6 and CBA/J inbred strains of mice, from 20 to 385 days of age, were exposed to 65 dB acoustic clicks at rates of 10, 20, 40 and 80 per second. For both genotypes, increasing the stimulus repetition rate increased latencies by 66, 141, 163, 188, and 356 mu sec for PI-V of the BSER, respectively. For the CBA/J mouse, there was a concurrent decline of all BSER amplitudes by approximately 45%. The C57BL/6 mouse showed this same 45% decline for PI, PII and PIV, although its PIII and PV amplitudes only declined by 25% as the repetition rate increased. Age had no observable influence on these variables. When binaural and monaural responses were compared, all ages and genotypes showed the same effect. For PI-III, binaural stimulation produced the same effect as did summing the responses obtained by monaurally stimulating the two ears. For PIV and PV, however, binaural stimulation reduced the amplitudes by 25 and 71%, respectively. These results were compared with data obtained from the cat and human. Although the rate-dependent BSER changes varied as a function of genotype, no genetic differences were observed in the binaural interactive effect, in spite of large differences of hearing ability in these inbred strains of mice.