Comparison of Cochlear Microphonics Magnitude with Broad and Narrow Band Stimuli in Healthy Adult Wistar Rats

OBJECTIVE: Cochlear microphonic (CM) is a cochlear AC electric field, recorded within, around, and remote from its sources. Nowadays it can contribute to the differential diagnosis of different auditory pathologies such as auditory neuropathy spectrum disorder (ANSD). This study compared CM waveforms (CMWs) and amplitudes with broad and narrow band stimuli in 25 healthy male young adults Wistar rats. MATERIALS & METHODS: This experimental study was accomplished in the School of Rehabilitation Sciences of Iran University of Medical Sciences, Tehran, Iran (April, 2016). Using an extratympanic technique in ECochG (Electrocochleography) recording, CMWs in response to click and tonal stimuli with different octave frequencies were recorded at a high intensity level in subjects. The CMW amplitudes were calculated by a graphical user interface (GUI) designed in MATLAB. RESULTS: The CMW magnitude increased upon an increase in bandwidth stimulation. CM amplitude with click stimulation was larger than tonal stimuli. Across tonal stimuli, the CMW amplitudes at lower frequency tones were larger than those at higher frequency tones. Those findings were statistically significant (P<0.001). CONCLUSION: CMW amplitude with click as broadband stimulus was larger than those with tone bursts as narrowband stimulation. Click stimulation due to the width of spectral involves greater regions of cochlear partition. Therefore, CMW most likely is a reflection of spatial summation of voltage drops generated by hair cell groups in response to acoustic stimulation. In order to production nature of CM potentials as well as their very small magnitudes especially with tonal stimuli, thus, we recommend using click stimulation for CM potential recording.