Keiichi Murata

Characteristics of electrically induced otoacoustic emission

Acoustic emissions were detected using the fast Fourier analysis of sounds in an ear canal during injection of alternating currents at different frequencies into the scala media of guinea pigs anaesthetized with urethane (1.2 g/kg i.p.). The amplitude of the distortion products relative to the fundamentals in the emitted sound was about ten times as large as that in the cochlear current, which was already slightly distorted, probably due to nonlinearity at the metal electrode surface. This discrepancy implies a larger additional nonlinearity in the cochlea. During COCB stimulation or after moderately intense sound exposure, the emitted distortion products were suppressed reversibly, in contrast to almost no change in the fundamental emissions. All the emissions were suppressed reversibly after temporary anoxia or furosemide administration, and they disappeared completely after severe acoustic trauma or death. These results suggest that the normal metabolic activity of the cochlea is required for generatio...

Tonotopic representation of the auditory cortex of the rat

Representation of the best frequencies (BFs) was studied by a tungsten microelectrode method in the auditory cortex of Wistar‐strain rats (200–350 g) anesthetized with Nembutal (40 mg/kg of initial and 5 mg/kg/h of supplement doses). BFs of 0.5–63 kHz were represented in the auditory cortex concentrically, with high BFs in the center and low BFs in the periphery. From the tonotopic representation, this area can be separated into two areas: the primary auditory area (AI) (posterior half), and the anterior area (A) (anterior half). However, the response latency distributions in these areas (6–14 ms were not significantly different. Other smaller areas with concentrations of high BFs were located anteroventrally (AV) and posterodorsally (PD) to the main area (AI and A). The response latencies of the neurons in AV and PD (12–24 ms) were significantly longer than those in the main area. Sixty‐seven percent of the 33 tuning curves obtained from the neurons in the main area were closed (showing nonmonotonic inte...