Acoustically and electrically evoked contralateral suppression of otoacoustic emissions in guinea pigs

It is generally accepted that stimulation of the efferent auditory system r esults in changes of cochlear activity. A simple method of activating the o livocochlear pathway by contralateral electrical stimulation of the round w indow (ES-RW) was used in this study with the aim of comparing the efficacy of acoustically and/or electrically evoked contralateral suppression. The suppression of transient evoked otoacoustic emissions (TEOAEs) and distorti on product otoacoustic emissions (DPOAEs) was elicited by contralateral aco ustic stimulation (AS) (61 dB SPL continuous white noise), and/or by electr ical stimulation of an electrode implanted at the contralateral round windo w (monopolar rectangular pulses 0.1 ms, repetition rate 300 Hz, intensity 5 0-100 mu A) in 12 guinea pigs. The average value of contralateral suppressi on of TEOAEs amounted to 1.04 +/- 0.48 dB for acoustic stimulation and 0.97 +/- 0.53 dB for round window electrical stimulation. The simultaneous pres entation of both acoustic and electrical stimulation had only a slight addi tive effect and resulted in 1.27+/-0.79 dB diminution of TEOAEs. The suppre ssion of DPOAEs during contralateral acoustic and electrical stimulation wa s evident mainly at low and middle frequencies (1-4 kHz). In two guinea pig s the maximum DPOAE suppression was present at high frequencies. The averag e values of contralateral suppression measured at individual f(2) frequenci es of DPOAEs were similar to those calculated from 1/4 octave power spectru m analysis of the TEOAEs in half of the animals. The results demonstrated t hat contralateral ES-RW had a similar suppressive effect on TEOAEs and DPOA Es as did contralateral AS and simultaneous AS+(ES-RW). The results of spec tral analysis suggested that both modes of contralateral stimulation excite d similar sensory cochlear elements and induce comparable suppression of bo th TEOAEs and DPOAEs. (C) 1999 Elsevier Science B.V. All rights reserved.