Electrophysiological Studies on the Spatial Distribution of the Crossed Olivocochlear Bundle along the Guinea Pig Cochlea

Abstract

The effectiveness of electrical stimulation of the crossed olivocochlear bundle (COCB) was measured at different locations along the cochlear partition. Differential electrodes were used to sample the cochlear microphonic (CM) at turns I, II, and III. A pipette inserted into scala media in turns I, II, and III was used to measure the slow negative potential associated with electrical stimulation of the COCB. The responses of auditory nerve fibers were sampled within the modiolus and included a wide range of best frequencies. The magnitude of the slow negative potential was maximum in turn I and decreased in turns II and III. The increment in CM, produced by COCB stimulation, depended not only upon the location along the cochlear partition from which it was recorded, but also upon acoustic frequency. For low-frequency acoustic signals (below 700 Hz), the increment in CM was greatest at turn I and decreased toward the apex. At 5 kHz, COCB stimulation produced no detectable increment in CM at turn I. The reduction in discharges of auditory nerve fibers produced by COCB stimulation was greatest (16–20 dB in titration) when best frequency lay between 7 and 10 kHz. As best frequency decreased, the reduction in discharge rate with COCB stimulation decreased. Nerve fibers with very high best frequencies also showed minimal COCB effects. These data are discussed in relation to other recent information.

Efferent control of cochlear inner hair cell responses in the guinea‐pig.

“…This effect was equivalent to increasing the s.p.l. by 1-3 dB as observed by Fex (1959) and Teas et al (1972). At the conclusion of the experiment, the stimulating site was histologically confirmed in eight guinea-pigs by passing a direct current of 200 ,#A for 2 min to deposit ferric ions in the brain, and perfusing the vascular system through the left ventricle with 09% saline followed by 10% formalin containing 1 % potassium ferrocyanide.…”

“…Previous studies (Fex, 1962;Wiederhold & Kiang, 1970;Wiederhold, 1970;Teas, Konishi & Nielsen, 1972) have shown that electrical stimulation of the c.o.c.b. decreases sound-evoked activity of single auditory afferents, which are presumed to innervate inner hair cells (Kiang, Rho, Northrop, Liberman & Ryugo, 1982;Liberman, 1982).…”

Effects of Electrical Stimulation of Olivocochlear Fibers in Cochlear Potentials in the Chinchilla

“…This peak in the strength of MOC effect for frequencies represented at about the center of the cochlea is also found in other species. In cat, guinea pig and mouse, most MOC effects on both CAPs and auditory-nerve fibers, and also the anatomical distribution of MOC fibers, display a single broad peak in the mid-frequencies; at 4-10 kHz in cat (Liberman et al 1990;Guinan and Gifford 1988a), at 7-10 kHz in guinea pig (Teas et al 1972), and at about 10 kHz in mouse (Maison et al 2003). However, our finding of another smaller peak of CAP efferent inhibition for frequencies around 8 kHz was unexpected (discussed in next section).…”

Efferent desensitization of auditory nerve fibre responses in the cochlea of the turtle Pseudemys scripta elegans.

“…Electrical stimulation of the crossed olivocochlear bundle, comprising a component of the efferents to the mammalian cochlea, has been shown to cause a desensitization and loss of frequency selectivity in the responses of inner hair cells (Brown, Nuttall & Masta, 1983) and auditory afferents (Wiederhold & Kiang, 1970; Wiederhold, 1970; Kiang, Moxon & Levine, 1970;Teas, Konishi & Nielsen, 1972). Single cochlear efferents can be driven by either ipsilateral or contralateral acoustic stimulation (Fex, 1962(Fex, , 1965Cody & Johnstone, 1982) and this has led to the suggestion that they form part of a reflex for controlling the gain of the cochlear output (Fex, 1962).…”