Discharge patterns of cochlear ganglion neurons in the chicken

Abstract

Physiological recordings were made of the compound action potential from the round window and single neurons in the cochlear ganglion of normal adult chickens (Gallus domesticus). The compound action potential threshold to tone bursts decreased from approximately 42 dB at 0.25 kHz to 30 dB between 1 and 2 kHz and then increased to 51 dB at 4 kHz. Most of the cochlear ganglion cells had characteristic frequencies below 2 kHz and the thresholds of most neurons were roughly 30-35 dB lower than the compound action potential thresholds. At any given characteristic frequency, thresholds varied by as much as 60 dB and units with the highest thresholds tended to have the lowest spontaneous rates. Spontaneous discharge rates ranged from 0 to 200 spikes/s with a mean rage of 86 spikes/s. Interspike interval histograms of spontaneous activity often contained regular peaks with the time interval between peaks approximately equal to 1/(characteristic frequency). Tuning curves were sharply tuned and V-shaped with approximately equal slopes to the curves above and below characteristic frequency. Q10dB and Q30dB values for the tuning curves increased with characteristic frequency. Post stimulus time histograms showed sustained firing during the stimulus and were characterized by a slight-to-moderate peak at stimulus onset. Most units showed vigorous phase-locking to tones at characteristic frequency although the degree of phase-locking declined sharply with increasing characteristic frequency. Discharge rate-level functions at characteristic frequency had a mean dynamic range of 42 dB and a mean saturation firing rate of 327 spikes/s. In general, the firing patterns of cochlear ganglion neurons are similar in most respects to those reported in other avians, but differ in several important respects from those seen in mammals.

Tonotopic Gradients of Membrane and Synaptic Properties for Neurons of the Chicken Nucleus Magnocellularis

“…The low CF NM neurons that we discuss here probably have a CF lower than 0.5 kHz, and this region of CF may not have been fully investigated in the barn owl. The vector strength of NM firing was reported as being ϳ0.8 at 0.4 kHz CF region in the chicken (Warchol and Dallos, 1990), and this is the same level of synchronization as that found in the ANFs at these CFs (Salvi et al, 1992). Both in the chicken and in the barn owl, additional examinations will be necessary regarding the temporal jitter and the possible improvement of temporal coding of neurons in the low CF region of NM by in vivo experiments.…”

Phase Locking to High Frequencies in the Auditory Nerve and Cochlear Nucleus Magnocellularis of the Barn Owl,Tyto alba

“…In this respect, the barn owl exceeds all other species investigated by an octave or more (Sachs et al, 1974(Sachs et al, , 1980Johnson, 1980;Sullivan and Konishi, 1984;Kettner et al, 1985;Palmer and Russell, 1986;Hillery and Narins, 1987;Gleich and Narins, 1988;Rose and Weiss, 1988;Hill et al, 1989;Carr and Konishi, 1990;Manley et al, 1990Manley et al, , 1997Salvi et al, 1992;Joris et al, 1994). Although Teich et al (1993) claimed phase locking up to 18 kHz in auditory nerve fibers of the cat, this does not change the general conclusion of superior phase locking in the owl.…”

Emergence of Hearing in the Chicken Embryo

“…This required some effort especially for the highest CFs Ͼ4,000 Hz. This added procedural difficulty presumably arose from the fact that there is a natural barrier, noted by others (Manley 1990;Manley et al 1985Manley et al , 1991Salvi et al 1992), that reduces access to the extreme basal regions of the ganglion. Adjustments in the electrode path were effective in mitigating this problem.…”

“…Studies in embryos to date have reported the absence of primary afferent CFs տ2,200 Hz (primary afferents: Jones and Jones 1995a,b;central relays: Lippe andRubel 1983, 1985). The absence of primary afferent neurons with high-frequency CFs in late embryos has been hypothetically attributed to a functionally immature base, reduced transfer of high-frequency sound to the cochlea, and/or technical difficulties that prevent the assessment of the cochlear base (e.g., Jones and Jones 1995b;Manley 1990;Manley et al 1985Manley et al , 1991Salvi et al 1992). The research reported here was undertaken to critically examine these hypotheses.…”