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PubMed1994

Lateral suppression and inhibition in the cochlear nucleus of the cat.

1. The ability of cells in the cochlear nucleus (CN) to encode frequency information in the presence of background noise on the basis of "place/rate" information was investigated by measuring the threshold, magnitude, and extent of lateral suppression in the ventral and dorsal CN of the anesthesized cat. The suppression regions were delineated through the use of "masked" response areas (MRAs). The MRA is a family of isointensity curves derived from the average discharge rate in response to a tone of variable frequency and sound pressure level in the presence of a concurrently presented broadband, quasi-flat-spectrum noise. Tonal stimuli of sufficient intensity are often effective in significantly reducing the average discharge rate of CN neurons over a wide frequency range. 2. Most units in the CN exhibit prominent lateral suppressive sidebands, but the variability in threshold, magnitude, and extent of suppression is large. Primary-like and onset units of the ventral CN manifest the least suppression and have the highest suppression thresholds. Pauser/buildup units in the dorsal division and choppers distributed throughout the CN show the largest amount of suppression and have the lowest suppression thresholds. 3. Auditory nerve fibers manifest some degree of lateral suppression, particularly fibers of low and medium spontaneous rate. However, in few instances are the threshold, magnitude, and extent comparable with that observed among the majority of chopper and pauser/buildup units. For this reason the lateral suppression observed among the latter unit types is unlikely to originate entirely from cochlear processes, but rather is likely to reflect largely neural mechanisms intrinsic to the CN. In contrast, the MRAs of most primary-like and onset units suggest that the suppression behavior of most of these cells originates mostly, if not entirely, in the cochlea and auditory nerve. 4. A primary consequence of lateral suppression is to preserve the sharp frequency selectivity of CN neurons at moderate to high sound pressure levels, particularly in background noise. In this fashion lateral suppressive mechanisms potentially enhance the representation of spectral information on the basis of place/rate information relative to that in the auditory nerve under noisy background conditions. 5. Lateral suppressive mechanisms probably underlie the dynamic range shift seen in the presence of a simultaneously presented noise. This mechanism may be crucial for preserving the ability to perceive signals in a noisy background.

Animals↗

PubMed1988

Cochlear nucleus inputs to olivocochlear neurones revealed by combined anterograde and retrograde labelling in the guinea pig.

Injections of the fluorescent tracer, Fast blue (FB), into cochlear nucleus complex in guinea pig produced strong anterograde labelling of ascending projections from this nucleus. When combined with retrograde labelling of olivocochlear efferent neurones by intracochlear injection of a second fluorescent tracer, Diamidino yellow (DY), the synaptic terminals formed on these cells by projections from the cochlear nucleus could be identified. The results provide direct support for the notion that many of the ipsilateral-monaural cochlear efferents identified in physiological studies correspond to the olivocochlear neurones located in brainstem nuclei contralateral to their target cochlea.

Amidines↗

PubMed2004

Isoflurane/N2O anesthesia suppresses narrowband but not wideband inhibition in dorsal cochlear nucleus.

Anesthesia alters the response properties of neurons in the dorsal cochlear nucleus (DCN). Barbiturates decrease spontaneous activity and the prevalence of inhibitory responses, so that DCN principal cells show less inhibition by narrowband stimuli (e.g. tones at best frequency). Here we present the effects on cat DCN of anesthesia using isoflurane plus nitrous oxide (N2O). Because the cellular anesthetic mechanisms of isoflurane differ from those of pentobarbital, the effects of the two anesthetics in DCN might be different. The strength of two inhibitory circuits in the DCN, the narrowband and wideband inhibitor, were studied and compared with results in unanesthetized decerebrate animals. The primary effects of isoflurane/N2O anesthesia were to lower spontaneous activity and increase the thresholds of units. All the response types seen in the decerebrate preparation were also seen with isoflurane/N2O, but the prevalence of predominantly inhibitory responses to narrowband stimuli (type IV units) decreased (from approximately 31% to approximately 11%). However, responses to band-reject noise were similar to those seen in unanesthetized animals. Together, these results suggest that the effects of isoflurane/N2O are primarily on the narrowband inhibitory circuit, rather than the wideband inhibitor.

Anesthetics, Inhalation↗

PubMed1995

Muscarinic receptor subtypes in rat dorsal cochlear nucleus.

We previously reported that responses of spontaneously active rat dorsal cochlear nucleus (DCN) neurons to cholinergic agonists are mediated predominantly by muscarinic receptors. We have now tested the effects of 7 antagonists with differing affinities for the muscarinic receptor subtypes M1-M4 on the responses to constant, submaximal doses of carbachol in rat brainstem slices. Each slice was exposed to one or more concentrations of one antagonist applied during extracellular recording of a DCN neuron. The concentrations yielding 50% reduction of test responses (IC50) of regular and bursting neurons were estimated for each antagonist. Correlation coefficients were calculated between log(IC50) values and log(Ki) values of the drugs for the receptor subtypes. Correlation coefficients for both regular and bursting neurons were not significant (P > 0.05) for M1 and M3, but were significant (P < 0.02) for M4. Bursting but not regular neurons also showed a significant correlation for M2 (P < 0.05). Our results suggest that (1) M4 contributes to the cholinergic responses in DCN and M2 may also contribute to the responses of bursting neurons, but the contribution of other subtypes cannot be completely excluded; (2) muscarinic subtypes in DCN probably differ from those reported for cochlea and some brain regions.

Animals↗

PubMed2002

Protein kinase C mediates potentiation of synaptic transmission by phorbol ester at parallel fibers in the dorsal cochlear nucleus.

Many cells in the outer two layers of the dorsal cochlear nucleus (DCN) express high levels of the phospholipid-activated, calcium dependent kinase, protein kinase C (PKC), an enzyme that can phosphorylate numerous proteins involved in neurotransmission and postsynaptic signaling. We investigated the effects of stimulating PKC with phorbol esters (phorbol 12-13 diacetate; PDAc) on parallel fiber synaptic transmission in brain slices of the guinea pig DCN. Phorbol esters increased the amplitude of the postsynaptic components of the field potential, including the excitatory post-synaptic field potential (fEPSP) and the population spike following electric stimulation of parallel fibers. Phorbol esters simultaneously decreased paired-pulse facilitation, suggesting that transmitter release mechanisms were affected. Potentiation of synaptic transmission and diminished paired-pulse potentiation were also observed in intracellular recordings of DCN neurons. The effects of phorbol esters were antagonized by the specific PKC blockers bisindolylmaleimide and calphostin C. Although modulation of the synaptic potentials appears to be mediated by presynaptic PKC, the differential effects of PDAc on the fEPSP and the population spike also suggest the involvement of postsynaptic PKC and postsynaptic targets. These experiments demonstrate that protein kinase C is capable of profoundly modulating synaptic transmission at parallel fiber synapses in the DCN.

Acoustic Stimulation↗

PubMed2006

Analysis of responses to noise in the ventral cochlear nucleus using Wiener kernels.

Responses to noise were recorded in ventral cochlear nucleus (VCN) neurons of anesthetized chinchillas and cats, then analyzed using Wiener-kernel theory. First-order kernels, which are proportional to reverse-correlation functions, of primary-like (PL) and primary-like with notch (PLN) neurons having low characteristic frequency (CF) are similar to those obtained in auditory nerve fibers (ANFs). Such kernels consist of lightly damped transient oscillations with frequency equal to the neuron's CF. The first-order kernel of high-CF PL and PLN neurons displays no evidence of tuning to CF. Second-order kernels of the aforementioned VCN neuron types also resemble those in the nerve, irrespective of CF. In general, first- and second-order Wiener kernels of chopper neurons are similar to those obtained in high-CF ANFs. This is likely the consequence of the poor phase-locking capabilities to near-CF tones exhibited by chopper neurons. By analyzing second-order kernels using singular-value decomposition, it was possible to estimate group delays for the entire neuronal population, regardless of the neuron's type or CF. This was done by analyzing the highest-ranking singular vector (FSV). Amplitude values of FSVs in chopper neurons in the cat are substantially larger than in high-spontaneous ANFs.

Acoustic Stimulation↗

PubMed1997

Mechanisms of onset responses in octopus cells of the cochlear nucleus: implications of a model.

The octopus cells of the posteroventral cochlear nucleus receive inputs from auditory-nerve fibers and form one of the major ascending auditory pathways. They respond to acoustic and electrical stimulation transiently and are believed to carry temporal information in the precise timing of their action potentials. The mechanism whereby onset responses are generated is not clear. Proposals aimed at elucidating the mechanism range from neural circuitry and/or inhibition, "depolarization block" (or inactivation of Na+ channels), and the involvement of a 4-aminopyridine (4-AP)-sensitive, low-threshold channel (K(LT)). In the present study, we used a compartment model to investigate possible mechanisms. The model cell contains a soma, an axon, and four passive dendrites. Four kinds of ionic channels were included in the soma compartment: the Hodgkin-Huxley-like Na+ and K+ channels, a 4-AP-sensitive, low-threshold channel, K(LT), and a Cs+-sensitive, hyperpolarization-activated inward rectifier, Ih. DC currents and half-wave-rectified sine waves were used as stimuli. Our results showed that an onset response can be generated in the absence of neuronal circuitry of any form, thus suggesting that the onset response in octopus cells is regulated intrinsically. Among the many factors involved, low-input impedance, partly contributed by Ih, appears to be essential to the basic onset response pattern; also, the K(LT) conductance plays a major role, whereas the inactivation of Na+ channels probably plays only a secondary role. The dynamics of Ih also can modify the response pattern, but due to its slow kinetics, its role is probably limited to longer-term regulation under the conditions simulated in this study.

Acoustic Stimulation↗

PubMed1996

Eighth nerve activity regulates intracellular calcium concentration of avian cochlear nucleus neurons via a metabotropic glutamate receptor.

1. Neurons in the cochlear nucleus, nucleus magnocellularis (NM), of embryonic and neonatal chicks are dependent on eighth nerve activity for their maintenance and survival. Removing this input results in the death of 20-40% of the NM neurons and profound changes in the morphology and metabolism of surviving neurons. 2. One of the first changes in NM neurons after an in vivo cochlea removal is an increase in intracellular calcium concentration ([Ca2+]i). Increased [Ca2+]i has been implicated in a number of neuropathologic conditions. 3. In this study, we orthodromically and antidromically stimulated NM neurons in an in vitro brain stem slice preparation and monitored NM field potentials while simultaneously assessing the [Ca2+]i of NM neurons using fura-2. 4. During continuous orthodromic stimulation, [Ca2+]i of NM neurons remained constant at 80 nM. In the absence of stimulation, NM neuron [Ca2+]i increased steadily to 230 nM by 90 min. Antidromic and contralateral stimulation produced a [Ca2+]i increase in NM neurons that was similar in magnitude but slightly more rapid than that observed in the absence of stimulation. 5. Addition of the metabotropic glutamate receptor (mGluR) antagonists (R,S)-alpha-methyl-4-carboxyphenylglycine or 2-amino-3-phosphonopropionic acid to the superfusate during continued orthodromic stimulation resulted in a dose-dependent, rapid, and dramatic increase in NM neuron [Ca2+]i without affecting the postsynaptic field potentials recorded from NM. 6. The ionotropic glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione and 2-amino-5-phosphonovalerate eliminated NM field potentials during continued orthodromic stimulation but did not result in an increase in [Ca2+]i. 7. Continuous superfusion of trans-(+/-)-aminocyclopentane dicarboxylate, but not glutamate, prevented the increase in [Ca2+]i in the absence of stimulation. 8. These results suggest that NM neurons rely on eighth nerve activity-dependent activation of a mGluR to maintain physiological [Ca2+]i. Removal of this mGluR activation results in an increase in [Ca2+]i that may contribute to the early stages of degeneration and eventual death of these neurons.

2-Amino-5-phosphonovalerate↗

PubMed1982

Morphology of primary axosomatic endings in the anteroventral cochlear nucleus of the cat: a study of the endbulbs of Held.

The central axons of Type I spiral ganglion neurons travel in the auditory nerve and terminate in the cochlear nucleus. The ascending branches of these axons innervate the anteroventral cochlear nucleus and give rise to large axosomatic endings, called the endbulbs of Held, and smaller boutons. This paper reports a study of the endbulbs of Held, stained by horseradish peroxidase and variants of the Golgi method in kittens 2, 5, 10, 20, and 45 days postnatal and adult cats. Endbulbs tend to fall into two extreme groups with some endbulbs having an intermediate appearance; consequently, we have defined three descriptive stages of endbulbs that are conceived of as representing a developmental sequence. One group of endbulbs is found mostly in kittens younger than 10 days postnatal and is similar to the classic description of endbulbs by Ramón y Cajal ('09). The other extreme group of endbulbs is found mostly in adult cats. In these cases, the parent axonal trunk divides into several thick, gnarled branches that in turn branch again, sometimes repeatedly. These branches display irregular varicosities and form a cup-shaped arborization into which the postsynaptic cell body nestles. A chronology of postnatal endbulb development has been inferred from the relative proportions of the different endbulb stages at various ages. Maturation transforms the endbulb of Held from a large, spoon-shaped swelling having many filipodia into an elaborate tree with broad trunks and many smaller branches. Some implications of the proposed development sequence are discussed.

Aging↗

PubMed1987

Characterization of HRP-labeled globular bushy cells in the cat anteroventral cochlear nucleus.

We report on the anatomical and physiological features of globular bushy cells in the posterior division of the anteroventral cochlear nucleus based on the characteristics of 20 cells from this population. Each of these cells was recorded from and characterized intracellularly and/or extracellularly, injected with horseradish peroxidase, and studied at the light and/or electron microscopic level. Intracellular records from the vicinity of the globular bushy cell body displayed large, fast synaptic potentials, and in some instances a larger presumed action potential both in silence and during short tone stimulation. Intraaxonal recordings displayed large action potentials in addition to small, fast potentials, which evidence indicates may be the decrementally conducted subthreshold synaptic potentials. Both recording situations indicated that these auditory nerve inputs need not be suprathreshold. Bushy cells with high characteristic frequencies (CFs greater than 3 kHz) typically showed primary-like-with-notch responses to short tones at CF or on-type L responses if the sustained level of discharge after the notch was not as robust. Low-CF bushy cells phase-locked after a well-timed onset spike. Light microscopic anatomy revealed a typically oval cell body giving rise to one or two primary dendrites that branched profusely and an axon that gave off no collaterals within the cochlear nucleus before entering the trapezoid body. Electron microscopic analysis showed a high concentration of large, round, vesicle-containing terminals on the cell body and primary dendrite while the population of terminals on the initial segment and sparsely covered distal dendrites was made up mostly of flat and pleomorphic vesicle-containing terminals.

Animals↗

PubMed2003

Discharge properties of identified cochlear nucleus neurons and auditory nerve fibers in response to repetitive electrical stimulation of the auditory nerve.

Using the in vitro isolated whole brain preparation of the guinea pig maintained at 29 degrees C, we intracellularly recorded and stained cochlear nucleus (CN) neurons and auditory nerve (AN) fibers. Discharge properties of CN cells and AN axons were tested in response to 50-ms trains of electrical pulses delivered to the AN at rates ranging from 100 to 1000 pulses per second (pps). At low stimulation rates (200-300 pps), the discharges of AN fibers and a large proportion of principal cells (bushy, octopus, stellate) in the ventral cochlear nucleus (VCN) followed with high probability each pulse in the train, resulting in synchronization of discharges within large populations of AN fibers and CN cells. In contrast, at high stimulation rates (500 pps and higher), AN fibers and many VCN cells exhibited "primary-like", "onset" and some other discharge patterns resembling those produced by natural sound stimuli. Unlike cells in the VCN, principal cells (pyramidal, giant) of the dorsal CN did not follow the stimulating pulses even at low rates. Instead, they often showed "pauser" and "build-up" patterns of activity, characteristic for these cells in conditions of normal hearing. We hypothesize that, at low stimulation rates, the response behavior of AN fibers and VCN cells is different from the patterns of neuronal activity related to normal auditory processing, whereas high stimulation rates produce more physiologically meaningful discharge patterns. The observed differences in discharge properties of AN fibers and CN cells at different stimulation rates can contribute to significant advantages of high- versus low-rate electrical stimulation of the AN used for coding sounds in modern cochlear implants.

Action Potentials↗

PubMed1994

Inhibitory inputs modulate discharge rate within frequency receptive fields of anteroventral cochlear nucleus neurons.

1. The amino acid neurotransmitters gamma-aminobutyric acid (GABA) and glycine function as inhibitory neurotransmitters associated with nonprimary inputs onto spherical bushy and stellate cells, two principal cell types located in the anteroventral cochlear nucleus (AVCN). These neurons are characterized by primary-like (including phase-locked) and chopper temporal response patterns, respectively. 2. Inhibition directly adjacent to the excitatory response area has been hypothesized to sharpen or limit the breadth of the tonal frequency receptive field. This study was undertaken to test whether GABA and glycine circuits function primarily to sharpen the lateral edges of the tonal excitatory response area or to modulate discharge rate within central portions of the excitatory response area of AVCN neurons. 3. To test this, iontophoretic application of the glycineI antagonist, strychnine, or the GABAA antagonist, bicuculline, was used to block inhibitory inputs after obtaining control families of isointensity contours (response areas) from extracellularly recorded AVCN neurons. 4. Blockade of GABA and/or glycine inputs was found to increase discharge rate primarily within the excitatory response area of neurons displaying chopper and primary-like temporal responses with little or no change in bandwidth or in off-characteristic frequency (CF) discharge rate. 5. The principal sources of inhibitory inputs onto AVCN neurons are cells located in the dorsal cochlear nucleus and superior olivary complex, which appear to be tonotopically matched to their targets. In agreement with these morphological studies, the data presented in this paper suggest that most GABA and/or glycine inhibition is tonotopically aligned with excitatory inputs. 6. These findings support models that suggest that GABA and/or glycine inputs onto AVCN neurons are involved in circuits that adjust gain to enable the detection of signals in noise by enhancing signal relative to background.

Animals↗

PubMed1994

Subcellular localization of the inositol 1,4,5-trisphosphate receptor, P400, in the vestibular complex and dorsal cochlear nucleus of the rat.

The subcellular localization of the inositol 1,4,5-trisphosphate receptor protein, P400, was studied in the vestibular complex, an area to which Purkinje cells project, as well as in neurons of the dorsal cochlear nucleus and in ectopic Purkinje cells of adult rat brain. The receptor was demonstrated by electron microscopical immunocytochemistry using the avidin-biotin peroxidase complex procedure, with the monoclonal antibody 4C11 raised against mouse cerebellar inositol 1,4,5-trisphosphate receptor protein. Immunoreactivity was found in preterminal fibres and terminal boutons in the nuclei of the vestibular complex, generally associated with the subsurface systems and stacks or fragments of smooth endoplasmic reticulum. Ectopic Purkinje cells and cartwheel cells of the dorsal cochlear nucleus also displayed immunoreactivity, but this was much less intense in the latter. The results of the present study suggest that this receptor protein, involved in the release of Ca2+, is located in sites that enable it to influence the synthesis, transport and release of neurotransmitters.

Animals↗

PubMed2003

Auditory peripheral influences on calcium binding protein immunoreactivity in the cochlear nucleus during aging in the C57BL/6J mouse.

The C57BL/6J (C57) mouse was selected as a suitable model for early presbyacusis to determine if there were correlations between peripheral pathology (spiral ganglion loss, inner and outer hair cell loss) and calcium binding immunoreactivity in the cochlear nucleus during aging. The quantitative stereological method, the optical fractionator, was used for determining the total number of neurons and calcium binding immunopositive neurons (calbindin, parvalbumin and calretinin) during aging in the posteroventral- and dorsal cochlear nucleus (PVCN and DCN) in C57 mice. Comparing 30-month-old to 1-month-old C57 mice, a percent increase in parvalbumin and calbindin immunoreactivity was evident in both the PVCN and DCN. Correlations were made between peripheral pathology (spiral ganglion and inner and outer hair cell loss) and calcium binding protein expression. Significant correlations between cochlear pathology and the percentage of parvalbumin and calretinin immunoreactive neurons were demonstrated in the DCN. Moreover, significant correlations were found between cochlear pathology and parvalbumin and calbindin in the PVCN. In summary, the findings imply that degenerative changes in the auditory periphery can modulate neuronal homeostasis by increasing calcium binding proteins in the PVCN and DCN during aging. Taken together, these findings suggest a role for calcium binding proteins in protecting against age-induced calcium toxicity.

Aging↗

PubMed2003

Effects of age and cochlear damage on the metabolic activity of the avian cochlear nucleus.

Most aging commercially raised broiler chickens display a progressive loss of cochlear hair cells in a pattern similar to the cochlear degeneration found in aging humans: basal (high frequency) hair cells are affected first, followed by apical (low frequency) hair cells [Durham et al., Hear. Res. 166 (2002) 82-95]. Here, cochlear anatomy was assessed from scanning electron micrographs. Then, the metabolic activity of cochlear nucleus (nucleus magnocellularis, NM) neurons in 15-19, 30, 39, 40, and 65-66 week old broiler chickens was examined using cytochrome oxidase histochemistry and compared to the degree of cochlear abnormality. Cochleae of 15-19 week old birds are largely normal; therefore the level of NM metabolic activity is considered the baseline. Cochleae of the 30 week old group display mild damage and hair cell regeneration in the base. Metabolic activity in rostral (high frequency) NM is increased relative to the baseline, while activity remains unchanged in caudal (low frequency) NM. The 39 and 65-66 week old groups display severe and total damage extending into the apex of the cochlea. Metabolic activity is decreased in rostral and caudal NM at these ages. These results suggest that auditory central nervous system metabolism (cytochrome oxidase activity) is affected by changes in the aging chicken cochlea.

Acoustic Stimulation↗

PubMed1985

Evidence for an excitatory amino acid as the transmitter of the auditory nerve in the in vitro mouse cochlear nucleus.

Microionophoretically applied excitatory amino acids induced firing of extracellularly recorded single units in a tissue slice preparation of the mouse cochlear nucleus, and the similarly applied antagonist 2-amino-5-phosphonovalerate (2APV) was demonstrated to be a selective N-methyl-D-aspartate (NMDA) receptor antagonist. In addition, the effect of various bath-applied excitatory amino acid receptor antagonists on auditory nerve evoked field potentials was studied. Antagonists which block NMDA type receptors, blocked auditory nerve evoked potentials in a dose-dependent manner. The 50% effective concentration (EC50) for three of the antagonists used was: D-alpha-aminoadipate, 7.8 mM; 2APV, 4.2 mM; and 2,3-cis-piperidine dicarboxylate, 1.1 mM. Glutamate diethylester (5 mM) had no effect. The results suggest that NMDA, kainate and quisqualate receptors are present in the cochlear nucleus and that auditory nerve transmission in the mouse is mediated by an NMDA type receptor. This is consistent with the concept that the auditory nerve postsynaptic receptor in mammals is of the NMDA type.

2-Amino-5-phosphonovalerate↗

PubMed1976

Dynamic properties of primary auditory fibers compared with cells in the cochlear nucleus.

The dynamic properties of the responses of single primary auditory fibers were compared with those of single cells in the cochlear nucleus. The stimuli were tones (at the unit's characteristic frequency, CF) that were amplitude-modulated with pseudorandom noise. The dynamic properties were described by the cross-covariance and integrated cross-covariance functions between the recorded discharge rate and the modulation. These two measures have earlier been shown to be valid approximations of the system's impulse and step response function, i.e. the change in discharge rate in response to a short impulsive increase (or decrease) in the stimulus intensity and a step increment (or decrement) in the stimulus intensity. The cross-covariance function computed from the responses of fibers had a narrower peak than that of cells indicating that a brief change in stimulus intensity gives rise to a faster change in the discharge rate of fibers than that of cells. The nodulation of the discharge rate of cells for a certain degree of amplitude modulation of the sound is usually greater than that of cells. The modulation of the discharge rate of cells for a certain degree of amplitude modulation of the sound is usually greater than that of fibers. The range of stimulus intensities where a change in stimulus intensity gives rise to a change in discharge rate rate is smaller for fibers (about 30 dB) than what was shown earlier for cells (70-80 dB). The cross-covariance function computed from the slow wave responses recorded from the surface of the cochlear nucleus in response to an amplitude-modulated tone has individual peaks that reflect distinct classes of units with regard to latency of unit dishcarges.

Acoustic Stimulation↗

PubMed1989

Statistical and receiver operating characteristic analysis of empirical spike-count distributions: quantifying the ability of cochlear nucleus units to signal intensity changes.

Analytical methods from signal detection theory were applied in an effort to quantify the ability of cochlear nucleus (CN) units to signal changes in intensity. Of particular interest was the relation between this ability and the different patterns of discharge that characterize auditory neurons. Single-unit responses to best-frequency (BF) tone bursts were recorded from neurons in the gerbil cochlear nucleus, and empirical spike-count distributions were generated. The mean-to-variance ratios for regular units were generally larger than those of irregular units. Receiver operating characteristic (ROC) curves were generated from empirical spike-count distributions. The area under the ROC curve [P(A)] was computed and used to define the performance of an observer detecting whether or not a change in firing rate has occurred, thus signaling a change in intensity. For a given change in mean spike count, units characterized by regular interspike-interval (ISI) histograms typically gave larger P(A) values than did units characterized by irregular ISI histograms. In addition, onset units gave larger values of P(A) than did irregular units for a given change in mean spike count. These results suggest that regular and onset units are better able to signal intensity changes than are irregular units.

Acoustic Stimulation↗