Temporal Measures and Neural Strategies for Detection of Tones in Noise Based on Responses in Anteroventral Cochlear Nucleus

To examine possible neural strategies for the detection of tones in broadband noise, single-neuron extracellular recordings were obtained from the anteroventral cochlear nucleus (AVCN) in anesthetized gerbils. Detection thresholds determined by average discharge rate and several temporal metrics were compared with previously reported psychophysical detection thresholds in cats ( Costalupes 1985 ). Because of their limited dynamic range, the average discharge rates of single neurons failed to predict psychophysical detection thresholds for relatively high-level noise at all measured characteristic frequencies (CFs). However, temporal responses changed significantly when a tone was added to a noise, even for neurons with flat masked rate-level functions. Three specific temporal analyses were applied to neural responses to tones in noise. First, temporal reliability, a measure of discharge time consistency across stimulus repetitions, decreased with increasing tone level for most AVCN neurons at all measured CFs. Second, synchronization to the tone frequency, a measure of phase-locking to the tone, increased with tone level for low-CF neurons. Third, rapid fluctuations in the poststimulus time histograms (PSTHs) decreased with tone level for a number of neurons at all CFs. For each of the three temporal measures, some neurons had detection thresholds at or below psychophysical thresholds. A physiological model of a higher-stage auditory neuron that received simple excitatory and inhibitory inputs from AVCN neurons was able to extract the PSTH fluctuation information in a form of decreased rate with tone level.

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Signs of functional maturation of peripheral auditory system in discharge patterns of neurons in anteroventral cochlear nucleus of kitten

Journal of Neurophysiology ◽

10.1152/jn.1978.41.6.1557 ◽

1978 ◽

Vol 41 (6) ◽

pp. 1557-1559 ◽

Cited By ~ 97

Author(s):

J. F. Brugge ◽

E. Javel ◽

L. M. Kitzes

Keyword(s):

Cochlear Nucleus ◽

Auditory Nerve ◽

Discharge Rate ◽

Phase Locking ◽

Low Frequency ◽

Second Phase ◽

Extended Phase ◽

Anteroventral Cochlear Nucleus ◽

Peripheral Auditory System ◽

Different Response

1. Responses to pure tones were recorded from single neurons in the anteroventral cochlear nucleus (AVCN) in kittens ranging in age from 4 to 45 days. Different response properties mature at different times after birth. 2. The shapes of response areas of AVCN neurons after the 1st postnatal week resemble those recorded in the AVCN and auditory nerve of the adult. During the 1st wk after birth the high-frequency portion of the response area is extended. Phase-locked responses to stimulus frequencies below about 600 Hz occur at this time. Phase vs. frequency measurements and shapes of response areas indicate that by the end of the 1st postnatal week the cochlear partition may be capable of supporting a traveling wave along most of its length. 3. Functional development proceeds through a second phase which lasts until the end of the 2nd or the beginning of the 3rd wk of life. During that time threshold, maximal discharge rate, and average first-spike latency achieve adult values. 4. Phase-locking to low-frequency tones, to the extent displayed by phase-sensitive neurons in the adult AVCN or auditory nerve, is achieved last, after the 3rd or 4th wk postpartum.

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Level dependence of cochlear nucleus onset unit responses and facilitation by second tones or broadband noise

Journal of Neurophysiology ◽

10.1152/jn.1995.73.1.141 ◽

1995 ◽

Vol 73 (1) ◽

pp. 141-159 ◽

Cited By ~ 124

Author(s):

I. M. Winter ◽

A. R. Palmer

Keyword(s):

Cochlear Nucleus ◽

Discharge Rate ◽

Nerve Fibers ◽

Sound Level ◽

Spike Timing ◽

Broadband Noise ◽

Sound System ◽

Rate Level ◽

Sound Levels ◽

Level Function

1. The responses of onset units in the cochlear nucleus of the anesthetized guinea pig have been measured to single tones, two-tone complexes, and broadband noise (BBN; 20-kHz bandwidth). The onset units were subdivided into three groups, onset-I (OnI), onset-L (OnL), and onset-C (OnC), on the basis of a decision tree using their peristimulus time histogram (PSTH) shape and discharge rate in response to suprathreshold best-frequency (BF) tone bursts. 2. PSTHs were constructed from responses either to single tones at a unit's BF or to BBN as a function of level. When sufficient sustained activity could be elicited from the unit, arbitrarily defined as > 100 spikes/s, a coefficient of variation (CV) was calculated; the majority were characterized by a CV that was similar to transient chopper units (0.35 < CV < 0.5). First spike latency decreased monotonically with increasing sound level. For the majority of onset units, the first spike timing was very precise. 3. BF rate-level functions recorded from OnL and OnC units did not show any signs of discharge rate saturation at the highest sound levels we have used (100-115 dB SPL). No systematic relationship was observed between the threshold at BF and the shape of the rate-level function. BBN rate-level functions were typically characterized by higher discharge rates than in response to BF tones. However, for OnI units and a minority of other onset units, there was little difference in the shape of their rate-level functions in response to BF tones or BBN. 4. The threshold of most onset units to BBN was similar to the threshold to a BF tone that had similar overall root-mean-square (RMS) energy. The BBN threshold was, on average, 5.5 dB greater than the BF threshold. This result contrasts with that found in auditory-nerve fibers recorded in the same species, with the use of an identical sound system, where the threshold to BBN was, on average, 19.4 dB higher. The mean threshold difference between BBN and BF tones for a population of chopper units recorded in the same series of experiments was 17.7 dB. The relative thresholds to BBN and BF tones indicated that the bandwidths near the onset units' BF threshold were broader than could be estimated with the use of single tones. Ten units were characterized by bimodal response areas.(ABSTRACT TRUNCATED AT 400 WORDS)

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

Journal of Neurophysiology ◽

10.1152/jn.1994.72.5.2124 ◽

1994 ◽

Vol 72 (5) ◽

pp. 2124-2133 ◽

Cited By ~ 104

Author(s):

D. M. Caspary ◽

P. M. Backoff ◽

P. G. Finlayson ◽

P. S. Palombi

Keyword(s):

Cochlear Nucleus ◽

Discharge Rate ◽

Cell Types ◽

Dorsal Cochlear Nucleus ◽

Superior Olivary Complex ◽

Gamma Aminobutyric Acid ◽

Excitatory Response ◽

Morphological Studies ◽

Anteroventral Cochlear Nucleus ◽

Response Area

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.

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Classification of unit types in the anteroventral cochlear nucleus: PST histograms and regularity analysis

Journal of Neurophysiology ◽

10.1152/jn.1989.62.6.1303 ◽

1989 ◽

Vol 62 (6) ◽

pp. 1303-1329 ◽

Cited By ~ 198

Author(s):

C. C. Blackburn ◽

M. B. Sachs

Keyword(s):

Cochlear Nucleus ◽

Interspike Interval ◽

Discharge Rate ◽

Low Frequency ◽

Initial Response ◽

Instantaneous Rate ◽

Anteroventral Cochlear Nucleus ◽

The Mean ◽

Spike Latency

1. The responses of neurons in the anteroventral cochlear nucleus (AVCN) of barbiturate-anesthetized cats are characterized with regard to features of their responses to short tone bursts (STBs; 25 ms). A "decision tree" is presented to partition AVCN units on the basis of post-stimulus time histogram (PSTH) shape, first spike latency, and discharge rate and regularity calculated as functions of time during responses to STBs. The major classes of AVCN units (primary-like, primary-like-with-notch, chopper, and onset) have been described previously; in this paper, special attention is given to clarifying and systematizing boundaries between classes. Certain types of "unusual" units that may be confused with units in one of the major classes are also examined. 2. When STBs are presented synchronously (constant phase at onset), PSTHs of responses to very-low-frequency (less than 1.0 kHz) tones are difficult if not impossible to resolve into the classes listed above because all unit types phase-lock to low-frequency tones. However, when STBs are presented asynchronously, the responses of units with low best frequencies can be categorized on the basis of PSTH shape and first spike latency. 3. Primary-like, primary-like-with-notch, and onset units are distinguished primarily on the basis of PSTH shape. These three unit types have comparable minimum first spke latencies and synchronization to tones. One type of "unusual" response poses a particular hazard with respect to the generation of uncontaminated primary-like populations. Such "unusual" units have PSTHs that appear primary-like; these units are, however, distinguished by their unusually long first spike latencies. Unlike primary-like units, these "unusual" units show extremely poor synchronization to tones. 4. Chopper units are defined as having an initial response that is highly regular, resulting in the characteristic multimodal PSTH. "Unusual" units with multimodal PSTHs but whose initial responses are not highly regular (measured by the reproducibility of the initial firing pattern in response to multiple repetitions of a STB) are eliminated from the chopper populations. 5. In barbiturate-anesthetized cats, at least three patterns of chopper response can be distinguished on the basis of temporal patterns of rate and regularity adaptation. "Sustained" choppers show no adaptation of instantaneous rate (measured by the inverse of the mean interspike interval), and their discharge remains highly regular throughout the response. "Transiently adapting" choppers undergo a very rapid (less than 10 ms) decrease in instantaneous rate accompanied by a sharp increase in discharge irregularity.(ABSTRACT TRUNCATED AT 400 WORDS)

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Spectral Integration by Type II Interneurons in Dorsal Cochlear Nucleus

Journal of Neurophysiology ◽

10.1152/jn.1999.82.2.648 ◽

1999 ◽

Vol 82 (2) ◽

pp. 648-663 ◽

Cited By ~ 43

Author(s):

George A. Spirou ◽

Kevin A. Davis ◽

Israel Nelken ◽

Eric D. Young

Keyword(s):

Auditory System ◽

Cochlear Nucleus ◽

Discharge Rate ◽

Inhibitory Interneuron ◽

Nerve Fibers ◽

Broadband Noise ◽

Dorsal Cochlear Nucleus ◽

Type I ◽

Type Ii ◽

Inhibitory Processes

The type II unit is a prominent inhibitory interneuron in the dorsal cochlear nucleus (DCN), most likely recorded from vertical cells. Type II units are characterized by low rates of spontaneous activity, weak responses to broadband noise, and vigorous, narrowly tuned responses to tones. The weak responses of type II units to broadband stimuli are unusual for neurons in the lower auditory system and suggest that these units receive strong inhibitory inputs, most likely from onset-C neurons of the ventral cochlear nucleus. The question of the definition of type II units is considered here; the characteristics listed in the preceding text define a homogeneous type II group, but the boundary between this group and other low spontaneous rate neurons in DCN (type I/III units) is not yet clear. Type II units in decerebrate cats were studied using a two-tone paradigm to map inhibitory responses to tones and using noisebands of varying width to study the inhibitory processes evoked by broadband stimuli. Iontophoresis of bicuculline and strychnine and comparisons of two-tone responses between type II units and auditory nerve fibers were used to differentiate inhibitory processes occurring near the cell from two-tone suppression in the cochlea. For type II units, a significant inhibitory region is always seen with two-tone stimuli; the bandwidth of this region corresponds roughly to the previously reported excitatory bandwidth of onset-C neurons. Bandwidth widening experiments with noisebands show a monotonic decline in response as the bandwidth increases; these data are interpreted as revealing strong inhibitory inputs with properties more like onset-C neurons than any other response type in the lower auditory system. Consistent with these properties, iontophoresis of inhibitory antagonists produces a large increase in discharge rate to broadband noise, making tone and noise responses nearly equal.

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Enhanced Temporal Response Properties of Anteroventral Cochlear Nucleus Neurons to Broadband Noise

Journal of Neuroscience ◽

10.1523/jneurosci.4742-04.2005 ◽

2005 ◽

Vol 25 (6) ◽

pp. 1560-1570 ◽

Cited By ~ 38

Author(s):

D. H. G. Louage

Keyword(s):

Cochlear Nucleus ◽

Broadband Noise ◽

Temporal Response ◽

Response Properties ◽

Anteroventral Cochlear Nucleus

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Lateral suppression and inhibition in the cochlear nucleus of the cat

Journal of Neurophysiology ◽

10.1152/jn.1994.71.2.493 ◽

1994 ◽

Vol 71 (2) ◽

pp. 493-514 ◽

Cited By ~ 83

Author(s):

W. S. Rhode ◽

S. Greenberg

Keyword(s):

Cochlear Nucleus ◽

Auditory Nerve ◽

Background Noise ◽

Sound Pressure ◽

Dynamic Range ◽

Discharge Rate ◽

Nerve Fibers ◽

Range Shift ◽

Rate Information ◽

Noisy Background

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.

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