Wideband Inhibition of Dorsal Cochlear Nucleus Type IV Units in Cat: A Computational Model

10.1114/1.150 ◽  
1999 ◽  
Vol 27 (1) ◽  
pp. 73-87 ◽  
Author(s):  
Kenneth E. Hancock ◽  
Herbert F. Voigt
Keyword(s):  
Computational Model ◽  
Cochlear Nucleus ◽  
Dorsal Cochlear Nucleus ◽  
Type Iv

Two separate inhibitory mechanisms shape the responses of dorsal cochlear nucleus type IV units to narrowband and wideband stimuli

1994 ◽  
Vol 71 (6) ◽  
pp. 2446-2462 ◽  
Author(s):  
I. Nelken ◽  
E. D. Young
Keyword(s):  
Firing Rate ◽  
Cochlear Nucleus ◽  
Inhibitory Effect ◽  
Broadband Noise ◽  
Dorsal Cochlear Nucleus ◽  
Inhibitory Input ◽  
Inhibitory Influence ◽  
Type Ii ◽  
Rate Level ◽  
Type Iv

1. The principal cells of the dorsal cochlear nucleus (DCN) are mostly inhibited by best frequency (BF) tones but are mostly excited by broadband noise (BBN), producing the so-called type IV response characteristic. The narrowband inhibitory responses can be explained by the inhibitory influence of interneurons with type II response characteristics. However, it is not clear that all the details of the type IV responses can be accounted for by this neural circuit. In particular, many type IV units are inhibited by band-reject noise (notch noise); type II units tend to be only weakly excited by these stimuli, if at all. In this paper we study the relationships between the narrowband, inhibitory and the wideband, excitatory regimens of the type IV responses and present the case for the existence of a second inhibitory source in DCN, called the wideband inhibitor (WBI) below. 2. Type IV units were studied using pure tones, noise bands arithmetically centered on BF, notch noise centered on BF, and BBN. We measured the rate-level function (response rate as function of stimulus level) for each stimulus. This paper is based on the responses of 28 type IV units. 3. Evidence for low-threshold inhibitory input to type IV units is derived from analysis of rate-level functions at sound levels just above threshold. Notch noise stimuli of the appropriate notch width produce inhibition at threshold in this regime. When BBN is presented, this inhibition appears to summate with excitation produced by energy in the band of noise centered on BF, resulting in BBN rate-level functions with decreased slope and maximum firing rate. A range of slopes and maximal firing rates is observed, but these variables are strongly correlated and they are negatively correlated with the strength of the inhibition produced by notch noise; this result supports the conclusion that a single inhibitory source is responsible for these effects. 4. By contrast, there is a weak (nonsignificant) positive correlation between the strength of the inhibitory effect of notch noise and the slope/maximal firing rate in response to narrowband stimuli, including BF tones. The contrast between this positive nonsignificant correlation and the significant negative correlation mentioned above suggests that more than one inhibitory effect operates: specifically, the type II input is responsible for inhibition by narrowband stimuli and a different inhibitory source, the WBI, produces inhibition by notch stimuli. 5. Several lines of evidence are given to show that type II units cannot produce the inhibition seen with notch noise stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

Responses to tones and noise of single cells in dorsal cochlear nucleus of unanesthetized cats

1976 ◽  
Vol 39 (2) ◽  
pp. 282-300 ◽  
Author(s):  
E. D. Young ◽  
W. E. Brownell
Keyword(s):  
Cochlear Nucleus ◽  
Discharge Rate ◽  
Single Cells ◽  
Broad Band ◽  
Inhibitory Response ◽  
Nerve Fibers ◽  
Dorsal Cochlear Nucleus ◽  
Type Ii ◽  
Type Iv ◽  
Band Noise

1. Single-unit responses in the dorsal cochlear nucleus of unanesthetized, decerebrate cats have been divided into two categoreis. These have been differentiated on the basis of responses to best-frequency tones. Type IV units responded to best-frequency tones with excitation from threshold to about 20 or 30 dB above threshold; at higher levels, their response was inhibitory. In a few cases, the excitatory area near threshold was not seen and in a few others, the response became excitatory again at high levels. Type IV units could be divided into two groups based on the length of time that inhibition was maintained in response to long tones. Type IV units are not seen in anesthetized cats. 2. Type II/III units responded to best-frequency tones of all levels with excitation. Nonmonotonic rate versus level functions were seen in type II/III units, but they were of much less drastic character; the discharge rate of nonmonotonic type II/III units was still well above spontaneous rate for tones 50 dB above threshold. Type II/III units defined in this way were found to have, on the average, lower rates of spontaneous activity and higher thresholds than type IV units. 3. Type II/III units responded weakly to broad-band noise in comparison to auditory nerve fibers and many of them did not respond at all to noise. Type IV units, with best frequencies above 0.9 kHz, gave excitatory responses to noise. 4. The inhibitory response areas of type IV units could be divided into two areas: a central inhibitory area in the vicinity of best frequency where on- and off-discharges and afterdischarges were seen; and inhibitory side bands at higher and lower frequencies where simple inhibitory responses were seen. In four units, it was possible to show that the central inhibitory area was converted to an excitatory area after administration of an anesthetic dose of pentobarbital. 5. Most type II/III and type IV units could be excited or inhibited by stimuli in the contralateral ear. Broad-band noise was a more effective contralateral stimulus than tones at the ipsilateral best frequency. 6. On the basis of the properties of type II/III and type IV cells, it is suggested that type II/III responses are recorded from interneurons which provide a large share of the inhibitory imput to type IV cells.

Linear and Nonlinear Spectral Integration in Type IV Neurons of the Dorsal Cochlear Nucleus. II. Predicting Responses With the Use of Nonlinear Models

1997 ◽  
Vol 78 (2) ◽  
pp. 800-811 ◽  
Author(s):  
Israel Nelken ◽  
Peter J. Kim ◽  
Eric D. Young
Keyword(s):  
Cochlear Nucleus ◽  
Nonlinear Models ◽  
Broadband Noise ◽  
Dorsal Cochlear Nucleus ◽  
Center Frequency ◽  
Nonlinear Method ◽  
Spectral Integration ◽  
Type Iv ◽  
Integration Mechanisms ◽  
Linear And Nonlinear

Nelken, Israel, Peter J. Kim, and Eric D. Young. Linear and nonlinear spectral integration in type IV neurons of the dorsal cochlear nucleus. II. Predicting responses with the use of nonlinear models. J. Neurophysiol. 78: 800–811, 1997. Two nonlinear modeling methods were used to characterize the input/output relationships of type IV units, which are one principal cell type in the dorsal cochlear nucleus (DCN). In both cases, the goal was to derive predictive models, i.e., models that could predict the responses to other stimuli. In one method, frequency integration was estimated from response maps derived from single tones and simultaneous pairs of tones presented over a range of frequencies. This model combined linear integration of energy across frequency and nonlinear interactions of energy at different frequencies. The model was used to predict responses to noisebands with varying width and center frequency. In almost all cases, predictions using two-tone interactions were better than linear predictions based on single-tone responses only. In about half the cases, reasonable quantitative fits were achieved. The fits were best for noisebands with narrow bandwidth and low sound levels. In the second nonlinear method, the spectrotemporal receptive field (STRF) was derived from responses to broadband stimuli. The STRF could account for some qualitative features of the responses to broad noisebands and spectral notches embedded in broad noisebands. Quantitatively, however, the STRFs failed to predict the responses of type IV units even to simple broadband noise stimuli. For narrowband stimuli, the STRF failed to predict even qualitative features (such as excitatory and inhibitory frequency bands). The responses of DCN type IV units presumably result from interactions of two inhibitory sources, a strong one that is preferentially activated by narrowband stimuli and a weaker one that is preferentially activated by broadband stimuli. The results presented here suggest that the STRF measures effects related to the broadband inhibition, whereas two-tone interactions measure mostly effects related to narrowband inhibition. This explains why models based on two-tone interactions predict the responses to narrow noisebands much better then models based on STRFs. It is concluded that a minimal stimulus set for characterizing type IV units must contain both broadband and narrowband stimuli, because each stimulus class by itself activates only partially the integration mechanisms that shape the responses of type IV units. Similar conclusions are expected to hold in other parts of the auditory system: when characterizing a complex auditory unit, it is necessary to use a range of stimuli to ensure that all integration mechanisms are activated.

Cross-correlation analysis of inhibitory interactions in dorsal cochlear nucleus

1990 ◽  
Vol 64 (5) ◽  
pp. 1590-1610 ◽  
Author(s):  
H. F. Voigt ◽  
E. D. Young
Keyword(s):  
Correlation Analysis ◽  
Cochlear Nucleus ◽  
Cross Correlation ◽  
Discharge Rate ◽  
Dorsal Cochlear Nucleus ◽  
Type Ii ◽  
Type Iii ◽  
Type Iv ◽  
Cross Correlation Analysis ◽  
The Cross

1. Cross-correlation analysis was used to study the organization of inhibitory connections between type II or type III units and type IV principal cells in cat dorsal cochlear nucleus (DCN). Pairs of units were isolated using two microelectrodes so that information about the distance over which connections are made could be analyzed. Data were obtained from 51 pairs consisting of a type II and a type IV unit and from 22 pairs consisting of a type III and a type IV unit. The analyses in this paper concentrate on type II-type IV pairs. 2. Inhibitory troughs (ITs) are observed in the cross-correlograms of type II-type IV pairs (21/51 cases). An IT is a transient decrease in discharge probability in the postsynaptic (type IV) unit immediately after spikes in the presynaptic unit (type II). The average latency to the start of ITs is 0.73 ms, and the troughs are asymmetric with a faster leading phase. Small excitatory peaks accompany the ITs in type II units, but these are probably secondary effects associated with the IT. ITs are consistent with a monosynaptic, inhibitory connection between type II and type IV units. A variety of evidence suggests that type II responses are recorded from vertical cells, an interneuron in the deep layer of the DCN that may be glycinergic. 3. The cross-correlograms of type III-type IV pairs are more complex and variable than those of type II-type IV pairs--ITs are seen in 4/22 cases, and peaks of correlation that are symmetrically located around the origin (central mound or CM) are seen in 4/22 cases; two cases have both an IT and a CM. CMs result from shared sources of input. Whereas type II-type IV correlogram features change primarily in amplitude as stimulus conditions change, correlogram features in some type III-type IV pairs change qualitatively with stimulus conditions; correlograms are flat for some stimuli and show ITs or CMs or mixtures of the two for others. This variability suggests that the circuitry associated with type III-type IV pairs is more complex than a monosynaptic connection, and further analysis of type III-type IV pairs was not done. 4. The strength of inhibition for an IT is measured as the area under the IT (effectiveness) and as effectiveness divided by the postsynaptic discharge rate (association index).(ABSTRACT TRUNCATED AT 400 WORDS)

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