Physiological studies and neural mechanisms of echo suppression in the inferior colliculus of the cat

1999 ◽  
Vol 105 (2) ◽  
pp. 1150-1150
Author(s):  
Ruth Y. Litovsky ◽  
Bertrand Delgutte ◽  
Tom C. T. Yin
Keyword(s):  
Inferior Colliculus ◽  
Neural Mechanisms ◽  
Physiological Studies ◽  
Echo Suppression

Physiological Studies of the Precedence Effect in the Inferior Colliculus of the Cat. II. Neural Mechanisms

1998 ◽  
Vol 80 (3) ◽  
pp. 1302-1316 ◽  
Author(s):  
Ruth Y. Litovsky ◽  
Tom C. T. Yin
Keyword(s):  
Inferior Colliculus ◽  
Free Field ◽  
Neural Mechanisms ◽  
Precedence Effect ◽  
Medial Superior Olive ◽  
Mixed Effect ◽  
Source Level ◽  
Physiological Studies ◽  
Interaural Differences ◽  
Lead Location

Litovsky, Ruth Y. and Tom C. T. Yin. Physiological studies of the precedence effect in the inferior colliculus of the cat. II. Neural mechanisms. J. Neurophysiol. 80: 1302–1316, 1998. We studied the responses of neurons in the inferior colliculus (IC) of cats to stimuli known to evoke the precedence effect (PE). This paper focuses on stimulus conditions that probe the neural mechanisms underlying the PE but that are not usually encountered in a natural situation. Experiments were conducted under both free-field (anechoic chamber) and dichotic (headphones) conditions. We found that in free field the amount of suppression of the lagging response depended on the location of the leading source. With stimuli in the azimuthal plane, the majority (84%) of units showed stronger suppression of the lagging response for a leading stimulus placed in the cell's responsive area as compared with a lead in the unresponsive field. A smaller number of units showed stronger suppression for a lead placed in the unresponsive field, and a few showed little effect of the lead location. In the elevational plane, there was less sensitivity of the leading source to changes in location, but for those cells in which there was sensitivity, suppression was always stronger when the lead was in the cell's responsive area. Studies on stimulus locations also were conducted under dichotic conditions by varying the interaural differences in time (ITD) of the leading source. Results were consistent with those obtained in free field, suggesting that ITDs play an important role in determining the amount of suppression that was observed as a function of leading stimulus location. In addition to location and ITD, we also studied the effect of varying the relative levels of the lead and lag as well as stimulus duration. For all units studied, increasing the level of the leading stimulus while holding the lagging stimulus constant resulted in increased suppression. Similar effects of leading source level were observed in azimuth and elevation. The effect of varying the duration of the leading source also showed that longer duration stimuli produce stronger suppression; this finding was observed both in azimuth and elevation. We also compared the suppression observed under binaural and monaural contralateral conditions and found a mixed effect: some neurons show stronger suppression under binaural conditions, others to monaural contralateral conditions, and still others show no effect. The results presented here support the hypothesis that the PE reflects a long-lasting inhibition evoked by the leading stimulus. Five possible sources for the inhibition are considered: the auditory nerve, intrinsic circuits in the cochlear nucleus, medial and lateral nuclei of the trapezoid body inhibition to the medial superior olive, dorsal nucleus of the lateral lemniscus (DNLL) inhibition to the ICC, and intrinsic circuits in the ICC itself.

scholarly journals Physiological Studies of the Precedence Effect in the Inferior Colliculus of the Cat. I. Correlates of Psychophysics

1998 ◽  
Vol 80 (3) ◽  
pp. 1285-1301 ◽  
Author(s):  
Ruth Y. Litovsky ◽  
Tom C. T. Yin
Keyword(s):  
Inferior Colliculus ◽  
Free Field ◽  
Median Plane ◽  
Stimulus Level ◽  
Central Nucleus ◽  
Precedence Effect ◽  
Discharge Rates ◽  
Physiological Studies ◽  
Echo Suppression ◽  
Maximal Suppression

Litovsky, Ruth Y. and Tom C. T. Yin. Physiological studies of the precedence effect in the inferior colliculus of the cat. I. Correlates of psychophysics. J. Neurophysiol. 80: 1285–1301, 1998. The precedence effect (PE) is experienced when two spatially separated sounds are presented with such a brief delay that only a single auditory image at or toward the location of the leading source is perceived. The responses of neurons in the central nucleus of the inferior colliculus (ICC) of cats were studied using stimuli that are known to elicit the PE, focusing on the effects of changes in stimulus conditions that a listener might encounter in a natural situation. Experiments were conducted under both free-field (anechoic chamber) and dichotic (headphones) conditions. In free field, the PE was simulated by presenting two sounds from different loudspeakers with one sound delayed relative to the other. Either click or noise stimuli (2- to 10-ms duration) were used. Dichotically, the same conditions were simulated by presenting two click or noise pairs separated by an interstimulus delay (ISD) with interaural time differences (ITDs) imposed separately for each pair. At long ISDs, all neurons responded to both leading and lagging sources as if they were delivered alone. As the ISDs were shortened, the lagging response became suppressed. The ISD of half-maximal suppression varied considerably within the population of neurons studied, ranging from 2 to 100 ms, with means of 35 and 38 ms for free field and dichotic conditions, respectively. Several correlates of psychophysical findings were observed in ICC neurons: suppression was usually stronger with lower overall stimulus level and longer duration stimuli. Suppression also was compared along the azimuth and elevation in free field by placing the lagging source at (0°,0°), which is common to both axes, and the leading sources at locations along either plane that generated similar discharge rates. All neurons that showed suppression along the azimuth also did so in the elevation. In addition, there was a high correlation in the ISD of half-maximal suppression along the two planes ( r = 0.87). These findings suggest that interaural difference cues, which are robust along the horizontal axis but minimal in the median plane, are not necessary for neural correlates of the PE to be manifested. Finally, single-neuron responses did not demonstrate a correlate of build-up of suppression, a phenomenon whereby echo suppression accumulates with ongoing stimulation. This finding adds credibility to theories about the PE that argue for a “higher order” component of the PE.

Effects of Amplitude Modulation on the Coding of Interaural Time Differences of Low-Frequency Sounds in the Inferior Colliculus. II. Neural Mechanisms

2003 ◽  
Vol 90 (5) ◽  
pp. 2827-2836 ◽  
Author(s):  
W. R. D'Angelo ◽  
S. J. Sterbing ◽  
E.-M. Ostapoff ◽  
S. Kuwada
Keyword(s):  
Inferior Colliculus ◽  
Background Noise ◽  
Modulation Depth ◽  
Interaural Time Difference ◽  
Low Frequency ◽  
Companion Paper ◽  
Neural Mechanisms ◽  
Physical Factors ◽  
Correlation Spectrum ◽  
The Difference

In our companion paper, we reported on interaural time difference (ITD)-sensitive neurons that enhanced, suppressed, or did not change their response when identical AM was added to both ears. Here, we first examined physical factors such as the difference in the interaural correlation, spectrum, or energy between the modulated and unmodulated signals. These were insufficient to explain the observed enhancement and suppression. We then examined neural mechanisms by selectively modulating the signal to each ear, varying modulation depth, and adding background noise to the unmodulated signal. These experiments implicated excitatory and inhibitory monaural inputs to the inferior colliculus (IC). These monaural inputs are postulated to adapt to an unmodulated signal and adapt less to a modulated signal. Thus enhancement or suppression is created by the convergence of these excitatory or inhibitory inputs with the inputs from the binaural comparators. Under modulation, the role of the monaural input is to shift the threshold of the IC neuron. Consistent with this role, background noise mimicked the effect of modulation. Functionally, enhancement and suppression may serve in detecting the degree of modulation in a sound source while preserving ITD information.

scholarly journals Roles of Inhibition in Complex Auditory Responses in the Inferior Colliculus: Inhibited Combination-Sensitive Neurons

2006 ◽  
Vol 95 (4) ◽  
pp. 2179-2192 ◽  
Author(s):  
Kiran Nataraj ◽  
Jeffrey J. Wenstrup
Keyword(s):  
Inferior Colliculus ◽  
Low Frequency ◽  
Neural Mechanisms ◽  
The Other ◽  
Inhibitory Neurons ◽  
Type I ◽  
Excitatory Response ◽  
Frequency Responses ◽  
Auditory Responses ◽  
Vocal Signals

We studied the functional properties and underlying neural mechanisms associated with inhibitory combination-sensitive neurons in the mustached bat's inferior colliculus (IC). In these neurons, the excitatory response to best frequency tones was suppressed by lower frequency signals (usually in the range of 12–30 kHz) in a time-dependant manner. Of 143 inhibitory units, the majority (71%) were type I, in which low-frequency sounds evoked inhibition only. In the remainder, however, the low-frequency inhibitory signal also evoked excitation. Of these, excitation preceded the inhibition in type E/I units (16%), whereas in type I/E units (13%), excitation followed the inhibition. Type E/I and I/E units were distinct in the tuning and threshold sensitivity of low-frequency responses, whereas type I units overlapped the other types in these features. In 71 neurons, antagonists to receptors for glycine [strychnine (STRY)] or GABA [bicuculline (BIC)] were applied microiontophoretically. These antagonists failed to eliminate combination-sensitive inhibition in 92% (STRY), 93% (BIC), and 87% (BIC + STRY) of the type I units tested. However, inhibition was reduced in many neurons. Results were similar for type E/I and I/E inhibitory neurons. The results indicate that there are distinct populations of combination-sensitive inhibited neurons in the IC and that these populations are at least partly independent of glycine or GABAA receptors in the IC. We propose that these populations originate in different brain stem auditory nuclei, that they may be modified by interactions within the IC, and that they may perform different spectrotemporal analyses of vocal signals.

scholarly journals Prevalence of Stereotypical Responses to Mistuned Complex Tones in the Inferior Colliculus

2005 ◽  
Vol 94 (5) ◽  
pp. 3523-3537 ◽  
Author(s):  
Donal G. Sinex ◽  
Hongzhe Li ◽  
David S. Velenovsky
Keyword(s):  
Inferior Colliculus ◽  
Major Effect ◽  
Stimulus Level ◽  
Neural Mechanisms ◽  
Discharge Pattern ◽  
Harmonic Complex ◽  
Long Latency ◽  
Complex Tones ◽  
Discharge Patterns ◽  
Response Envelope

The human auditory system has an exceptional ability to separate competing sounds, but the neural mechanisms that underlie this ability are not understood. Responses of inferior colliculus (IC) neurons to “mistuned” complex tones were measured to investigate possible neural mechanisms for spectral segregation. A mistuned tone is a harmonic complex tone in which the frequency of one component has been changed; that component may be heard as a separate sound source, suggesting that the mistuned tone engages the same mechanisms that contribute to the segregation of natural sounds. In this study, the harmonic tone consisted of eight harmonics of 250 Hz; in the mistuned tone, the frequency of the fourth harmonic was increased by 12% (120 Hz). The mistuned tone elicited a stereotypical discharge pattern, consisting of peaks separated by about 8 ms and a response envelope modulated with a period of 100 ms, which bore little resemblance to the discharge pattern elicited by the harmonic tone or to the stimulus waveform. Similar discharge patterns were elicited from many neurons with a range of characteristic frequencies, especially from neurons that exhibited short-latency sustained responses to pure tones. In contrast, transient and long-latency neurons usually did not exhibit the stereotypical discharge pattern. The discharge pattern was generally stable when the stimulus level or component phase was varied; the major effect of these manipulations was to shift the phase of the response envelope. Simulation of IC responses with a computational model suggested that off-frequency inhibition could produce discharge patterns with these characteristics.

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