Topographic organization of interaural‐intensity‐difference sensitivity in deep superior colliculus

1983 ◽  
Vol 73 (S1) ◽  
pp. S61-S61
Author(s):  
Lisa Z. Wise ◽  
Dexter R. F. Irvine
Keyword(s):  
Superior Colliculus ◽  
Intensity Difference ◽  
Topographic Organization ◽  
Interaural Intensity Difference

Topographic organization of interaural intensity difference sensitivity in deep layers of cat superior colliculus: implications for auditory spatial representation

1985 ◽  
Vol 54 (2) ◽  
pp. 185-211 ◽  
Author(s):  
L. Z. Wise ◽  
D. R. Irvine
Keyword(s):  
Superior Colliculus ◽  
Dynamic Range ◽  
Excitatory Input ◽  
Stimulus Level ◽  
Intensity Difference ◽  
Topographic Organization ◽  
Interaural Intensity Difference ◽  
F Cells ◽  
Deep Layers ◽  
I Cells

Sensitivity to interaural intensity difference (IID) was examined for 103 neurons in the deep layers of superior colliculus (SC) in ketamine barbiturate-anesthetized cats. Noise stimuli were presented dichotically, and IID sensitivity functions were generated while keeping the average binaural intensity (ABI) of stimulation constant. Neurons of three binaural classes were found to be IID sensitive. Neurons receiving excitatory contralateral input and inhibitory ipsilateral input (EO/I cells, 55% of sample) had steplike IID functions, with maximum response at IIDs corresponding to contralateral azimuths (positive IIDs), total suppression at IIDs corresponding to ipsilateral azimuths (negative IIDs), and cutoffs at different positions along the IID axis for different neurons. Neurons responsive only to binaural stimulation (OO/F cells, 15% of sample) had IID functions with a sharp peak in the range of 0 to 10 dB IID. Cells receiving excitatory input contralaterally and a facilitatory ipsilateral input (EO/F cells, 7% of sample) had IID functions of intermediate shape, with a peak in the range of 10 to 20 dB IID and a sharper cutoff near zero IID than at larger positive IIDs. The sharpness of IID cutoff for EO/I cells was quantified by measuring an 80% IID dynamic range. Neurons with 80% IID dynamic ranges of less than 26 dB were judged to have sharp cutoffs. The position along the IID axis of the IID cutoff for these cells was quantified by recording the IID at which the response was at 50% of maximum (half-maximal IID). A topographic organization of EO/I cells with sharp IID cutoffs was found along the rostrocaudal axis of SC, such that rostral EO/I cells had IID functions with half-maximal IIDs near zero, while increasingly caudal EO/I cells had progressively larger (positive) half-maximal IIDs. Although detailed maps could not be obtained in individual animals, the topography was observed in each of nine experiments in which EO/I cells were located in two or more rostrocaudal locations (P = 0.00002). The effect of stimulus level on the stability of IID cutoff was examined for 13 EO/I cells. The majority (85%) showed less than 10 dB variation in half-maximal IID across a range of suprathreshold ABIs, indicating that EO/I cells in SC generally exhibit stability in cutoff with changes in intensity of broadband stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

Interaural intensity difference and ear advantage in listening to dichotic consonant–vowel syllable pairs

2007 ◽  
Vol 1185 ◽  
pp. 195-200 ◽  
Author(s):  
Jussi Tallus ◽  
Kenneth Hugdahl ◽  
Kimmo Alho ◽  
Svjatoslav Medvedev ◽  
Heikki Hämäläinen
Keyword(s):  
Intensity Difference ◽  
Interaural Intensity Difference ◽  
Ear Advantage

Topographic organization of the retinocollicular projection in the neonatal rat

1990 ◽  
Vol 4 (4) ◽  
pp. 313-329 ◽  
Author(s):  
J. Peter ◽  
A. Yhip ◽  
Michael A. Kirby
Keyword(s):  
Superior Colliculus ◽  
Retinal Ganglion Cells ◽  
Ganglion Cells ◽  
Neonatal Rat ◽  
Retinal Ganglion ◽  
Topographic Organization ◽  
Retinocollicular Projection

AbstractThe topographic order of the retinocollicular projection in the rat was examined from birth until maturity. Small, localized deposits of rhodamine-filled latex microspheres were placed into the superior colliculus at different locations. To minimize labeling fibers of passage deposit sites were typically, although not exclusively, placed into the caudal-lateral pole of the colliculus. Examination of the area and density of labeled cells in the retinae of these animals led to the following conclusions: (1) At each age examined, the location of the majority of labeled cells was observed to be in appropriate topographic register with the deposit site in the superior colliculus. (2) Confirming the work of previous investigators, errors in topographic projection were observed. These were present in both the contralateral and ipsilateral retinae and decreased with increasing postnatal age. The mature pattern was present by P10. (3) Quantitatively, the number of retinal ganglion cells terminating nontopographically within the colliculus constituted a relatively minor proportion of the total number of labeled cells in both retinae. It is concluded that the majority of the retinal ganglion cells make topographically appropriate terminations within the superior colliculus during development.

IID Sensitivity Differs Between Two Principal Centers in the Interaural Intensity Difference Pathway: the LSO and the IC

1998 ◽  
Vol 79 (5) ◽  
pp. 2416-2431 ◽  
Author(s):  
Thomas J. Park
Keyword(s):  
High Frequency ◽  
Direct Evidence ◽  
Extracellular Recording ◽  
Intensity Difference ◽  
Interaural Intensity Difference ◽  
Pharmacological Studies ◽  
Strong Excitation ◽  
The Difference ◽  
Intense Signal ◽  
Response Feature

Park, Thomas J. IID sensitivity differs between two principal centers in the interaural intensity difference pathway: the LOS and the IC. J. Neurophysiol. 79: 2416–2431, 1998. Interaural intensity differences (IIDs) are the chief cues that animals use to localize high-frequency sounds. Neurons that are sensitive to IIDs are excited by sound at one ear and inhibited by sound at the other. Thus a given IID generates a combination of excitation and inhibition that is reflected in a cell's spike count. In mammals, the so-called “IID pathway” begins in the lateral superior olive (LSO), which is dominated by the type of IID-sensitive neurons just described. The LSO then sends a prominent projection to the inferior colliculus (IC), which also contains a substantial population of IID-sensitive cells. Recent pharmacological studies have suggested that the response properties of IID-sensitive neurons in the IC undergo considerable processing and thus should not simply reflect the output of the LSO. However, we have no direct evidence as to whether IID sensitivity, the defining response feature of these cells, differs at these two levels. The present study makes this direct comparison in the Mexican free-tailed bat, a species that relies greatly on high-frequency hearing and thus on IIDs for localizing sounds in space. Extracellular recording techniques were used to obtain IID functions from 50 IC neurons. Comparable data from 50 LSO cells were available from a previous study. The main result was that IID sensitivity significantly differed between cells in the LSO and the IC. Among LSO cells, sensitivity was centered ∼0 dB (no intensity difference between the ears) whereas, in the IC, sensitivity was biased toward the inhibitory ear: on average, IC cells required a more intense signal at the inhibitory ear to reach the same degree of suppression as observed in LSO cells. Further analysis showed that the vast majority of IC cells (88%) exhibited a mismatch in the latencies of their inputs: inhibition arrived later when an equally strong excitation and inhibition were elicited; this reduced the effectiveness of the inhibition. Because latency shortens with increasing stimulus intensity, an IID with a more intense signal at the inhibitory ear could equate the latencies of excitation and inhibition, increasing the effectiveness of the inhibition. This result suggests that latency mismatches account, to a great extent, for the difference in sensitivity between the LSO and the IC; and when mismatches were negated by electronically time shifting the signals to the ears, sensitivity was no longer significantly different between the two nuclei.

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