Limits...
Low-frequency envelope sensitivity produces asymmetric binaural tuning curves.

Agapiou JP, McAlpine D - J. Neurophysiol. (2008)

Bottom Line: This suggests a stereotyped pattern of input to the IC.In the course of this analysis, we were also able to determine the contribution of time and phase components to neurons' internal delays.These findings have important consequences for the neural representation of interaural timing differences and interaural correlation-cues critical to the perception of acoustic space.

View Article: PubMed Central - PubMed

Affiliation: Ear Institute, Department of Neuroscience, Physiology and Pharmacology, University College London, London, UK. john.agapiou@mail.rockefeller.edu

ABSTRACT
Neurons in the auditory midbrain are sensitive to differences in the timing of sounds at the two ears--an important sound localization cue. We used broadband noise stimuli to investigate the interaural-delay sensitivity of low-frequency neurons in two midbrain nuclei: the inferior colliculus (IC) and the dorsal nucleus of the lateral lemniscus. Noise-delay functions showed asymmetries not predicted from a linear dependence on interaural correlation: a stretching along the firing-rate dimension (rate asymmetry), and a skewing along the interaural-delay dimension (delay asymmetry). These asymmetries were produced by an envelope-sensitive component to the response that could not entirely be accounted for by monaural or binaural nonlinearities, instead indicating an enhancement of envelope sensitivity at or after the level of the superior olivary complex. In IC, the skew-like asymmetry was consistent with intermediate-type responses produced by the convergence of ipsilateral peak-type inputs and contralateral trough-type inputs. This suggests a stereotyped pattern of input to the IC. In the course of this analysis, we were also able to determine the contribution of time and phase components to neurons' internal delays. These findings have important consequences for the neural representation of interaural timing differences and interaural correlation-cues critical to the perception of acoustic space.

Show MeSH

Related in: MedlinePlus

Testing the model of convergence. The CD and CP are negatively correlated in both DNLL (A) and IC (D), matching the relationship predicted in Fig. 10F. The dotted line indicates the relationship y = 1/8 − x/2, which corresponds to a linear shift from a stereotypical peak-type neuron (CD = 1/8 cyc re CF, CP = 0 cyc) to a stereotypical trough-type neuron (CD = −1/8 cyc re CF, CP = 0.5 cyc). In DNLL, the CP is not correlated with the rate asymmetry (B) or the delay asymmetry (C). However, in IC, the CP is negatively correlated with the rate asymmetry index (RAI, E) and the delay asymmetry appears to show a dependence on the squared sine of the CP (F). This is a close match to the relationships shown in Fig. 10, G and H. Both peak-type responses (upward triangles) and trough-type responses (downward triangles) are shown.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2576218&req=5

f11: Testing the model of convergence. The CD and CP are negatively correlated in both DNLL (A) and IC (D), matching the relationship predicted in Fig. 10F. The dotted line indicates the relationship y = 1/8 − x/2, which corresponds to a linear shift from a stereotypical peak-type neuron (CD = 1/8 cyc re CF, CP = 0 cyc) to a stereotypical trough-type neuron (CD = −1/8 cyc re CF, CP = 0.5 cyc). In DNLL, the CP is not correlated with the rate asymmetry (B) or the delay asymmetry (C). However, in IC, the CP is negatively correlated with the rate asymmetry index (RAI, E) and the delay asymmetry appears to show a dependence on the squared sine of the CP (F). This is a close match to the relationships shown in Fig. 10, G and H. Both peak-type responses (upward triangles) and trough-type responses (downward triangles) are shown.

Mentions: To test whether this model of convergence could explain the observed responses, the correlations between the CP and the other parameters were examined. As discussed earlier, a strong negative correlation was observed between the CP and the CD in both DNLL and IC (Fig. 11, A and D), which was consistent with that predicted by the model. In IC, the RAI showed a strong negative correlation with the CP (Fig. 11E; Dn = 0.50, P < 0.01, Mardia's linear-circular rank correlation coefficient), with peak-type neurons showing large positive RAIs, and trough-type neurons showing large negative RAIs. The delay asymmetry was also correlated with CP (Dn = 0.34, P < 0.05), showing a correlation with the squared sine of the CP (Fig. 11F; r = 0.53, P = 0.018, Spearman's rank correlation coefficient). In the DNLL, the CP showed no relationship with the RAI (Fig. 11B; P > 0.1) and, although the CP appeared to be positively correlated with the delay asymmetry (Fig. 11C), this was not significant (P > 0.1).


Low-frequency envelope sensitivity produces asymmetric binaural tuning curves.

Agapiou JP, McAlpine D - J. Neurophysiol. (2008)

Testing the model of convergence. The CD and CP are negatively correlated in both DNLL (A) and IC (D), matching the relationship predicted in Fig. 10F. The dotted line indicates the relationship y = 1/8 − x/2, which corresponds to a linear shift from a stereotypical peak-type neuron (CD = 1/8 cyc re CF, CP = 0 cyc) to a stereotypical trough-type neuron (CD = −1/8 cyc re CF, CP = 0.5 cyc). In DNLL, the CP is not correlated with the rate asymmetry (B) or the delay asymmetry (C). However, in IC, the CP is negatively correlated with the rate asymmetry index (RAI, E) and the delay asymmetry appears to show a dependence on the squared sine of the CP (F). This is a close match to the relationships shown in Fig. 10, G and H. Both peak-type responses (upward triangles) and trough-type responses (downward triangles) are shown.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2576218&req=5

f11: Testing the model of convergence. The CD and CP are negatively correlated in both DNLL (A) and IC (D), matching the relationship predicted in Fig. 10F. The dotted line indicates the relationship y = 1/8 − x/2, which corresponds to a linear shift from a stereotypical peak-type neuron (CD = 1/8 cyc re CF, CP = 0 cyc) to a stereotypical trough-type neuron (CD = −1/8 cyc re CF, CP = 0.5 cyc). In DNLL, the CP is not correlated with the rate asymmetry (B) or the delay asymmetry (C). However, in IC, the CP is negatively correlated with the rate asymmetry index (RAI, E) and the delay asymmetry appears to show a dependence on the squared sine of the CP (F). This is a close match to the relationships shown in Fig. 10, G and H. Both peak-type responses (upward triangles) and trough-type responses (downward triangles) are shown.
Mentions: To test whether this model of convergence could explain the observed responses, the correlations between the CP and the other parameters were examined. As discussed earlier, a strong negative correlation was observed between the CP and the CD in both DNLL and IC (Fig. 11, A and D), which was consistent with that predicted by the model. In IC, the RAI showed a strong negative correlation with the CP (Fig. 11E; Dn = 0.50, P < 0.01, Mardia's linear-circular rank correlation coefficient), with peak-type neurons showing large positive RAIs, and trough-type neurons showing large negative RAIs. The delay asymmetry was also correlated with CP (Dn = 0.34, P < 0.05), showing a correlation with the squared sine of the CP (Fig. 11F; r = 0.53, P = 0.018, Spearman's rank correlation coefficient). In the DNLL, the CP showed no relationship with the RAI (Fig. 11B; P > 0.1) and, although the CP appeared to be positively correlated with the delay asymmetry (Fig. 11C), this was not significant (P > 0.1).

Bottom Line: This suggests a stereotyped pattern of input to the IC.In the course of this analysis, we were also able to determine the contribution of time and phase components to neurons' internal delays.These findings have important consequences for the neural representation of interaural timing differences and interaural correlation-cues critical to the perception of acoustic space.

View Article: PubMed Central - PubMed

Affiliation: Ear Institute, Department of Neuroscience, Physiology and Pharmacology, University College London, London, UK. john.agapiou@mail.rockefeller.edu

ABSTRACT
Neurons in the auditory midbrain are sensitive to differences in the timing of sounds at the two ears--an important sound localization cue. We used broadband noise stimuli to investigate the interaural-delay sensitivity of low-frequency neurons in two midbrain nuclei: the inferior colliculus (IC) and the dorsal nucleus of the lateral lemniscus. Noise-delay functions showed asymmetries not predicted from a linear dependence on interaural correlation: a stretching along the firing-rate dimension (rate asymmetry), and a skewing along the interaural-delay dimension (delay asymmetry). These asymmetries were produced by an envelope-sensitive component to the response that could not entirely be accounted for by monaural or binaural nonlinearities, instead indicating an enhancement of envelope sensitivity at or after the level of the superior olivary complex. In IC, the skew-like asymmetry was consistent with intermediate-type responses produced by the convergence of ipsilateral peak-type inputs and contralateral trough-type inputs. This suggests a stereotyped pattern of input to the IC. In the course of this analysis, we were also able to determine the contribution of time and phase components to neurons' internal delays. These findings have important consequences for the neural representation of interaural timing differences and interaural correlation-cues critical to the perception of acoustic space.

Show MeSH
Related in: MedlinePlus