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A modeling study of the responses of the lateral superior olive to ipsilateral sinusoidally amplitude-modulated tones.

Wang L, Colburn HS - J. Assoc. Res. Otolaryngol. (2011)

Bottom Line: In the model, AHP channels alone were not sufficient to induce the observed rate decrease at high modulation frequencies.In contrast, both the small and large rate decreases were replicated when KLT channels were included in the LSO neuron model.These results support the conclusion that KLT channels may play a major role in the large rate decreases seen in some units and that background inhibition may be a contributing factor, a factor that could be adequate for small decreases.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Center for Hearing Research, Boston University, Boston, MA 02215, USA.

ABSTRACT
The lateral superior olive (LSO) is a brainstem nucleus that is classically understood to encode binaural information in high-frequency sounds. Previous studies have shown that LSO cells are sensitive to envelope interaural time difference in sinusoidally amplitude-modulated (SAM) tones (Joris and Yin, J Neurophysiol 73:1043-1062, 1995; Joris, J Neurophysiol 76:2137-2156, 1996) and that a subpopulation of LSO neurons exhibit low-threshold potassium currents mediated by Kv1 channels (Barnes-Davies et al., Eur J Neurosci 19:325-333, 2004). It has also been shown that in many LSO cells the average response rate to ipsilateral SAM tones decreases with modulation frequency above a few hundred Hertz (Joris and Yin, J Neurophysiol 79:253-269, 1998). This low-pass feature is not directly inherited from the inputs to the LSO since the response rate of these input neurons changes little with increasing modulation frequency. In the current study, an LSO cell model is developed to investigate mechanisms consistent with the responses described above, notably the emergent rate decrease with increasing frequency. The mechanisms explored included the effects of after-hyperpolarization (AHP) channels, the dynamics of low-threshold potassium channels (KLT), and the effects of background inhibition. In the model, AHP channels alone were not sufficient to induce the observed rate decrease at high modulation frequencies. The model also suggests that the background inhibition alone, possibly from the medial nucleus of the trapezoid body, can account for the small rate decrease seen in some LSO neurons, but could not explain the large rate decrease seen in other LSO neurons at high modulation frequencies. In contrast, both the small and large rate decreases were replicated when KLT channels were included in the LSO neuron model. These results support the conclusion that KLT channels may play a major role in the large rate decreases seen in some units and that background inhibition may be a contributing factor, a factor that could be adequate for small decreases.

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Average firing rate plotted as a function of modulation frequency for spherical bushy cells (A) and LSO units (B: ipsilateral modulation; C: contralateral modulation). Different curves in each panel represent different units [figure from Joris and Yin (1998)].
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Fig1: Average firing rate plotted as a function of modulation frequency for spherical bushy cells (A) and LSO units (B: ipsilateral modulation; C: contralateral modulation). Different curves in each panel represent different units [figure from Joris and Yin (1998)].

Mentions: While LSO responses to binaural SAM tones could largely be explained by the interaction between excitation and inhibition (Joris 1996), the responses to monaural SAM tones are less well understood. Specifically, the firing rate of LSO cells in response to ipsilateral SAM tones generally decreases rapidly with the increase in the modulation frequency (Joris and Yin 1998). In 12 of 13 LSO units shown in FigureĀ 1B, for example, the firing rate decreased with increasing modulation frequency (fm). However, the magnitude of the rate decrease and the firing rate at the highest modulation frequency varied among units.FIG. 1


A modeling study of the responses of the lateral superior olive to ipsilateral sinusoidally amplitude-modulated tones.

Wang L, Colburn HS - J. Assoc. Res. Otolaryngol. (2011)

Average firing rate plotted as a function of modulation frequency for spherical bushy cells (A) and LSO units (B: ipsilateral modulation; C: contralateral modulation). Different curves in each panel represent different units [figure from Joris and Yin (1998)].
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3298618&req=5

Fig1: Average firing rate plotted as a function of modulation frequency for spherical bushy cells (A) and LSO units (B: ipsilateral modulation; C: contralateral modulation). Different curves in each panel represent different units [figure from Joris and Yin (1998)].
Mentions: While LSO responses to binaural SAM tones could largely be explained by the interaction between excitation and inhibition (Joris 1996), the responses to monaural SAM tones are less well understood. Specifically, the firing rate of LSO cells in response to ipsilateral SAM tones generally decreases rapidly with the increase in the modulation frequency (Joris and Yin 1998). In 12 of 13 LSO units shown in FigureĀ 1B, for example, the firing rate decreased with increasing modulation frequency (fm). However, the magnitude of the rate decrease and the firing rate at the highest modulation frequency varied among units.FIG. 1

Bottom Line: In the model, AHP channels alone were not sufficient to induce the observed rate decrease at high modulation frequencies.In contrast, both the small and large rate decreases were replicated when KLT channels were included in the LSO neuron model.These results support the conclusion that KLT channels may play a major role in the large rate decreases seen in some units and that background inhibition may be a contributing factor, a factor that could be adequate for small decreases.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Center for Hearing Research, Boston University, Boston, MA 02215, USA.

ABSTRACT
The lateral superior olive (LSO) is a brainstem nucleus that is classically understood to encode binaural information in high-frequency sounds. Previous studies have shown that LSO cells are sensitive to envelope interaural time difference in sinusoidally amplitude-modulated (SAM) tones (Joris and Yin, J Neurophysiol 73:1043-1062, 1995; Joris, J Neurophysiol 76:2137-2156, 1996) and that a subpopulation of LSO neurons exhibit low-threshold potassium currents mediated by Kv1 channels (Barnes-Davies et al., Eur J Neurosci 19:325-333, 2004). It has also been shown that in many LSO cells the average response rate to ipsilateral SAM tones decreases with modulation frequency above a few hundred Hertz (Joris and Yin, J Neurophysiol 79:253-269, 1998). This low-pass feature is not directly inherited from the inputs to the LSO since the response rate of these input neurons changes little with increasing modulation frequency. In the current study, an LSO cell model is developed to investigate mechanisms consistent with the responses described above, notably the emergent rate decrease with increasing frequency. The mechanisms explored included the effects of after-hyperpolarization (AHP) channels, the dynamics of low-threshold potassium channels (KLT), and the effects of background inhibition. In the model, AHP channels alone were not sufficient to induce the observed rate decrease at high modulation frequencies. The model also suggests that the background inhibition alone, possibly from the medial nucleus of the trapezoid body, can account for the small rate decrease seen in some LSO neurons, but could not explain the large rate decrease seen in other LSO neurons at high modulation frequencies. In contrast, both the small and large rate decreases were replicated when KLT channels were included in the LSO neuron model. These results support the conclusion that KLT channels may play a major role in the large rate decreases seen in some units and that background inhibition may be a contributing factor, a factor that could be adequate for small decreases.

Show MeSH