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Responses of neurons in the marmoset primary auditory cortex to interaural level differences: comparison of pure tones and vocalizations.

Lui LL, Mokri Y, Reser DH, Rosa MG, Rajan R - Front Neurosci (2015)

Bottom Line: ILD sensitivity was heavily dependent on ABL: changes in ABL by ±20 dB SPL from the optimal level for ILD sensitivity led to significant decreases in ILD sensitivity for all stimuli, although ILD sensitivity to pure tones and Ock calls was most robust to such ABL changes.Our results demonstrate differences in ILD coding for pure tones and vocalizations, showing that ILD sensitivity in A1 to complex sounds cannot be simply extrapolated from that to pure tones.They also show A1 neurons do not show level-invariant representation of ILD, suggesting that such a representation of auditory space is likely to require population coding, and further processing at subsequent hierarchical stages.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Monash University Clayton, VIC, Australia ; Australian Research Council, Centre of Excellence for Integrative Brain Function, Monash University Clayton, VIC, Australia.

ABSTRACT
Interaural level differences (ILDs) are the dominant cue for localizing the sources of high frequency sounds that differ in azimuth. Neurons in the primary auditory cortex (A1) respond differentially to ILDs of simple stimuli such as tones and noise bands, but the extent to which this applies to complex natural sounds, such as vocalizations, is not known. In sufentanil/N2O anesthetized marmosets, we compared the responses of 76 A1 neurons to three vocalizations (Ock, Tsik, and Twitter) and pure tones at cells' characteristic frequency. Each stimulus was presented with ILDs ranging from 20 dB favoring the contralateral ear to 20 dB favoring the ipsilateral ear to cover most of the frontal azimuthal space. The response to each stimulus was tested at three average binaural levels (ABLs). Most neurons were sensitive to ILDs of vocalizations and pure tones. For all stimuli, the majority of cells had monotonic ILD sensitivity functions favoring the contralateral ear, but we also observed ILD sensitivity functions that peaked near the midline and functions favoring the ipsilateral ear. Representation of ILD in A1 was better for pure tones and the Ock vocalization in comparison to the Tsik and Twitter calls; this was reflected by higher discrimination indices and greater modulation ranges. ILD sensitivity was heavily dependent on ABL: changes in ABL by ±20 dB SPL from the optimal level for ILD sensitivity led to significant decreases in ILD sensitivity for all stimuli, although ILD sensitivity to pure tones and Ock calls was most robust to such ABL changes. Our results demonstrate differences in ILD coding for pure tones and vocalizations, showing that ILD sensitivity in A1 to complex sounds cannot be simply extrapolated from that to pure tones. They also show A1 neurons do not show level-invariant representation of ILD, suggesting that such a representation of auditory space is likely to require population coding, and further processing at subsequent hierarchical stages.

No MeSH data available.


Related in: MedlinePlus

Percentage of sensitivity type of for each stimulus type at each ABL. Each sub-plot shows data for each stimulus type, and each bar provides data for each ABL. Color code as illustrated by the legend on the right sub-plot indicates the type of ILD-sensitivity function.
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Figure 3: Percentage of sensitivity type of for each stimulus type at each ABL. Each sub-plot shows data for each stimulus type, and each bar provides data for each ABL. Color code as illustrated by the legend on the right sub-plot indicates the type of ILD-sensitivity function.

Mentions: Figure 2 shows the response patterns of four cells which exemplify the types of ILD sensitivity observed in A1. Cell A was always monotonically sensitive, favoring the contralateral ear regardless of stimulus type; this was the most frequently observed pattern in A1, representing approximately 59% of the total sample (Figure 3: red bars). Cell B is an example of a cell with sensitivity that, when present, is generally best described by a peaked function (here for pure tone, Tsik, and Twitter stimuli). Cell C's sensitivity to ILD depended on both stimulus type and ABL. Both peaked and monotonic responses were observed, depending on the stimulus and ABL (e.g., pure tone response). Interestingly, this cell was sensitive for ILDs in the Tsik call, but did not respond to the Twitter call, which has a similar frequency spectrum. The activity of Cell D can also be considered as complex, as its responses to certain stimuli were not predictable based on their spectral content; it responded only to the Ock stimulus, a stimulus which encompasses this cell's CF of 26 kHz, yet it did not show any response to ILDs in CF pure tones, or other calls.


Responses of neurons in the marmoset primary auditory cortex to interaural level differences: comparison of pure tones and vocalizations.

Lui LL, Mokri Y, Reser DH, Rosa MG, Rajan R - Front Neurosci (2015)

Percentage of sensitivity type of for each stimulus type at each ABL. Each sub-plot shows data for each stimulus type, and each bar provides data for each ABL. Color code as illustrated by the legend on the right sub-plot indicates the type of ILD-sensitivity function.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4403308&req=5

Figure 3: Percentage of sensitivity type of for each stimulus type at each ABL. Each sub-plot shows data for each stimulus type, and each bar provides data for each ABL. Color code as illustrated by the legend on the right sub-plot indicates the type of ILD-sensitivity function.
Mentions: Figure 2 shows the response patterns of four cells which exemplify the types of ILD sensitivity observed in A1. Cell A was always monotonically sensitive, favoring the contralateral ear regardless of stimulus type; this was the most frequently observed pattern in A1, representing approximately 59% of the total sample (Figure 3: red bars). Cell B is an example of a cell with sensitivity that, when present, is generally best described by a peaked function (here for pure tone, Tsik, and Twitter stimuli). Cell C's sensitivity to ILD depended on both stimulus type and ABL. Both peaked and monotonic responses were observed, depending on the stimulus and ABL (e.g., pure tone response). Interestingly, this cell was sensitive for ILDs in the Tsik call, but did not respond to the Twitter call, which has a similar frequency spectrum. The activity of Cell D can also be considered as complex, as its responses to certain stimuli were not predictable based on their spectral content; it responded only to the Ock stimulus, a stimulus which encompasses this cell's CF of 26 kHz, yet it did not show any response to ILDs in CF pure tones, or other calls.

Bottom Line: ILD sensitivity was heavily dependent on ABL: changes in ABL by ±20 dB SPL from the optimal level for ILD sensitivity led to significant decreases in ILD sensitivity for all stimuli, although ILD sensitivity to pure tones and Ock calls was most robust to such ABL changes.Our results demonstrate differences in ILD coding for pure tones and vocalizations, showing that ILD sensitivity in A1 to complex sounds cannot be simply extrapolated from that to pure tones.They also show A1 neurons do not show level-invariant representation of ILD, suggesting that such a representation of auditory space is likely to require population coding, and further processing at subsequent hierarchical stages.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Monash University Clayton, VIC, Australia ; Australian Research Council, Centre of Excellence for Integrative Brain Function, Monash University Clayton, VIC, Australia.

ABSTRACT
Interaural level differences (ILDs) are the dominant cue for localizing the sources of high frequency sounds that differ in azimuth. Neurons in the primary auditory cortex (A1) respond differentially to ILDs of simple stimuli such as tones and noise bands, but the extent to which this applies to complex natural sounds, such as vocalizations, is not known. In sufentanil/N2O anesthetized marmosets, we compared the responses of 76 A1 neurons to three vocalizations (Ock, Tsik, and Twitter) and pure tones at cells' characteristic frequency. Each stimulus was presented with ILDs ranging from 20 dB favoring the contralateral ear to 20 dB favoring the ipsilateral ear to cover most of the frontal azimuthal space. The response to each stimulus was tested at three average binaural levels (ABLs). Most neurons were sensitive to ILDs of vocalizations and pure tones. For all stimuli, the majority of cells had monotonic ILD sensitivity functions favoring the contralateral ear, but we also observed ILD sensitivity functions that peaked near the midline and functions favoring the ipsilateral ear. Representation of ILD in A1 was better for pure tones and the Ock vocalization in comparison to the Tsik and Twitter calls; this was reflected by higher discrimination indices and greater modulation ranges. ILD sensitivity was heavily dependent on ABL: changes in ABL by ±20 dB SPL from the optimal level for ILD sensitivity led to significant decreases in ILD sensitivity for all stimuli, although ILD sensitivity to pure tones and Ock calls was most robust to such ABL changes. Our results demonstrate differences in ILD coding for pure tones and vocalizations, showing that ILD sensitivity in A1 to complex sounds cannot be simply extrapolated from that to pure tones. They also show A1 neurons do not show level-invariant representation of ILD, suggesting that such a representation of auditory space is likely to require population coding, and further processing at subsequent hierarchical stages.

No MeSH data available.


Related in: MedlinePlus