An Overrepresentation of High Frequencies in the Mouse Inferior Colliculus Supports the Processing of Ultrasonic Vocalizations

1. The discharges of 632 units were isolated extracellularly during 42 penetrations of the central nucleus of the inferior colliculus (ICC) in 21 adult cats lightly anesthetized with pentobarbital and ketamine. Microelectrode penetrations were directed from caudal to rostral through ICC, parallel to the Horsley-Clarke (H-C) horizontal and sagittal planes. 2. The threshold best frequency (BF) and binaural response properties were examined for each unit, with the aim of elucidating the organization of these discharge characteristics within ICC. 3. Binaural unit classes consisted of monaural (contralateral) (EO), binaurally phase-sensitive (delay), contralateral excitatory/ipsilateral inhibitory (EI), binaurally excitatory (EE), and other more heterogeneous interaction patterns (other). 4. Detailed histological reconstruction of electrode tracks allowed the recording site for each unit to be related to the three dimensions of ICC. This structure was divided into three lateromedial and three rostrocaudal blocks such that each block contained a similar number of units, enabling meaningful statistical comparisons. Low (3.2 kHz greater than BF) and high (3.2 kHz less than BF) best-frequency classes provided a correlate of dorsoventral location. 5. The arrangements of BFs within ICC were found to be compatible with a model of this structure in which units having similar BFs are organized into layers lying in the H-C horizontal plane medially and gradually tilting in both a ventrolateral and ventrorostral direction. Low frequencies are concentrated dorsally and laterally; high frequencies, ventrally and medially. A rostrocaudal BF difference arises only in lateral aspects of the ICC, where lower frequencies are encountered rostrally. 6. Binaural response classes were distributed differentially throughout ICC. Thus, EO units were concentrated caudally, ventrally, and laterally, while delay units were in greatest numbers rostrally, dorsally, and laterally--almost totally segregated from EO and EI units. The latter populations overlapped ventrally and laterally, but EI units were in greatest density rostrally. The EE class occurred throughout the nucleus, but was most common medially. 7. It is suggested that the differential distributions of binaural responses reflect a partial segregation of the afferents, arising in the superior olive and cochlear nucleus, which terminate in ICC. The central nucleus of the inferior colliculus thus may be composed of several functionally segregated subregions contained within a common tonotopic organization.

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Inferior colliculus. I. Comparison of response properties of neurons in central, pericentral, and external nuclei of adult cat

Journal of Neurophysiology ◽

10.1152/jn.1975.38.5.1196 ◽

1975 ◽

Vol 38 (5) ◽

pp. 1196-1207 ◽

Cited By ~ 187

Author(s):

L. M. Aitkin ◽

W. R. Webster ◽

J. L. Veale ◽

D. C. Crosby

Keyword(s):

Inferior Colliculus ◽

Physiological Responses ◽

Cell Types ◽

Central Nucleus ◽

Low Frequencies ◽

High Frequencies ◽

The Common ◽

Adult Cat ◽

Tonal Stimuli ◽

Anesthetized Cat

The responses of 150 units in the central (ICC), pericentral (ICP), and external nuclei (ICX) of the inferior colliculus of the anesthetized cat were studied in relation to their tuning characteristics and binaural responses to tonal stimuli. Units in ICC were characterized by sharp tuning and binaural responses, while those in ICP and ICX were frequently very broadly tuned with a poorly defined best frequency. Nonetheless, in the latter nuclei a tendency existed for tonotopic organization to occur with high frequencies located externally and low frequencies at the margins of the central nucleus. Tuning measurements were hampered by the common occurrence of habituation in the discharges of single units in ICP and, to a lesser extend, ICX. The majority of units in ICP could be differentiated from those in ICX by their monaural input. Speculations were advanced linking anatomical cell types to physiological responses in the three nuclei and into the possible functional significance of the different behavior of units to tonal stimuli.

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Stimulus-frequency-dependent dominance of sound localization cues across the cochleotopic map of the inferior colliculus

Journal of Neurophysiology ◽

10.1152/jn.00713.2019 ◽

2020 ◽

Vol 123 (5) ◽

pp. 1791-1807 ◽

Cited By ~ 1

Author(s):

Ryan Dorkoski ◽

Kenneth E. Hancock ◽

Gareth A. Whaley ◽

Timothy R. Wohl ◽

Noelle C. Stroud ◽

...

Keyword(s):

Inferior Colliculus ◽

Division Of Labor ◽

Sound Localization ◽

High Frequency ◽

Stimulus Frequency ◽

Neural Responses ◽

Auditory Midbrain ◽

Sound Sources ◽

High Frequencies ◽

Midbrain Neurons

A “division of labor” has previously been assumed in which the directions of low- and high-frequency sound sources are thought to be encoded by neurons preferentially sensitive to low and high frequencies, respectively. Contrary to this, we found that auditory midbrain neurons encode the directions of both low- and high-frequency sounds regardless of their preferred frequencies. Neural responses were shaped by different sound localization cues depending on the stimulus spectrum—even within the same neuron.

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Representation of the Temporal Envelope of Sounds in the Human Brain

Journal of Neurophysiology ◽

10.1152/jn.2000.84.3.1588 ◽

2000 ◽

Vol 84 (3) ◽

pp. 1588-1598 ◽

Cited By ~ 228

Author(s):

Anne-Lise Giraud ◽

Christian Lorenzi ◽

John Ashburner ◽

Jocelyne Wable ◽

Ingrid Johnsrude ◽

...

Keyword(s):

Inferior Colliculus ◽

Auditory System ◽

Medial Geniculate Body ◽

Response Model ◽

Response Type ◽

Low Frequencies ◽

High Frequencies ◽

Temporal Envelope ◽

Medial Geniculate ◽

The Right

The cerebral representation of the temporal envelope of sounds was studied in five normal-hearing subjects using functional magnetic resonance imaging. The stimuli were white noise, sinusoidally amplitude-modulated at frequencies ranging from 4 to 256 Hz. This range includes low AM frequencies (up to 32 Hz) essential for the perception of the manner of articulation and syllabic rate, and high AM frequencies (above 64 Hz) essential for the perception of voicing and prosody. The right lower brainstem (superior olivary complex), the right inferior colliculus, the left medial geniculate body, Heschl's gyrus, the superior temporal gyrus, the superior temporal sulcus, and the inferior parietal lobule were specifically responsive to AM. Global tuning curves in these regions suggest that the human auditory system is organized as a hierarchical filter bank, each processing level responding preferentially to a given AM frequency, 256 Hz for the lower brainstem, 32–256 Hz for the inferior colliculus, 16 Hz for the medial geniculate body, 8 Hz for the primary auditory cortex, and 4–8 Hz for secondary regions. The time course of the hemodynamic responses showed sustained and transient components with reverse frequency dependent patterns: the lower the AM frequency the better the fit with a sustained response model, the higher the AM frequency the better the fit with a transient response model. Using cortical maps of best modulation frequency, we demonstrate that the spatial representation of AM frequencies varies according to the response type. Sustained responses yield maps of low frequencies organized in large clusters. Transient responses yield maps of high frequencies represented by a mosaic of small clusters. Very few voxels were tuned to intermediate frequencies (32–64 Hz). We did not find spatial gradients of AM frequencies associated with any response type. Our results suggest that two frequency ranges (up to 16 and 128 Hz and above) are represented in the cortex by different response types. However, the spatial segregation of these two ranges is not systematic. Most cortical regions were tuned to low frequencies and only a few to high frequencies. Yet, voxels that show a preference for low frequencies were also responsive to high frequencies. Overall, our study shows that the temporal envelope of sounds is processed by both distinct (hierarchically organized series of filters) and shared (high and low AM frequencies eliciting different responses at the same cortical locus) neural substrates. This layout suggests that the human auditory system is organized in a parallel fashion that allows a degree of separate routing for groups of AM frequencies conveying different information and preserves a possibility for integration of complementary features in cortical auditory regions.

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Neural Sensitivity to Interaural Envelope Delays in the Inferior Colliculus of the Guinea Pig

Journal of Neurophysiology ◽

10.1152/jn.00794.2004 ◽

2005 ◽

Vol 93 (6) ◽

pp. 3463-3478 ◽

Cited By ~ 45

Author(s):

Sarah J. Griffin ◽

Leslie R. Bernstein ◽

Neil J. Ingham ◽

David McAlpine

Keyword(s):

Fine Structure ◽

Guinea Pig ◽

Inferior Colliculus ◽

High Frequency ◽

Low Frequency ◽

Nerve Fibers ◽

Neural Firing ◽

Low Frequencies ◽

Interaural Time Differences ◽

High Frequencies

Interaural time differences (ITDs) are important cues for mammalian sound localization. At high frequencies, sensitivity to ITDs, which are conveyed only by the envelope of the waveforms, has been shown to be poorer than sensitivity to ITDs at low frequencies, which are conveyed primarily by the fine structure of the waveforms. Recently, human psychophysical experiments have demonstrated that sensitivity to envelope-based ITDs in high-frequency transposed tones can be equivalent to low-frequency fine-structure–based ITD sensitivity. Transposed tones are designed to provide high-frequency auditory nerve fibers (ANFs) with similar temporal information to that provided by low-frequency tones. We investigated neural sensitivity to ITDs in high-frequency transposed and sinusoidally amplitude modulated (SAM) tones, in the inferior colliculus of the guinea pig. Neural sensitivity to ITDs in transposed tones was found to be greater than that to ITDs in SAM tones; in response to transposed tones, neural firing rates were more modulated as a function of ITD and discrimination thresholds were found to be lower than those in response to SAM tones. Similar to psychophysical findings, ITD discrimination of single neurons in response to transposed tones for rates of modulation <250 Hz was comparable to neural discrimination of ITDs in low-frequency tones. This suggests that the neural mechanisms that mediate sensitivity to ITDs at high and low frequencies are functionally equivalent, provided that the stimuli result in appropriate temporal patterns of action potentials in ANFs.

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Quasi-Periodic Oscillations in Dwarf Novae

International Astronomical Union Colloquium ◽

10.1017/s0252921100073310 ◽

1979 ◽

Vol 46 ◽

pp. 77-88

Author(s):

Edward L. Robinson

Keyword(s):

Binary Systems ◽

Outer Edge ◽

Light Curves ◽

Close Binary ◽

Bright Spot ◽

Dwarf Novae ◽

Periodic Oscillations ◽

High Frequencies ◽

Short Period ◽

Typical Time

Three distinct kinds of rapid variations have been detected in the light curves of dwarf novae: rapid flickering, short period coherent oscillations, and quasi-periodic oscillations. The rapid flickering is seen in the light curves of most, if not all, dwarf novae, and is especially apparent during minimum light between eruptions. The flickering has a typical time scale of a few minutes or less and a typical amplitude of about .1 mag. The flickering is completely random and unpredictable; the power spectrum of flickering shows only a slow decrease from low to high frequencies. The observations of U Gem by Warner and Nather (1971) showed conclusively that most of the flickering is produced by variations in the luminosity of the bright spot near the outer edge of the accretion disk around the white dwarf in these close binary systems.

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