Periodicity coding in the auditory system.

1. The topographical distributions of single-unit and multiple-unit responses to amplitude-modulated tones--and to other relevant parameters of simple tonal stimuli--were defined across the main frequency representational gradient and within narrow frequency ranges represented in "frequency band laminae" in the principal midbrain auditory nucleus, the central nucleus of the inferior colliculus (ICC), in adult, barbiturate-anesthetized cats. 2. Responses to amplitude-modulated tones with the carrier set at the characteristic frequency (CF) of recorded neurons were obtained at many ICC locations in each experiment. The best modulation frequency (BMF) of neurons was defined at each site as that modulation frequency producing the highest neural discharge rate. Encountered BMFs ranged from approximately 10 to 1,000 Hz. A significant range of BMFs were recorded for neurons with any given characteristic frequency. BMF ranges varied as a systematic function of CF and of ICC recording depth. 3. Recorded BMFs were distributed topographically within functionally defined ICC frequency band laminae. Highest BMFs were found clustered in an ICC sector roughly between the middle and lateral third of its frequency band laminae. Progressively lower BMFs were recorded with increasing distance across the laminae in any direction away from the highest-BMF cluster. That is, "iso-BMF contours" were arrayed concentrically around the highest-BMF region. 4. Within frequency band laminae centered at approximately 3 and 12 kHz, quality factors (Q10 dBS) of frequency tuning curves were found to be between 0.8 and 8. Q10 dB values were distributed topographically within given frequency band laminae. Responses with narrow tuning curves (high Q10 dB values) were clustered in the middle third of the mediolateral extent of laminae; sharpness of tuning declined systematically away from this focus of highest Q10 dB values. The center of this distribution did not coincide with the center of the BMF distribution within the same lamina. 5. For neurons at greater than 90% of the ICC loci studied in these experiments, onset latencies to CF tones defined approximately 60 dB above response threshold fell within a range between 5 and 18 ms. Across a given frequency band lamina, onset latencies varied systematically, with longest response latencies recorded medially, and progressively shorter latencies recorded progressively more laterally. 6. Binaural interaction types were systematically distributed within frequency-band laminae. A cluster of excitatory-excitatory (EE) was seen, covering approximately one-third of the mapped area.(ABSTRACT TRUNCATED AT 400 WORDS)

Periodicity coding in the inferior colliculus of the cat. II. Topographical organization.

Tonotopic organization: review and analysis.

As cochlear implants have become increasingly successful in the rehabilitation of adults with profound hearing impairment, the number of pediatric implant subjects has increased. We have developed ...

https://www.physiology.org/doi/pdf/10.1152/jn.1999.82.6.2883

Temporal Properties of Chronic Cochlear Electrical Stimulation Determine Temporal Resolution of Neurons in Cat Inferior Colliculus

Time dependent features of adequate sound stimuli and the functional organization of central auditory neurons

1.

Neurons of the inferior colliculus are subdivided into groups on the basis of the type and temporal characteristics of their response to prolonged acoustic stimuli (noise, optimal frequency). Neurons with a prolonged discharge and marked temporal summation (over 10 db), on the one hand, and neurons with an on-discharge to acoustic stimulation and low temporal summation (0–5 db) on the other hand, belong to the extreme groups. An intermediate position is occupied by neurons with prolonged and grouped discharges and temporal summation of 5–10 db and by neurons with a phasic discharge and temporal summation within the same limits. Neurons of the inferior colliculus cover a wide range of response types: from neurons with minimal adaptation and marked temporal summation (up to 45 db) to neurons with an on-discharge of one spike to acoustic stimulation and with absence of temporal summation.




2.

Neurons with prolonged and grouped discharge respond to slow modulation frequencies by synchronized spike activity reproducing the rhythm of the modulating wave. They reproduce the modulation frequency up to a certain limit, above which disturbance of reproduction of the rhythm, followed by suppression of spike generation, are observed.




3.

Many neurons with on-discharge and low temporal summation (0–5 db) did not respond to the modulation frequencies used in the investigation,. A few neurons with low summation respond selectively within a certain range of high modulation frequencies either by reproduction of the modulation rhythm or by an increase in the general level of spike activity. Neurons of this group with temporal summation higher than 5 db respond to a modulated stimulus with repeated spike generation, starting at a definite modulation frequency not below 5 Hz. Rhythmic activity corresponding to the modulation frequency persists up to a certain limit, beyond which only the initial response arises.

Unit activity in inferior colliculus to amplitude-modulated acoustic stimuli

We investigated the impulse activity of 103 neurons in cats anesthetized with a mixture of chloralose and urethane. The following response characteristics were studied in detail: 1) the latent period of the first impulse as a function of tone intensity; 2) threshold as a function of duration; 3) the frequency-threshold curves under the action of short (1–2 msec) and long (100–200 msec) tones; 4) the discharge "pattern" and the number of impulses under the action of signals with different durations and intensities. We demonstrated that the temporal characteristics of different neurons exhibit substantial differences. The high positive correlation among the temporal characteristics investigated enabled us to distinguish three groups of neurons. The first group was characterized by the following properties: a) short latent periods with a threshold tone intensity; 2) a short summation time (or none at all); 3) similarity of the frequency-threshold curves for short and long signals; 4) an initial on-discharge of 1–3 impulses. The second group was characterized by: 1) long latent periods with a threshold tone intensity; 2) pronounced temporal summation; 3) steeper frequency-threshold curves when the tone duration was increased; 4) prolonged discharge.

Functional classification of neurons of the cat inferior colliculus on the basis of temporal characteristics

1.

Responses of two extreme types of neurons in the inferior colliculus of rats to acoustic stimuli of rising amplitude are described. Neurons of group I are characterized by a decrease in the number of spikes in the response, an increase in the latency, and small changes in threshold as the rise time of noise or the optimal frequency increases. Group II neurons are characterized by preservation of the original response of one or two spikes, slight changes in latency, and a sharp increase in threshold when the rise time of the stimulus (noise, optimal and nonoptimal frequencies) increases.




2.

For stimuli with rising amplitude the sharpness of the frequency-threshold curves of group I neurons increases because of a sharp increase in threshold to nonoptimal frequencies and no change in threshold to optimal frequencies. The sharpness of the frequency-threshold curves of group II neurons is unaltered, and thresholds to all acoustic frequencies are increased with a decrease in the steepness of rise of the stimuli.

Effect of time constant of acoustic stimulus on unit activity of inferior colliculus

Under ch lo ra lose -u re thane anesthes ia 103 neurons were invest igated and the following c h a r a c t e r i s t i c s studied\" 1) latency of f i r s t spike as a function of acoust ic s t imulat ion; 2) threshold as a function of duration; 3) f r equencyth resho ld cu rves to b r ie f (1-2 msec) v e r s u s prolonged (100-200 msee) s t imuli ; 4) the \" p a t t e r n \" of d i scharge and number of spikes to s t imul i differ ing in duration and intensi ty. The t empora l c h a r a c t e r i s t i c s of individual neurons differ considerably . A high posi t ive co r r e l a t i on between the inves t i gated t empora l c h a r a c t e r i s t i c s led to the recogni t ion of two groups of neurons. Group i is cha r ac t e r i z ed by the following p roper t i e s : 1) shor t latency at threshold intensi ty; 2) low tempora l summation (or its comple te absence); 3) s im i l a r i t y between f requencyth resho ld cu rves cor responding to shor t and long s t imuli ; 4) ini t ial on-d i scharge of between 1 and 3 spikes. Group 2 is c h a r a c t e r i z e d by 1) long la tency at threshold intensi ty; 2) marked t empora l summation; 3) \" p e a k i n g \" of the f r equencyth re sho ld cu rves with an i nc r ea se in duration of s t imulat ion; 4) a longer d ischarge .

I. A. Vartanyan

Papers

Unit activity in inferior colliculus to amplitude-modulated acoustic stimuli

Functional classification of neurons of the cat inferior colliculus on the basis of temporal characteristics

Effect of time constant of acoustic stimulus on unit activity of inferior colliculus

Temporal characteristics classifying neurons of inferior colliculus in the cat