Encoding of steady‐state vowels in the auditory nerve: Representation in terms of discharge rate

1979 ◽  
Vol 66 (2) ◽  
pp. 470-479 ◽  
Author(s):  
Murray B. Sachs ◽  
Eric D. Young
Keyword(s):  
Steady State ◽  
Auditory Nerve ◽  
Discharge Rate

Auditory nerve representation of vowels in background noise

1983 ◽  
Vol 50 (1) ◽  
pp. 27-45 ◽  
Author(s):  
M. B. Sachs ◽  
H. F. Voigt ◽  
E. D. Young
Keyword(s):  
Steady State ◽  
Auditory Nerve ◽  
Background Noise ◽  
Discharge Rate ◽  
Nerve Fibers ◽  
Noise Levels ◽  
Stimulus Component ◽  
Signal Noise ◽  
Formant Frequencies ◽  
Second Formant

Responses of auditory nerve fibers to steady-state vowels presented alone and in the presence of background noise were obtained from anesthetized cats. Representation of vowels based on average discharge rate and representation based primarily on phase-locked properties of responses are considered. Profiles of average discharge rate versus characteristic frequency (CF) ("rate-place" representation) can show peaks of discharge rate in the vicinity of formant frequencies when vowels are presented alone. These profiles change drastically in the presence of background noise, however. At moderate vowel and noise levels and signal/noise ratios of +9 dB, there are not peaks of rate near the second and third formant frequencies. In fact, because of two-tone suppression, rate to vowels plus noise is less than rate to noise alone for fibers with CFs above the first formant. Rate profiles measured over 5-ms intervals near stimulus onset show clear formant-related peaks at higher sound levels than do profiles measured over intervals later in the stimulus (i.e., in the steady state). However, in background noise, rate profiles at onset are similar to those in the steady state. Specifically, for fibers with CFs above the first formant, response rates to the noise are suppressed by the addition of the vowel at both vowel onset and steady state. When rate profiles are plotted for low spontaneous rate fibers, formant-related peaks appear at stimulus levels higher than those at which peaks disappear for high spontaneous fibers. In the presence of background noise, however, the low spontaneous fibers do not preserve formant peaks better than do the high spontaneous fibers. In fact, the suppression of noise-evoked rate mentioned above is greater for the low spontaneous fibers than for high. Representations that reflect phase-locked properties as well as discharge rate ("temporal-place" representations) are much less affected by background noise. We have used synchronized discharge rate averaged over fibers with CFs near (+/- 0.25 octave) a stimulus component as a measure of the population temporal response to that component. Plots of this average localized synchronized rate (ALSR) versus frequency show clear first and second formant peaks at all vowel and noise levels used. Except at the highest level (vowel at 85 dB sound pressure level (SPL), signal/noise = +9 dB), there is also a clear third formant peak. At signal-to-noise ratios where there are no second formant peaks in rate profiles, human observers are able to discriminate second formant shifts of less than 112 Hz. ALSR plots show clear second formant peaks at these signal/noise ratios.

Encoding of amplitude and rate of forces applied to the teeth by human periodontal mechanoreceptive afferents

1994 ◽  
Vol 72 (4) ◽  
pp. 1734-1744 ◽  
Author(s):  
M. Trulsson ◽  
R. S. Johansson
Keyword(s):  
Steady State ◽  
Discharge Rate ◽  
Inferior Alveolar Nerve ◽  
Steady State Response ◽  
Force Amplitude ◽  
Stimulus Response ◽  
State Response ◽  
Dynamic Sensitivity ◽  
Linear Relationships ◽  
State Force

1. The encoding of force amplitude and force rate by human periodontal mechanoreceptive afferents was studied. Recordings were obtained from 19 single periodontal afferents in the inferior alveolar nerve with the use of tungsten microelectrodes. Loads consisting of a force increase (loading ramp), a phase of maintained force (static phase), and a force decrease (unloading ramp) were applied to the receptor bearing tooth, which was most often an incisor. The static forces applied ranged between 0.05 and 5 N, and the rate of force applied during the loading ramps ranged between 0.4 and 70 N/s. The forces were primarily applied in one of six directions (lingual, labial, mesial, distal, upward, or downward) that evoked the greatest discharge activity. 2. For each force application, the steady-state response was defined as the mean discharge rate during a 1-s period starting 0.5 s after the end of the loading ramp. Most afferents (15/19) exhibited a “hyperbolic” (viz., negatively accelerating) relationship between the amplitude of the stimulation force and the steady-state response, featuring a pronounced saturation tendency: the highest sensitivity to changes in static force was observed at force levels below 1 N. At higher force levels the sensitivity gradually diminished. Moreover, the dynamic sensitivity similarly decreased with increasing amplitude of static background force. For a subsample of afferents studied, comparable stimulus-response relationships were obtained in directions other than the most responsive one, but the discharge rates were lower. 3. In contrast to the response of most afferents, four (4/19) differed in that they consistently exhibited a nearly linear relationship between force amplitude and the steady-state response. Moreover, these afferents maintained their dynamic sensitivity as the amplitude of the background force was increased. 4. The steady-state response of all afferents was well described as a constant times F/ (F + c), where F represents the steady-state force, and c the force generating one-half the estimated maximum discharge rate that could be evoked by steady-state force stimulation. The c-parameter was on average 0.42 N (range 0.05–1.1 N) for the afferents exhibiting hyperbolic stimulus-response relationships. In contrast it ranged between 5 and 22 N for those exhibiting “nearly linear” relationships. A hypothetical model of the mechanics of the periodontal ligament supporting the F/(F + c) transform is proposed. 5. A general transfer function was developed to predict the instantaneous discharge rate of an individual afferent to arbitrary force profiles applied to the receptor bearing tooth.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation to hypercapnia vs. intracellular pH in cat carotid body: responses in vitro

1996 ◽  
Vol 80 (4) ◽  
pp. 1090-1099 ◽  
Author(s):  
S. Lahiri ◽  
R. Iturriaga ◽  
A. Mokashi ◽  
F. Botre ◽  
D. Chugh ◽  
...  
Keyword(s):  
Steady State ◽  
Intracellular Ph ◽  
Baseline Level ◽  
Discharge Rate ◽  
Initial Response ◽  
Extracellular Ph ◽  
Carotid Bodies ◽  
Initial Peak ◽  
Initial Change

The hypotheses that the chemosensory discharge rate parallels the intracellular pH (pHi) during hypercapnia and that the initial change in pHi (delta pHi) is always more than the stead-state delta pHi were studied by using cat carotid bodies in vitro at 36.5 degrees C in the absence and presence of methazolamide (30-100 mg/l). Incremental acidic hypercapnia was followed by an incremental initial peak response and a greater adaptation. A given acidic hypercapnia elicited a rapid initial response followed by a slower adaptation; isohydric hypercapnia produced an equally rapid initial response but of smaller magnitude that returned to near-baseline level; alkaline hypercapnia induced a similar rapid initial response but one of still smaller magnitude that decreased rapidly to below the baseline. Methazolamide eliminated the initial overshoot, which also suggested involvement of the initial rapid pHi in the overshoot. These results show that the initial delta pHi is always greater than the steady-state delta pHi and during hypercapnia. Also, the steady-state chemoreceptor activity varied linearly with the extracellular pH, indicating a linear relationship between extracellular pH and pHi.

Effect of electrical stimulation of the crossed olivocochlear bundle on auditory nerve response to tones in noise

1987 ◽  
Vol 57 (4) ◽  
pp. 1002-1021 ◽  
Author(s):  
R. L. Winslow ◽  
M. B. Sachs
Keyword(s):  
Auditory Nerve ◽  
Noise Level ◽  
Dynamic Range ◽  
Response Rate ◽  
Discharge Rate ◽  
Nerve Fibers ◽  
Range Shift ◽  
Auditory Nerve Fiber ◽  
Auditory Nerve Fibers ◽  
Rate Suppression

The discharge rates of single auditory-nerve fibers responding to best-frequency (BF) tones of varying level presented simultaneously with fixed level broadband noise were recorded with and without electrical stimulation of the crossed olivocochlear bundle (COCB). In the absence of COCB stimulation, monotonic increases in noise level produce monotonic increases in the low-level noise-driven response rate of auditory nerve fibers. As a result of adaptation, these increases in noise-driven response rate produce monotonic decreases in saturation discharge rate. At high noise levels, these compressive effects may eliminate the differential rate response of auditory nerve fibers to BF tones. COCB stimulation can restore this differential rate response by producing large decreases in noise-driven response rate and large increases in saturation discharge rate. In backgrounds of quiet, COCB stimulation is known to shift the dynamic range of single auditory nerve fiber BF tone responses to higher stimulus levels. In the presence of background noise, COCB stimulation produces upward shift of dynamic range, which decreases with increasing noise level. At high noise levels, COCB-induced decompression of rate-level functions may occur with little or no dynamic range shift. This enables auditory nerve fibers to signal changes in tone level with changes in discharge rate at lower signal-to-noise ratios than would be possible otherwise. Broadband noise also produces upward shift of the dynamic range of single auditory nerve fiber BF tone response. Noise-induced dynamic range shift of BF tone response was measured as a function of noise level with and without COCB stimulation. COCB stimulation elevates the threshold of noise-induced dynamic range shift. This shift is thought to result from two-tone rate suppression. Increases in the threshold of noise-induced shift due to COCB stimulation therefore suggests an interaction between the mechanism of two-tone rate suppression and the mechanism by which COCB stimulation produces dynamic range shift. These interactions were further investigated by recording auditory nerve fiber rate responses to fixed-level BF excitor tones presented simultaneously with fixed-frequency variable level suppressor tones. Rate responses were recorded with and without COCB stimulation. Experimental results were quantified using a phenomenological model of two-tone rate suppression presented by Sachs and Abbas.

Effective synaptic current can be estimated from measurements of neuronal discharge

1992 ◽  
Vol 68 (3) ◽  
pp. 964-968 ◽  
Author(s):  
R. K. Powers ◽  
F. R. Robinson ◽  
M. A. Konodi ◽  
M. D. Binder
Keyword(s):  
Steady State ◽  
Synaptic Input ◽  
Discharge Rate ◽  
Triceps Surae ◽  
Repetitive Firing ◽  
Basic Question ◽  
Detailed Knowledge ◽  
Synaptic Efficacy ◽  
Synaptic Current ◽  
Discharge Rates

1. The basic question of how motoneurons transform synaptic inputs into spike train outputs remains unresolved, despite detailed knowledge of their morphology, electrophysiology, and synaptic connectivity. We have approached this problem by making measurements of a synaptic input under steady-state conditions and combining them with quantitative assessments of their effects on the discharge rates of cat spinal motoneurons. 2. We used a modified voltage-clamp technique to measure the steady-state effective synaptic currents (IN) produced by rubrospinal input to cat triceps surae motoneurons. In the same motoneurons we measured the slope of the firing rate-injected current (f-i) relation in the primary range. We then reactivated the rubrospinal input during steady, repetitive firing to assess its effect on motoneuron discharge rate. 3. We found that changes in the steady-state discharge rate of a motoneuron produced by this synaptic input could be described simply as the product of the net effective synaptic current measured at the soma and the slope of the motoneuron's f-i relation. This expression essentially redefines synaptic efficacy in terms of a cell's basic input-output function. Further, measurements of effective synaptic current simplify the task of estimating synaptic efficacy, because detailed knowledge of neither the electrotonic architecture of the postsynaptic cell nor of the locations of the presynaptic boutons is required.

Using a first-order autonomous dynamical system to evaluate residence time of the Greenland freshwater anomaly in the Subpolar Gyre

2020 ◽  
Author(s):  
Dmitry Dukhovskoy
Keyword(s):  
Steady State ◽  
Residence Time ◽  
North Atlantic ◽  
Thermohaline Circulation ◽  
Discharge Rate ◽  
Subpolar Gyre ◽  
The North ◽  
Salinity Anomaly ◽  
Great Salinity Anomaly ◽  
Autonomous Dynamical System

<p>Increasing Greenland discharge has contributed more than 5000 km<sup>3</sup> of surplus fresh water to the Subpolar North Atlantic since the early 1990s. The volume of this freshwater anomaly is projected to cause freshening in the North Atlantic leading to changes in the intensity of deep convection and thermohaline circulation in the subpolar North Atlantic. This is roughly half of the freshwater volume of the Great Salinity Anomaly of the 1970s that caused notable freshening in the Subpolar North Atlantic. In analogy with the Great Salinity Anomaly, it has been proposed that, over the years, this additional Greenland freshwater discharge might have a great impact on convection driving thermohaline circulation in the North Atlantic with consequent impact on climate. Previous numerical studies demonstrate that roughly half of this Greenland freshwater anomaly accumulates in the Subpolar Gyre. However, time scales over which the Greenland freshwater anomaly can accumulate in the subpolar basins is not known. This study estimates the residence time of the Greenland freshwater anomaly in the Subpolar Gyre by approximating the process of the anomaly accumulation in the study domain with a first order autonomous dynamical system forced by the Greenland freshwater anomaly discharge. General solutions are obtained for two types of the forcing function. First, the Greenland freshwater anomaly discharge is a constant function imposed as a step function. Second, the surplus discharge is a linearly increasing function. The solutions are deduced by utilizing results from the numerical experiments that tracked spreading of the Greenland fresh water with a passive tracer. The residence time of the freshwater anomaly is estimated to be about 10–15 years. The main differences in the solutions is that under the linearly increasing discharge rate, the volume of the accumulated Greenland freshwater anomaly in the Subpolar Gyre does not reach a steady state. By contrast, solution for the constant discharge rate reaches a steady state quickly asymptoting the new steady state value for time exceeding the residence time. Estimated residence time is compared with the numerical experiments and observations.</p>

Signs of functional maturation of peripheral auditory system in discharge patterns of neurons in anteroventral cochlear nucleus of kitten

1978 ◽  
Vol 41 (6) ◽  
pp. 1557-1559 ◽  
Author(s):  
J. F. Brugge ◽  
E. Javel ◽  
L. M. Kitzes
Keyword(s):  
Cochlear Nucleus ◽  
Auditory Nerve ◽  
Discharge Rate ◽  
Phase Locking ◽  
Low Frequency ◽  
Second Phase ◽  
Extended Phase ◽  
Anteroventral Cochlear Nucleus ◽  
Peripheral Auditory System ◽  
Different Response

1. Responses to pure tones were recorded from single neurons in the anteroventral cochlear nucleus (AVCN) in kittens ranging in age from 4 to 45 days. Different response properties mature at different times after birth. 2. The shapes of response areas of AVCN neurons after the 1st postnatal week resemble those recorded in the AVCN and auditory nerve of the adult. During the 1st wk after birth the high-frequency portion of the response area is extended. Phase-locked responses to stimulus frequencies below about 600 Hz occur at this time. Phase vs. frequency measurements and shapes of response areas indicate that by the end of the 1st postnatal week the cochlear partition may be capable of supporting a traveling wave along most of its length. 3. Functional development proceeds through a second phase which lasts until the end of the 2nd or the beginning of the 3rd wk of life. During that time threshold, maximal discharge rate, and average first-spike latency achieve adult values. 4. Phase-locking to low-frequency tones, to the extent displayed by phase-sensitive neurons in the adult AVCN or auditory nerve, is achieved last, after the 3rd or 4th wk postpartum.

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