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At least 937 records · Page 52Linked to original sources
PubMed2001

Spectral integration in the inferior colliculus: role of glycinergic inhibition in response facilitation.

This study examined the contribution of glycinergic inhibition to the time-sensitive spectral integration performed by neurons in the inferior colliculus of the mustached bat (Pteronotus parnellii). These neurons are sometimes called combination-sensitive because they display facilitatory (or inhibitory) responses to the combination of distinct spectral elements in sonar or social vocalizations. Present in a wide range of vertebrates, their temporally and spectrally selective integration is thought to endow them with the ability to discriminate among social vocalizations or to analyze particular cues concerning sonar targets. The mechanisms that underlie these responses or the sites in the auditory system where they are created are not known. We examined combination-sensitive neurons that are facilitated by the presentation of two different harmonic elements of the bat's sonar call and echo. Responses of 24 single units were recorded before and during local application of strychnine, an antagonist of glycinergic inhibition. For each of the 24 units, strychnine application eliminated or greatly reduced temporally sensitive facilitation. There was no difference in this effect for neurons tuned to frequencies associated with the frequency-modulated or the constant-frequency sonar components. These results are unusual because glycine is considered to be an inhibitory neurotransmitter, but here it appears to be essential for the expression of combination-sensitive facilitation. The findings provide strong evidence that facilitatory combination-sensitive response properties present throughout the mustached bat's auditory midbrain, thalamus, and cortex originate through neural interactions in the inferior colliculus.

Acoustic Stimulation↗
PubMed2001

Oscillation may play a role in time domain central auditory processing.

To study how sound intensity altered the temporal response pattern of a unit, we recorded from 92 single neurons in the inferior colliculus (IC) of the little brown bat and investigated their firing patterns in response to brief tone pulses (2 msec duration) at the characteristic frequency of the unit over a wide dynamic range (10-90 dB sound pressure level). We found two unusual response characteristics at high sound levels in approximately one-third of the IC neurons investigated. For 16 IC neurons (17%), an increase in sound level not only elicited a shorter response latency and an increase in spike count but also transformed the firing pattern of the unit from phasic to periodic; this pattern was more pronounced at higher sound levels. The firing periodicity was unit specific, ranging from 1.3 to 6.7 msec. Twenty-seven IC neurons (29%) exhibited a longer response latency at higher sound levels compared with lower sound levels [i.e., paradoxical latency shift (PLS)]. The majority of this population showed a one or more quantum increase in latency when sound level was elevated. The quantum shift was also unit specific, ranging from 1.2 to 8.2 msec. We further investigated the firing patterns of 14 IC neurons showing PLS before, during, and after iontophoretic application of bicuculline. For 12 of these neurons, drug application abolished the PLS and transformed the firing patterns of the unit at high sound levels from phasic into sustained periodic discharges. Our results suggest that neural oscillation in combination with ordinary inhibition may be responsible for the creation of PLSs shown previously to be important for temporal information processing.

Acoustic Stimulation↗
PubMed2001

Reversible inactivation of the dorsal nucleus of the lateral lemniscus reveals its role in the processing of multiple sound sources in the inferior colliculus of bats.

Neurons in the inferior colliculus (IC) that are excited by one ear and inhibited by the other [excitatory-inhibitory (EI) neurons] can code interaural intensity disparities (IIDs), the cues animals use to localize high frequencies. Although EI properties are first formed in a lower nucleus and imposed on some IC cells via an excitatory projection, many other EI neurons are formed de novo in the IC. By reversibly inactivating the dorsal nucleus of the lateral lemniscus (DNLL) in Mexican free-tailed bats with kynurenic acid, we show that the EI properties of many IC cells are formed de novo via an inhibitory projection from the DNLL on the opposite side. We also show that signals excitatory to the IC evoke an inhibition in the opposite DNLL that persists for tens of milliseconds after the signal has ended. During that period, strongly suppressed EI cells in the IC are deprived of inhibition from the DNLL and respond to binaural signals as weakly inhibited or monaural cells. By relieving inhibition at the IC, we show that an initial binaural signal essentially reconfigures the circuit and thereby allows IC cells to respond to trailing binaural signals that were inhibitory when presented alone. Thus, DNLL innervation creates a property in the IC that is not possessed by lower neurons or by collicular EI neurons that are not innervated by the DNLL. That property is a change in responsiveness to binaural signals, a change dependent on the reception of an earlier sound. These features suggest that the circuitry linking the DNLL with the opposite central nucleus of the IC is important for the processing of IIDs that change over time, such as the IIDs generated by moving stimuli or by multiple sound sources that emanate from different regions of space.

Acoustic Stimulation↗
PubMedDate not supplied

[Phenomenological model of the system for exact determination of target direction by the bat echolator].

A functional scheme of correlation treatment of an echosignal during the determination of a direction to the target by rats echolator is considered. The scheme proceeds from a suggestion that for an exact measurement of angle coordinates of the target the rat applies a location method of unisignal zones resulting from the pulsation of direction diagram when LFM impulse is emitted. Some considerations in favour of the suggested phenomenological model are presented. An experimental set-up which permits to test and specify the model is proposed.

Animals↗
PubMed2003

Temporal masking reveals properties of sound-evoked inhibition in duration-tuned neurons of the inferior colliculus.

The inferior colliculus (IC) is the first place in the central auditory pathway where duration-selective neurons are found. Previous neuropharmacological and electrophysiological studies have shown that they are created there and have led to a conceptual model in which excitatory and inhibitory inputs are offset in time so that the cell fires only when sound duration is such that onset- and offset-evoked excitation coincide; the response is suppressed by inhibition at other durations. We tested predictions from the model using paired tone stimulation and extracellular recording in the IC of the big brown bat, Eptesicus fuscus. Responses to a best duration (BD) tone were used as a probe to examine the strength and time course of inhibition activated by a nonexcitatory (NE) tone of the same frequency but differing in duration. As the relative time between the BD and NE tones was varied, the activity evoked by the BD tone was affected in ways comparable with backward, simultaneous, and forward masking. Responses to the BD tone were completely suppressed at short interstimulus intervals when the BD tone preceded the NE tone. Suppression was also seen when the stimuli temporally overlapped and summed and at intervals when the BD tone followed the NE tone. The results show that duration-selective neurons receive an onset-evoked, inhibitory input that precedes their excitatory input. The period of leading inhibition was correlated with BD and first spike latency. The results suggest how inhibition in the CNS could explain temporal masking phenomena, including backward masking.

Animals↗
PubMed2003

GABAergic inhibition and the effect of sound direction on rate-intensity functions of inferior collicular neurons of the big brown Bat, Eptesicus fuscus.

GABAergic inhibition shapes many auditory response properties of neurons in the inferior colliculus of the big brown bat, Eptesicus fuscus. This study examined the role of GABAergic inhibition on direction-dependent rate-intensity functions of bat inferior collicular neurons. When plotted at three sound directions (60 degrees contralateral, 0 degrees and 60 degrees ipsilateral relative to recording site), most collicular neurons had nonmonotonic and saturated rate-intensity functions at 60 degrees contralateral and 0 degrees but had monotonic rate-intensity functions at 60 degrees ipsilateral. The dynamic range of rate-intensity functions of majority (>90%) of collicular neurons significantly decreased as the sound direction changed from 60 degrees contralateral to 60 degrees ipsilateral. Bicuculline application increased or decreased the dynamic range of IC neurons in different degrees with sound direction and abolished direction-dependent intensity sensitivity of these IC neurons. Possible mechanisms for these observations are discussed.

Animals↗
PubMed2004

Ultrasonic ranging sensor using simultaneous emissions from different transducers.

In recent applications based on ultrasound, several ultrasonic transducers have been geometrically and electronically associated to constitute a global sensor. There are several different methods used to process the ultrasonic signals obtained from these transducers. In this work, multimode techniques using Golay complementary sequences are proposed for processing the ultrasonic signal. The system increases scan rate, precision, and reliability. It is also capable of echo discrimination, allowing simultaneous measurements to be made and detection of the same obstacle by different transducers without cross-talk problems. The real-time implementation of the algorithm is presented on a field-programmable gate array (FPGA) device.

Algorithms↗
PubMed2005

[Mechanisms of determining target locator velocity by dolphins and technical applications in hydrolocation and radiolocation].

Dolphin's (Tursiops truncatus) capacity to discriminate between dynamic characteristics of the object location (the target moving radially) was studied. The dolphin sensitivity thresholds for target velocity (2.6 cm/s) and for target acceleration (0.6 cm/s2) were measured. It has been shown that the animal emits two-pulse probe signal to locate the target moving with constant velocity, or three-pulse probe signal--to locate the accelerated target. New highly efficient technical methods of hydro- and radiolocation were suggested on the basis of these peculiarities.

Acoustics↗
PubMed2006

Duration selectivity of bat inferior collicular neurons improves with increasing pulse repetition rate.

Insectivorous big brown bats, Eptesicus fuscus, progressively increase the pulse repetition rate (PRR) throughout the course of hunting. While increasing PRR conceivably facilitates bats to extract information about the targets, it also inevitably affects sensitivity of their auditory neurons to pulse parameters. The present study examined the effect of increasing PRR on duration selectivity of this bat's inferior collicular (IC) neurons by comparing their impulse-duration functions determined at different PRRs. Impulse-duration functions plotted with the number of impulses in response to single pulses against pulse duration at different PRRs were described as short-pass, band-pass, long-pass, and all-pass. Short- or long-pass neurons discharged maximally to a range of short or long pulse durations. Band-pass neurons discharged maximally to one pulse duration. These three types of IC neurons were called duration tuned neurons. All-pass neurons were not duration tuned because they did not discharge maximally to any pulse duration. Increasing PRR improved duration selectivity of IC neurons by (1) increasing the number of duration tuned neurons; (2) decreasing the critical duration concomitant with increasing slope of the impulse-duration function; and (3) decreasing the 50% duration range of the impulse-duration function. This improved duration selectivity with PRR may potentially facilitate prey capture by bats.

Acoustic Stimulation↗
PubMedDate not supplied

[The recovery of the reactivity of the auditory system in the dolphin Tursiops truncatus to paired acoustic stimuli with different spectra].

Recovery cycles of the auditory brainstem responses were studied in the bottle-nosed dolphin, Tursiops truncatus, using paired acoustic clicks. The recovery time was longer if both clicks had identical spectra (50% recovery at 0.9 ms), as compared with that of different spectra (50% recovery at 0.35 ms). These results can explain a different recovery time of evoked responses after an artificial sound and after own locating one.

Acoustic Stimulation↗
PubMed1991

Directional sensitivity of bat inferior collicular neurons determined under normal and monaurally plugged ear conditions.

In an effort to further understand the combined effect of binaural intensity difference and pinna position on the directional sensitivity of an auditory neuron, we used free field stimulation to study the directional sensitivity of inferior collicular (IC) neurons of the big brown bat, Eptesicus fuscus, under the following three ear conditions: normal ears, monaurally plugged ear and monaurally plugged plus pinna bending backward. The best frequency (BF) and minimum threshold (MT) of each neuron were first determined for a sound (4 ms duration, 0.5 ms rise-decay times) delivered from 40 degrees contralateral in azimuth, 0 degrees in elevation relative to the recording site. Then, the neuron's MT to a BF sound delivered from 7 selected azimuthal angles with respect to the bat's head were determined. The number of impulses to a BF sound delivered at two intensities (10 and 20 dB re MT determined at 40 degrees contralateral) from each of 7 azimuthal angles was also subsequently determined. Although different IC neurons showed different variations in MT and number of impulses with sound source azimuth, most had a lowest MT and/or maximal number of impulses to BF sounds delivered from contralateral azimuthal angles regardless of ear conditions. However, among 117 neurons studied, there were 12 neurons in which the number of impulses did not vary significantly with sound direction thus showing nondirectional characteristics. Monaural plugging (a wet cotton ball) with or without backward bending of the pinna not only increased the MT of a recorded neuron but also greatly reduced the number of impulses of the neuron so that the directional sensitivity of the neuron was also modified. The effect of monaural plugging on the threshold of a neuron and the degree of modification on directional sensitivity varied among individual IC neurons. Thus, while the directional sensitivity of some IC neurons became sharper, for other neurons the same monaural plugging reduced the sharpness of their directional sensitivity curve. Directional sensitivity of IC neurons is dependent upon stimulus frequency regardless of ear conditions. High frequency neurons generally have sharper directional sensitivity than low frequency neurons. The angle of lowest MT and maximal number of impulses tended to move toward the middle portion of a bat's frontal auditory space with increasing BF.

Acoustic Stimulation↗