Physiology of the Auditory Brainstem

Irvine, Dexter R. F.

doi:10.1007/978-1-4612-2838-7_4

Cited by 188 publications

(122 citation statements)

References 206 publications

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“…This pattern was not seen in previously gathered data on the effects of iontophoresed serotonin (Fig 8B), and is especially interesting when viewed in the light of the orientation of frequency laminae within the IC. Anatomical and physiological evidence suggests the presence of fibrodendritic frequency laminae that are oriented roughly dorsolateral to ventromedial when viewed in the transverse plane within the IC of most mammals (reviewed in Irvine 1992;Schreiner and Langner 1997;Oliver and Huerta 1992;Malmierca 2003). The pattern of effects of fenfluramine seen in figure 8A is suggestive of the regionalization of neurons that exhibit serotonin-evoked latency increases within this laminar organization.…”

Section: A Difference In the Effects Of Fenfluramine Versus Serotoninmentioning

confidence: 95%

“…In the inferior colliculus (IC), a midbrain nucleus that integrates ascending auditory information from multiple brainstem nuclei (reviewed in Irvine 1992;Oliver and Huerta 1992;Pollak et al 2003), serotonin has strong effects on the responses of neurons to auditory stimuli, and can alter such fundamental properties as spike count, frequency tuning, and response latency (Hurley andPollak 2001,2005b). In all previous studies, these changes have been evoked by the application of exogenous serotonin.…”

Section: Introductionmentioning

confidence: 99%

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The serotonin releaser fenfluramine alters the auditory responses of inferior colliculus neurons

Hall

Hurley

2007

Hearing Research

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Local direct application of the neuromodulator serotonin strongly influences auditory response properties of neurons in the inferior colliculus (IC), but endogenous stores of serotonin may be released in a distinct spatial or temporal pattern. To explore this issue, the serotonin releaser fenfluramine was iontophoretically applied to extracellularly recorded neurons in the IC of the Mexican free-tailed bat (Tadarida brasiliensis). Fenfluramine mimicked the effects of serotonin on spike count and first spike latency in most neurons, and its effects could be blocked by co-application of serotonin receptor antagonists, consistent with fenfluramine-evoked serotonin release. Responses to fenfluramine did not vary during single applications or across multiple applications, suggesting that fenfluramine did not deplete serotonin stores. A predicted gradient in the effects of fenfluramine with serotonin fiber density was not observed, but neurons with fenfluramine-evoked increases in latency occurred at relatively greater recording depths compared to other neurons with similar characteristic frequencies. These findings support the conclusion that there may be spatial differences in the effects of exogenous and endogenous sources of serotonin, but that other factors such as the identities and locations of serotonin receptors are also likely to play a role in determining the dynamics of serotonergic effects.

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Section: A Difference In the Effects Of Fenfluramine Versus Serotoninmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

The serotonin releaser fenfluramine alters the auditory responses of inferior colliculus neurons

Hall

Hurley

2007

Hearing Research

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“…33-35), because stimulus frequencies in the auditory system and stimulus locations in the visual and somatosensory systems are all encoded topographically on the receptor surfaces. Similarly, the generalization of learning to an untrained standard value is reminiscent of the generalization of improvements in visual stereoacuity to untrained visual depths at the trained location (36), because interaural and interocular cues are both encoded, by similar mechanisms (37), through the convergence of information from the two ears in the auditory brainstem or from the two eyes in the visual cortex.…”

Section: Relationship Between Pretest Thresholds and The Amount Of Lementioning

confidence: 99%

Different patterns of human discrimination learning for two interaural cues to sound-source location

Wright

Fitzgerald²

2001

Proc. Natl. Acad. Sci. U.S.A.

145

144

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Two of the primary cues used to localize the sources of sounds are interaural level differences (ILDs) and interaural time differences (ITDs). We conducted two experiments to explore how practice affects the human discrimination of values of ILDs and ongoing ITDs presented over headphones. We measured discrimination thresholds of 13 to 32 naive listeners in a variety of conditions during a pretest and again, 2 weeks later, during a posttest. Between those two tests, we trained a subset of listeners 1 h per day for 9 days on a single ILD or ITD condition. Listeners improved on both ILD and ITD discrimination. Improvement was initially rapid for both cue types and appeared to generalize broadly across conditions, indicating conceptual or procedural learning. A subsequent slower-improvement stage, which occurred solely for the ILD cue, only affected conditions with the trained stimulus frequency, suggesting that stimulus processing had fundamentally changed. These different learning patterns indicate that practice affects the attention to, or low-level encoding of, ILDs and ITDs at sites at which the two cue types are processed separately. Thus, these data reveal differences in the effect of practice on ILD and ITD discrimination, and provide insight into the encoding of these two cues to sound-source location in humans.A listener who determines the position of a singing bird concealed among tree leaves, a jet passing overhead hidden by clouds, or a car approaching from behind, does so by using several auditory cues to the location of sound sources. Here we report the results of two investigations into how practice influences the ability of human listeners to discriminate small differences in each of two of these cues, interaural level differences (ILDs) and interaural time differences (ITDs).In humans, the horizontal location, or azimuth, of sound sources is computed from differences in the information that arrives at the two ears. At frequencies above about 1.5 kHz, listeners determine sound azimuth primarily from sensitivity to differences in sound level at the two ears. These interaural level differences occur because the head forms a sound barrier between the two ears, so sounds are attenuated at the ear farthest from the source relative to the ear nearest to the source (1, 2). At frequencies below about 1.5 kHz, listeners determine sound azimuth primarily from sensitivity to differences in the arrival time of the sound at the two ears. These interaural time differences arise because there is distance between the two ears, so sounds reach the ear nearest to the sound source first and the other ear later (1, 2). For sound durations greater than about 150 ms, listeners are far more sensitive to differences at the two ears in the ongoing fine time structure of the sound than in the onset time of the sound (3, 4). These ongoing time differences are equivalent to interaural phase differences (IPDs) for tonal stimuli, but will be referred to as ITDs in this paper.There have been many investigations into whether huma...

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“…An important structure within this chain is the midbrain inferior colliculus (IC), because it acts as the primary relay center between ascending projections from the lower brainstem nuclei and ascending projections to the thalamus. Because of its unique makeup of converging ascending and corticofugal projections (Irvine, 1992;Zhang and Suga, 2005), animal studies have identified the IC as a site of both activity-and experience-dependent developmental plasticity in both vertebrate and, most recently, mammalian brains (Brainard and Knudsen, 1993;Knudsen, 1998;Zheng and Knudsen, 1999;DeBello et al, 2001;Yu et al, 2007). However, similar studies on developmental plasticity in the human auditory brainstem have been limited primarily because of the obvious limitations in the use of parallel technique and experimental design.…”

Section: Introductionmentioning

confidence: 99%

Developmental Plasticity in the Human Auditory Brainstem

Johnson¹,

Nicol²,

Zecker³

et al. 2008

J. Neurosci.

146

126

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Development of the human auditory brainstem is thought to be primarily complete by the age of ϳ2 years, such that subsequent sensory plasticity is confined primarily to the cortex. However, recent findings have revealed experience-dependent developmental plasticity in the mammalian auditory brainstem in an animal model. It is not known whether the human system demonstrates similar changes and whether experience with sounds composed of acoustic elements relevant to speech may alter brainstem response characteristics. We recorded brainstem responses evoked by both click and speech syllables in children between the ages of 3 and 12 years. Here, we report a neural response discrepancy in brainstem encoding of these two sounds, observed in 3-to 4-year-old children but not in school-age children. Whereas all children exhibited identical neural activity to a click, 3-to 4-year-old children displayed delayed and less synchronous onset and sustained neural response activity when elicited by speech compared with 5-to 12-year-olds. These results suggest that the human auditory system exhibits developmental plasticity, in both frequency and time domains, for sounds that are composed of acoustic elements relevant to speech. The findings are interpreted within the contexts of stimulus-related differences and experience-dependent plasticity.

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Physiology of the Auditory Brainstem

Cited by 188 publications

References 206 publications

The serotonin releaser fenfluramine alters the auditory responses of inferior colliculus neurons

The serotonin releaser fenfluramine alters the auditory responses of inferior colliculus neurons

Different patterns of human discrimination learning for two interaural cues to sound-source location

Developmental Plasticity in the Human Auditory Brainstem

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