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de Cheveigné A. Why is the perceptual octave stretched? An account based on mismatched time constants within the auditory brainstem. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2023; 153:2600. [PMID: 37129672 DOI: 10.1121/10.0017978] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2023] [Accepted: 04/12/2023] [Indexed: 05/03/2023]
Abstract
This paper suggests an explanation for listeners' greater tolerance to positive than negative mistuning of the higher tone within an octave pair. It hypothesizes a neural circuit tuned to cancel the lower tone that also cancels the higher tone if that tone is in tune. Imperfect cancellation is the cue to mistuning of the octave. The circuit involves two neural pathways, one delayed with respect to the other, that feed a coincidence-sensitive neuron via excitatory and inhibitory synapses. A mismatch between the time constants of these two synapses results in an asymmetry in sensitivity to mismatch. Specifically, if the time constant of the delayed pathway is greater than that of the direct pathway, there is a greater tolerance to positive mistuning than to negative mistuning. The model is directly applicable to the harmonic octave (concurrent tones) but extending it to the melodic octave (successive tones) requires additional assumptions that are discussed. The paper reviews evidence from auditory psychophysics and physiology in favor-or against-this explanation.
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Affiliation(s)
- Alain de Cheveigné
- Laboratoire des Systèmes Perceptifs, Unité Mixte de Recherche 8248, Centre National de la Recherche Scientifique, Paris, France
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Yin TC, Smith PH, Joris PX. Neural Mechanisms of Binaural Processing in the Auditory Brainstem. Compr Physiol 2019; 9:1503-1575. [DOI: 10.1002/cphy.c180036] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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Wu C, Shore SE. Multisensory activation of ventral cochlear nucleus D-stellate cells modulates dorsal cochlear nucleus principal cell spatial coding. J Physiol 2018; 596:4537-4548. [PMID: 30074618 DOI: 10.1113/jp276280] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2018] [Accepted: 08/02/2018] [Indexed: 01/27/2023] Open
Abstract
KEY POINTS Dorsal cochlear nucleus fusiform cells receive spectrally relevant auditory input for sound localization. Fusiform cells integrate auditory with other multisensory inputs. Here we elucidate how somatosensory and vestibular stimulation modify the fusiform cell spatial code through activation of an inhibitory interneuron: the ventral cochlear nucleus D-stellate cell. These results suggests that multisensory cues interact early in an ascending sensory pathway to serve an essential function. ABSTRACT In the cochlear nucleus (CN), the first central site for coding sound location, numerous multisensory projections and their modulatory effects have been reported. However, multisensory influences on sound location processing in the CN remain unknown. The principal output neurons of the dorsal CN, fusiform cells, encode spatial information through frequency-selective responses to direction-dependent spectral features. Here, single-unit recordings from the guinea pig CN revealed transient alterations by somatosensory and vestibular stimulation in fusiform cell spatial coding. Changes in fusiform cell spectral sensitivity correlated with multisensory modulation of ventral CN D-stellate cell responses, which provide direct, wideband inhibition to fusiform cells. These results suggest that multisensory inputs contribute to spatial coding in DCN fusiform cells via an inhibitory interneuron, the D-stellate cell. This early multisensory integration circuit likely confers important consequences on perceptual organization downstream.
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Affiliation(s)
- Calvin Wu
- Kresge Hearing Research Institute, Department of Otolaryngology, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Susan E Shore
- Kresge Hearing Research Institute, Department of Otolaryngology, University of Michigan, Ann Arbor, MI, 48109, USA
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Spencer MJ, Nayagam DAX, Clarey JC, Paolini AG, Meffin H, Burkitt AN, Grayden DB. Broadband onset inhibition can suppress spectral splatter in the auditory brainstem. PLoS One 2015; 10:e0126500. [PMID: 25978772 PMCID: PMC4433210 DOI: 10.1371/journal.pone.0126500] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2014] [Accepted: 04/02/2015] [Indexed: 12/02/2022] Open
Abstract
In vivo intracellular responses to auditory stimuli revealed that, in a particular population of cells of the ventral nucleus of the lateral lemniscus (VNLL) of rats, fast inhibition occurred before the first action potential. These experimental data were used to constrain a leaky integrate-and-fire (LIF) model of the neurons in this circuit. The post-synaptic potentials of the VNLL cell population were characterized using a method of triggered averaging. Analysis suggested that these inhibited VNLL cells produce action potentials in response to a particular magnitude of the rate of change of their membrane potential. The LIF model was modified to incorporate the VNLL cells’ distinctive action potential production mechanism. The model was used to explore the response of the population of VNLL cells to simple speech-like sounds. These sounds consisted of a simple tone modulated by a saw tooth with exponential decays, similar to glottal pulses that are the repeated impulses seen in vocalizations. It was found that the harmonic component of the sound was enhanced in the VNLL cell population when compared to a population of auditory nerve fibers. This was because the broadband onset noise, also termed spectral splatter, was suppressed by the fast onset inhibition. This mechanism has the potential to greatly improve the clarity of the representation of the harmonic content of certain kinds of natural sounds.
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Affiliation(s)
- Martin J. Spencer
- NeuroEngineering Laboratory, Department of Electrical and Electronic Engineering, University of Melbourne, Melbourne, Australia
- National ICT Australia, Department of Electrical and Electronic Engineering, University of Melbourne, Melbourne, Australia
- Centre for Neural Engineering, University of Melbourne, Melbourne, Australia
- * E-mail:
| | - David A. X. Nayagam
- Bionics Institute, Melbourne, Australia
- Department of Pathology, University of Melbourne, Melbourne, Australia
| | | | - Antonio G. Paolini
- Health Innovations Research Institute, RMIT University, Melbourne, Australia
| | - Hamish Meffin
- NeuroEngineering Laboratory, Department of Electrical and Electronic Engineering, University of Melbourne, Melbourne, Australia
- National ICT Australia, Department of Electrical and Electronic Engineering, University of Melbourne, Melbourne, Australia
- Centre for Neural Engineering, University of Melbourne, Melbourne, Australia
| | - Anthony N. Burkitt
- NeuroEngineering Laboratory, Department of Electrical and Electronic Engineering, University of Melbourne, Melbourne, Australia
- National ICT Australia, Department of Electrical and Electronic Engineering, University of Melbourne, Melbourne, Australia
- Centre for Neural Engineering, University of Melbourne, Melbourne, Australia
- Bionics Institute, Melbourne, Australia
| | - David B. Grayden
- NeuroEngineering Laboratory, Department of Electrical and Electronic Engineering, University of Melbourne, Melbourne, Australia
- National ICT Australia, Department of Electrical and Electronic Engineering, University of Melbourne, Melbourne, Australia
- Centre for Neural Engineering, University of Melbourne, Melbourne, Australia
- Bionics Institute, Melbourne, Australia
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Abstract
The cochlear nuclei are the first central processors of auditory information and provide inputs to all the major brainstem and midbrain auditory nuclei. Although the local circuits within the cochlear nuclei are understood at a cellular level, the spatial patterns of connectivity and the connection strengths in these circuits have been less well characterized. We have applied a novel, quantitative approach to mapping local circuits projecting to cells in the mouse anteroventral cochlear nucleus (AVCN) using laser-scanning photostimulation and glutamate uncaging. The amplitude and kinetics of individual evoked synaptic events were measured to reveal the patterns and strengths of synaptic connections. We found that the two major excitatory projection cell classes, the bushy and T-stellate cells, receive a spatially broad inhibition from D-stellate cells in the AVCN, and a spatially confined inhibition from the tuberculoventral cells of the dorsal cochlear nucleus. Furthermore, T-stellate cells integrate D-stellate inhibition from an area that spans twice the frequency range of that integrated by bushy cells. A subset of both bushy and T-stellate cells receives inhibition from an unidentified cell population at the dorsal-medial boundary of the AVCN. A smaller subset of cells receives local excitation from within the AVCN. Our results show that inhibitory circuits can have target-specific patterns of spatial convergence, synaptic strength, and receptor kinetics, resulting in different spectral and temporal processing capabilities.
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Spencer MJ, Nayagam DAX, Clarey J, Meffin H, Burkitt AN, Grayden DB. Onset-inhibition in the auditory brainstem: a potential mechanism for signal enhancement of speech-like sounds. BMC Neurosci 2013. [PMCID: PMC3704287 DOI: 10.1186/1471-2202-14-s1-p148] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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Manzoor NF, Licari FG, Klapchar M, Elkin RL, Gao Y, Chen G, Kaltenbach JA. Noise-induced hyperactivity in the inferior colliculus: its relationship with hyperactivity in the dorsal cochlear nucleus. J Neurophysiol 2012; 108:976-88. [PMID: 22552192 DOI: 10.1152/jn.00833.2011] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Intense noise exposure causes hyperactivity to develop in the mammalian dorsal cochlear nucleus (DCN) and inferior colliculus (IC). It has not yet been established whether the IC hyperactivity is driven by hyperactivity from extrinsic sources that include the DCN or instead is maintained independently of this input. We have investigated the extent to which IC hyperactivity is dependent on input from the contralateral DCN by comparing recordings of spontaneous activity in the IC of noise-exposed and control hamsters before and after ablation of the contralateral DCN. One group of animals was binaurally exposed to intense sound (10 kHz, 115 dB SPL, 4 h), whereas the control group was not. Both groups were studied electrophysiologically 2-3 wk later by first mapping spontaneous activity along the tonotopic axis of the IC to confirm induction of hyperactivity. Spontaneous activity was then recorded at a hyperactive IC locus over two 30-min periods, one with DCNs intact and the other after ablation of the contralateral DCN. In a subset of animals, activity was again mapped along the tonotopic axis after the time course of the activity was recorded before and after DCN ablation. Following recordings, the brains were fixed, and histological evaluations were performed to assess the extent of DCN ablation. Ablation of the DCN resulted in major reductions of IC hyperactivity. Levels of postablation activity in exposed animals were similar to the levels of activity in the IC of control animals, indicating an almost complete loss of hyperactivity in exposed animals. The results suggest that hyperactivity in the IC is dependent on support from extrinsic sources that include and may even begin with the DCN. This finding does not rule out longer term compensatory or homeostatic adjustments that might restore hyperactivity in the IC over time.
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Affiliation(s)
- N F Manzoor
- Department of Neurosciences, Lerner Research Institute, Head and Neck Institute, The Cleveland Clinic, Cleveland, OH, USA
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Mauger SJ, Shivdasani MN, Rathbone GD, Argent RE, Paolini AG. An in vivo investigation of first spike latencies in the inferior colliculus in response to multichannel penetrating auditory brainstem implant stimulation. J Neural Eng 2010; 7:036004. [PMID: 20440054 DOI: 10.1088/1741-2560/7/3/036004] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The cochlear nucleus (CN) is the first auditory processing site within the brain and the target location of the auditory brainstem implant (ABI), which provides speech perception to patients who cannot benefit from a cochlear implant (CI). Although there is variance between ABI recipient speech performance outcomes, performance is typically low compared to CI recipients. Temporal aspects of neural firing such as first spike latency (FSL) are thought to code for many speech features; however, no studies have investigated FSL from CN stimulation. Consequently, ABIs currently do not incorporate CN-specific temporal information. We therefore systematically investigated inferior colliculus (IC) neuron's FSL response to frequency-specific electrical stimulation of the CN in rats. The range of FSLs from electrical stimulation of many neurons indicates that both monosynaptic and polysynaptic pathways were activated, suggesting initial activation of multiple CN neuron types. Electrical FSLs for a single neuron did not change irrespective of the CN frequency region stimulated, indicating highly segregated projections from the CN to the IC. These results present the first evidence of temporal responses to frequency-specific CN electrical stimulation. Understanding the auditory system's temporal response to electrical stimulation will help in future ABI designs and stimulation strategies.
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Affiliation(s)
- Stefan J Mauger
- School of Psychological Science, La Trobe University, VIC 3086, Australia. The Bionic Ear Institute, East Melbourne, VIC 3002, Australia
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Shivdasani MN, Mauger SJ, Rathbone GD, Paolini AG. Neural synchrony in ventral cochlear nucleus neuron populations is not mediated by intrinsic processes but is stimulus induced: implications for auditory brainstem implants. J Neural Eng 2009; 6:065003. [PMID: 19850978 DOI: 10.1088/1741-2560/6/6/065003] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The aim of this investigation was to elucidate if neural synchrony forms part of the spike time-based theory for coding of sound information in the ventral cochlear nucleus (VCN) of the auditory brainstem. Previous research attempts to quantify the degree of neural synchrony at higher levels of the central auditory system have indicated that synchronized firing of neurons during presentation of an acoustic stimulus could play an important role in coding complex sound features. However, it is unknown whether this synchrony could in fact arise from the VCN as it is the first station in the central auditory pathway. Cross-correlation analysis was conducted on 499 pairs of multiunit clusters recorded in the urethane-anesthetized rat VCN in response to pure tones and combinations of two tones to determine the presence of neural synchrony. The shift predictor correlogram was used as a measure for determining the synchrony owing to the effects of the stimulus. Without subtraction of the shift predictor, over 65% of the pairs of multiunit clusters exhibited significant correlation in neural firing when the frequencies of the tones presented matched their characteristic frequencies (CFs). In addition, this stimulus-evoked neural synchrony was dependent on the physical distance between electrode sites, and the CF difference between multiunit clusters as the number of correlated pairs dropped significantly for electrode sites greater than 800 microm apart and for multiunit cluster pairs with a CF difference greater than 0.5 octaves. However, subtraction of the shift predictor correlograms from the raw correlograms resulted in no remaining correlation between all VCN pairs. These results suggest that while neural synchrony may be a feature of sound coding in the VCN, it is stimulus induced and not due to intrinsic neural interactions within the nucleus. These data provide important implications for stimulation strategies for the auditory brainstem implant, which is used to provide functional hearing to the profoundly deaf through electrical stimulation of the VCN.
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Affiliation(s)
- Mohit N Shivdasani
- School of Psychological Science, La Trobe University, Bundoora, VIC 3086, Australia
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Abstract
A synchronization model of pitch processing was extended to include lateral inhibition mechanisms that have been observed in the mammalian mid brain, and information integration mechanisms consistent with observed changes to response fields of mammalian auditory cortex neurons. Model parameters for the inhibition mechanisms were adapted to fit model outputs to observed temporal dynamics of pitch height difference limens from the literature. Pitch strength was defined as the certainty of pitch height judgment, and was calculated by normalizing model responses by their mean. The model was adapted to fit experimental pitch strength data reported in the literature for pure tones and harmonic complexes. It was proposed that pitch height is first estimated in relation to patterns (or templates) of tonotopic activation on the auditory nerve for particular stimulus types. These patterns are stored in long term memory. This pitch height estimation primes cortical pitch neurons to integrate finely tuned pitch information from the inferior colliculus across the periodotopic and tonotopic dimensions. Predicted pitch strength for complexes of unresolved harmonics, iterated rippled noise and amplitude modulated tones using this model also conformed to behavioral data from the literature.
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Sun H, Wu SH. Modification of membrane excitability of neurons in the rat's dorsal cortex of the inferior colliculus by preceding hyperpolarization. Neuroscience 2007; 154:257-72. [PMID: 18155851 DOI: 10.1016/j.neuroscience.2007.10.055] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2007] [Revised: 10/09/2007] [Accepted: 10/10/2007] [Indexed: 11/24/2022]
Abstract
The inferior colliculus (IC) is among the largest nuclei in the central auditory system and is considered to be a major integration center in the auditory pathway. To understand how IC contributes to auditory processing, we investigated the effects of preceding hyperpolarization on membrane excitability and firing behavior of neurons located in the dorsal cortex of the inferior colliculus (ICD). We made whole-cell patch clamp recordings from ICD neurons (n=96) in rat brain slices. We classified ICD neurons into three types, i.e. sustained-regular, sustained-adapting and buildup, according to their responses to depolarizing current injection. Nearly 91% of the neurons had sustained firing throughout the period of current injection, showing either regular or adapting pattern. About 9% of the neurons exhibited a buildup pattern, in which sustained firing started after a long delay. Rebound depolarization and spikes after hyperpolarization were seen in 51.7% of the sustained neurons, but were not seen in buildup neurons. When depolarizing current was preceded by a hyperpolarizing current, various forms of the modification on membrane excitability were observed. For non-rebound neurons, the membrane excitability was either suppressed or unchanged after pre-hyperpolarization. The first spike latency lengthened in neurons whose firing changed to a buildup pattern, shortened in those whose firing changed to a pauser pattern, and remained unchanged in those whose discharge pattern remained sustained. For rebound neurons, the firing rate decreased in neurons whose firing pattern was changed to onset or pauser, increased in neurons whose firing was changed to adapting, or remained unchanged in neurons whose firing became irregular. The first spike latency was shortened in all the rebound cells. The results suggest that intrinsic membrane properties can play an important role in integration of excitatory and inhibitory inputs and thereby in determination of the output of ICD neurons.
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Affiliation(s)
- H Sun
- Institute of Neuroscience, Carleton University, 335 Life Sciences Research Building, 1125 Colonel By Drive, Ottawa, Ontario, Canada K1S 5B6
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Shivdasani MN, Mauger SJ, Rathbone GD, Paolini AG. Inferior colliculus responses to multichannel microstimulation of the ventral cochlear nucleus: implications for auditory brain stem implants. J Neurophysiol 2007; 99:1-13. [PMID: 17928560 DOI: 10.1152/jn.00629.2007] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Multichannel techniques were used to assess the frequency specificity of activation in the central nucleus of the inferior colliculus (CIC) produced by electrical stimulation of localized regions within the ventral cochlear nucleus (VCN). Data were recorded in response to pure tones from 141 and 193 multiunit clusters in the rat VCN and the CIC, respectively. Of 141 VCN sites, 126 were individually stimulated while recording responses in the CIC. A variety of CIC response types were seen with an increase in both electrical and acoustic stimulation levels. The majority of sites exhibited monotonic rate-level types acoustically, whereas spike rate saturation was achieved predominantly with electrical stimulation. In 20.6% of the 364 characteristic frequency aligned VCN-CIC pairs, the CIC sites did not respond to stimulation. In 26% of the 193 CIC sites, a high correlation was observed between acoustic tuning and electrical tuning obtained through VCN stimulation. A high degree of frequency specificity was found in 58% of the 118 lowest threshold VCN-CIC pairs. This was dependent on electrode placement within the VCN because a higher degree of frequency specificity was achieved with stimulation of medial, central, and posterolateral VCN regions than more anterolateral regions. Broadness of acoustic tuning in the CIC played a role in frequency-specific activation. Narrowly tuned CIC sites showed the lowest degree of frequency specificity on stimulation of the anterolateral VCN regions. These data provide significant implications for auditory brain stem implant electrode placement, current localization, power requirements, and facilitation of information transfer to higher brain centers.
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Affiliation(s)
- Mohit N Shivdasani
- The Bionic Ear Institute, East Melbourne Victoria, Melbourne, Victoria, Australia
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Needham K, Paolini AG. The commissural pathway and cochlear nucleus bushy neurons: An in vivo intracellular investigation. Brain Res 2007; 1134:113-21. [PMID: 17174943 DOI: 10.1016/j.brainres.2006.11.058] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2006] [Revised: 11/16/2006] [Accepted: 11/20/2006] [Indexed: 10/23/2022]
Abstract
A direct commissural connection formed between cochlear nuclei allows information from the contralateral ear to rapidly influence the processing of the ascending auditory signal. Among the neuronal groups proposed to both receive, and contribute to, commissural input is the bushy cell population in the ventral cochlear nucleus (VCN). In this in vivo electrophysiological study we examine the intracellular recordings of bushy neurons during electrical stimulation of the contralateral cochlear nucleus (CN) for evidence of both their contribution to, and input from commissural projections. Activation of the commissural pathway revealed short-latency fast hyperpolarisation in 19.5% of the 41 bushy neurons examined. The hyperpolarising potentials were small in amplitude, displayed a highly variable time course between neurons, and in some cases were eliminated with injection of depolarising current. There was no indication of antidromic activity, or short-latency excitatory potentials. These results suggest that i) bushy neurons do not contribute projections to the commissural connection, and ii) a small portion of bushy neurons are hyperpolarised following commissural stimulation.
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Affiliation(s)
- Karina Needham
- Department of Otolaryngology, The University of Melbourne, and The Bionic Ear Institute, 384-388 Albert Street, East Melbourne, Victoria 3002, Australia.
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Nayagam DAX, Clarey JC, Paolini AG. Intracellular responses and morphology of rat ventral complex of the lateral lemniscus neurons in vivo. J Comp Neurol 2007; 498:295-315. [PMID: 16856136 DOI: 10.1002/cne.21058] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The function of the ventral and intermediate nuclei of the lateral lemniscus (VNLL and INLL), collectively termed ventral complex of the lateral lemniscus (VCLL), is unclear. Several studies have suggested that it plays a role in coding the temporal aspects of sound. In our study, a sample (n = 161) of intracellular responses to dichotically presented noise or tone bursts was collected from the VCLL of urethane-anesthetized rats in vivo. Intracellular recordings revealed six distinct response types to tones, distinguished by their synaptic and membrane characteristics as well as firing pattern. Three of these response types were correlated with distinct cellular morphologies revealed by intracellular injection of neurobiotin. 3D reconstructions of recorded neurons within the VCLL showed the spatial distribution of various response properties, including response type, laterality, characteristic frequency (CF), and binaural influences. Cells that responded to monaural (55%) or binaural (45%) stimulation were distributed throughout the VCLL. Almost all VCLL units were responsive to contralateral stimulation (97%). Most neurons were excited by contralateral stimulation (83%), many exclusively (43%), and some in conjunction with ipsilateral inhibition (28%) or excitation (12%). The INLL contained mostly binaural neurons (65%), typically with ipsilateral inhibition and contralateral excitation. These results indicate that the VCLL is not a monaural structure and there is a dorsal-ventral segregation of binaural and monaural cells. 3D reconstructions of intracellular CFs did not reveal the presence of any tonotopic arrangement within the VCLL. Presumably, the proposed timing role of this structure does not require a systematic representation of tonal frequency.
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Doucet JR, Ryugo DK. Structural and functional classes of multipolar cells in the ventral cochlear nucleus. ACTA ACUST UNITED AC 2006; 288:331-44. [PMID: 16550550 PMCID: PMC2566305 DOI: 10.1002/ar.a.20294] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Multipolar cells in the ventral cochlear nucleus (VCN) are a structurally and functionally diverse group of projection neurons. Understanding their role in the ascending pathway involves partitioning multipolar cells into distinct populations and determining where in the brain each sends its coded messages. In this study, we used retrograde labeling techniques in rats to identify multipolar neurons that project their axons to the ipsilateral dorsal cochlear nucleus (DCN), the contralateral CN, or both structures. Three rats received injections of biotinylated dextran amine in the ipsilateral DCN and diamidino yellow in the contralateral CN. Several radiate multipolar neurons (defined by their axonal projections to the ipsilateral DCN and their dendrites that traverse VCN isofrequency sheets) were double-labeled but over 70% were not. This result suggests two distinct populations: (1) radiate-commissural (RC) multipolar cells that project to the ipsilateral DCN and the contralateral CN, and (2) radiate multipolar cells that project exclusively (in this context) to the ipsilateral DCN. In a different group of animals, we retrogradely labeled multipolar neurons that project their axons to the contralateral CN and measured the size of their cell bodies. The mean size of this population (266 +/- 156 microm2) was significantly smaller than those of RC-multipolar cells (418 +/- 140 microm2). We conclude that the CN commissural pathway is composed of at least two components: (1) RC multipolar cells and (2) commissural multipolar cells that are small- and medium-sized neurons that project exclusively (in this context) to the contralateral CN. These results identify separate structural groups of multipolar cells that may correspond to physiological unit types described in the literature. They also provide protocols for isolating and studying different populations of multipolar cells to determine the neural mechanisms that govern their responses to sound.
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Affiliation(s)
- John R Doucet
- Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
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Needham K, Paolini AG. Neural timing, inhibition and the nature of stellate cell interaction in the ventral cochlear nucleus. Hear Res 2006; 216-217:31-42. [PMID: 16554129 DOI: 10.1016/j.heares.2006.01.016] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/31/2005] [Revised: 01/25/2006] [Accepted: 01/26/2006] [Indexed: 10/24/2022]
Abstract
The ventral cochlear nucleus (VCN) stellate cell population comprises two clusters: narrowly-tuned, excitatory T stellate neurons, and D stellate neurons, a broadly-tuned population of inhibitory cells. These neurons respond to best frequency (BF) tone bursts in a chopper or onset manner, respectively. Through extensive local and commissural projections the D stellate population provides a source of fast inhibitory input to both intrinsic and contralateral T stellate neurons. Whilst the nature of interactions between intrinsic stellate populations is difficult to examine, our previous intracellular investigations of the commissural pathway have provided a means by which to study this relationship in the in vivo preparation. It is the aim of this paper to both review and extend our understanding of the link between stellate populations and their involvement in the commissural pathway by presenting an overview of the results attained in our recently expanded study. The sample of 17 intracellular and 34 extracellular onset chopper (O(C)) and late/ideal (On(L)/On(I)) neurons revealed antidromic activity in 31.4% of neurons following contralateral stimulation, providing physiological evidence that On(L)/On(I) neurons also contribute projections to the commissural connection. Alternatively, 64.7% of the 34 intracellularly-recorded chopper neurons displayed fast, monosynaptic inhibitory potentials. This commissural input was found to influence the timing of neural activity in chopper neurons, providing insight into the relationship that exists between T and D stellate neurons.
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Affiliation(s)
- Karina Needham
- Department of Otolaryngology, The University of Melbourne, 32 Gisborne Street, East Melbourne, Vic. 3002, Australia.
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Walmsley B, Berntson A, Leao RN, Fyffe REW. Activity-dependent regulation of synaptic strength and neuronal excitability in central auditory pathways. J Physiol 2006; 572:313-21. [PMID: 16469782 PMCID: PMC1779684 DOI: 10.1113/jphysiol.2006.104851] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Neural activity plays an important role in regulating synaptic strength and neuronal membrane properties. Attempts to establish guiding rules for activity-dependent neuronal changes have led to such concepts as homeostasis of cellular activity and Hebbian reinforcement of synaptic strength. However, it is clear that there are diverse effects resulting from activity changes, and that these changes depend on the experimental preparation, and the developmental stage of the neural circuits under study. In addition, most experimental evidence on activity-dependent regulation comes from reduced preparations such as neuronal cultures. This review highlights recent results from studies of the intact mammalian auditory system, where changes in activity have been shown to produce alterations in synaptic and membrane properties at the level of individual neurons, and changes in network properties, including the formation of tonotopic maps.
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Affiliation(s)
- Bruce Walmsley
- John Curtin School of Medical Research, Australian National University, Canberra, ACT.
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Leao RN, Sun H, Svahn K, Berntson A, Youssoufian M, Paolini AG, Fyffe REW, Walmsley B. Topographic organization in the auditory brainstem of juvenile mice is disrupted in congenital deafness. J Physiol 2005; 571:563-78. [PMID: 16373385 PMCID: PMC1805808 DOI: 10.1113/jphysiol.2005.098780] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
There is an orderly topographic arrangement of neurones within auditory brainstem nuclei based on sound frequency. Previous immunolabelling studies in the medial nucleus of the trapezoid body (MNTB) have suggested that there may be gradients of voltage-gated currents underlying this tonotopic arrangement. Here, our electrophysiological and immunolabelling results demonstrate that underlying the tonotopic organization of the MNTB is a combination of medio-lateral gradients of low-and high-threshold potassium currents and hyperpolarization-activated cation currents. Our results also show that the intrinsic membrane properties of MNTB neurones produce a topographic gradient of time delays, which may be relevant to sound localization, following previous demonstrations of the importance of the timing of inhibitory input from the MNTB to the medial superior olive (MSO). Most importantly, we demonstrate that, in the MNTB of congenitally deaf mice, which exhibit no spontaneous auditory nerve activity, the normal tonotopic gradients of neuronal properties are absent. Our results suggest an underlying mechanism for the observed topographic gradient of neuronal firing properties in the MNTB, show that an intrinsic neuronal mechanism is responsible for generating a topographic gradient of time-delays, and provide direct evidence that these gradients rely on spontaneous auditory nerve activity during development.
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Affiliation(s)
- Richardson N Leao
- Synapse and Hearing Laboratory, Division of Neuroscience, The John Curtin School of Medical Research, The Australian National University, PO Box 334, Canberra, ACT 0200, Australia
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Paolini AG, Clarey JC, Needham K, Clark GM. Balanced inhibition and excitation underlies spike firing regularity in ventral cochlear nucleus chopper neurons. Eur J Neurosci 2005; 21:1236-48. [PMID: 15813933 DOI: 10.1111/j.1460-9568.2005.03958.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Ventral cochlear nucleus stellate cells respond to characteristic frequency (CF) tones with sustained (C(S)), transient (C(T)) or onset chopping (O(C)) activity. The mechanisms underlying these different response patterns are not fully understood, and the present study used in vivo intracellular recordings (n = 42) in urethane-anaesthetized rats to examine the possible influence of inhibition on action potential regularity. Hyperpolarization following the offset of a CF tone burst was used as a measure of on-CF inhibition. A cluster analysis based on several membrane potential features, including on-CF inhibition, discriminated three groups in addition to the C(S) response type - two types of C(T) responses and the O(C) type. The different patterns of firing regularity exhibited by C(S/T) neurons reflected different thresholds or degrees of overlap between these cells' narrowly tuned excitatory and inhibitory inputs. C(T) cells with closely matched inhibitory and excitatory response areas showed substantial on-CF inhibition and the greatest decline in firing regularity during a CF tone, whereas those with a mismatch between their response areas showed lateral inhibition and a less marked decline in firing regularity. The presence of inhibition in C(S) neurons did not alter their firing regularity, possibly because of the lower threshold for excitation compared with inhibition. The latency, duration and frequency extent of sustained hyperpolarization in C(S/T) cells is inconsistent with the response properties of O(C) neurons, suggesting that another source(s) of inhibition influences firing regularity, and presumably response magnitude, in these neurons.
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Affiliation(s)
- Antonio G Paolini
- School of Psychological Science, La Trobe University, Bundoora, Victoria 3086, Australia.
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Nayagam DAX, Clarey JC, Paolini AG. Powerful, onset inhibition in the ventral nucleus of the lateral lemniscus. J Neurophysiol 2005; 94:1651-4. [PMID: 15817650 DOI: 10.1152/jn.00167.2005] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The function of the ventral nucleus of the lateral lemniscus (VNLL), a secondary processing site within the auditory brain stem, is unclear. It is known to be a major source of inhibition to the inferior colliculus (IC). It is also thought to play a role in coding the temporal aspects of sound, such as onsets and the periodic components of complex stimuli. In vivo intracellular recordings from VNLL neurons (n = 56) in urethane anesthetized rats revealed the presence of large-amplitude, short-duration, onset inhibition in a subset of neurons (14.3%). This inhibition occurred before the first action potential (AP) elicited by noise or tone bursts, was broadly tuned to tonal frequency and was shown to delay the first AP. Our data suggest it is a result of an intrinsic circuit activated by the octopus cell pathway originating in the contralateral cochlear nucleus; this pathway is known to convey exquisitely timed and broadly tuned onset information. This powerful inhibition within the VNLL appears to control the timing of this structure's inhibitory output to higher centers, which has important auditory processing outcomes. The circuit also provides a pathway for fast, broadly tuned, onset inhibition to the IC.
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