Processing of Interaural Temporal Disparities in the Medial Division of the Ventral Nucleus of the Lateral Lemniscus

2002 ◽  
Vol 88 (2) ◽  
pp. 666-675 ◽  
Author(s):  
Ranjan Batra ◽  
Douglas C. Fitzpatrick
Keyword(s):  
Auditory Pathway ◽  
Medial Superior Olive ◽  
Lateral Lemniscus ◽  
Accurate Localization ◽  
Secondary Stage ◽  
Random Intervals ◽  
Ventral Nucleus ◽  
Onset Response ◽  
Specialized Population ◽  
Contralateral Stimulus

The medial division of the ventral nucleus of the lateral lemniscus (VNLLm) contains a specialized population of neurons that is sensitive to interaural temporal disparities (ITDs), a potent cue for sound localization along the azimuth. Unlike many ITD-sensitive neurons elsewhere in the auditory system, neurons in the VNLLm respond only at the onset of tones. An onset response may be significant for behavior because, under echoic conditions, tones require sharp onsets for accurate localization. In contrast, noise can generally be localized even with gradual onsets, presumably because transients occur at random intervals in noise. We recorded responses of neurons in the VNLLm to tones and noise in unanesthetized rabbits. We found that although tones elicited a transient response, noise elicited a sustained response as if it was a sequence of transients. The responses to tones indicate that these neurons represent a secondary stage in the processing of ITDs. The onset response to tones was only weakly synchronized to the phase of the tone, indicating that neurons in the VNLLm inherit their sensitivity to ITDs from their inputs. The latencies were short (∼8 ms), implying that the ITD sensitivity is derived from ascending inputs. Most neurons in the VNLLm discharged maximally at the same ITD at all frequencies, a characteristic shared with neurons of the medial superior olive. However, the latency of neurons in the VNLLm to interaurally delayed stimuli is linked strongly to the timing of the contralateral stimulus. This suggests that these neurons receive a suprathreshold, contralateral input that is modulated by a subthreshold input conveying information about ITDs. Other stations in the auditory pathway contain a subset of neurons that respond transiently to tones and are sensitive to ITDs. These neurons may represent a novel pathway that assists in localizing sounds in the presence of reflections.

Responses of Neurons in the Ventral Nucleus of the Lateral Lemniscus to Sinusoidally Amplitude Modulated Tones

2006 ◽  
Vol 96 (5) ◽  
pp. 2388-2398 ◽  
Author(s):  
Ranjan Batra
Keyword(s):  
Spontaneous Activity ◽  
Transfer Functions ◽  
Modulation Frequency ◽  
Auditory Pathway ◽  
Modulation Transfer ◽  
Lateral Lemniscus ◽  
Modulation Transfer Functions ◽  
Band Pass ◽  
Acoustic Space ◽  
Ventral Nucleus

Fluctuations in the amplitude of a sound play an important role in our perception of pitch and acoustic space, but their neural analysis has not been fully elucidated. The ventral nucleus of the lateral lemniscus (VNLL) has been implicated in the processing of such temporal features of a sound. This study examines responses of neurons in the VNLL of unanesthetized rabbits to sinusoidally amplitude modulated tones, a type of stimulus that has often been used to investigate encoding of temporal information. Modulation transfer functions of responses were calculated in two ways: based on discharge rates (rMTFs) and on synchronization to the envelope (tMTFs). Among the variety of rMTFs, two types were readily identifiable: flat and band-pass. The responses of neurons exhibiting these types of rMTF differed in several ways. Neurons with flat rMTFs typically had moderate rates of spontaneous activity, sustained responses to short tone bursts, and low-pass or band-pass tMTFs. Neurons with band-pass rMTFs typically had low spontaneous activity, onset responses to short tone bursts, and flat tMTFs. The vast majority synchronized strongly to the modulation envelope. The best modulation frequencies of neurons with band-pass rMTFs extended from 14 to 283 Hz. The presence of neurons with band-pass rMTFs in the VNLL suggests that this nucleus plays a role in converting the temporal code for modulation frequency used in lower structures into a rate-based code for use higher in the auditory pathway. The substantial number of neurons with more complex modulation transfer functions indicates that the VNLL has other functions.

scholarly journals Dopamine in Auditory Nuclei and Lemniscal Projections is Poised to Influence Acoustic Integration in the Inferior Colliculus

2021 ◽  
Vol 15 ◽  
Author(s):  
Sharonda Harris ◽  
Renee Afram ◽  
Takashi Shimano ◽  
Bozena Fyk-Kolodziej ◽  
Paul D. Walker ◽  
...  
Keyword(s):  
Tyrosine Hydroxylase ◽  
Inferior Colliculus ◽  
Auditory Pathway ◽  
Superior Olivary Complex ◽  
Lateral Lemniscus ◽  
Adult Rats ◽  
Dorsal Nucleus ◽  
Key Enzyme ◽  
6 Hydroxydopamine ◽  
Ventral Nucleus

Dopamine (DA) modulates the activity of nuclei within the ascending and descending auditory pathway. Previous studies have identified neurons and fibers in the inferior colliculus (IC) which are positively labeled for tyrosine hydroxylase (TH), a key enzyme in the synthesis of dopamine. However, the origins of the tyrosine hydroxylase positive projections to the inferior colliculus have not been fully explored. The lateral lemniscus (LL) provides a robust inhibitory projection to the inferior colliculus and plays a role in the temporal processing of sound. In the present study, immunoreactivity for tyrosine hydroxylase was examined in animals with and without 6-hydroxydopamine (6-OHDA) lesions. Lesioning, with 6-OHDA placed in the inferior colliculus, led to a significant reduction in tyrosine hydroxylase immuno-positive labeling in the lateral lemniscus and inferior colliculus. Immunolabeling for dopamine beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT), enzymes responsible for the synthesis of norepinephrine (NE) and epinephrine (E), respectively, were evaluated. Very little immunoreactivity for DBH and no immunoreactivity for PNMT was found within the cell bodies of the dorsal, intermediate, or ventral nucleus of the lateral lemniscus. The results indicate that catecholaminergic neurons of the lateral lemniscus are likely dopaminergic and not noradrenergic or adrenergic. Next, high-pressure liquid chromatography (HPLC) analysis was used to confirm that dopamine is present in the inferior colliculus and nuclei that send projections to the inferior colliculus, including the cochlear nucleus (CN), superior olivary complex (SOC), lateral lemniscus, and auditory cortex (AC). Finally, fluorogold, a retrograde tracer, was injected into the inferior colliculus of adult rats. Each subdivision of the lateral lemniscus contained fluorogold within the somata, with the dorsal nucleus of the lateral lemniscus showing the most robust projections to the inferior colliculus. Fluorogold-tyrosine hydroxylase colocalization within the lateral lemniscus was assessed. The dorsal and intermediate nuclei neurons exhibiting similar degrees of colocalization, while neurons of the ventral nucleus had significantly fewer colocalized fluorogold-tyrosine hydroxylase labeled neurons. These results suggest that several auditory nuclei that project to the inferior colliculus contain dopamine, dopaminergic neurons in the lateral lemniscus project to the inferior colliculus and that dopaminergic neurotransmission is poised to play a pivotal role in the function of the inferior colliculus.

Differential Response Properties to Amplitude Modulated Signals in the Dorsal Nucleus of the Lateral Lemniscus of the Mustache Bat and the Roles of GABAergic Inhibition

1997 ◽  
Vol 77 (1) ◽  
pp. 324-340 ◽  
Author(s):  
Lichuan Yang ◽  
George D. Pollak
Keyword(s):  
Phase Locking ◽  
Modulation Frequency ◽  
Tone Burst ◽  
Differential Response ◽  
Gabaergic Inhibition ◽  
Lateral Lemniscus ◽  
Response Properties ◽  
Dorsal Nucleus ◽  
Modulated Signals ◽  
Onset Response

Yang, Lichuan and George D. Pollak. Differential response properties to amplitude modulated signals in the dorsal nucleus of the lateral lemniscus of the mustache bat and the roles of GABAergic inhibition. J. Neurophysiol. 77: 324–340, 1997. We studied the phase-locking of 89 neurons in the dorsal nucleus of the lateral lemniscus (DNLL) of the mustache bat to sinusoidally amplitude modulated (SAM) signals and the influence that GABAergic inhibition had on their response properties. Response properties were determined with tone bursts at each neuron's best frequency and then with a series of SAM signals that had modulation frequencies ranging from 50–100 to 800 Hz in 100-Hz steps. DNLL neurons were divided into two principal types: sustained neurons (55%), which responded throughout the duration of the tone burst, and onset neurons (45%), which responded only at the beginning of the tone burst. Sustained and onset neurons responded differently to SAM signals. Sustained neurons responded with phase-locked discharges to modulation frequencies ≤400–800 Hz. In contrast, 70% of the onset neurons phase-locked only to low modulation frequencies of 100–300 Hz, whereas 30% of the onset neurons did not phase-lock to any modulation frequency. Signal intensity differentially affected the phase-locking of sustained and onset neurons. Sustained neurons exhibited tight phase-locking only at low intensities, 10–30 dB above threshold. Onset neurons, in contrast, maintained strong phase-locking even at relatively high intensities. Blocking GABAergic inhibition with bicuculline had different effects on the phase-locking of sustained and onset neurons. In sustained neurons, there was an overall decline in phase-locking at all modulation frequencies. In contrast, 70% of the onset neurons phase-locked to much higher modulation frequencies than they did when inhibition was intact. The other 30% of onset neurons phase-locked to SAM signals, although they fired only with an onset response to the same signals before inhibition was blocked. In both cases, blocking GABAergic inhibition transformed their responses to SAM signals into patterns that were more like those of sustained neurons. We also propose mechanisms that could explain the differential effects of GABAergic inhibition on onset neurons that locked to low modulation frequencies and on onset neurons that did not lock to any SAM signals before inhibition was blocked. The key features of the proposed mechanisms are the absolute latencies and temporal synchrony of the excitatory and inhibitory inputs.

scholarly journals Auditory brainstem models: adapting cochlear nuclei improve spatial encoding by the medial superior olive in reverberation

2019 ◽  
Author(s):  
Andrew Brughera ◽  
Jason Mikiel-Hunter ◽  
Mathias Dietz ◽  
David McAlpine
Keyword(s):  
Spatial Information ◽  
Interaural Time Difference ◽  
Auditory Pathway ◽  
Auditory Brainstem ◽  
Coincidence Detection ◽  
Type Model ◽  
Medial Superior Olive ◽  
Sound Energy ◽  
Superior Olive ◽  
Cochlear Nuclei

AbstractListeners perceive sound-energy as originating from the direction of its source, even as direct sound is followed milliseconds later by reflected sound from multiple different directions. Early-arriving sound is emphasised in the ascending auditory pathway, including the medial superior olive (MSO) where binaural neurons encode the interaural time difference (ITD) cue for spatial location. Behaviourally, weighting of ITD conveyed during rising sound-energy is stronger at 600 Hz, a frequency with higher reverberant energy, than at 200 Hz where reverberant energy is lower. Here we computationally explore the combined effectiveness of adaptation before ITD-encoding, and excitatory binaural coincidence detection within MSO neurons, in emphasising ITD conveyed in early-arriving sound. With excitatory inputs from adapting model spherical bushy cells (SBCs) of the bilateral cochlear nuclei, a Hodgkin-Huxley-type model MSO neuron reproduces the frequency-dependent emphasis of rising vs. peak sound-energy in ITD-encoding. Maintaining the adaptation in model SBCs, and adjusting membrane speed in model MSO neurons, hemispheric populations of model SBCs and MSO neurons, with simplified membranes for computational efficiency, also reproduce the stronger weighting of ITD information conveyed during rising sound-energy at 600 Hz compared to 200 Hz. This hemispheric model further demonstrates a link between strong weighting of spatial information during rising sound-energy, and correct unambiguous lateralisation of reverberant speech.

Responses of Neurons in the Rat's Ventral Nucleus of the Lateral Lemniscus to Monaural and Binaural Tone Bursts

2006 ◽  
Vol 95 (4) ◽  
pp. 2501-2512 ◽  
Author(s):  
Huiming Zhang ◽  
Jack B. Kelly
Keyword(s):  
Ampa Receptor ◽  
Frequency Tuning ◽  
Synaptic Activity ◽  
Temporal Response ◽  
Lateral Lemniscus ◽  
Tuning Curves ◽  
Temporal Firing ◽  
Excitatory Responses ◽  
Ventral Nucleus ◽  
Sustained Responses

Responses to monaural and binaural tone bursts were recorded from neurons in the rat's ventral nucleus of the lateral lemniscus (VNLL). Most of the neurons (55%) had V- or U-shaped frequency-tuning curves with a single clearly defined characteristic frequency (CF). However, many neurons had more complex, multipeaked tuning curves (37%), or other patterns (8%). Temporal firing patterns included both onset and sustained responses to contralateral tone bursts. Onset and sustained responses were distributed along the dorsoventral length of VNLL with no indication of segregation into different regions. Onset neurons had shorter average first-spike latencies than neurons with sustained responses (means, 8.3 vs. 14.8 ms). They also had less jitter, as reflected in the SD of first-spike latencies, than neurons with sustained responses (means, 0.59 and 4.2 ms, respectively). The extent of jitter decreased with an increase in stimulus intensity for neurons with sustained responses, but remained unchanged for onset neurons tested over the same range. Many neurons had binaural responses, primarily of the excitatory/inhibitory (EI) type, widely distributed along the dorsoventral extent of VNLL. Local application of the AMPA receptor antagonist NBQX reduced excitatory responses, indicating that responses were dependent on synaptic activity and not recorded from passing fibers. The results show that many neurons in VNLL have a precision of timing that is well suited for processing auditory temporal information. In the rat, these neurons are intermingled among cells with less precise temporal response features and include cells with binaural as well as monaural responses.

Functional organization of lateral cell groups of cat superior olivary complex

1977 ◽  
Vol 40 (2) ◽  
pp. 296-318 ◽  
Author(s):  
C. Tsuchitani
Keyword(s):  
Superior Olivary Complex ◽  
Maximum Output ◽  
Medial Superior Olive ◽  
Superior Olive ◽  
Response Characteristics ◽  
Cell Groups ◽  
Discharge Patterns ◽  
Intensity Functions ◽  
Contralateral Stimulus ◽  
Stimulation Of

1. Single-unit discharges to auditory stimuli were recorded extracellularly from superior olivary complex (SOC) units located lateral to the medial superior olive. Stimuli consisted of monaurally or binaurally presented tone bursts. The response measures obtained were effective ear, nature of effect, stimulus-frequency representation, maximum output, latency of response, and temporal pattern of tone burst-elicited discharges. Electrolytic marks were made at the unit studied or at the end of the electrode tract and in the medial superior olive. Following each experiment the locations of the units studied were determined histologically. An atlas of the laterally located SOC cell groups was developed to permit classification of units on the basis of localization within cell groups. Units were also classified according to the effects of stimulating the two ears. 2. All SOC units located lateral to the medial superior olive were excited by stimulation of the ipsilateral ear. Stimulation of the contralateral ear either excited, inhibited, had no effect, or had a potentiating effect on the discharges elicited by stimulating the ipsilateral ear. 3. Most lateral superior olivary (LSO) units were inhibited by contralateral stimulation, were narrowly tuned, produced low to high levels of maximum output, had short latencies, and produced regular discharge patterns characterized by chopper PST histograms with narrow initial peaks. 4. Most units within the caudal margins of the LSO (pLSO) were not affected or were inhibited by a contralateral stimulus; many were broadly tuned and exhibited intensity functions with large dynamic range and low slope. These units also had long latencies and produced chopper PST histograms with wide initial peaks. 5. Most units located dorsal to the LSO (DPO and DLPO) were not affected by the contralateral stimulus, were narrowly tuned, produced moderate levels of maximum discharge, had long latencies, and produced chopper PST histograms with wide initial peaks. 6. Units located ventral to the LSO appeared to have response characteristics related to unit location. Most units below the ventral hilum of the LSO (VLPO) were inhibited by the contralateral stimulus and many were broadly tuned VLPO units produced wide or poorly defined narrow-chopper discharge patterns and intensity functions with high maximum output. Most units located ventral to the lateral loop of the LSO (LNTB) were not affected by the contralateral stimulus and had response characteristics that may be related to the rostrocaudal location of the unit. 7. The cell groups located dorsal and ventral to the LSO were tonotopically organized with low-frequency-sensitive units located laterally and high-frequency-sensitive units located medially. The units located along the caudal margins of the LSO had a tonotopic organization similar to that of the LSO.

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