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Journal of Neurophysiology Jun 2016Masking effects of a preceding stimulus on the detection or perception of a signal have been found in several sensory systems in mammals, including humans and rodents....
Masking effects of a preceding stimulus on the detection or perception of a signal have been found in several sensory systems in mammals, including humans and rodents. In the auditory system, it has been hypothesized that a central "OFF-inhibitory" mechanism, which is generated by neurons that respond after a sound is terminated, may contribute to the observed psychophysics. The present study constructed a systems model for the inferior colliculus that includes major ascending monaural and binaural auditory pathways. The fundamental characteristics of several neuron types along the pathways were captured by Hodgkin-Huxley models with specific membrane and synaptic properties. OFF responses were reproduced with a model of the superior paraolivary nucleus containing a hyperpolarization-activated h current and a T-type calcium current. When the gap between the end of the masker and the onset of the signal was large, e.g., >5 ms, OFF inhibition generated strong suppressive effects on the signal response. For smaller gaps, an additional inhibitory source, which was modeled as ON inhibition from the contralateral dorsal nucleus of the lateral lemniscus, showed the potential of explaining the psychophysics. Meanwhile, the effect of a forward masker on the binaural sensitivity to a low-frequency signal was examined, which was consistent with previous psychophysical findings related to sound localization.
Topics: Animals; Calcium Channels, T-Type; Humans; Inferior Colliculi; Membrane Potentials; Models, Neurological; Neural Inhibition; Neurons; Perceptual Masking; Potassium Channels, Voltage-Gated; Voltage-Gated Sodium Channels
PubMed: 26912597
DOI: 10.1152/jn.00892.2015 -
The European Journal of Neuroscience Jul 2014Animal models of tinnitus allow us to study the relationship between changes in neural activity and the tinnitus percept. Here, guinea pigs were subjected to unilateral...
Animal models of tinnitus allow us to study the relationship between changes in neural activity and the tinnitus percept. Here, guinea pigs were subjected to unilateral noise trauma and tested behaviourally for tinnitus 8 weeks later. By comparing animals with tinnitus with those without, all of which were noise-exposed, we were able to identify changes unique to the tinnitus group. Three physiological markers known to change following noise exposure were examined: spontaneous firing rates (SFRs) and burst firing in the inferior colliculus (IC), evoked auditory brainstem responses (ABRs), and the number of neurons in the cochlear nucleus containing nitric oxide synthase (NOS). We obtained behavioural evidence of tinnitus in 12 of 16 (75%) animals. Both SFRs and incidences of burst firing were elevated in the IC of all noise-exposed animals, but there were no differences between tinnitus and no-tinnitus animals. There were significant decreases in ipsilateral ABR latencies in tinnitus animals, contrary to what might be expected with a small hearing loss. Furthermore, there was an ipsilateral-contralateral asymmetry in NOS staining in the ventral cochlear nucleus (VCN) that was only apparent in tinnitus animals. Tinnitus animals had a significantly greater number of NOS-containing neurons on the noise-exposed side, whereas no-tinnitus animals did not. These data suggest that measuring NOS in the VCN and recording ABRs supplement behavioural methods for confirming tinnitus in animals, and that nitric oxide is involved in plastic neural changes associated with tinnitus.
Topics: Animals; Cochlear Nucleus; Evoked Potentials, Auditory, Brain Stem; Female; Guinea Pigs; Hearing Loss, Noise-Induced; Inferior Colliculi; Male; Neurons; Nitric Oxide Synthase; Reaction Time; Tinnitus
PubMed: 24702651
DOI: 10.1111/ejn.12580 -
Frontiers in Neural Circuits 2023The auditory cortex (AC) modulates the activity of upstream pathways in the auditory brainstem via descending (corticofugal) projections. This feedback system plays an...
The auditory cortex (AC) modulates the activity of upstream pathways in the auditory brainstem via descending (corticofugal) projections. This feedback system plays an important role in the plasticity of the auditory system by shaping response properties of neurons in many subcortical nuclei. The majority of layer (L) 5 corticofugal neurons project to the inferior colliculus (IC). This corticocollicular (CC) pathway is involved in processing of complex sounds, auditory-related learning, and defense behavior. Partly due to their location in deep cortical layers, CC neuron population activity patterns within neuronal AC ensembles remain poorly understood. We employed two-photon imaging to record the activity of hundreds of L5 neurons in anesthetized as well as awake animals. CC neurons are broader tuned than other L5 pyramidal neurons and display weaker topographic order in core AC subfields. Network activity analyses revealed stronger clusters of CC neurons compared to non-CC neurons, which respond more reliable and integrate information over larger distances. However, results obtained from secondary auditory cortex (A2) differed considerably. Here CC neurons displayed similar or higher topography, depending on the subset of neurons analyzed. Furthermore, specifically in A2, CC activity clusters formed in response to complex sounds were spatially more restricted compared to other L5 neurons. Our findings indicate distinct network mechanism of CC neurons in analyzing sound properties with pronounced subfield differences, demonstrating that the topography of sound-evoked responses within AC is neuron-type dependent.
Topics: Animals; Auditory Cortex; Auditory Pathways; Inferior Colliculi; Neurons; Pyramidal Cells; Acoustic Stimulation
PubMed: 37521334
DOI: 10.3389/fncir.2023.1210057 -
ELife Apr 2015The time it takes a sound to travel from source to ear differs between the ears and creates an interaural delay. It varies systematically with spatial direction and is...
The time it takes a sound to travel from source to ear differs between the ears and creates an interaural delay. It varies systematically with spatial direction and is generally modeled as a pure time delay, independent of frequency. In acoustical recordings, we found that interaural delay varies with frequency at a fine scale. In physiological recordings of midbrain neurons sensitive to interaural delay, we found that preferred delay also varies with sound frequency. Similar observations reported earlier were not incorporated in a functional framework. We find that the frequency dependence of acoustical and physiological interaural delays are matched in key respects. This suggests that binaural neurons are tuned to acoustical features of ecological environments, rather than to fixed interaural delays. Using recordings from the nerve and brainstem we show that this tuning may emerge from neurons detecting coincidences between input fibers that are mistuned in frequency.
Topics: Acoustic Stimulation; Animals; Auditory Pathways; Cats; Cochlear Nerve; Ear; Inferior Colliculi; Reaction Time; Sound; Spatial Processing; Time Factors
PubMed: 25915620
DOI: 10.7554/eLife.06072 -
Frontiers in Neural Circuits 2020Corticofugal modulation of auditory responses in subcortical nuclei has been extensively studied whereas corticofugal synaptic transmission must still be characterized....
Corticofugal modulation of auditory responses in subcortical nuclei has been extensively studied whereas corticofugal synaptic transmission must still be characterized. This study examined postsynaptic potentials of the corticocollicular system, i.e., the projections from the primary auditory cortex (AI) to the central nucleus of the inferior colliculus (ICc) of the midbrain, in anesthetized C57 mice. We used focal electrical stimulation at the microampere level to activate the AI (ES) and whole-cell current-clamp to record the membrane potentials of ICc neurons. Following the whole-cell patch-clamp recording of 88 ICc neurons, 42 ICc neurons showed ES-evoked changes in the membrane potentials. We found that the ES induced inhibitory postsynaptic potentials in 6 out of 42 ICc neurons but only when the stimulus current was 96 μA or higher. In the remaining 36 ICc neurons, excitatory postsynaptic potentials (EPSPs) were induced at a much lower stimulus current. The 36 ICc neurons exhibiting EPSPs were categorized into physiologically matched neurons ( = 12) when the characteristic frequencies of the stimulated AI and recorded ICc neurons were similar (≤1 kHz) and unmatched neurons ( = 24) when they were different (>1 kHz). Compared to unmatched neurons, matched neurons exhibited a significantly lower threshold of evoking noticeable EPSP, greater EPSP amplitude, and shorter EPSP latency. Our data allow us to propose that corticocollicular synaptic transmission is primarily excitatory and that synaptic efficacy is dependent on the relationship of the frequency tunings between AI and ICc neurons.
Topics: Animals; Auditory Cortex; Electric Stimulation; Excitatory Postsynaptic Potentials; Female; Inferior Colliculi; Mice; Neural Inhibition; Neurons; Patch-Clamp Techniques; Synaptic Transmission
PubMed: 33192337
DOI: 10.3389/fncir.2020.591986 -
Journal of Nuclear Medicine : Official... Mar 2020Our purpose was to use PET to evaluate the glucose metabolism of the inferior colliculus (IC) and primary auditory cortex (PAC) in patients with asymmetric hearing loss...
Our purpose was to use PET to evaluate the glucose metabolism of the inferior colliculus (IC) and primary auditory cortex (PAC) in patients with asymmetric hearing loss (AHL). Normalized regional F-FDG uptake of the IC and PAC (reference: cerebellum) was assessed in 13 subjects with AHL using a fully digital clinical PET/CT system. Regional metabolism of both the IC and the PAC was significantly reduced contralateral to the most hearing-impaired ear compared with the ipsilateral side. Duration of deafness correlated positively with metabolism of the contralateral PAC but not with metabolism of the ipsilateral PAC or either of the ICs. Fully digital, high-resolution clinical PET scanners allow for investigating small brain stem nuclei. AHL has a significant impact on the regional glucose metabolism of the auditory pathway. Mitigation of this effect by a longer duration of deafness might indicate reorganization at the cortical level.
Topics: Adult; Aged; Aged, 80 and over; Female; Fluorodeoxyglucose F18; Hearing Loss; Humans; Inferior Colliculi; Male; Middle Aged; Positron Emission Tomography Computed Tomography
PubMed: 31481576
DOI: 10.2967/jnumed.119.231407 -
Behavioral Neuroscience Dec 2016A fundamental task of sensory systems is to extract relevant social information from a range of environmental stimuli in the face of changing behavioral contexts and...
A fundamental task of sensory systems is to extract relevant social information from a range of environmental stimuli in the face of changing behavioral contexts and reproductive states. Neuromodulatory pathways that interact with such contextual variables are 1 mechanism for achieving this. In the mouse inferior colliculus (IC), a midbrain auditory region, the neuromodulator serotonin increases in females interacting with courting males, but events downstream of serotonin release have not been investigated. Here, we manipulated serotonin levels in female mice with the serotonin releaser fenfluramine or the serotonin depleter para-chlorophenylalaninemethyl ester (pCPA). Females were then exposed to an empty cage, a male partner, or a playback of courtship vocalizations, and the numbers of neurons in the IC with positive immunoreactivity for the immediate early gene product c-Fos were measured. The effects of drug treatments depended on social context and estrous state. Fenfluramine had greater effects in the nonsocial than in the partner social treatments. Females in proestrus or estrus and given fenfluramine had higher densities of c-Fos immunoreactive neurons, while females in diestrus had fewer immunoreactive neurons. The drug pCPA had the expected opposite effect of fenfluramine, causing a decreased response in pro/estrus females and an increased response in diestrus females. These findings show that the effects of serotonin on c-Fos activity in the IC of females is dependent on both external context and reproductive state, and suggest that these effects occur downstream of serotonin release. (PsycINFO Database Record
Topics: Acoustic Stimulation; Anesthetics, Inhalation; Animals; Enflurane; Estrus; Female; Genes, fos; Humans; Inferior Colliculi; Mice; Serotonin; Social Environment; Time Factors
PubMed: 27657308
DOI: 10.1037/bne0000165 -
Frontiers in Neural Circuits 2015Periodicities in sound waveforms are widespread, and shape important perceptual attributes of sound including rhythm and pitch. Previous studies have indicated that, in...
Periodicities in sound waveforms are widespread, and shape important perceptual attributes of sound including rhythm and pitch. Previous studies have indicated that, in the inferior colliculus (IC), a key processing stage in the auditory midbrain, neurons tuned to different periodicities might be arranged along a periodotopic axis which runs approximately orthogonal to the tonotopic axis. Here we map out the topography of frequency and periodicity tuning in the IC of gerbils in unprecedented detail, using pure tones and different periodic sounds, including click trains, sinusoidally amplitude modulated (SAM) noise and iterated rippled noise. We found that while the tonotopic map exhibited a clear and highly reproducible gradient across all animals, periodotopic maps varied greatly across different types of periodic sound and from animal to animal. Furthermore, periodotopic gradients typically explained only about 10% of the variance in modulation tuning between recording sites. However, there was a strong local clustering of periodicity tuning at a spatial scale of ca. 0.5 mm, which also differed from animal to animal.
Topics: Acoustic Stimulation; Animals; Auditory Pathways; Auditory Perception; Brain Mapping; Cluster Analysis; Gerbillinae; Inferior Colliculi; Membrane Potentials; Neurons; Periodicity; Psychophysics; Sound Localization; Time Factors
PubMed: 26379508
DOI: 10.3389/fncir.2015.00037 -
Hearing Research Jan 2020We examined the sensitivity of the neurons in the mouse inferior colliculus (IC) to the interaural time differences (ITD) conveyed in the sound envelope. Utilizing... (Comparative Study)
Comparative Study
We examined the sensitivity of the neurons in the mouse inferior colliculus (IC) to the interaural time differences (ITD) conveyed in the sound envelope. Utilizing optogenetic methods, we compared the responses to the ITD in the envelope of identified glutamatergic and GABAergic neurons. More than half of both cell types were sensitive to the envelope ITD, and the ITD curves were aligned at their troughs. Within the physiological ITD range of mice (±50 μs), the ITD curves of both cell types had a higher firing rate when the contralateral envelope preceded the ipsilateral envelope. These results show that the circuitry to process ITD persists in the mouse despite its lack of low-frequency hearing. The sensitivity of IC neurons to ITD is most likely to be shaped by the binaural interaction of excitation and inhibition in the lateral superior olive.
Topics: Acoustic Stimulation; Animals; Audiometry, Pure-Tone; Auditory Pathways; Female; GABAergic Neurons; Glutamic Acid; Hearing; Inferior Colliculi; Male; Mice, Transgenic; Neural Inhibition; Neurons; Optogenetics; Time Factors
PubMed: 31759235
DOI: 10.1016/j.heares.2019.107844 -
Frontiers in Neural Circuits 2013We used optical imaging with voltage-sensitive dyes to investigate the spatio-temporal dynamics of synaptically evoked activity in brain slices of the inferior...
We used optical imaging with voltage-sensitive dyes to investigate the spatio-temporal dynamics of synaptically evoked activity in brain slices of the inferior colliculus (IC). Responses in transverse slices which preserve cross-frequency connections and in modified sagittal slices that preserve connections within frequency laminae were evoked by activating the lateral lemniscal tract. Comparing activity between small and large populations of cells revealed response areas in the central nucleus of the IC that were similar in magnitude but graded temporally. In transverse sections, these response areas are summed to generate a topographic response profile. Activity through the commissure to the contralateral IC required an excitation threshold that was reached when GABAergic inhibition was blocked. Within laminae, module interaction created temporal homeostasis. Diffuse activity evoked by a single lemniscal shock re-organized into distinct spatial and temporal compartments when stimulus trains were used, and generated a directional activity profile within the lamina. Using different stimulus patterns to activate subsets of microcircuits in the central nucleus of the IC, we found that localized responses evoked by low-frequency stimulus trains spread extensively when train frequency was increased, suggesting recruitment of silent microcircuits. Long stimulus trains activated a circuit specific to post-inhibitory rebound neurons. Rebound microcircuits were defined by a focal point of initiation that spread to an annular ring that oscillated between inhibition and excitation. We propose that much of the computing power of the IC is derived from local circuits, some of which are cell-type specific. These circuits organize activity within and across frequency laminae, and are critical in determining the stimulus-selectivity of auditory coding.
Topics: Acoustic Stimulation; Animals; Auditory Pathways; Fluorescent Dyes; Inferior Colliculi; Mice; Mice, Inbred CBA; Nerve Net; Rats; Rats, Long-Evans; Voltage-Sensitive Dye Imaging
PubMed: 23518906
DOI: 10.3389/fncir.2013.00041