Auditory Neurophysiology publications

Habituation is a crucial sensory filtering mechanism whose dysregulation can lead to a continuously intense world in disorders with hypersensitivity. Although habituation is often termed the simplest form of learning, its circuit mechanisms remain elusive. Conventional peripheral explanations fail to fully account for long-term habituation in complex sensory environments, leading to theories proposing top-down regulation. Here we evaluated two competing top-down mechanistic explanations for habituation in mice (growth in predictive filtering and waning of novelty-driven amplification) and identified an unexpected role for the orbitofrontal cortex (OFC) in predictive filtering. After daily sound exposure, neural habituation in the primary auditory cortex (A1) was reversed by inactivating the OFC. Top-down projections from the OFC, but not other frontal areas, carried predictive signals that grew with daily sound experience and suppressed A1 via somatostatin-expressing inhibitory neurons. Thus, prediction signals from the OFC cancel out anticipated stimuli by generating their 'negative images' in sensory cortices.

Introduction Spectral information of speech sounds is spatially arranged from low to high frequencies in the auditory cortex, known as tonotopic maps. Recently, we identified an envelope steepness map encoding the rise-ramp steepness of sounds, which is located orthogonally to the tonotopic map. Temporal components, particularly the sound envelope defined by the rise-ramp steepness, play a crucial role in speech perception. We hypothesized that the ability to sense temporal components of sounds, such as envelope steepness, would be diminished in aged mice. Methods Responses to variations in rise-ramp time were investigated using transcranial macroscale calcium imaging of the auditory cortices of GCaMP6f-expressing mice. Normalized distance relative to the rise-ramp time of 0.01 ms was plotted for each rise-ramp time (0.1, 1, 10, and 100 ms) in the logarithmic scale graph: the steeper the slope of the fitted regression lines, the greater the distance between the peaks of the rise-ramp time of 0.01 ms and 100 ms. The slope of this regression line was compared between the different age groups: 1/3 months and 6/9/12 months after birth. Results The slope of the fitted regression line for 5 kHz in the bilateral anterior auditory field and 20 kHz in the bilateral primary auditory field was significantly less steep in mice at 6/9/12 months after birth than at 1/3 months after birth. Conclusion The shorter distance from the peak of 0.01 ms to 100 ms in animals 6/9/12 months after birth suggests difficulty in the separation of the rise-ramp time in aged animals. These findings may support the cortical mechanisms underlying age-related decline in speech perception.

Hearing loss is a pervasive global health challenge with profound impacts on communication, cognitive function, and quality of life. Recent studies have established age-related hearing loss as a significant risk factor for dementia, highlighting the importance of hearing loss research. Auditory brainstem responses (ABRs), which are electrophysiological recordings of acoustically evoked synchronized neural activity from the auditory nerve and brainstem, serve as in vivo correlates for sensory hair cell and synaptic function, hearing sensitivity, and other critical readouts of auditory pathway physiology, making them highly valuable for both basic neuroscience and clinical research. Despite the utility of the ABR, traditional ABR analyses rely heavily on subjective manual interpretation, which may introduce variability and pose challenges for reproducibility across studies. Here, we introduce Auditory Brainstem Response Analyzer (ABRA), a novel suite of open-source ABR analysis tools powered by deep learning, which automates and standardizes ABR waveform analysis. ABRA employs convolutional neural networks trained on diverse datasets collected from multiple experimental settings, achieving rapid and unbiased extraction of key ABR metrics, including peak amplitude, latency, and auditory threshold estimates. We demonstrate that ABRA’s deep learning models provide performance comparable to expert human annotators while dramatically reducing analysis time and enhancing reproducibility across datasets from different laboratories. By bridging hearing research, sensory neuroscience, and advanced computational techniques, ABRA facilitates broader interdisciplinary insights into auditory function. An online version of the tool is available for use at no cost at https://abra.ucsd.edu .

In the mammalian cochlea upon acoustic stimulation, outer hair cells (OHCs) push and pull the basilar membrane, amplifying its vibration and therefore expanding the dynamic range of hearing. As a result, spiking patterns in auditory nerve fibers (ANFs) are believed to be significantly different, but how the central nervous system adapts to this substantial change is poorly understood. In this study, we took advantage of Prestin −/− mice of either sex where prestin, the motor protein in OHCs, was genetically knocked out, therefore removing cochlear amplification completely without changing the cellular structure of the cochlea significantly. While exocytosis from inner hair cells in the cochlea was largely intact, transmission at the endbulb of Held synapse between ANFs and bushy cells in the cochlear nucleus was significantly changed in Prestin −/− mice. Specifically, excitability of bushy cells was significantly increased, due to combination of slightly more depolarized resting membrane potential, increased membrane input resistance, and smaller and briefer afterhyperpolarization. Furthermore, synaptic strength was greatly reduced, caused by substantial decrease in the readily releasable pool (RRP) of synaptic vesicles. Significantly, paired-pulse plasticity at this synapse was reversed from depression in WT mice to facilitation in Prestin −/− mice, likely caused by quicker refilling of RRP observed in Prestin −/− mice. In conclusion, we found that transmission at the endbulb of Held synapse is significantly altered in absence of cochlear amplification, revealing interplay between the peripheral and central processing of auditory signals that contributes to expanded dynamic range of hearing seen in mammals and humans.

Cell types are the basic units of the cerebral cortex. Broad and narrow spike waveforms (BW and NW) are the primary criteria for classifying putative excitatory and inhibitory cortical neurons, particularly in non-human primates where genetic accessibility is limited. We have classified cell types in the auditory cortex of marmosets using spike waveforms and firing patterns and identified a new type of neuron: the NW-burst neuron. NW-burst neurons are excitatory, as they drive but do not suppress the firing of connected neurons. Furthermore, NW-burst neurons displayed shorter response latencies, lower response variability, smaller receptive fields, stronger correlations between spatial and non-spatial selectivity, and higher decoding accuracy than other neurons. Together, these findings suggest that cortical NW-burst neurons in non-human primates represent a distinct excitatory cell type. Significance Statement Classifying cell types in non-human primates is challenging due to limited genetic tools. Traditionally, neurons with narrow spikes are assumed to be inhibitory. Challenging this view, we analyzed 1,816 high-quality single units in the marmoset auditory cortex and discovered that narrow-spike burst-firing neurons were excitatory. These neurons exhibited shorter response latencies, smaller receptive fields, and higher decoding accuracy. Crucially, they showed a positive correlation between "where" and "what" selectivity, defying the standard trade-off between spatial and non-spatial response properties. These findings reveal a specific excitatory cell type in the auditory cortex of a non-human primate species that integrates sound information with high temporal fidelity and feature selectivity.

Astrocytes control neural communications by influencing GABAergic transmission through uptake and synthesis of GABA. Impaired GABAergic signaling is thought to underlie cortical hyperexcitability in autism. Here we show that dysregulation of astrocyte GABA transport in Fragile X syndrome (FXS), a leading genetic cause of autism, contributes to circuit hyperexcitability. Human FXS astrocytes derived from patient-specific induced pluripotent stem cells and mouse Fmr1 knockout (KO) astrocytes display a significant increase in levels of GABA and GABA-synthesizing enzyme GAD65/67. Our astrocyte-specific Fmr1 KO (cKO) mouse model reveals reduced inhibitory connectivity and impaired cortical responses to sound. Abnormal GABA transport in cortical astrocytes contributes to impaired fidelity of temporal processing and abnormal behaviors in cKO mice. Blocking astrocyte GABA transport enables higher PV expression, improves EEG responses to frequency-modulated sound, and corrects aberrant exploratory behavior. Our findings suggest astrocyte GABA transport plays a key role in regulating cortical inhibition, and contributes to autism-associated phenotypes.

Atypical sensory processing is a common feature of autism, yet the neural computations that give rise to these differences, particularly in relation to biological sex and etiological origin, remain unclear. Here we examine predictive auditory processing at the single-neuron level in the inferior colliculus of two adult rat models of autism: a genetic model with a heterozygous Grin2b deletion (Grin2b + /-) and an environmental model based on prenatal valproic acid exposure. We recorded neuronal responses to an auditory oddball paradigm and a cascade control sequence across lemniscal and non-lemniscal IC divisions under high-intensity stimulation, allowing us to derive indices of repetition suppression, prediction error and neuronal mismatch. Using generalized linear mixed-effects models that accounted for animal identity, inferior colliculus division, sex, and rat model, followed by hierarchical group-level comparisons, we identified robust alterations in predictive processing in both autism-like models. These effects varied across inferior colliculus divisions and differed between sexes, revealing distinct phenotype-specific signatures. The results indicate that sex and etiology jointly modulate early auditory computations in autism. More broadly, our findings highlight the translational value of predictive coding frameworks and support the use of complementary animal models to capture neurobiological heterogeneity across the autism spectrum.

The flexibility of human vocal production is well studied, but the direct role of the auditory system in regulating vocalizations in rodents remains largely unexplored. We show that during vocalizations, a fraction of rat auditory cortex neurons shows pre-call activity and different patterns of responses during calls and playback of calls. Additionally, we classified five auditory cortical vocalization responses: pre-call activated, onset activated, onset suppressed, ramping activated and ramping suppressed neurons. Intriguingly, onset suppressed cells can predict vocalization duration and occurrence. Injecting the auditory cortex with muscimol (GABA_A receptor agonist) prolonged vocalizations, while injecting the auditory cortex with gabazine (GABA_A receptor antagonist) shortened them. Similar reductions in call duration were observed during external white-noise stimulation of the auditory cortex and/or other auditory brain structures, resembling the effects of gabazine. Together, neuronal recordings, pharmacological interference and noise induced vocal modifications indicate direct modulation of vocal productions by the rat auditory cortex.

SignificanceAlthough the transmission of auditory information in the brain has been extensively studied, the mechanism underlying fine auditory discrimination remains incompletely understood. The basal region of the ventromedial nucleus of the thalamus (bVM) has recently been found to convey frequency-specific auditory information to the primary auditory cortex (A1). Inhibition of the bVM significantly impairs fine auditory discrimination in mice. These findings indicate that the bVM plays an important role in frequency information processing. However, direct functional evidence for tonotopic organization within the bVM is still lacking.AimWe aimed to investigate whether bVM neurons exhibit a spatially ordered frequency preference, using a simple yet efficient in vivo functional mapping strategy.ApproachTo characterize the response properties of bVM neurons projecting to A1, we combined Cre-dependent retrograde viral labeling with fiber photometry in awake mice. Using a “one recording site per animal” strategy, we systematically recorded from 26 distinct locations and successfully reconstructed the tonotopic map of the bVM.ResultsWe identified a mediolateral tonotopic gradient within the bVM, with best frequencies progressing from low in medial regions to high in lateral regions.ConclusionsOur findings provide direct functional evidence of tonotopic organization within the bVM, supporting its role as an auditory relay and its contribution to fine auditory discrimination.

Coordinated neuronal activity plays an important role in information processing and transmission in the brain. While ensembles’ activity provides a more specific and less noisy version of sensory stimulus information than single neurons, their role in information transmission in the auditory pathway remains unclear. We investigated the effects of ensemble activity in the medial geniculate body (MGB) on the activation of neurons in the primary auditory cortex (A1) in female rats. MGB ensembles synchronized within narrow time windows more effectively induced A1 responses than single neurons or ensembles defined in broader time windows. This was facilitated by the convergence of ensemble inputs onto target neurons. Transmission efficacy was higher for narrow-spiking (NS) A1 neurons compared with broad-spiking (BS) neurons. Cortical UP states in isolation had no discernable effect on the transmission efficacy of thalamic cNEs. These findings highlight neuronal ensembles as focal functional units that enhance information transmission in the brain.

Background With age, even mild acoustic injuries can accumulate - ultimately leading to a characteristic clinical picture of age-related hearing loss with the risk of cognitive decline. Age-related hearing loss is currently attributed to the loss of a most vulnerable auditory fiber type contributing to hearing in background noise. Here, we investigated the potential of a new drug, a more stable chemical variant of Dendrogenin B (DX243) that is predicted to display a protective function on neurite outgrowth, rather than on cell survival. Methodology In the rat animal model, DX243 was tested on hearing thresholds, cortical local field potentials (LFP), auditory steady-state responses (ASSR), auditory brainstem responses (ABR), growth function of notched-noise stimuli, inner hair cell (IHC) ribbon numbers, and multi-click pulse responses (MCP) before and after auditory trauma (AT). Results No auditory evoked LFP response changes were seen in the prefrontal cortex, visual cortex, or hippocampus. In contrast, a permanent decline of auditory evoked LFP amplitudes in the auditory cortex (AC) was measured 2 weeks after AT. Daily injection of DX243 for 2 weeks prevented the AT-induced decline in LFP activity, a protective effect that continued for 6 weeks following the final injection. Through a protective effect of DX243 on a trauma-induced decline of LFP in response to amplitude-modulated tones >80 Hz, a subcortical origin of the drug-effect was suggested. DX243 showed no effect on hearing sensitivity and did not affect subcortical processing of sound features that depend on phase-locking at the stimulus onset (e.g., near-threshold ASSR responses, close-to-threshold ABR growth functions, or spontaneous cortical LFP responses). However, with the same dose-response dependency as shown for cortical LFP effects, DX243 significantly protected from AT-induced decreases in ABR growth functions for loud sound stimuli and in background noise, protected from AT-induced loss of IHC ribbons and AT-induced decline of fast ABRs with decreasing time intervals. Conclusion These findings suggest DX243 as a novel neuroprotective drug, that specifically protects auditory fibers contributing to the coding of the temporal envelope and detection of tones in masking noise, tasks of our auditory senses, both of which, if they fail, lead to age-related speech-in-noise comprehension deficits.

This work presents three open datasets featuring various levels of processing, containing neural recordings from the auditory cortex of rats. These recordings were obtained during experiments using the auditory oddball paradigm before, during and after the local microiontophoretic application of acetylcholine. The primary objective of these datasets is to investigate how the brain processes predictable versus unexpected auditory stimuli, and the role of cholinergic inputs during such processing. The data include multi-unit recordings of neuronal activity during the presentation of standard and deviant tones, classified by stimulus type and cortical sub-region. These resources enable quantitative investigations of deviance detection, stimulus-specific adaptation, cholinergic modulation and predictive-coding mechanisms at multiple temporal scales.

Cisplatin is a broad-spectrum anticancer agent. Its main side effect - ototoxicity - may impact the quality of patient’s life. Eleutheroside E (EE), the main active component of Acanthopanax , exhibits antioxidant and anti-inflammatory properties. This study investigates the protective effects of EE against cisplatin-induced ototoxicity and its underlying mechanisms. We use C57BL/6 J mice, the House Ear Institute-Organ of Corti 1 (HEI-OC1) cells, and cultured cochlear basement membranes in our experiments. We employ network pharmacology and 4D-FastDIA quantitative proteomic analysis. Our results demonstrate that Cisplatin significantly impairs auditory function in mice. However, EE co-treatment preserves auditory function across most measured frequencies, correlating with reduced damage to cochlear hair cells and spiral ganglion neurons(SGNs). Here, we show that EE attenuates cisplatin-induced pro-inflammatory responses and cellular pyroptosis, possibly via downregulation of the MAPK/NF-κB/NLRP3 signaling pathway. In conclusion, EE may offer a promising strategy for reducing Cisplatin’s ototoxicity without affecting its antitumor efficacy.

Context modulates neural processing of sensory stimuli. Neural responses are suppressed to stimuli that are typical in their context and augmented to stimuli that deviate from their context. The latter has been conceptualized as a “prediction error”, which can serve to enhance the salience, direct attention, or support learning about behaviorally relevant events. Predictive coding theories posit that prediction errors act to signal the difference between internal predictions and actual sensory input, yet most paradigms simultaneously alter both predictions and input, so cannot test for a true difference signal. Increased neural responses to deviants could, instead, encode generalized surprise or augmented bottom-up signaling. Here we compare neural responses to auditory stimuli across oddball paradigm variants. We found that responses of putative excitatory neurons in primary auditory cortex (A1) to auditory deviants contain frequency change information and a memory trace of contextual information. Interestingly, in a fixed-deviant oddball paradigm where predictions are altered but deviant input remains constant, neural response patterns encoded standard-to-deviant frequency difference. These results support the interpretation that A1 deviance detection can be interpreted as a sensory prediction error that represents the difference between prediction and sensory input, a corollary of the predictive coding framework.

Parvalbumin-expressing inhibitory neurons (PVNs) stabilize cortical network activity, generate gamma rhythms, and regulate experience-dependent plasticity. We found that PVNs act like a volume knob in the mouse auditory cortex (ACtx), bi-directionally adjusting neural and perceptual sensitivity to sound level over a 20 dB range. PVN-based gain adjustments were "sticky," such that a single bout of PVN activation at 40 Hz-but not at 1 or 70 Hz-sustainably dampened ACtx sound responsiveness, enhanced feedforward inhibition, and behaviorally desensitized mice to loudness. We then developed a mouse model of adult-onset hyperacusis by demonstrating ACtx hyperactivity, PVN hypofunction, and loudness hypersensitivity following a restricted noise-induced cochlear lesion. We found that several minutes of 40-Hz PVN stimulation in noise-exposed mice sustainably dampened ACtx hyperactivity and restored normal loudness sensitivity for 1 week. These findings demonstrate that sensory disorders caused by permanent peripheral injuries can be reversed by patterned stimulation of cortical circuits that directly regulate perception.

The inner hair cells (IHCs) in the inner ear form synapses with auditory nerve fibers (ANFs) that send sound signals to the brain. ANFs have been grouped by their level of spontaneous firing rates (SRs) into high-, medium-, and low-SR ANFs. Based on their molecular profiles evaluated by RNAseq experiments, ANFs have been divided into three groups (1A, 1B, and 1C) that likely correspond to high-, medium-, and low-SR ANFs, respectively. In guinea pigs, the synapses between IHCs and low-SR ANFs have been shown to be more vulnerable to noise exposure compared to other ANF subtypes, but not in a study performed in CBA/CaJ mice, questioning if these results can be generalized. Here, an LYPD1 reporter mouse model on a C57Bl/6J background with specifically labeled group 1C, low-SR ANFs was used to examine whether LYPD1 positive ANF synapses are more vulnerable to noise exposure. Six-week-old mice were exposed to an 8-16 kHz octave band noise presented at 100 dB-SPL for 2 h. One week later, cochlear tissue was harvested to quantify ANF synapses and compare the percentage of LYPD1 positive ANF synapses in noise-exposed and unexposed animals. Auditory brainstem response measurements were performed to assess hearing function after noise exposure. The number of all ANF synapses and the percentage of LYPD1-positive ANF synapses were reduced following noise exposure, concurrent with increased ABR thresholds and decreased ABR wave 1 amplitudes. The reduction in the percentage of LYPD1-positive ANF synapses specifically indicates greater vulnerability of LYPD1 positive ANF synapses to noise exposure compared to other ANFs in C57Bl/6J mice.

There is growing evidence that perceptual difficulties associated with age-related hearing loss are not solely due to cochlear damage and are exacerbated by central nervous system changes. We examined electrophysiological (EEG) responses to clicks and diffusion kurtosis imaging in 49 older (29 female) and 26 younger (20 female) adults to determine the extent to which auditory nerve (AN) deficits in older adults contributed to functional and structural changes throughout the auditory system. Older adults exhibited smaller AN responses, similar brainstem responses, and larger auditory cortex (AC) responses, demonstrating progressive "central gain." Audiometric thresholds were not predictive of EEG measures. Reduced AN function predicted deficits in cortical microstructure (lower AC fractional anisotropy) in older adults, consistent with microstructure degeneration. These lower fractional anisotropy values in the AC of older adults also predicted larger AC responses and more central gain. Older adults exhibited significantly lower AC fractional anisotropy and kurtosis fractional anisotropy coupled with higher mean and radial diffusivity compared to younger adults. AC fractional anisotropy, radial diffusivity, axial diffusivity, and mean diffusivity were all significant predictors of speech-in-noise (SIN) recognition in older adults. The results suggest that reduced afferent input in older adults not only results in functional changes throughout the auditory system consistent with progressive gain but also contributes to deficits in AC structure beyond those explained by age alone, contributing to SIN recognition deficits. Understanding the complex effects of age, reduced AN input, central gain, and AC microstructure on SIN recognition may provide potential therapeutic targets for intervention.

In birds, detection of sound source azimuth begins in the nucleus laminaris (NL), which computes interaural time differences (ITDs). Inhibition has been proposed to protect NL neurons from losing ITD sensitivity with increasing sound level, although the nature of this inhibition is incompletely understood. Anatomical studies show GABAergic synapses throughout NL and first order nuclei, while in vitro studies in chicken NL showed that GABAergic inhibitory postsynaptic potentials (IPSPs) shorten membrane time constants, perhaps to allow the membrane potential to follow rapid synaptic currents accurately over a range of sound levels. Given the importance of inhibition in regulating auditory brainstem activity, we examined the nature of inhibitory input to NL in vivo. The Superior Olivary Nucleus (SON) is the major source of descending GABAergic inhibition to the ipsilateral nucleus magnocellularis (NM), nucleus angularis (NA) and NL, and receives excitatory input from NA and NL. We used viral tracers to reveal projections from SON to NL, and characterized response types within SON. In NL, we isolated inhibitory synaptic contributions from extracellular field potentials through the iontophoretic application of blockers of GABA (gabazine) or glycine (strychnine). These blockers increase onset and offset responses evoked by tonal stimuli, but did not shift best ITD. The co-application of gabazine and strychnine revealed supra-linear summation of GABA and glycine. Profiles of synaptic activation revealed more prominent inhibition following stimulus offset, suggesting inputs to NL originate from both sustained and offset response types of the SON. These heterogeneous responses may represent separate SON neuronal populations. Together, our results support the role of SON inhibition in increasing the dynamic range of ITD tuning of NL neurons.

Basal forebrain cholinergic neurons (BFCNs) densely innervate auditory cortex (ACtx), conveying signals linked to internal brain states and external sensory cues. Acetylcholine (ACh) is known to rapidly modulate cortical circuits through nicotinic ACh receptor (nAChR)-mediated activation of layer 1 inhibitory neurons (L1-INs). However, BFCN terminals are also abundant in deeper layers, where their functional impact has received less attention. Using multi-plex in situ labeling across cortical layers and cell types, we found that layer 6 pyramidal neurons (L6-PNs) are highly enriched in diverse transcripts for nAChR subunits and muscarinic ACh receptors (mAChRs). In vivo optogenetic activation of BFCN axons revealed persistent modulation of regular spiking units in L2-6 but a rapid phasic activation only in L6. In acute slices, optogenetic activation of BFCN axons elicited fast nAChR-mediated excitatory post-synaptic potentials in L6-PNs, comparable to responses in L1-INs, and slower mAChR-mediated inhibitory responses. These findings identify L1-INs and excitatory L6-PNs as two major hubs for BFCN modulation of cortical circuits. By recruiting distinct receptor mechanisms and circuit motifs in L1 and L6, BFCNs may engage parallel pathways of cholinergic control that couple fast, transient modulation with slower, sustained regulation to shape cortical perception and plasticity.

Auditory evoked responses undergo notable changes during childhood, likely reflecting modifications in synaptic signaling in the auditory cortex. Particularly robust response, observed around 200 to 300 ms post stimulus (N/M250), has been consistently reported in children but is absent in adults. This long-latency response, evoked even in passive listening conditions, may indicate heightened sensory pathway responsiveness, facilitating experience-driven cortical plasticity. However, it remains unclear whether this delayed activation pattern is an intrinsic, species-general feature of brain development. We recorded cortical auditory evoked responses to monaural sine-wave tones/click sounds in 3 age groups (preadolescents, adolescents, and young adults) of human subjects and rats. Following short-lived early responses, both species exhibited a long-latency (150 to 450 ms) response in the auditory cortex. In both species, the relative amplitude of the long-latency response, compared to early responses, was increased in younger individuals. In human children, single-trial analysis demonstrated more consistent trial-by-trial timing of the response in this later time window than in the adult-typical 100-ms response in the earlier time window. Given its emergence in purely passive conditions, and across species, the robust current activity in late time window could represent a distinct synaptic event and may serve as a marker of the maturational stage, particularly in GABAergic cortical circuits.