Auditory Research publications

Focused ultrasound (FUS) is a promising noninvasive neuromodulation approach, but whether it can directly activate central auditory neurons in vivo remains unresolved. We applied high-frequency FUS (20 MHz) to the central nucleus of the inferior colliculus (CNIC) in anesthetized guinea pigs while recording electrophysiological responses from the auditory pathway and cochlea. FUS evoked cortical activity through indirect cochlear activation, possibly via skull-mediated mechanical coupling, rather than direct inferior colliculus activation, with ultrasound-evoked compound action potentials predominating in the ipsilateral cochlea. More interestingly, FUS stimulation of the CNIC induced activation of neurons and glial cells in the CNIC and auditory cortex as demonstrated by c-Fos expression, suggesting that FUS stimulation activated the afferent pathway. We also show that FUS engaged the auditory efferent system, likely via medial olivocochlear neurons, producing reduced compound action potential amplitudes, enhanced cochlear microphonics, and persistent effects lasting at least two hours, consistent with long-lasting efferent plasticity. Strikingly, FUS administered before acoustic trauma almost completely prevented noise-induced hearing loss, limiting auditory brainstem response threshold shifts to <10 dB versus ∼60 dB in controls. Gentamicin abolished these physiological and protective effects, implicating medial olivocochlear activation. These findings identify FUS as a potent noninvasive strategy for engaging auditory efferent circuits and protecting against acoustic injury.

The brain computes sound location from auditory spatial cues. Humans and barn owls both localize sounds accurately, yet they rely on fundamentally different cue configurations shaped by their ear anatomy and neural circuitry. In humans, symmetrical ears provide interaural time and level differences (ITD and ILD) for horizontal localization, while vertical localization depends primarily on high‐frequency, monaural spectral cues generated by the pinnae. Barn owls, by contrast, possess asymmetrical ears and use binaural cues for both azimuth and elevation. Because auditory pathways are tuned to species‐specific cue statistics, it remains unclear whether humans can adapt when binaural level cues are also made informative about elevation. We tested this by fitting human listeners with asymmetric ear molds that disrupted normal spectral cues, introduced elevation‐dependent ILDs, and left ITDs unaffected. Participants wore the molds during daily life and were tested with broadband, high‐pass, and low‐pass noise bursts. Acute mold exposure severely degraded elevation localization, whereas horizontal localization remained largely unaffected. With prolonged exposure, elevation localization improved, but adaptation was limited, variable across listeners, and fluctuated across sessions. Improvement was strongest for broadband sounds. Because broadband and high‐pass sounds both contained high‐frequency information, this broadband advantage cannot be explained by access to additional spectral cues alone. Instead, it suggests that low‐frequency ITDs helped listeners exploit the altered binaural cue structure, including the elevation‐dependent ILDs introduced by the molds. These findings show that humans can partially adapt to asymmetric outer‐ear acoustics when complementary spatial cues help resolve ambiguity in the altered cue structure.

Difficulties understanding speech in noise remain a common complaint even among listeners with normal hearing sensitivity, highlighting the need for objective, more effective measures of real-world listening. The goal of this study was to validate the use of a novel, chirped-speech (Cheech) stimulus—continuous, naturally-spoken speech fused with chirps designed to elicit robust auditory evoked potentials—to characterize relationships between speech recognition, listening effort, and auditory neural encoding. Twenty-five normal-hearing adults completed a sentence-recognition task using both original (unmodified) and Cheech-modified AzBio sentence lists in quiet, +3 dB, and −3 dB signal-to-noise ratio (SNR) conditions while neural responses from the brainstem through cortex were recorded simultaneously. Speech recognition remained near ceiling in quiet but declined with decreasing SNR for both original and Cheech stimuli. Compared with clean speech, Cheech-modified speech showed slightly poorer recognition performance as SNR decreased and somewhat higher perceived effort overall. Yet, Cheech was highly effective at evoking auditory responses from the brainstem (auditory brainstem response, ABR) through the cortex (including middle- and late-latency responses, MLR and LLR) even with <5 minutes listening time per condition. Neural responses showed reduced amplitudes and prolonged latencies as SNR decreased. In general, ABR latencies and wave I amplitudes were associated with speech-in-noise recognition performance, whereas cortical responses (MLR Na, Nb, and LLR P1) were associated with subjective workload. These findings show that Cheech-modified speech preserves intelligibility while yielding robust, multilevel neural recordings during sentence perception, offering a promising approach to examine hierarchical auditory processing under ecologically relevant speech-in-noise conditions.

In nature, animals learn to replace predisposed behaviors with new strategies, yet the neural constraints on these transitions are unclear. Using an ethological search task in mice, we reveal medial prefrontal cortical (mPFC) neural correlates of a predisposed win-stay strategy that decays as animals learn to follow a more reliable auditory cue. Auditory cortex (ACx) activity predicts correct trial-by-trial sound-guided search, even on day one of training. This prognostic coding strengthens with learning and emerges from suppressed spiking, most pronounced in neurons tuned laterally to the cue’s spectrum. Chemogenetic disruption reveals ACx contributions to improving performance. Unexpectedly, the global silencing of mPFC accelerates successful usage of sound-tracking, contrary to its canonical role in flexible or stimulus-dependent behavior. Instead, a decentralized multiexpert competition model best predicts behavior and causal perturbations. These findings suggest that mPFC implements a default strategy based on prior knowledge, which actively hinders the expression of more efficient strategies.

Background: Prolonged exposure to moderate and loud noise is known to impair hearing; however, the safety of long-duration exposure to low-level sound, such as that encountered during everyday conversation, remains unclear. This study aimed to determine the effect of continuous exposure to sound at a 65 dB sound pressure level (SPL) on auditory processing. Methods: Auditory brainstem responses (ABRs) were recorded in C57BL/6 mice before and after a 1 h exposure to a continuous pure tone at 65 dB SPL. Changes in ABR thresholds, wave amplitudes, and latencies were analyzed across frequencies and time points. Correlations between amplitude and latency changes across ABR waves were also assessed. Results: Tone exposure induced a significant, frequency-specific increase in ABR thresholds, with a mean elevation of approximately 6 dB and a maximum shift of 15 dB. Significant reductions in amplitudes and prolongations of latencies were observed in Waves I–III, while Wave V amplitude remained relatively stable. A strong negative correlation between amplitude reduction and latency increase was found in Wave I, which progressively weakened from Wave II to Wave V. These functional changes persisted for up to three hours following exposure before gradually returning to baseline. Conclusions: Prolonged exposure to low-level sound at intensities typical of conversational speech can transiently impair auditory function and alter early neural processing in the auditory pathway. These findings suggest that sound levels commonly considered safe may still pose a risk when exposure is sustained, with implications for understanding hidden hearing loss and improving early diagnostic approaches.

Age-related hearing loss is a global public health issue that impacts the quality of life in the elderly population. Macrophages are the main immune cell population in the cochlea, yet the role in the development and progression of age-related hearing loss is still unclear. This study analyzed single-cell sequencing data from cochlear tissues of C57BL/6J mice across different ages and identified notable increase in CD74 expression in macrophages with aging. Validation revealed that CD74 levels were elevated in the aged cochlea, while macrophage migration inhibitory factor (MIF) levels decreased. MIF was significantly reduced in both senescent HEI-OC1 cells and supernatant. Notably, the senescent HEI-OC1 supernatant stimulated BV2 cells CD74 expression increased. rCD74 significantly upregulated apoptosis-related genes expression levels in HEI-OC1 cells, while decreasing MIF levels. In the co-culture system of scrambled/CD74 - BV2 cells and HEI-OC1 cells, CD74 - BV2 cells markedly reduced the apoptosis-related genes expression in senescent HEI-OC1 cells. MIF could improve the mitochondrial membrane potential of both groups of HEI-OC1 cells, and decreased the TUNEL positive cells significantly. Our findings using the HEI-OC1 cell model reveal that macrophages secrete CD74 into the microenvironment, where it interacts with MIF, reducing local MIF levels. This interaction weakens MIF’s protective effect on senescent HEI-OC1 cells, promoting apoptosis in these auditory cells. This suggests a potential mechanism whereby elevated CD74 in the aging cochlear microenvironment may contribute to the loss of hair cells in vivo . Targeting macrophage CD74 may offer therapeutic potential for preventing and treating age-related hearing loss.

BACKGROUND: Noise-induced hearing loss (NIHL) has been traditionally attributed to outer hair cell (OHC) damage, but synaptic injury at inner hair cell (IHC)–spiral ganglion neuron (SGN) junctions may better explain persistent functional deficits. OBJECTIVE: To test whether IHC ribbon loss and functional synapse loss scale with pathological noise intensity and to define their longitudinal relationship to hearing function. METHODS: A rodent NIHL model was exposed to 100 dB SPL for 2 h or 110 dB SPL for 4 h. Cochleae were immunolabeled for CtBP2 (presynaptic ribbons) and GluA2 (postsynaptic AMPA receptor puncta). Putative functional synapses were quantified as closely apposed CtBP2/GluA2 pairs. Hearing function was assessed longitudinally and correlated with synaptic measures. RESULTS: Both exposure conditions produced graded reductions in IHC ribbon counts and CtBP2/GluA2 pairs, with greater losses after 110 dB/4 h. The number of CtBP2/GluA2 apposed pairs closely tracked preserved hearing function, providing a stronger association with functional outcome than ribbon counts alone. Ribbon loss remained largely stable across post-exposure intervals, whereas functional synapse loss was disproportionately larger at early time points, consistent with transient pre–post misalignment. Over time, CtBP2/GluA2 pairing partially recovered toward levels predicted by surviving ribbons, suggesting re-alignment or reconnection of a subset of remaining synaptic elements. CONCLUSION: Pathological noise intensity drives exposure-dependent IHC synaptopathy in addition to OHC injury. Functional synapse counts (CtBP2/GluA2 pairs) sensitively reflect stored hearing function and indicate a potential post-exposure window for synaptic re-establishment.

It is widely accepted that tinnitus arises from maladaptive neuroplasticity in the central auditory system, which compensates for reduced peripheral input; notably, the loss of inner hair cell (IHC) synapses is considered a key underlying factor. IHC synapses can immediately and permanently degenerate after noise exposure, independent of hair cell loss, whereas the cell bodies and central projections of cochlear neurons can survive for months to years, providing an extended therapeutic window for improving afferent input through synapse regeneration. Using NHPN-1010 (a combination of 2,4-disulfophenyl-N-tert-butylnitrone and N-acetylcysteine), we propose a delayed treatment strategy (≥ 4 weeks after trauma) for noise-induced tinnitus (NIT) in rats. NHPN-1010 enhanced gap-prepulse inhibition of acoustic startle responses-indicative of diminished tinnitus-like deficits-coupled with a concomitant upregulation of GABAergic inhibition in the dorsal cochlear nucleus, relative to vehicle alone (saline). Furthermore, NHPN-1010, compared to saline, led to increased wave-I amplitudes of auditory brainstem responses, the effect accompanied by a corresponding rise in the number of presynaptic ribbons in IHCs. Our findings suggest that NHPN-1010 plays a therapeutic role in NIT by promoting cochlear synaptogenesis and normalizing central auditory signaling.

Prairie voles ( Microtus ochrogaster ) are a semi-fossorial rodent that are an emerging model in social neuroscience. Comparing laboratory-reared and wild-caught individuals is essential for understanding how environmental history shapes neural and sensory traits and for assessing the ecological validity of laboratory findings. Despite this, relatively few studies have taken this approach. We used auditory brainstem responses (ABRs) to compare ABR thresholds and ABR wave characteristics between laboratory-reared and wild-caught prairie voles. ABR recordings show that, similar to other semi-fossorial rodents, M. ochrogaster exhibit a hearing range of 1–46 kHz with peak sensitivity between 8–24 kHz in wild-caught and 8–32 kHz in laboratory-reared voles. However, wild-caught prairie voles displayed significantly lower ABR thresholds at 1, 4, 8, 16, and 24 kHz compared to laboratory-reared prairie voles. There were significant differences in interpeak latency between both tested groups, with laboratory-reared prairie voles showing faster interpeak latency responses than wild-caught voles. However, there were no differences in amplitude ratios between groups. Laboratory-reared prairie voles showed faster normalized latencies and higher relative amplitude of the binaural interaction component (BIC) of the ABR than wild-caught voles. There were no significant differences in ABR thresholds, interpeak latency, amplitude ratio, normalized latency, and relative amplitude between the sexes. These differences in auditory processing support the importance of integrating both wild and captive populations to advance comparative auditory research.

The Rubber Voice Illusion is an auditory analogue of the classic Rubber Hand Illusion, a “mind-trick” for the voice. When speakers hear a stranger’s utterances that are perfectly time‑locked and syllable‑matched to their own voice, many momentarily adopt that alien voice as self‑generated. We used this illusion to probe the integrity of predictive auditory mechanisms across the psychosis continuum. Sixty healthy adults completed three Talk‑Listen conditions while high‑density EEG was recorded: veridical (live playback of own voice), stranger‑match (congruent stranger voice) and stranger‑mismatch (incongruent). Behaviorally, only the congruent condition evoked a sense of Ownership and Agency over the stranger’s voice, paired with an upward shift in fundamental frequency toward the higher-pitched stranger voice - an implicit indication of voice adaptation. Neurophysiologically, the canonical speaking-induced suppression was replicated, and suppression was significantly smaller in participants who scored high on Peters et al. Delusions Inventory. In controls, greater pitch shift was associated with stronger neural suppression, suggesting a functioning self-suppression mechanism; conversely, in high-schizotypy individuals, the relationship reversed, despite pitch shifting toward the stranger’s pitch, they exhibited reduced suppression, indicating decoupling between motor output and sensory prediction. The study provides further evidence to the intricate relationship of neural mechanisms underlying self-generated actions with sensory processing in the psychosis continuum.

Auditory hypersensitivity is a prominent symptom in Fragile X syndrome (FXS), the most prevalent monogenic cause of autism and intellectual disability. FXS arises through the loss of the protein encoded by the FMR1 (Fragile X Messenger Ribonucleoprotein 1) gene, FMRP, required for normal neural circuit excitability. In the brainstem, FMRP is necessary for normal development of acoustic reactivity, and its loss has been implicated in audiogenic seizures (AGS) in Fmr1 knockout (KO) mice, modeling auditory hypersensitivity and seizures in FXS patients. The present study investigated the correlation between auditory brainstem function and behavioral expression of AGS at the early (postnatal day P20, infancy) and late (P32, juvenile) stages of auditory development in Fmr1 KO mice compared with wildtype (WT) mice, and in both females and males. We tested responsiveness to pure tones of select auditory pathway elements through auditory brainstem responses, and neural synchronization to amplitude envelopes of modulated acoustic stimuli through auditory steady‐state responses. AGS behavior was categorized for severity during 5‐min exposure to loud sound. Expression of the immediate early gene cFos was quantified as a marker for neuronal activity in the inferior colliculus. During infancy, more severe AGS expression in Fmr1 KO mice compared with WT mice was accompanied by increased responsiveness to acoustic stimuli at the level of the superior olivary complex and inferior colliculus, and stronger neural synchronicity in subcortical auditory neurons. Fmr1 KO mice also had higher cFos positive cell counts in the inferior colliculus after exposure to loud sound. With age, both AGS susceptibility and exaggerated acoustic stimulus‐evoked activity in the Fmr1 KO mice subsided. Intriguingly, Fmr1 KO mice displayed an altered developmental profile in both the threshold and amplitude of auditory brainstem response. Our findings support evidence that AGS activity relies upon hyperexcitability in the auditory system, including in the lower brainstem, possibly due to disturbed auditory maturation. Hyper‐synchronization to modulated sounds in subcortical auditory neurons seemed to predict AGS severity. The developmental trajectory of the auditory hyperresponsiveness and hypersynchrony suggests a transient processing alteration underlying heightened AGS susceptibility in Fmr1 KO mice. A better understanding of FXS‐related circuit and behavioral symptoms of auditory processing across development provides the potential to identify therapeutic strategies to achieve auditory function recovery in FXS.

Tinnitus, the perception of a phantom sound, often occurs as a clinical sequela of auditory traumas. However, the underlying mechanisms of tinnitus are largely unknown. In our previous studies, we found more gamma-aminobutyric acid A receptor alpha 1 subunit (GABAAR-α1)-positive cells in the dorsal cochlear nucleus (DCN) after noise exposure, however, we were not able to identify the specific types of DCN cells that up-regulated GABAAR-α1 after the insult. In the current study, we used Nissl staining, Purkinje cell protein 4 (PCP4) and glutamic acid decarboxylase 67 (GAD67) immunolabeling to identify GABAAR-α1-positive cells in the DCN. Each type of GABAAR-α1-positive cells was quantified and statistically analyzed using immunostaining and Nissl staining according to their morphology, size and location in the DCN. GABAAR-α1-positive cartwheel cells, Golgi cells, as well as ML-stellate and vertical cells were confirmed by dual immunolabeling. In the DCN, the most common GABAAR-α1-positive cells were Golgi cells followed by vertical cells and cartwheel cells while very few other cells were GABAAR-α1-positive in all conditions. We found significantly more GABAAR-α1-positive Golgi cells in the DCN of noise-exposed rats without behavioral evidence of tinnitus compared to normal controls and noise-exposed rats with behavioral evidence of tinnitus. This heightened "context-dependent" inhibition may help to maintain a balanced neuronal network, preventing the potential for tinnitus-related hyperactivity in the auditory pathways.

Introduction Bilateral cochlear implants (BiCIs) do not restore sound localization abilities to the full extent exhibited by typical hearing (TH) listeners, partly due to poor encoding of interaural time differences (ITDs). ITD cues have been provided and investigated using synchronized research processors that ensure the precise delivery of ITD cues. These studies have been conducted in a direct stimulation setting, which bypasses the processor microphones and, in most cases, removes interaural level difference cues (ILDs). To our knowledge, this is the first study that evaluated the efficacy of synchronized stimulation in restoring sensitivity to ITDs in a free field localization experiment. This was made possible by the CCi-MOBILE, a portable and real-time processing research platform that allows for synchronizing microphone inputs. Methods Fourteen BiCI listeners were tested with experimental real-time coding strategies in comparison to unsynchronized clinical processors. We calculated the binaural cues from the acoustic stimuli at the level of microphone input. Results The recordings show that the experimental coding strategies in this study deliver ITDs with greater precision than the clinical strategy. However, psychophysical testing did not show the benefit of an ITD-encoding strategy in improving localization in a free field. The ITD encoding strategies preserved ITDs, which better differentiated unique loudspeaker locations than interaural level differences (ILDs), suggesting that listeners could achieve improved performance if they accessed these cues. As expected, ILDs were similar across all strategies, including the ITD encoding strategies. The lack of improvement in localization performance is likely because ILDs remained to be the dominant cue in acute localization testing, even when ITD cues were available. Discussion Providing BiCI listeners with adequate experiences with ITD cues may be necessary to shift their reliance from ILD dominance to a combined reliance on ILD and ITD cues in free-field conditions. The CCi-MOBILE could enable take-home practice with novel stimulation strategies for extended experiences and long-term evaluation in real-world listening environments.

The ability to pick out and attend to one sound in a noisy mixture underpins successful communication in many natural scenarios. Selective attention has been shown to drastically alter sound encoding in the cortex and has been hypothesized to modulate subcortical processing via an extensive efferent network. The body of work investigating this possibility in humans has not resulted in a clear consensus, possibly owing to limitations in the available methodologies. Here, we used new experimental tools that allowed distinct neural responses from across the auditory pathway to be simultaneously acquired from human listeners attending to the sound of one person talking while ignoring a second. Our series of experiments provide convergent evidence that selective attention does not influence sound encoding in the auditory periphery or brainstem, with an effect first appearing in the cortex. Humans’ ability to focus their attention on a single sound even in the presence of many others is as remarkable as it is essential. These findings add needed clarity regarding the mechanisms that make this feat possible.

Early sensory experience can exert lasting perceptual consequences. For example, a brief period of auditory deprivation early in life can lead to persistent spatial hearing deficits. Some forms of hearing loss (i.e., conductive; CHL) can distort acoustical cues needed for spatial hearing, which depend on inputs from both ears. We hypothesize that asymmetric acoustic input during development disrupts auditory circuits that integrate binaural information. Here, we identify prolonged maturation of the binaural auditory brainstem in the guinea pig by tracking auditory evoked potentials across development. Using this age range, we induce a reversible unilateral CHL and ask whether behavioral and neural maturation are disrupted. We find that developmental CHL is associated with alterations in a brainstem readout of binaural function, an effect that was not observed in a separate cohort with adult-onset CHL. Startle-based behavioral measures suggest that Early CHL animals exhibit reduced spatial resolution for high-frequency sound sources. Finally, single-unit recordings of auditory midbrain neurons reveal significantly poorer neural acuity to a sound location cue that largely depends on high-frequency sounds. Thus, these findings show that unilateral deprivation can disrupt developing auditory circuits that integrate binaural information and may give rise to lingering spatial hearing deficits.

Autism is a common neurodevelopmental disorder that despite its complex etiology, is marked by deficits in prediction that manifest in a variety of domains including social interactions, communication, and movement. The tendency of individuals with autism to focus on predictable schedules and interests that contain patterns and rules highlights the likely involvement of the cerebellum in this disorder. One candidate-autism gene is contactin-associated protein 2 ( CNTNAP2 ), and variants in this gene are associated with sensory deficits and anatomical differences. It is unknown, however, whether this gene directly impacts the brain’s ability to make and evaluate predictions about future events. The current study was designed to answer this question by training a genetic knockout rat on a rapid speech sound discrimination task. Rats with Cntnap2 knockout (KO) and their littermate wildtype controls (WT) were trained on a validated rapid speech sound discrimination task that contained unpredictable and predictable targets. We found that although both genotype groups learned the task in both unpredictable and predictable conditions, the KO rats responded more often to distractors during training as well as to the target sound during the predictable testing conditions compared to the WT group. There were only minor effects of sex on performance and only in the unpredictable condition. The current results provide preliminary evidence that removal of this candidate-autism gene may interfere with the learning of unpredictable scenarios and enhance reliance on predictability. Future research is needed to probe the neural anatomy and function that drives this effect.

Background: Acoustic trauma is a common cause of acute sensorineural hearing loss associated with tinnitus; however, the underlying molecular mechanisms remain unclear. Extracellular signal-regulated kinase 2 (ERK2), a member of the mitogen-activated protein kinase family, is crucial in cellular signaling, especially in the nervous system, where it helps regulate neuroprotection, neurogenesis, and neuronal plasticity. ERK2 is activated in the cochlea by acoustic stimuli and plays a protective role in cochlear hair cells (HCs), which are the primary sensory receptors for hearing. However, the significance of ERK2 expression in HCs associated with development and etiology of tinnitus is largely unexplored. Methods: To investigate the role of ERK2 in tinnitus development, the gap detection test (GAP) was used to evaluate HC-specific ERK2-conditional knockout mice (HC-E2CKO) exposed to moderate acoustic stimuli. Results: Both control and HC-E2CKO mice showed normal prepulse inhibition levels (<0.6) before and after auditory damage, indicating normal functioning of sensorimotor gating pathways, excluding gross sensorimotor deficits. This confirmed that the animals were eligible for the GAP. HC-E2CKO mice showed a transient increase in the GAP ratio, indicating tinnitus development, 1 week after noise exposure, although the hearing threshold was not significantly elevated. The GAP ratio returned to normal after 2 weeks. In contrast, control mice did not exhibit elevation in hearing threshold and the GAP ratio remained normal. Conclusion: Our findings suggest that ERK2 in the inner ear plays a role in tinnitus onset or perception after acoustic stress, potentially through inhibitory mechanisms.

The preservation of synaptic integrity and physiological activity is pivotal for post-traumatic auditory rehabilitation following acoustic overexposure. Neuritin, a neurotrophic factor that facilitates synapse formation, maturation, and enhanced synaptic transmission, is essential for synapse development. In this study, we established a noise-induced cochlear synaptopathy model in CBA/CaJ mice, revealing a temporal association between endogenous Neuritin expression and synaptic density. Furthermore, administration of recombinant Human Neuritin (rhNeuritin) effectively preserves synaptic density in the cochlear basal turn at 7 days and 14 days following noise exposure. Importantly, it preserves the density of functional synapses (represented by overlapping CtBP2 and GluA2 puncta) and synapse function (indicated by ABR I wave amplitudes), thus diminishing the impairment of auditory function. In addition, rhNeuritin reverses the decrease in phosphorylated extracellular signal-regulated protein kinase 1/2 (p-ERK1/2) levels resulting from noise exposure. By primarily preserving both the number and functionality of synapses in the basal turn, potentially via the induction of ERK1/2 phosphorylation, rhNeuritin mitigated hearing loss. These findings underscore the protective efficacy of rhNeuritin against noise-induced synaptic injury.

Introduction Tinnitus is the perception of non-meaningful sound in the absence of external stimuli. Although tinnitus behavior in animal models is associated with altered central nervous system activity, it is not currently possible to identify tinnitus using neuronal activity alone. In the mouse inferior colliculus (IC), a subpopulation of neurons demonstrates a sustained increase in spontaneous activity after a long-duration sound (LDS). Methods Here, we use the “ LDS test ” to reveal tinnitus-specific differences in sound-evoked plasticity through IC extracellular recordings and the auditory brainstem response (ABR LDS ) in CBA/CaJ mice after sound exposure and behavioral tinnitus assessment. Results Sound-exposed mice showed stronger and shorter tone-evoked responses in the IC compared to unexposed controls, but these differences were not strong predictors of tinnitus. In contrast, in the LDS test, non-tinnitus mice had a significantly stronger suppression in tone-evoked spike rate compared to tinnitus and unexposed control mice. ABR peak amplitudes also revealed robust differences between tinnitus and non-tinnitus mice, with ABR peaks from non-tinnitus mice exhibiting significantly stronger suppression in the LDS test compared to tinnitus and control mice. No significant differences were seen between cohorts in ABR amplitude, latency, wave V:I ratio, wave V:III ratio, I-V intra-peak latency, and I-VI intra-peak latency. We found high-frequency tone stimuli better suited to reveal tinnitus-specific differences for both extracellular IC and ABR recordings. Discussion We successfully used the LDS test to demonstrate that tinnitus-specific differences in sound-evoked plasticity can be shown using both multi-unit near-field recordings in the IC and non-invasive far-field recordings, providing a foundation for future electrophysiological research into the causes and treatment of tinnitus.

To navigate real-world listening conditions, the auditory system relies on the integration of multiple sources of information. However, to avoid inappropriate cross-talk between inputs, highly connected neural systems need to strike a balance between integration and segregation. Here, we develop a novel approach to examine how repeated neurochemical modules in the mouse inferior colliculus lateral cortex (LC) allow controlled integration of its multimodal inputs. The LC had been impossible to study via imaging because it is buried in a sulcus. Therefore, we coupled two-photon microscopy with the use of a microprism to reveal the first-ever sagittal views of the LC to examine neuronal responses with respect to its neurochemical motifs under anesthetized and awake conditions. This approach revealed marked differences in the acoustic response properties of LC and neighboring non-lemniscal portions of the inferior colliculus. In addition, we observed that the module and matrix cellular motifs of the LC displayed distinct somatosensory and auditory responses. Specifically, neurons in modules demonstrated primarily offset responses to acoustic stimuli with enhancement in responses to bimodal stimuli, whereas matrix neurons showed onset response to acoustic stimuli and suppressed responses to bimodal stimulation. Thus, this new approach revealed that the repeated structural motifs of the LC permit functional integration of multimodal inputs while retaining distinct response properties.