Electrophysiology publications

Objective: The purpose of this paper is to present a chronic, preclinical, pilot study of a multi-electrode auditory nerve implant. To date, the most successful auditory neuroprosthesis is the cochlear implant, but these devices have known limitations. Intraneural stimulation of the auditory nerve is a promising alternative, but preclinical investigations of multi-electrode devices have been limited to acute or semi-chronic studies. Methods: Six cats were chronically implanted in the right auditory nerve with a 15-channel Utah Slant ArrayTM. The array's position in the internal auditory canal was confirmed using computed tomography. Electrode impedance and evoked responses were recorded regularly during the indwelling period to evaluate performance. Results: Two of the six implants met endpoint criteria at 6 months, with stable electrode impedances and robust evoked responses on at least 50% of their channels. Another two implants exhibited stable electrode impedances, but activation thresholds increased over three months. Two implants failed within the first two weeks due to device migration caused by connector-related issues. Conclusion: This study reports the first successful chronic deployment of an multi-electrode auditory nerve implant in a preclinical model. Two implanted cats exhibited stable chronic performance, marked by a consistent set of electrodes capable of eliciting evoked responses. The failure modes of the remaining four cats are discussed and recommendations are made to stabilize implant placement. The study lays a solid foundation for future chronic safety and efficacy investigations as part of an effort to translate this new neuroprosthetic technology into the clinic.

The hippocampus is classically linked to memory, yet increasing evidence points to a broader role in perceptual inference and deviance detection. Predictive coding theories propose that perception minimizes mismatches between expected and actual sensory input, expressed in neural signatures such as mismatch negativity (MMN) and P300. Although MMN arises mainly from sensory and prefrontal cortices, the hippocampus is anatomically interconnected with both and may also contribute to prediction error processing. We recorded single- and multi-unit activity and local field potentials (LFPs) from DG and CA1 in urethane-anesthetized rats during an auditory oddball paradigm and a no-repetition control sequence to dissociate prediction error from repetition suppression. Approximately 20% of hippocampal neurons were sound responsive, and a subset showed deviant selectivity. Spiking activity predominantly reflected prediction errors, while LFPs revealed complementary contributions from repetition suppression and prediction error. Early LFP components were enhanced for randomly presented deviants, whereas later components within the P300 latency range were stronger for predictable deviants, indicating temporally distinct phases of error signaling and top-down modulation. These findings identify the hippocampus as an active contributor to auditory deviance detection and support a hierarchical model in which hippocampal circuits participate in predictive sensory processing beyond memory.

The axon initial segment (AIS) is the site of action potential generation and exhibits structural and functional plasticity upon adaptation of neuronal excitability and disease. Performing in vivo longitudinal two-photon imaging of AIS in the medial prefrontal cortex of male mice, we reveal dynamic AIS remodeling during associative fear learning and extinction. These results demonstrate that AIS plasticity is not only crucial for homeostatic adaptation but also a hallmark of memory formation.

Hearing loss is the most common sensory disorder, with a substantial proportion caused by genetic mutations. KCNQ4, a voltage-gated potassium channel highly expressed in cochlear outer hair cells, is a common genetic etiology implicated in autosomal dominant progressive hearing loss (DFNA2). The dominant-negative KCNQ4 p.W276S (c.827G>C) mutation represents a mutational hotspot in DFNA2, yet no effective treatments exist. Here, we developed allele-preferential antisense oligonucleotides (ASOs) targeting this dominant-negative KCNQ4 mutation. In a systemic in vitro screen, ASO-123 demonstrated a knockdown of mutant Kcnq4 while preserving wild-type transcripts. In a Kcnq4 p.W277S knockin mouse model mimicking DFNA2, ASO-123 preferentially suppressed mutant transcripts, attenuated progressive hearing loss, and improved outer hair cell survival while enhancing their electrophysiologic function. Comprehensive transcriptomic analyses further validated the efficacy of ASO-123. Thus, our findings establish ASO-based therapy as a promising strategy for treating hereditary hearing loss caused by dominant-negative KCNQ4 mutations.

Outer hair cells (OHCs) in the cochlea contain specialized stereociliary structures essential for auditory function. These include horizontal top connectors (HTCs), linking adjacent stereocilia and tectorial membrane (TM)-attachment crowns (ACs), anchoring the tallest stereocilia to the TM. The known molecular components of these structures, such as stereocilin, otogelin, otogelin-like, and tubby, lack transmembrane domains, suggesting the existence of anchoring proteins. This study identifies TMEM145, a transmembrane protein with a Golgi dynamics domain, as a crucial OHC stereocilia component. TMEM145 is expressed in both OHCs and spiral ganglion neurons, with specific localization to TM-ACs and HTCs in OHCs. Tmem145 knockout (KO) mice exhibit profound hearing impairment at 3 weeks of age, with complete loss of distortion product otoacoustic emissions, indicating OHC dysfunction. Immunostaining and scanning electron microscopy reveal the absence of TM-ACs and HTCs in Tmem145 KO mice. In heterologous cell systems, TMEM145 interacts with stereocilin and tubby, facilitating their extracellular secretion. TMEM145 is undetectable in Stereocilin KO and tubby mutant mice, indicating interdependence among these proteins. These findings establish TMEM145 as an essential membrane protein for the structural integrity of OHC stereocilia, providing insights into the molecular architecture of cochlear hair cells and their role in auditory function.

Context‐dependent sensory processing within the predictive coding framework relies on detecting mismatches between incoming stimuli and internal predictive models. Sensory deviants elicit prediction errors, seen as enhanced neural responses, that update these models and influence attention and behaviour. Although prediction errors have been widely observed across brain regions, the downstream processes remain poorly understood. In this study, we recorded electrocorticography in five urethane‐anaesthetised rats and identified cortical slow oscillations, characterised by spontaneous transitions between ‘Up’ and ‘Down’ states. Deviant stimuli in an auditory oddball paradigm evoked an initial positive prediction error, followed by a prolonged, all‐or‐nothing response which spread in a travelling wave across the cortex. Identified as putative evoked cortical Up states, these responses were not evoked by standards, omissions or a many‐standards control. Up states following deviants occurred more recently after a previous Up state when compared to spontaneous Up states. In preliminary data from an awake rat, long‐latency Up states were not present spontaneously or evoked. In a different rat, anaesthetic depth was key to spontaneous and evoked Up states, with more robust Up/Down states and more reliable triggering of Up states under deeper anaesthesia. These results suggest that sensory deviants may cause shifts in cortical state under anaesthesia, explaining the long‐latency mismatch response under anaesthesia and sleep.

Objectives: Following deafness, a cochlear implant (CI) can be used for the restoration of hearing. CI effectiveness relies on the condition of the auditory nerve, which typically degenerates after deafness. The nerve’s condition can be assessed with the electrically evoked compound action potential (eCAP), the whole-nerve response to an electric pulse. Changes in the eCAP following an increase in the inter-phase gap (IPG) of a biphasic pulse have been reported to be informative of neural survival. This IPG effect can be explained by the temporal separation of the hyperpolarizing phase from the depolarizing phase. We hypothesize that increasing the phase duration (PD) has a similar effect. Design: We investigated the PD effect in normal hearing and in ototoxically deafened guinea pigs (total N = 40) with various conditions of the auditory nerve by recording eCAPs to biphasic current pulses with alternating polarity and with varying PD and IPG. The eCAP data were obtained from both chronically and acutely implanted guinea pigs by using CI stimulation paradigms with a fixed charge and varying PD (30, 50, or 100 µs) and IPG (2.1 or 30 µs). We evaluated six eCAP measures: five derived from the amplitude growth function and the N 1 latency. We examined the relationships of PD and IPG effects with the survival of the spiral ganglion cells. Results: The PD effects were stronger for latency than IPG effects, but weaker for the other five evaluated eCAP measures. The PD effect did not correlate as well with neural survival as the IPG effect. The IPG effect decreased with increasing PD, and accordingly, the stronger correlations between the IPG effect and neural survival were found for a short PD. Notably, the latency increase with increasing PD was greater than 1, which indicates the second phase of the pulse significantly contributes to the eCAP. This second-phase contribution was larger for lower neural survival. Conclusions: The PD effect of latency has predictive power in assessing neural survival. When using other eCAP measures than latency, the best approach to assess neural survival is using the IPG effect with a short PD (around 30 µs).

Background CLN3 disease, also known as juvenile Batten disease, is a recessively inherited neurodevelopmental disorder caused by mutations in the CLN3 gene. It represents the most common form of Neuronal Ceroid Lipofuscinoses (NCLs), a group of lysosomal storage disorders that impair brain function. Clinical features include progressive vision loss, language impairment, and cognitive decline. The early onset of visual deficits complicates the neurological assessment of cognitive dysfunction, while the rarity of CLN3 cases limits the study of sex-specific disease trajectories in humans. Therefore, there is a critical need for objective, translational biomarkers to monitor disease progression and support therapeutic development in preclinical animal models. Methods Building on our recent studies in individuals with CLN3 disease, we developed a parallel experimental paradigm using high-density electroencephalography (EEG) in Cln3 knockout ( Cln3-/-) mice to longitudinally assess auditory neurophysiological changes. We applied a duration-based mismatch negativity (MMN) paradigm, similar to that used in our human studies, to evaluate automatic detection of auditory pattern changes in male and female mice between 3 and 9 months of age. Results Wild-type (WT) mice of both sexes showed robust and stable duration MMN responses across this age range. In contrast, Cln3-/- mice showed marked sex- and age-dependent deficits: female mutants displayed persistent MMN deficits, whereas male mutants exhibited early MMN abnormalities that unexpectedly improved with age. Auditory brainstem responses confirmed intact peripheral hearing in Cln3-/- mice, indicating a central origin for the observed abnormalities. Further analyses revealed that MMN impairments were driven by age- and sex-specific alterations in auditory evoked potentials to both standard and deviant stimuli. Conclusions These findings demonstrate sex- and age-dependent disruptions in central auditory processing in Cln3-/- mice and support auditory duration MMN as a sensitive, translational biomarker of brain dysfunction in CLN3 disease. This approach offers a functional, cross-species measure for tracking disease progression and evaluating therapeutic interventions in Batten disease.

Autism is an early‐onset neurodevelopmental disorder characterized by restricted, repetitive behaviors and atypical patterns of social communication and interaction. A considerable proportion of autistic individuals experience divergent auditory perception, which can interfere with their ability to navigate everyday sound environments. Auditory brainstem responses are electrophysiological potentials elicited by auditory stimuli that evaluate neural activity along the auditory nerve and brainstem. Importantly, the auditory brainstem response varies by sex, with females typically showing higher amplitudes and shorter latencies than males. This sex‐specific neurophysiological profile is especially relevant in autism research, where the male‐to‐female diagnosis ratio is approximately 3:1. Thus, exploring the neurobiological mechanisms underlying sex‐specific variations in autistic traits is essential. Furthermore, autism sensory profiles may vary based on the independent and mutual effects of environmental and genetic factors. To deepen this understanding, we examined auditory brainstem responses in two rat models of autism: the GRIN2B rare mutation model and the prenatal valproic acid induction model, alongside control animals. We assessed peak amplitudes and latencies (Waves I through V), inter‐peak intervals (I–III, I–V, and III–V), and amplitude ratios (III:I, V:I, and V:III). Female rats generally exhibited greater amplitudes and longer latencies across waveforms. Regarding rat models, control animals consistently showed larger amplitudes and shorter latencies compared to autism‐like models. Exploratory analyses further suggested pairwise interactions between sex and rat model, indicating modulation of auditory phenotypes linked to autism. Thus, our findings reveal key insights into the effects of sex and rat model, as well as their interactions.

Fragile X Syndrome (FXS) is a leading genetic cause of intellectual disability and autism-like behaviors. Glutamatergic mGluR5 receptors and matrix metalloproteinase-9 (MMP-9) are therapeutic targets to treat FXS, but clinical trials targeting each of these pathways have not been successful. Here, we tested if the electroencephalography (EEG) phenotypes associated with FXS are reversed with a novel combination of treatments affecting the two pathways. Fmr1 knockout (KO) mice were given 10 days of CTEP (mGluR5 antagonist) alone or in combination with minocycline (MMP-9 inhibitor). EEG was recorded during resting (no acoustic stimulation) and during sound presentations (to produce sound-evoked EEG) at 1 day and 10 days after the beginning of treatment administration to test acute effects and potential tachyphylaxis. In pre-treatment WT and KO mice comparisons, we replicated previously published Fmr1 KO mouse EEG phenotypes including elevated power in the resting gamma band, elevated single trial power, and reduced phase-locking to spectrotemporally dynamic auditory stimuli. We found that CTEP treatment alone did not show any benefit compared to vehicle in Fmr1 KO mice after either 1 or 10 days of treatment. CTEP + minocycline reduced resting gamma band power in the Fmr1 KO mice to a greater extent than vehicle at both treatment time points. There were no effects on sound-evoked responses. These data suggest that combined CTEP and minocycline treatment alters resting EEG measures while each treatment administered separately does not yield similar changes. High power in broadband gamma frequency correlates with irritability, stereotyped behaviors, and hyperactivity in FXS patients, suggesting a combination of drugs that reduce mGluR5 and MMP-9 activity may be beneficial in FXS.

The pre‐hearing mouse cochlea undergoes critical periods of spontaneous Ca 2+ ‐dependent activity that spreads across non‐sensory supporting cells and inner hair cells (IHCs). These signals have been shown to regulate not only the refinement of neural circuits along the auditory pathway towards functional maturity, but also the maturation of the hair cells into sensory receptors. Although the origin and interplay of these Ca 2+ signals during cochlear development have recently been investigated in live mice, the impact of anaesthesia on in vivo functional measurements was not explored. Here, we investigate the effects of different anaesthetic regimes (ketamine and xylazine; 2.5% isoflurane; and 1.0%–1.5% isoflurane with the sedative acepromazine) that provided an effective unconsciousness to perform the surgery and Ca 2+ ‐imaging recordings from the intact cochlea of live mice. The IHCs, supporting cells and spiral ganglion neuron terminals onto the IHCs showed spontaneous Ca 2+ ‐dependent activity under all anaesthetic regimes, with a few significant differences observed between conditions. Calcium waves from supporting cells synchronized the activity of IHCs. Moreover, we found that the endocochlear potential, which is crucial for cochlear function, was unaffected by the different anaesthetics. However, low concentrations of isoflurane produced the most stable recordings of vital physiological signs in mice, including heart rate and breathing rate. Although all anaesthetic regimes tested appeared to be suitable for performing Ca 2+ imaging from the cochlea of pre‐hearing live mice, a low concentration of isoflurane (1.0%–1.5%), combined with the pre‐anaesthetic sedative acepromazine and oxygenation, represents the most suitable approach to maintain a stable and long‐lasting depth of anaesthesia.

Mutations in MYO7A , the gene encoding the unconventional myosin 7a, cause hereditary deafness in mice and humans. In the cochlea, MYO7A is present in the sensory hair cells from embryonic stages of development, and plays a critical role in the development and maintenance of the mechanosensitive hair bundles composed of actin‐rich stereocilia. Shaker‐1 mutant mice ( Myo7a Sh1/Sh1 ), the murine model of Usher 1B syndrome, exhibit a progressive loss of the stereocilia, subsequent degeneration of the sensory epithelium and ultimately profound deafness. In addition to the hair bundle defects, we found that the shaker‐1 mutation prevented both inner hair cells (IHCs) and outer hair cells (OHCs) from acquiring their fully mature basolateral current profile. Delivering exogenous Myo7a to newborn Myo7a Sh1/Sh1 mice using dual‐adeno‐associated virus 8 (AAV8)‐ Myo7a or dual‐AAV9‐PhP.eB‐ Myo7a , which primarily target IHCs, led to a substantial rescue of their hair bundle structure. The rescued bundles regained their ability to generate mechanoelectrical transducer (MET) currents in response to fluid jet displacement. Although the average MET current was smaller than in control IHCs, the normal resting open probability of the MET channel was fully restored. The IHCs of the treated cochlea also regained a mature basolateral membrane current profile. Functionally, rescue of the IHC structure and function, but not that of OHCs, leads to an average improvement of 20–30 dB in hearing thresholds across most frequencies. These results support dual AAV‐induced gene replacement therapy as an effective strategy to recover hair‐cell function in Myo7a Sh1/Sh1 mice. image Key points Shaker‐1 mutant mice ( Myo7a Sh1/Sh1 ), which carry a mutation in the unconventional myosin MYO7A and are the murine model of Usher 1B syndrome, become profoundly deaf at 1 month of age or soon after. In the mammalian cochlea, MYO7A is expressed in the hair cells, including within their actin‐rich stereociliary bundles. We show that hair cells of Myo7a Sh1/Sh1 mice progressively lose their transducing stereocilia and mechanoelectrical transduction, and fail to acquire their fully mature basolateral current profile. Delivering exogenous Myo7a to newborn Myo7a Sh1/Sh1 mice using dual‐adeno‐associated virus (AAVs) led to a substantial rescue of the bundle structure and function of inner hair cells, including mechanoelectrical transduction. This functional rescue led to a 20–30 dB improvement in hearing thresholds across most frequencies. These results support dual AAV‐induced gene replacement therapy as an effective strategy to recover the hair‐cell function in Myo7a Sh1/Sh1 mice.

The neural representations of acoustic features that differ in the location or timbre of the emitter elicit similar perceptions, suggesting the existence of a robust stimulus‐response function between complex sounds and the activity of neural populations at all stages of the auditory system. This hypothesis is tested by decoding a random sound stream, using spike trains from a biophysical model of the auditory nerve and from large‐scale recordings in the inferior colliculus, the auditory thalamus, and the auditory cortex of awake mice. At the level of individual neurons, the reliability of temporal and rate codes is found to decrease along the ascending auditory pathways. Rate coding is progressively favored with increasing independence of neuron frequency tuning. Firing in the auditory cortex is found to be synergistic, whereas that in subcortical areas is more redundant. Finally, combinatorial codes involving neural firing and neural silence within neuron pairs are shown to efficiently encode sound information, particularly in the auditory cortex. Overall, these findings reveal a progressive transformation of the neural code from an individual, redundant, and temporal code at the periphery to a more distributed rate‐based code in the auditory cortex.

This study compared the behavioral minimum audible angle (MAA) and the electrophysiological acoustic change complex (ACC) elicited by an azimuthal shift in sound location. To examine age effects, 63 participants with normal or near-normal hearing were divided into three age groups (Young, Mid-Aged, and Older). The stimuli were narrow bands of noise centered at 500 Hz to facilitate reliance on primarily binaural temporal cues. Putative spatial location was manipulated by means of head-related transfer functions under headphones. MAA results showed that performance was dependent on the reference location, with performance becoming poorer as the reference location shifted away from midline. The Young group had smaller MAAs than the Older group, and performance of the Mid-Age group was intermediate. Measurement of the ACC was restricted to shifts away from midline, and results showed no ACC for shifts of 4.5° and 9° but present ACCs for shifts of 13.5°, 18°, and 36°. The robustness of the ACC, as measured with the intertrial phase coherence metric, grew with increasing azimuthal shift. For shifts of 13.5° and 18°, Young participants had more robust ACCs than Older participants. Although age-related deficits were found in both the MAA and in the robustness of the ACC, no associations were observed at the individual level between MAA and ACC measures. Further work is necessary to evaluate the ACC elicited by shifts from off-midline reference locations before a firm conclusion can be reached that the ACC is not a viable objective proxy for the MAA.

The ability to recognize speakers by their voice despite acoustical variation plays a substantial role in primate social interactions. Although neurons in the macaque anterior temporal lobe (ATL) show invariance to face viewpoint, whether they also encode abstract representations of caller identity is not known. Here, we demonstrate that neurons in the voice-selective ATL of two macaques support invariant voice identity representations through dynamic population-level coding. These representations minimize neural distances across different vocalizations from the same individual while preserving distinct trajectories for different callers. This structure emerged from the coordinated activity of the broader neuronal ensemble, although a small subset of highly identity-selective neurons carried high identity information. Our findings provide a neural basis for voice identity recognition in primates and highlight the ATL as a key hub for integrating perceptual voice features into higher-level identity representations.

Objective Cisplatin is a chemotherapeutic agent with the undesirable side effect of ototoxicity. Transtympanic injections of antioxidant formulations may provide local otoprotection. We tested a novel antioxidant‐eluting microparticle for its otoprotective capability from systemic cisplatin as measured by cochlear electrophysiology. Study Design Basic science. Setting Translational research laboratory. Methods Eighteen mice were assigned to three groups. All mice underwent baseline click‐evoked auditory brainstem response (ABR) audiometry and right ear microparticle injections before beginning 42‐day intraperitoneal administration regimens of either saline (healthy control empty microparticle [HCEMP] group) or cisplatin (cisplatin empty microparticle [CEMP] group and cisplatin N ‐acetylcysteine microparticle [CNAC] group). These regimens consisted of three 4‐day cycles of intraperitoneal saline or cisplatin administration followed by 10 rest days. HCEMP and CEMP received right‐sided transtympanic empty microparticles, and CNAC received transtympanic N ‐acetylcysteine eluting microparticles. On day 43, all mice underwent posttreatment ABR. ABR thresholds and threshold shifts were analyzed with mixed‐effects models and Tukey's post hoc tests and were compared across pretreatment/posttreatment ears, treatment groups, and injected and non‐injected ears. Results We found that threshold shifts in the ears that received a transtympanic injection of N ‐acetylcysteine and three cycles of intraperitoneal cisplatin were similar to the paired ears of mice that received no cisplatin. Mice that received a transtympanic injection without N ‐acetylcysteine and intraperitoneal cisplatin had increased thresholds compared to mice that received a transtympanic injection of N ‐acetylcysteine and cisplatin. Conclusion Transtympanic N ‐acetylcysteine microparticle injections provided functional otoprotection in cisplatin‐exposed mice.

Diverse biological factors, such as sex and age, confer heterogeneity on sensory processing challenges in autism. These factors result in major difficulties in the processing of contextual information in social and non-social situations. To assess divergence in autistic traits, it is critical to consider sex- and age-related variability. Nevertheless, these differences remain largely elusive. Animal models of autism offer the possibility to examine contextual processing at the single-neuron level. Here, we investigated predictive processing of contextual auditory cues in the auditory midbrain of control and prenatally valproic acid-induced rats, a well-established animal model of autism. The rats were prepubertal and adult female and male animals. We performed single-unit recordings in the inferior colliculus of control and prenatally, or in utero , exposed rats under the classical oddball paradigm and non-repetitive cascade control sequences to study neuronal mismatch. This is the neuronal correlate of mismatch negativity, the brain’s automatic response to interruptions in environmental regularity. When comparing control and exposed rats, our results demonstrated a reduction in neuronal mismatch in rats exposed to valproic acid. However, exposed adult females exhibited an increased neuronal mismatch compared to their control counterparts. With respect to sex distinctions, valproic acid induced sex differences in neuronal mismatch of prepubertal and adult rats that are not observable in control animals. Moreover, we detected an age-dependent refinement in prediction error that is not affected by the drug. But valproic acid altered typical developmental trajectory of neuronal mismatch in both sexes. Such observations support sex- and age-related effects of in utero valproic acid exposure in contextual auditory processing at the neural level of the inferior colliculus. In autism, atypical predictive processing of environmental regularities underlies unusual responses to novel experiences. The present study highlights the importance of sex and age, that confer heterogeneity to these challenges.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by complex sensory processing deficits, which continue to elude comprehensive mechanistic understanding. A key unresolved question is how alterations in neural connectivity and communication translate into the behavioral manifestations seen in ASD. Here, we investigate how oligodendrocyte dysfunction alters myelin plasticity and neuronal activity, leading to auditory processing disorder associated with ASD. We focus on the SCN2A gene, an ASD-risk factor, to understand its role in myelination and neural processing within the auditory nervous system. Transcriptional profiling suggests alterations in the expression of myelin-associated genes in Scn2a conditional knockout mice, highlighting the cellular consequences engendered by Scn2a deletion in oligodendrocytes. The results reveal a nuanced interplay between oligodendrocytes and axons, where Scn2a deletion causes alterations in the intricate process of myelination. This disruption instigates changes in axonal properties, presynaptic excitability, and synaptic plasticity at the single cell level. Furthermore, oligodendrocyte-specific Scn2a deletion compromises the integrity of neural circuitry within auditory pathways, leading to auditory hypersensitivity. Our findings reveal a pathway linking myelin deficits to synaptic activity and sensory abnormalities in ASD.

Fragile X Syndrome (FXS) is a leading genetic cause of autism spectrum disorders (ASD)- associated behaviors, including sensory processing deficits. Sensory sensitivity and temporal processing deficits in the auditory domain will affect development of language and cognitive functions. The mouse model for FXS, Fmr1 KO, has shown remarkably similar auditory processing phenotypes to patients with FXS. In vitro cortical slice recordings show layer-specific differences in Fmr1 KO mouse local circuits, but it is unclear how these differences translate to changes in sensory processing. In this study, we used a depth multielectrode to record in vivo spikes and local field potentials across layers of the auditory cortex in Fmr1 KO and wildtype mice (WT), converting the latter to current source density (CSD) profiles for improved spatial resolution analysis. We observed reduced CSD sink amplitudes and inter-trial phase coherence, and an increase in trial-to-trial variability for temporally modulated stimuli in the KO mice. Results indicated a differential cortical layer pattern of activity in KO mice, with higher baseline gamma power in superficial and deep layers and higher resting delta and theta power in granular layers. Significantly elevated inter-trial variability was observed for CSD and spikes in KO mice. Auditory steady state responses to clicks or gaps at 40 Hz showed considerable trial-to-trial variability in a layer-specific manner in KO mice. Neural generators in the Fmr1 KO mouse auditory cortex failed to detect short gaps in noise, indicating severe temporal processing deficits. Altogether, this study indicates layer-specific cortical mechanisms of sensory hypersensitivity and temporal processing deficits in FXS.

Machine learning (ML) techniques are increasingly being used to improve disease diagnosis and treatment. However, the application of these computational approaches to the early diagnosis of age-related hearing loss (ARHL), the most common sensory deficit in adults, remains underexplored. Here, we demonstrate the potential of ML for identifying early signs of ARHL in adult mice. We used auditory brainstem responses (ABRs), which are non-invasive electrophysiological recordings that can be performed in both mice and humans, as a readout of hearing function. We recorded ABRs from C57BL/6N mice (6N), which develop early-onset ARHL due to a hypomorphic allele of Cadherin23 (Cdh23ahl), and from co-isogenic C57BL/6NTacCdh23+ mice (6N-Repaired), which do not harbour the Cdh23ahl allele and maintain good hearing until later in life. We evaluated several ML classifiers across different metrics for their ability to distinguish between the two mouse strains based on ABRs. Remarkably, the models accurately identified mice carrying the Cdh23ahl allele even in the absence of obvious signs of hearing loss at 1 month of age, surpassing the classification accuracy of human experts. Feature importance analysis using Shapley values indicated that subtle differences in ABR wave 1 were critical for distinguishing between the two genotypes. This superior performance underscores the potential of ML approaches in detecting subtle phenotypic differences that may elude manual classification. Additionally, we successfully trained regression models capable of predicting ARHL progression rate at older ages from ABRs recorded in younger mice. We propose that ML approaches are suitable for the early diagnosis of ARHL and could potentially improve the success of future treatments in humans by predicting the progression of hearing dysfunction.