Publications using TDT

Auditory processing in the cerebral cortex is considered to begin with thalamocortical inputs to layer 4 (L4) of the primary auditory cortex (A1). In this canonical model, A1 L4 inputs initiate a hierarchical cascade that propagates to higher-order cortices for slower integration of complex sounds. Here, we identify parallel ascending pathways in mice that bypass A1 and directly reach the secondary auditory cortex (A2), alongside the canonical hierarchical route. We found that layer 6 (L6) of both A1 and A2 receive short-latency (<10 ms) sound inputs via higher-order thalamic nuclei. Additionally, A2 L4 is innervated by a caudal subdivision of the traditionally defined primary thalamus, which we now re-classify as non-primary. Notably, both identified thalamic regions receive projections from distinct subdivisions of the higher-order inferior colliculus, which in turn receive direct projections from cochlear nucleus neurons. Thus, higher-order auditory cortex integrates both slower, pre-processed information and rapid, direct sensory inputs, enabling parallel processing of fast sensory information across cortical areas.

Atypical sensory processing, particularly in the auditory domain, is one of the most common and quality-of-life affecting symptoms seen in autism spectrum disorders (ASD). Fragile X Syndrome (FXS) is a leading inherited cause of ASD and a majority of FXS individuals present with auditory processing alterations. While auditory hypersensitivity is a common phenotype observed in FXS and Fmr1 knockout (KO) rodent models, it is important to consider other auditory coding impairments that could contribute to sound processing difficulties and disrupted language comprehension in FXS. We have shown previously that a Fmr1 KO rat model of FXS exhibits heightened sound sensitivity that coincided with abnormal perceptual integration of stimulus bandwidth, indicative of altered spectral processing. Frequency discrimination is a fundamental aspect of sound encoding that is important for a range of auditory processes, such as source segregation and speech comprehension, and disrupted frequency coding could thus contribute to a range of auditory issues in FXS and ASD. Here we explicitly characterized spectral processing deficits in male Fmr1 KO rats using an operant conditioning tone discrimination assay and in vivo electrophysiological recordings from the auditory cortex and inferior colliculus. We found that Fmr1 KO rats exhibited poorer frequency resolution, which corresponded with neuronal hyperactivity and broader frequency tuning in auditory cortical but not collicular neurons. Using an experimentally informed population model, we show that these cortical physiological differences can recapitulate the observed behavior discrimination deficits, with decoder performance being tightly linked to differences in cortical tuning width and signal-to-noise ratios. Together, these findings indicate that cortical hyperexcitability in Fmr1 KO rats may act to preserve signal-to-noise ratios and signal detection threshold at the expense of sound sensitivity and fine feature discrimination, highlighting a potential mechanistic locus for a range of auditory behavioral phenotypes in FXS.

The activity of neurotransmitter-based cell types in the cuneiform and pedunculopontine nuclei during locomotion, non-locomotor behaviors, and following sensory stimulation is not fully understood. Using fiber photometry in mice, we found cell-type specific responses to sensory stimuli. Glutamatergic and GABAergic cells responded to sound, visual looming, and air puffs, except for pedunculopontine GABAergic cells, which did not respond to visual looming. Cholinergic cells responded to air puffs. Air puffs triggered high-speed locomotion, whereas visual looming and sound stimuli evoked low-speed locomotion. During air puff–evoked locomotion, cuneiform glutamatergic neuron activity was higher than in trials without locomotion. In contrast, during locomotion evoked by visual looming or sound, activity in pedunculopontine glutamatergic neurons was higher than when no locomotion occurred. In the open-field arena, mice exhibited spontaneous low-speed locomotion during which activity increased in pedunculopontine glutamatergic cells. Activity also increased in a cell type-specific manner during grooming or rearing. Our study shows cell type-specific activity in the cuneiform or pedunculopontine nuclei during locomotion, non-locomotor behaviors, and following sensory stimulation. Sensory responsiveness likely has relevance in Parkinson’s disease, where sensory circuits are increasingly targeted to improve walking.

The prefrontal cortex plays a crucial role in procedural rule learning; however, the specific neuronal mechanism through which it represents rules is unknown. We hypothesized that sequential neuronal activities in the prefrontal cortex encode these rules. To investigate this, we recorded neuronal activities in the medial prefrontal cortex of mice during rule learning using Ca 2+ imaging. We utilized a method based on convolutional negative matrix factorization, iSeq, to automatically detect temporal neuronal sequences in the recorded data. As rule learning advanced, these neuronal sequences began to encode critical information for rule execution. In mice that had mastered the rule, the dynamics of neuronal sequences could predict success and failure of reward acquisition. Furthermore, the composition of cell populations within the neuronal sequences was rearranged throughout the learning process. These findings suggest that as animals learn a rule, the medial prefrontal cortex continually updates its neuronal sequences to assign significance to behavioural actions crucial for reward acquisition.

Identifying neural signatures of loss of consciousness is a major goal of neuroscience. The local/global auditory novelty paradigm has been useful in characterizing sensory processing across arousal states. Propofol suppresses responses to long‐term novelty (global deviance, GD) at subhypnotic doses; suppression of responses to short‐term novelty (local deviance, LD) outside auditory cortex may represent a biomarker of loss of consciousness. Dexmedetomidine is an alpha‐2 adrenergic agonist that induces sleep‐like sedation. This study examined whether the changes in auditory novelty processing observed with propofol, a GABA‐ergic agent, also occur with dexmedetomidine and during sleep. Intracranial recordings were obtained in neurosurgical patients undergoing monitoring for refractory epilepsy. Stimuli were vowel sequences incorporating LD and GD. Neural activity was recorded during wakefulness, administration of dexmedetomidine, and sleep and was examined as the averaged evoked potential (AEP) and high gamma (70–150 Hz) power. AEP responses were more broadly distributed than high gamma activity. Results previously observed with propofol were replicated with dexmedetomidine. Subhypnotic doses led to decreased LD effects and a precipitous decline in GD effects. Loss of responsiveness was associated with loss of LD effects outside the auditory cortex. Likewise, daytime sleep was associated with cessation of GD effects and confinement of LD effects to the auditory cortex. Results support the generalizability of changes in auditory novelty processing to dexmedetomidine and sleep. Preservation of LD effects in the auditory cortex indicates that the auditory cortex continues to monitor the environment following loss of responsiveness.

The neurotransmitter histamine is involved in control of food intake, yet its dynamics during individual feeding episodes remain unexplored. Therefore, we used the novel genetically‐encoded histamine sensor, HisLightG, combined with fiber photometry to measure histamine release in two hypothalamic regions critical for the food‐suppressive effects of histamine, the paraventricular nucleus of the hypothalamus (PVH), and the ventromedial hypothalamus (VMH). Male mice were tested under different conditions to assess whether hunger, time of day, or the caloric content of the solution they were given affected histamine fluctuations. We found that histamine levels changed rapidly in response to eating. These histamine fluctuations were influenced by experimental conditions, with slightly smaller responses when the test solution was sucralose (both regions) or during the light cycle (PVH only). Notable regional differences were identified, such that in the PVH histamine rebounded to above baseline levels, whereas in the VMH histamine remained lower than baseline for at least 10 s after licking ceased. In a separate cohort of male and female mice, enhancing histamine tone via administration of a histamine precursor (L‐histidine) reduced the number of licks across multiple sucrose concentrations. Together, these findings indicate that histaminergic activity is modulated rapidly during ingestive episodes, and that understanding these release patterns will give insight into histamine's role in appetite suppression. image

Analyzing the functional connectivity of the brain is an enormous challenge, as deciphering functional connectivity requires knowledge of functional responses and connections. One promising strategy is analyzing the spatial pattern of activity correlations across cell populations. In the primary auditory cortex (A1), cells respond to different sound features. On the large scale, there exists a tonotopic map, which is fractured at the small scale, raising the question of whether functional connections are spatially ordered or disordered. To test whether functional connectivity on a local and a global scale is also disordered, we first designed a robust statistical model to estimate parameters and test for the significance of the estimated correlation maps. We developed an inference method that allows efficient model fitting and statistical testing to project the correlation maps to 2D space. We then performed in vivo two-photon calcium imaging in layer 2/3 of A1 with pure tones (PT) or a combination of two tones (TT; harmonically related or not). We found that the spatial patterns of signal correlations (SCs) depend on the type of sound stimuli that were presented. The functional 2D maps of PT-driven SCs are more restricted to local neurons than TT signal correlations which showed more global textures. 2D SC patterns for harmonic stimuli showed spatially distinct relationships. TT SCs revealed spatially precise functional connectivity between harmonically related neurons. Thus, even though the frequency preference of neighboring neurons in A1 is functionally diverse, the functional connection pattern of these neurons is functionally precise and harmonically related.

Insects’ sound and vibration detection including proprioception rely on the scolopidium—a mechanosensory unit enclosing the sensory cilium of chordotonal organ neurons. The cilium, enclosed by a scolopale cell, contains mechanosensitive ion channels with the ciliary tip embedded in a cap. Despite knowledge of the scolopidial structure in multiple insects, the mechanism by which mechanical force elicits transduction remains speculative. We examined scolopidia in the auditory Müller’s organ of the desert locust and present a comprehensive three-dimensional (3D) ultrastructure of a scolopidium using Focused Ion Beam Scanning Electron Microscopy (FIB-SEM). Next, we characterised sound-evoked motions of Müller’s organ and the scolopidium using Optical Coherence Tomography (OCT) and high-speed light microscopy. Finally, we measured transduction currents via patch clamp electrophysiology during mechanical stimulation of individual scolopidia. By combining ultrastructure, sound-evoked motions, and transduction current recordings, our finding suggests that the scolopidium is activated best by stretch along the ciliary axis.

Attention samples visual space sequentially to enhance behaviorally relevant sensory representations. While traditionally conceptualized as a static continuous spotlight, contemporary models of attention highlight its discrete nature. But which neural mechanisms govern the temporally precise allocation of attention? Periodic brain activity as exemplified by neuronal oscillations as well as aperiodic temporal structure in the form of intrinsic neural timescales have been proposed to orchestrate the attentional sampling process in space and time. However, both mechanisms have been largely studied in isolation. To date, it remains unclear whether periodic and aperiodic temporal structure reflect distinct neural mechanisms. Here, we combined computational simulations with a multimodal approach encompassing five experiments, and three different variants of classic spatial attention paradigms, to differentiate aperiodic from oscillatory-based sampling. Converging evidence across behavior as well as scalp and intracranial electroencephalography (EEG) revealed that periodic and aperiodic temporal regularities can theoretically and experimentally be distinguished. Our results extend the rhythmic sampling framework of attention by demonstrating that aperiodic neural timescales predict behavior in a spatially-, context-, and demand-dependent manner. Aperiodic timescales increased from sensory to association cortex, decreased during sensory processing or action execution, and were prolonged with increasing behavioral demands. These results reveal that multiple, concurrent temporal regularities govern attentional sampling.

Most patients with sensorineural hearing loss (SNHL) may initially experience high‐frequency hearing loss linked to greater vulnerability of outer hair cells (OHCs) in the cochlear basal turn. However, the molecular mechanism underlying this susceptibility in the high‐frequency region remains unclear. Here, NOX2 is first identified as a differentially expressed gene related to oxidative damage in the apical and basal turns through single‐cell RNA sequencing. In mouse cochleae damaged by neomycin and noise, Nox2‐positive OHCs increase progressively from the apex to base, indicating that NOX2 expression clearly differed significantly between the apical and basal OHCs. In NOX2 knockout mice, OHC damage caused by neomycin and noise exposure is significantly reduced. Furthermore, knocking out NOX2 increases the expression of Nrf2 in the cytoplasm and Nrf2 nuclear translocation in OHCs. In addition, Nrf2 inhibitors counteract the protective effect of NOX2 knockout against neomycin. Finally, when Nox2 is used as the target, ginsenoside Rg1 is identified as a compound with protective effects against neomycin‐induced hearing loss. In summary, these results indicate NOX2 is highly correlated with high‐frequency OHCs vulnerability in the cochlea and is a potential intervention target for the clinical treatment of SNHL.

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 synchronized neural activity from the auditory nerve and brainstem, serve as in vivo readouts for sensory hair cell, synaptic integrity, hearing sensitivity, and other key features of auditory pathway functionality, making them highly valuable for both basic neuroscience research and clinical diagnostics. Despite their utility, traditional ABR analyses rely heavily on subjective manual interpretation, leading to considerable variability and limiting reproducibility across studies. Here, we introduce Auditory Brainstem Response Analyzer (ABRA), a novel open-source graphical user interface 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.

Negative feedback of the cochlear efferent system plays a critical role in control of hearing sensitivity and protection from noise trauma. Type II auditory nerves (ANs) innervate outer hair cells (OHCs) in the cochlea and provide an input to the cochlear efferent system to achieve hearing sensitivity controlling and protection; in particular, medial olivocochlear efferent nerves innervate OHCs to control OHC electromotility, which is an active cochlear amplifier in mammals. However, little is known about channel information underlying type II AN activity and consequent function. Here, we report that ATP-gated P2x7 receptor had a predominant expression at type II spiral ganglion (SG) neurons and the synaptic areas under inner hair cells and OHCs with lateral and medial olivocochlear efferent nerves. Knockout (KO) of P2x7 increased hearing sensitivity with enhanced acoustic startle response, auditory brainstem response, and cochlear microphonics by increasing OHC electromotility. P2x7 KO also increased susceptibility to noise and exacerbated ribbon synapse degeneration. Middle-level noise exposure could impair active cochlear mechanics resulting in hearing loss in P2x7 KO mice. These data demonstrate that P2x7 receptors have a critical role in type II SG neuron’s function and the cochlear efferent system to control hearing sensitivity; deficiency of P2x7 receptors can impair type II SG neuron’s function and the cochlear efferent suppression leading to increase of active cochlear amplification and hearing oversensitivity, i.e., hyperacusis, and susceptibility to noise, which may also associate with other hearing disorders, such as tinnitus.

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.

Introduction Prenatal exposure to valproic acid (VPA) is a common environmental cause of autism spectrum disorder (ASD) and often leads to expressive and receptive language impairments. Similar communication difficulties among individuals with ASD are often linked to abnormal subcortical and cortical sound processing. Rodents prenatally exposed to VPA exhibit degraded cortical responses to speech and an impaired ability to behaviorally discriminate speech sounds. Methods We sought to determine whether sound processing could be restored with paired vagus nerve stimulation (VNS). In a first experiment, we evaluated whether sound-paired VNS would alter in vivo extracellular multi-unit responses to tones, noise burst trains, and speech sounds from the anterior auditory field. We next sought to evaluate whether improvements to neural sound processing led to improvements in sound discrimination ability. In a second experiment, rats underwent go/no-go sound discrimination testing where VNS was paired with successful trials. Results We found that VPA-exposed rats had degraded spectral, temporal, and speech sound processing compared to saline-exposed control rats. VPA-exposed rats which received sound-paired VNS exhibited a partial or full restoration of processing across sound types. However, across several sound discrimination tasks, we did not observe changes in behavioral performance in response to prenatal exposure to VPA or VNS. Discussion Our study is the first to show that speech-paired VNS leads to a generalized improvement in cortical sound processing across sound types, rescuing neural processing among VPA-exposed rats. These results provide a framework for future studies to develop VNS-based interventions for communication disorders.

Distinct basolateral amygdala (BLA) cell populations influence emotions in manners thought important for anxiety and anxiety disorders. The BLA contains numerous cell types which can broadcast information into structures that may elicit changes in emotional states and behaviors. BLA excitatory neurons can be divided into two main classes, one of which expresses Ppp1r1b (encoding protein phosphatase 1 regulatory inhibitor subunit 1B) which is downstream of the genes encoding the D1 and D2 dopamine receptors (Drd1 and Drd2 respectively). The role of Drd1+ or Drd2+ BLA neurons in learned and unlearned emotional responses is unknown. Here, we identified that the Drd1+ and Drd2+ BLA neuron populations form two parallel pathways for communication with the ventral striatum. These neurons arise from the basal nucleus of the BLA, innervate the entire space of the ventral striatum, and are capable of exciting ventral striatum neurons. Further, through two separate behavioral assays, we found that the Drd1+ and Drd2+ parallel pathways distinctly influence both learned and unlearned emotional states when they are activated or suppressed and do so depending upon where they synapse in the ventral striatum - with unique contributions of Drd1+ and Drd2+ circuitry on negative emotional states. Overall, these results contribute to a model whereby parallel, genetically-distinct BLA to ventral striatum circuits inform emotional states in a projection-specific manner.

Hearing loss is common in conditions caused by ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) deficiency, such as generalized arterial calcification of infancy and autosomal recessive hypophosphatemic rickets type 2. Mechanistically, it is hypothesized that poor mineralization of the auditory ossicles leads to impaired sound transmission in the middle ear. Here we investigated whether enzyme replacement therapy (ERT) improves hearing loss in an Enpp1-deficient mouse model and whether this is associated with corrected bone properties in the ossicles. For this purpose, male Enpp1asj/asj mice were subjected to either a soluble or bone-targeted ERT of ENPP1-Fc. Hearing function and bone properties of the malleus, the first bone of the ossicular chain, were evaluated and compared to untreated Enpp1asj/asj and WT mice at the age of 17 wk. In untreated Enpp1-deficient mice, we found elevated hearing thresholds at stimulus frequencies of 8, 16, and 32 kHz, suggesting a generalized impairment of hearing. The hearing deficits observed in Enpp1asj/asj mice were partially or fully corrected by both soluble and bone-targeted ERT, as evidenced by the restoration of auditory brainstem response thresholds, with dose dependence and generally stronger effect of bone-targeted ERT. This was not only associated with corrected blood plasma markers of mineral metabolism but also improved matrix mineralization and restored osteocyte properties in the malleus. In addition, for the first time in mice, we were able to demonstrate the occurrence of mineralized osteocyte lacunae in Enpp1asj/asj mice, a phenomenon that was corrected by bone-targeted but not soluble ERT, underscoring the need for targeted delivery for effective treatment. In contrast to osteocyte lacunar mineralization in humans (ie, micropetrosis), the intra-lacunar mineral was overall less mineralized than the adjacent bone. In conclusion, our results point toward the potential benefit of correcting ossicular mineralization to prevent hearing loss in ENPP1 deficiency.

Food sensory perception has emerged as a potent regulator of specialized feeding circuits; yet, the consequences on feeding behaviour and the underlying neuronal basis remain poorly understood. Here, we reveal a sensory pathway that co-ordinately integrates food odours to control forthcoming nutrient intake in male mice. Unbiased whole-brain mapping of food odour-induced brain activity revealed a potent activation of the medial septum (MS), where food odours selectively activate MS glutamatergic neurons (MS VGLUT2 ). Activity dynamics of MS VGLUT2 neurons uncovered a biphasic modulation of their neuronal activity with a transient activation after detection of food odours and a long-lasting inhibition following food ingestion, independent of the caloric value and identity of the food. MS VGLUT2 neurons receive direct projections from the olfactory bulb (OB) and acute optogenetic stimulation of OB→MS projections selectively before food ingestion decreased feeding in lean mice. However, acute OB→MS optogenetic stimulation in diet-induced obese mice failed to reduce feeding, suggesting the involvement of this pathway in calorie-rich diet-induced hyperphagia and obesity development. Altogether, our study uncovered a sensory circuit by which the organism integrates olfactory food cues to prime satiety at the outset of a meal.

Many elderly listeners have difficulties with speech-in-noise perception, even if auditory thresholds in quiet are normal. The mechanisms underlying this compromised speech perception with age are still not understood. For identifying the physiological causes of these age-related speech perception difficulties, an appropriate animal model is needed enabling the use of invasive methods. In a comparative behavioral study, we used young-adult and quiet-aged Mongolian gerbils as well as young and elderly human subjects to investigate age-related changes in the discrimination of speech sounds in background noise, evaluating whether gerbils are an appropriate animal model for the age-related decline in speech-in-noise processing of human listeners. Gerbils and human subjects had to report a deviant consonant-vowel-consonant combination (CVC) or vowel-consonant-vowel combination (VCV) in a sequence of CVC or VCV standards, respectively. The logatomes were spoken by different speakers and masked by a steady-state speech-shaped noise. Response latencies were measured to generate perceptual maps employing multidimensional scaling, visualizing the subjects’ internal representation of the sounds. By analyzing response latencies for different types of vowels and consonants, we investigated whether aging had similar effects on the discrimination of speech sounds in background noise in gerbils compared to humans. For evaluating peripheral auditory function, auditory brainstem responses and audiograms were measured in gerbils and human subjects, respectively. We found that the overall phoneme discriminability in gerbils was independent of age, whereas consonant discriminability was declined in humans with age. Response latencies were generally longer in aged than in young gerbils and humans, respectively. Response latency patterns for the discrimination of different vowel or consonant types were different between species, but both gerbils and humans made use of the same articulatory features for phoneme discrimination. The species-specific response latency patterns were mostly unaffected by age across vowel types, while there were differential aging effects on the species-specific response latency patterns of different consonant types.

Dopamine (DA) neurons of the substantia nigra (SN) are essential for motor control and selectively degenerate in Parkinson’s disease (PD). However, DA neurons are molecularly heterogeneous, with some showing greater vulnerability and others resilience. Here, we show that the DA subtype marker Anxa1 , identified in mice, labels PD-vulnerable DA neurons in human SN. Using mice, we found that excitatory inputs from subthalamic (STN) and pedunculopontine (PPN) nuclei evoked frequency-dependent excitation in SN GABA neurons, but complex multiphasic DA neuron responses, suggesting heterogeneous DA subtype responses. Indeed, excitatory inputs evoked differential DA responses in striatal subregions, an increase in caudal striatum, but inhibition followed by rebound in dorsolateral striatum. Additionally, PD-resilient Vglut2+ DA neurons were excited by STN/PPN input, while vulnerable Anxa1+ DA neurons were inhibited. These findings demonstrate that DA subtypes are embedded in distinct functional networks, suggesting that some therapeutic interventions may differentially impact vulnerable and resilient DA subtypes.